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Posts Tagged ‘Physical exercise’


Innervation of Heart and Heart Rate

Writer and Curator: Larry H Bernstein, MD, FCAP

 

 

The heart is a four-chambered 350 gm semi-oval muscular organ composed of syncytial myocardium, innervated by the vagus nerve with a sino-atrial (SA) and a atrial ventricular (AV) node.  The blood circulates through it by way of the pulmonary artery and aorta, carrying blood away from the ventricles, to the lungs and the systemic circulation, respectively, and two veins, the vena cava and pulmonary, carrying blood to the atria from the systemic circulation and lungs, respectively.  The coronary arterial supply is the left anterior and left circumflex artery, and posteriorly, the right coronary artery, supplied by the aorta.  Much of the pathology has been referred to in the introduction, except for the molecular pathology of atherosclerosis, which has been well covered in this journal. The chambers are divided centrally by the interventricular septum, which is not completely closed in the blue-baby syndrome, which was repaired surgically by Helen Taussig and Richard Bing.  The piece that follows is primarily directed to the sympathetic innervation of the heart, variation in heart rate, and exercise or reaction to external threats.

What are the common observable events that stimulate or relax the heart:

  1. Running or a treadmill test
  2. Rowing or arm movement exercise
  3. A whole body workout
  4. Yoga or Ayurveda
  5. Sleep – normal or disruptive

Some things that can cause a disruption of balance in integrated circulation, neural innervation, innate immune and hormonal response are:

  1. Traumatic experience and/or Injuries
  2. Climate and seasonal changes
  3. Age
  4. Emotions

The basis for the physiological distress has long been the primary basis for acupuncture, holistic and transcendental medicine, and stress management.

I shall here examine the experimental work that supports such an approach – in principle.

Seattle Heart Watch: Initial Clinical, Circulatory and Electrocardiographic Responses to Maximal Exercise

Robert A Bruce, G0 Gey, Jr., Mn Cooper, Ld Fisher, Dr Peterson
Amer J Cardiol 1974; 33(4): 459-469.

A network of 15 maximal exercise testing facilities in four teaching hospitals, 10 private offices and clinics and an industrial medical department was organized in July 1971 to study prospectively the antecedents of myocardial infarction and sudden cardiac death. Within 18 months 2,332 men were tested: 1,275 healthy “normal” subjects, 97 with prior myocardial infarction, 306 with angina pectoris, 193 with hypertension and 461 with various mutually exclusive combinations of these diagnoses; among these clinical groups were five patients who had had a prior episode of ventricular fibrillation.
Historical, physical and laboratory data were recorded on self-teaching printed forms, with normal, borderline and abnormal responses arranged in three columns. Classification with respect to “unlikely,” “questionable” or “likely” risk of future cardiac events was assessed from the highest tally of items in these columns.
Analysis showed computer-averaged S-T segment responses were more consistent and reliable predictors than visual interpretations. Cardiac manifestations in healthy men varled with age and risk assessment, and in patients with cardiovascular disease varied with diagnosis and natural history of disease. Many significant differences provided insights into mechanisms of impaired cardiac function in relation to type of clinical disease. Testing was responsible for one post-exertional cardiac arrest. Recovery was effected promptly by defibrillation; there was no mortality.

Normal and Abnormal Heart Rate Responses to Exercise

  1. Kirk Hammond and Victor F. Froelicher
    Prog Cardiovasc Dis 1985; XXVII(4) (January/February), pp 27l-296

Of the many factors ultimately important in determining the cardiac output, the heart rate is certainly the easiest to measure. By analysis of the heart rate response to exercise in a variety of disease states we felt that the interrelationships of inotropic state, stroke volume, autonomic dysfunction, and myocardial disease could be clarified. This paper reviews the normal and abnormal heart rate responses to exercise.

The normal heart rate is determined by the frequency of depolarization of specialized cells within the sino-atrial node (S-A node). The S-A node, the vestigal sinus venosus, lies in the posterior portion of the heart near the demarcation between the right atrium and the superior vena cava. In about 80% of humans it receives its primary source of blood from a branch of the right coronary artery. Unlike other myocardial cells, the specialized cells of the S-A node have a slow sodium channel and a low resting potential which give these cells their special property. The slowly rising diastolic depolarization (stage four) leads to a rhythmic slow rising action potential.

The autonomic nervous system plays a key role in the regulation of heart rate (Fig 1). The sympathetic nervous system input to the heart originates in a nucleus in the medulla oblongata. Stimulation of this area with implanted electrodes results in increased heart rate and systemic vascular resistance due to increased sympathetic output. Axons from these nuclei descend to the sympathetic trunk via the intermediolateral columns of the spinal cord. From their synapses in cervical ganglia, postganglionic fibers directly innervate the atrial and ventricular musculature, the S-A node, and the A-V node. The effector neurotransmitter is norepinephrine and the receptors are of the beta adrenergic type. There is evidence from competitive binding studies that the postganglionic fibers are predominantly associated with type I beta receptors. The parasympathetic influence to the S-A node and the myocardium originates from nuclei very near the origin of the sympathetic nerves. From the motor nuclei of the vagus and the nucleus solitarius come fibers that form part of the vagus nerve. These fibers terminate at ganglia in the wall of the heart. The postganglionic cholinergic fibers end mostly near the S-A node and the A-V node; there is little evidence for the distribution of parasympathetic nerves to the ventricular myocardium although cholinergic muscarinic receptors have been characterized. In normal conditions there exists a well balanced autonomic tone influencing the S-A node.

There is a complex interrelation among many systems to determine the autonomic tone at the S-A node (Fig 2). [Arterial mechanoreceptors of the carotid sinus and aortic arch respond to changes in arterial pressure and result in appropriate adjustment in the sympathetic and vagal outflow to the heart and resistance and capacitance vessels. (Reprinted with permission from Shepherd JT, Van Houlte PM: The Human Cardiovascular System, Facts and Concepts. New York, Raven Press, 1979).]

There are cortical inputs to the medullary centers; for example, fear results in tachycardia by this pathway. Visceral afferent inputs increase parasympathetic tone resulting in bradycardia. Several reflexes are present for homeostasis. For example, the baroreflex is important in sensing changes in blood pressure and increasing or decreasing the heart rate via autonomic influences at the S-A node to maintain appropriate cardiac output.

Arterial mechanoreceptors of the carotid sinus and aortic arch respond to changes in arterial pressure and result in appropriate adjustment in the sympathetic and vagal outflow to the heart and resistance and capacitance vessels. (Reprinted with permission from Shepherd JT, Van Houlte PM: The Human Cardiovascular System, Facts and Concepts. New York, Raven Press, 1979).

Although the importance of autonomic influence is well accepted in the usual cardioacceleration to exercise, the role of the recovery or deceleration of heart rate following exercise may not be influenced by autonomic input. Six men were studied after peak treadmill exercise. To assess the contribution of autonomic factors in heart rate recovery, the men were given atropine, propranolol, or both agents. It was found that exponential cardio-deceleration occurred under each experimental condition. They concluded that heart rate recovery after exercise is regulated by changes in venous return mediated through atrial stretch receptors of pacemaker tissue. This study implies that deceleration depends primarily on factors intrinsic to the intact circulation that are independent of autonomic control.

The control of heart rate is complex; autonomic tone, central and peripheral reflexes, hormonal influences, and factors intrinsic to the heart are all important. Although easily measured, the heart rate reflects an integrated physiologic response.

The physiologic response to exercise depends on the type of exercise performed; the two major types are isometric and isotonic. Creating muscle tension with no movement against resistance is a pure form of isometric exercise; this results in increased muscle mass and strength. Isotonic exercise is the repetitive, rhythmic movement of large muscle masses against little resistance, known also as dynamic or aerobic exercise. Although most activities involve degrees of both, running is predominantly dynamic, and weight lifting is predominantly isometric.

Bezucha and colleagues investigated the cardiovascular responses to isometric (static) exercise (leg extension) and compared these to those observed during static-dynamic exercise (one arm cranking) and dynamic exercise (leg cycling) in normal men. Heart rate responses to these three tasks were markedly different with static exercise (holding a 30% of maximum voluntary contraction for 3 minutes) resulting in a mean heart rate of 110 + 6 compared with 164 + 4 beats/min in bicycle exercise at 80% of Vo max. Cardiac outputs were raised in all three activities in a proportional manner: 6.8 + 0.7 for static, 10.8 f 0.7 for arm cranking, and 31.9 + 1.0 L/min for bicycling. Stroke volume did not significantly change in the static or combined static-dynamic exercises. The increases in cardiac output were primarily the result of increases in heart rate. This study demonstrates the predominant pressor response and modest cardio-acceleration of isometric exercise.

Longhurst and coworkers, examined the response to acute and chronic exercise in two groups of athletes who typify the two major types of exercise: long distance runners (dynamic) and weight lifters (isometric). The runners responded to isometric exercise with lower double products than the weight lifters. The end-diastolic volume index (evaluated by echocardiography) in the runners was greater than control subjects both at rest and with exercise. In contrast, the weight lifters’ responses were similar to weight matched controls. Not only is the type of exercise an important determinant of acute physiologic response, but chronic static exercise results in physiologic responses that are no different from the responses of sedentary men.

Dynamic exercise, also called isotonic or aerobic, involves the rapid movement of large muscle masses that results in the need for the body to respond with increased ventilation to increase oxygen consumption. Such exercise is called aerobic since it must be performed by using oxygen. The heart must increase its output and performs flow work rather than pressure work. The response to dynamic muscular exercise consists of a complex series of cardiovascular adjustments designed to:

(1) see that active muscles receive a blood supply appropriate to their metabolic needs;

(2) dissipate the heat generated by active muscles; and,

(3) maintain the blood supply to the brain and the heart.

The regulation of the circulation during exercise involves the four following adaptations?

  • Local
  • Nervous adaptations
  • Humoral adaptations
  • Mechanical adaptations

The relationship of pressure, flow, and resistance in rigid tubes is defined by Poiseuille’s law. This law states that resistance is proportional to pressure divided by flow. Peripheral resistance increases in the tissues that do not function in the performance of the ongoing exercise and decreases in active muscle. The result is a decrease in systemic vascular resistance. While pressure only increases mildly, flow can increase by as much as five times during dynamic exercise. Since flow increases much more than pressure, the result is a decrease in systemic resistance. Another mechanical adaptation occurs when the increasing venous return dilates the left ventricle and cardiac function is enhanced via the Frank-Starling mechanism.

There is a highly predictable relationship between total body oxygen consumption and both the cardiovascular and respiratory responses to exercise (Fig 4). [ (A) The linear relationship between heart rate and oxygen uptake. The data was collected from 86 adult male and female subjects. (B) The linear relationship between cardiac output and oxygen uptake. C The data was collected from 23 adult male and female subjects. (C) The linear relationship between minute ventilation and oxygen uptake. ] The data was collected from 225 subjects.  (Reprinted with permission.) Both parameters increase linearly with increasing oxygen consumption until maximal oxygen consumption is approached.

In summary, the type of exercise is an important determinant of both acute and chronic cardiovascular responses. Isometric exercise can be viewed as a pressure load and dynamic exercise as a volume load to the left ventricle. The acute physiological adjustments to dynamic exercise include peripheral vasodilation in exercising muscle, neural mediated increases in sympathetic tone to the heart and the periphery, the release of catecholamines from the adrenal medulla, and changes in venous return due to mechanical and humoral factors. A linear relationship exists between the consumption of oxygen and cardiac output and minute ventilation such that the work performed is highly correlated with the amount of blood pumped and the oxygen consumed.

An increase in heart rate is a major factor contributing to the exercise-induced increased cardiac output. Bowditch demonstrated that the time interval between beats is a determinant of the force of myocardial contraction. This has been called the frequency-force relationship (Fig 5). [The frequency force relationship is demonstrated by a sudden increase in beat frequency in papillary muscle fixed for isometric contraction. A slow increase in isometric tension results from the change in rate implying in increased contractile state. Each vertical line represents an isometric contraction. (Reprinted with permission of W.B. Saunders.)] The increased tension that accompanies an increased heart rate is the result of increased contractility. Although the mechanism of this phenomenon is not known, it may have to do with calcium availability to contractile elements. Thus an increase in heart rate results in an increase in the force of contraction.

Variations in and Significance of Systolic Pressure During Maximal Exercise (Treadmill) Testing: Relation to Severity of Coronary Artery Disease and Cardiac Mortality

John B. Irving, Robert A. Bruce,, Timothy A. Derouen
Amer J Cardiol 1977; 39: 841-848.

Variations in clinical noninvasive systolic pressure at the point of symptom-limited exercise on a treadmill were examined in six groups of subjects: 5,459 men and 749 women classified into three categories each. Among the men, 2,532 were asymptomatic healthy, 592 were hypertensive and 1,586 had clinical manifestations of coronary heart disease (that is, typical angina pectoris, prior myocardial Infarction or sudden cardiac arrest with resuscitation). Among the women, 244, 158 and 347 were in the corresponding clinical categories. None had had cardiac surgery; all had follow-up status ascertained by periodic mail questionnaires.
Reported deaths were reviewed and classified by three cardiologists; 140 deaths were attributed to coronary heart disease, 118 of them in the men classified as having coronary heart disease. The majority of maximal systolic blood pressure readings were reported to the nearest centimeter rather than millimeter of pressure. Retesting of 156 persons from 1 to 32 months later showed that pressure values agreed within 10 percent in two thirds, the overall mean difference was only 8.6 mm Hg and the correlation at maximal exercise was superior to that of the resting observations just before exercise. Hypertensive patients had a significantly greater body weight than normotensive persons. Among men, the lowest maximal systolic pressure was observed in the group with coronary heart disease; among women, the lowest mean pressure was found in the healthy group. Patients with coronary heart disease were slightly older, and only the women showed a significant correlation in maximal pressure with age. Only 5 percent of the variation in maximal systolic pressure in the patients with coronary heart disease was due to a shortened duration of exercise. Maximal systolic pressures correlated fairly well (r = 0.46 to 0.68 for the various groups) with resting systolic pressure, and this relation was independent of the diagnosis of cardiovascular disease in both men and women. Relations between pressure and the number of stenotic coronary arteries and Impaired ejection fraction at rest were examined in 22 men without and 162 men with coronary artery disease. Lower maximal systolic pressures were often associated with two or three vessel disease or reduced ejection fraction, or both.

The prognostic value of maximal systolic pressure for subsequent death due to coronary heart disease was examined in the men with coronary heart disease. The annual rate of sudden cardiac death decreased from 97.9 per 1,000 men to 25.3 and 6.6 per 1,000 men as the range of maximal systolic pressure increased from less than 140 to 140 to 199 and to 200 mm Hg or more, respectively. Cardiomegaly, Q waves in the resting electrocardiogram and persistent postexertional S-T depression were more common in men with the lowest systolic pressure at maximal exercise.

Circulatory Adjustments to Dynamic Exercise and Effect of Physical Training in Normal Subjects and in Patients With Coronary Artery Disease

Jan Praetorius Clausen
Prog Cardiov Dis 1976; XVIII(6): 459-496

The present paper focuses upon the importance of peripheral circulatory alterations during adjustments to exercise and training. Although training results in central circulatory adaptations and may also improve left ventricular function, the prime importance of such adaptations as regards the circulatory and metabolic response to training will be questioned. The thesis that increased maximal exercise capacity can at least in part be attributed to local alterations in the trained muscles will be presented and analyzed. While it is accepted that maximal oxygen uptake is limited by the blood oxygen transport capacity, it will be postulated that the primary event normally responsible for an enhanced oxygen supply after training is an increased ability to reduce resistance to blood flow in exercising muscles rather than improved performance of the central pump.

adjustment to exercise is limited to factors pertinent to physical training of patients with CAD. More detailed accounts of the normal response to exercise can be found in recent books or reviews.

  1. Astrand, P-O, Rodahl K: Textbook of Work Physiology. New York, McGraw-Hill, 1970
  2. Ekblom B, Hermansen L: Cardiac outputs in athletes. J Appl Physiol 25:619, 1968
  3. Christensen EH: Beitrlge zur Physiologie schwerer kijrperlicher Arbeit. Arbeits physiol 4:470, 1931
  4. Saltin B, Blomqvist G, Mitchell JH, et al: Response to exercise after bed rest and after training. Circulation 38 (Suppl 7): 1, 1968
  5. Clausen JP, Klausen K, Blomqvist G, et al. Central and peripheral circulatory changes after training of the arms or legs. Am J Physiol 225:675, 1973

In connection with patients with CAD, only one type of muscular work is of interest; namely, rhythmic or dynamic exercise, in which a considerable part of the skeletal muscle mass is active. This applies to naturally occurring physical activity. Only these types of activity will be referred to and only at work intensities that can be continued for 3-5 min or more.

Dynamic muscular exercise is characterized by a high metabolic rate in the muscle cells with the skeletal muscle functioning in a manner similar to the myocardium, with regularly alternating contraction and relaxation phases. The mechanical energy expended is grossly proportional to the force and the frequency of contraction, and it is derived from the breakdown of adenosine triphosphate (ATP) and creatine phosphate (CP). Only a limited number of a muscle’s fibers, and thus, of its maximal contractile power, can be used in dynamic work continuing for several minutes. During maximal exercise on a bicycle ergometer with a pedaling frequency of 60 rpm, about 15%-2% of the maximal isometric strength of the quadriceps muscle is mobilized. This is thought related to the fact that skeletal muscle, in contrast to myocardium, is composed of several types of fibers with different enzymatic characteristics.29 Some fibers are similar to cardiac muscle being rich in oxidative intramitochondrial enzymes connected to the citric acid cycle, the fatty acid cycle, and the respiratory chain. These are the classical “red” muscle fibers. At the other end of a continuous spectrum is the typical “white” muscle fiber, with a high content of enzymes necessary for anaerobic glycolysis, but containing few mitochondria. Due to their great capability for aerobic metabolism, red fibers sustain rhythmic contractions for long periods of time, whereas the anaerobic white fibers require longer restitution phases even after short periods of activity.

Oxygen extraction per milliliter of blood perfusing the muscle may increase three- to fourfold, and the enhanced muscle blood flow (MBF) is responsible for the remainder of the augmented oxygen uptake. In human muscle, maximal MBF is in the order of 70-100 ml X 100 g-r X min--1 against a resting value of 2-5 ml X 100 g-r X min--1. The increase in MBF is locally controlled by release of vasodilator metabolites and thereby closely geared to the metabolic demands. Muscle blood flow per unit weight of muscle is closely related to the relative work load; i.e., percentage of maximal work load. The metabolites responsible for the exercise-induced vasodilation and hyperemia in muscle are not yet conclusively identified. The finding that both MBF and ATP-CP depletion are related to the relative work load supports the speculation that split products from high energy phosphates may be involved.

During strenuous exercise, VO2  can attain individually varying maximal values, typically ranging from 2.0 to 6.0 1 02/min. The maximal oxygen consumption (VO2 max) is a highly reproducible measure of a given subject’s capability to perform this type of exercise, and it constitutes a useful physiologic reference standard. The conditions required to obtain VO2 max, and its physiologic implications have recently been reviewed in detail by Rowe and by Hermansen. The VO2 max  for a given type of work is normally achieved at a work intensity that can be sustained for at least 3 min, but will cause complete exhaustion within 5-10 min.  At this intensity of exercise, the cardiovascular functional capacity with respect to increase in cardiac output (Q), widening of systemic arteriovenous oxygen difference (AVDO2), and elevation of heart rate (HR) will be challenged maximally for the given type of exercise. However, the relative contribution of Q and AVDO2.

The above description of the normal central and peripheral circulatory adjustment to exercise can be recapitulated as follows:

During dynamic exercise, Q increases in direct proportion to the augmentation of 30,. The increase in Q is directed to exercising skeletal muscles, to the myocardium and-if exercise is continued for more than approximately 5 min-also to the skin. Blood flow to most “nonexercising” tissues (SBF, RBF,
and noncontracting muscles) is reduced due to a general sympathetic vasoconstriction. At submaximal levels, muscle blood flow per unit tissue,
the degree of peripheral vasoconstriction, the acceleration of HR, and in consequence, the increase in myocardial blood flow and oxygen consumption are all functions of the relative V02 ; i.e., the actual VO2 expressed as a percentage of the highest achievable V02 for the given type of exercise.

Most patients with CAD who have been included in exercise and training studies have had healed myocardial infarction and/or stable angina pectoris and have been between 35 and 65 years of age. Both the aging process and myocardial lesions contribute to the modification of the circulatory response to exercise in this group, as compared to healthy young people. In advanced age-especially after 60 years-the circulation tends to become hypokinetic; i.e., Q/VO2 is reduced.  The decline of Q in l/min is almost the same during submaximal exercise as at rest, and thus the increase in Q with VO2 is essentially the same in older as in younger subjects. Stroke volume is lower at a given VO2 , while arterial blood pressures are higher; Q, HR, and VO2 max decline with aging.

Although patients with angina pectoris often exhibit a more profound impairment of left ventricular function and of working capacity than patients with CAD without angina, there seems not to be any specific differences in their central or peripheral circulatory response to exercise. Accordingly, the abnormalities in hemodynamic adaptations in a patient with angina pectoris are present also at workloads that do not provoke angina pectoris.

From the point of view of an exercise physiologist, the patient with angina pectoris is peculiar in that his capacity for dynamic work is not limited by his total body VO2 max, but by VO2 max in myocardial regions supplied by narrowed coronary arteries. If pain is prevented by prophylactic administration of nitroglycerin, a patient with angina pectoris can exercise longer at a given work load or achieve higher workloads and thus obtain a higher VO2 max.

The circulatory adjustment to exercise in patients with CAD typically differs from that of normal subjects in that the maximal values for Q (and thus for VO2), for HR, and for blood pressures are lower. During submaximal exercise, the relation between Q and VO2 tends to be reduced. Moreover, most of the patients with CAD exhibit signs of left ventricular failure during exercise, including a decrease in SV at higher workloads, reduced myocardial contractility, and increased LVEDp. Nonetheless, the peripheral circulatory regulation in patients with CAD corresponds in principle to that seen in healthy subjects of the same age.

Training changes the different local flows during exercise in such a way that, within the framework of an unchanged or reduced Q, its regional distribution at a given submaximal work load deviates less from that seen at rest: the perfusion of nonworking tissues is relatively greater and the flow to active muscles less elevated. However, this is only valid for exercise performed with trained muscles.

Although the precise mechanism mediating exercise hyperemia is unknown, it seems acceptable that enhanced content of oxidative enzymes enables a reduction in MBF at a given submaximal VO2 . After training, due to the increased capacity for oxidative phosphorylation, ATP and CP in active muscles stabilize at a higher steady state level. At the same time glycolysis occurs at a slower rate, pH is relatively increased, and the concentration of multiple intermediate metabolic products may be lower. In consequence, the intra- and intercellular biochemical milieu-concentrations of electrolytes and osmolality included-is less disturbed as compared to the conditions at rest. Whatever substance or combinations of chemical alterations cause the vasodilation, their extent of change is probably reduced at a given respiratory rate in trained muscle tissue, and the vasodilation is thus diminished.

Training improves exercise tolerance in most patients with angina pectoris. The main part of this effect can be related to the training-induced reduction in HR and SBP that decreases myocardial O2 requirements at a given total body O2 uptake. However, at the same time, higher values for the product of HR and SBP are tolerated before pain is provoked after training, suggesting that training has additional economizing effects on myocardial function or directly improves myocardial O2 supply. As judged from the results obtained in exercise tests, training and nitroglycerin seem almost equally potent in alleviating or preventing angina pectoris on exertion. Beta receptor blockade may be somewhat less efficient, whereas aorto-coronary bypass surgery, when practicable, may be the most efficient treatment of exertional angina available today.

Physical training is efficient in improving exercise capacity in about two thirds of all patients with angina pectoris. Patients with angina pectoris provoked only by exercise will often respond favorably to training, even if their exercise capacity is low.  In contrast, patients who suffer from angina at rest, especially nocturnal attacks, may be less likely to increase their exercise tolerance by training. Accordingly, Hellerstein reports that in patients with more severe coronary arteriosclerosis as assessed from coronary arteriograms and left ventricular function, physical fitness fails to improve from training.

Unfortunately, it appears that the patients who cannot be expected to respond favorably to training are also less likely to improve from other modes of treatment. According to Balcon, only younger patients with normal left ventricular function are prone to achieve substantial improvement in physical working capacity by vein graft surgery. Furthermore, the mortality from the operation is higher in patients with abnormal ventricular function. Thus, the appearance of an apparently efficient surgical intervention has not simplified the selection of treatment.

Characteristics of the Ventilatory Exercise Stimulus

F.M. Bennett and W.E. Fordyce
Respiration Physiology 1985; 59, 55-63

Simple mathematical models were used to quantitatively examine a number of hypotheses concerning the nature of the exercise stimulus. The modelling demonstrated the following for an exercise intensity of 5 times the resting metabolic rate.

(1) During the steady state, a deviation in the coupling between VE and metabolic rate by + 25 % of the value necessary for isocapnia, results in a deviation of Paco2 of + 2 torr from isocapnia.

(2) In the transient phase, a mismatch between VE and Q (and thus CO2 flow) of 50% results in a change of Paco2 of only 1 torr.

(3)When resting Paco2 is changed by 10 torr and it is assumed that the coupling between VE and Paco2 does not change, Paco2 deviates from isocapnia by less than 2 torr.

It is concluded that –

(1) to experimentally test hypotheses of the exercise stimulus requires resolution of small changes in Paco2;

(2)  good regulation of Paco2 does not necessarily imply precise coupling between VE and Vco2;

(3) the ventilatory exercise stimulus need not be a precise function of metabolic rate;

(4) in the steady state, the normal CO2 controller will be very effective in minimizing changes in Paco2 due to a mismatch between ventilation and metabolic rate.

Cardiorespiratory and Metabolic Responses to Positive, Negative and
Minimum-Load Dynamic Leg Exercise

Carl Magnus Hesser, Dag Linnarsson And Hilding Bjurstedt
Respiration Physiology 1977; 30, 5 I-67

Cardiorespiratory and metabolic responses to steady-state dynamic leg exercise were studied in seven male subjects who performed positive and negative work on a modified Krogh cycle ergometer at loads of 0. 16,33,49.98, and 147 W with a pedaling rate of60 rpm.
In positive work, O2 uptake increased with the ergometric load in a parabolic fashion. Net O2 uptake averaged 220 ml*min– 1 at 0 W (loadless pedaling), and was 75 ml* min– 1 lower at the point of physiological minimum load which occurred in negative work at approximately 9 W. The O2 cost of loadless pedaling is for one-third attributed to the work of overcoming elastic and viscous resistance, the remaining part being due mainly to the work of antagonistic muscle contraction in the moving legs. Although at a given Vo2 work rate was much higher in negative than in positive work, corresponding values for VE were similar, suggesting that the mechanical tension in working muscles is of little or no importance in the control of ventilation in steady-state exercise.
Heart rate increased linearly with Vo2 in both positive and negative work, with a steeper slope in negative work. Evidence is presented that none of the current definitions of muscular efficiency yields the true efficiency of muscular contraction in cycle ergometry, net efficiency calculation resulting in too low estimates, and work and delta efficiency calculations in overestimated values in the low-intensity work range, and in underestimated values in the high-intensity range.

The effect of exercise on left ventricular ejection time in patients with hypertension or angina pectoris

James R. Bowlby
Amer Heart J 1979; 97(3): 348-350

Using the method and regression equation of Lewis and associates, the present study confirms their findings in normal men up to the age of 65 years. Despite the significantly higher myocardial oxygen consumption, as measured by the double product, the hypertensive patients responded in a similar fashion. The patients with angina pectoris, however, showed a significantly prolonged post-exercise ejection time.

Cardiac Effects of Prolonged and Intense Exercise Training in Patients With Coronary Artery Disease

Ali A. Ehsani, Wade H. Martin Iii, Gregory W. Heath, Edward F. Coyle
Amer J Cardiol 1982; 50: 246-254

The effects of intense and prolonged exercise training on the heart were studied with echocardiography in eight men with coronary artery disease with a mean age (standard error of the mean) of 52 + 3 years. Training consisted of endurance exercise 3 times/week at 50 to 60 percent of the measured maximal oxygen uptake for 3 months followed by exercise 4 to 5 days/week at 70 to 60 percent of maximal oxygen uptake for 9 months. Maximal oxygen uptake capacity increased by 42 percent (26 + 1 versus 37 + 2 ml/kg per min; p <0.001). Heart rate at rest and submaximal heart rate and systolic blood pressure at a given work rate were significantly lower after training. Systolic blood pressure at the time of maximal exercise increased (145 + 9 before versus 166 + 6 mm Hg after training; probability [p] <0.01). Left ventricular end-diastolic diameter was increased after 12 months of training (from 47 + 1 to 51 + 1 mm; p <0.01. Left ventricular fractional shortening and mean velocity of circumferential shortening decreased progressively in response to graded iisometric handgrip exercise before training but not after training. At comparable levels of blood pressure during static exercise, mean velocity of circumferential shortening was significantly higher after training (0.76 + 0.04 versus 0.96 + 0.07 diameter/set, p <0.01). No improvement in echocardio-graphic or exercise variables was observed over a 12 month period in another group of five patients who did not exercise. Thus the data suggest that prolonged and vigorous exercise training in selected patients with coronary artery disease can elicit cardiac adaptations.

Physical activity and resting pulse rate in older adults: Findings from a randomized controlled trial

Bríain O’Hartaigh, Marco Pahor, Thomas W. Buford, John A. Dodson, et al.
Am Heart J 2014;168:597-604

Background Elevated resting pulse rate (RPR) is a well-recognized risk factor for adverse outcomes. Epidemiological evidence supports the beneficial effects of regular exercise for lowering RPR, but studies are mainly confined to persons younger than 65 years. We set out to evaluate the utility of a physical activity (PA) intervention for slowing RPR among older adults.
Methods A total of 424 seniors (ages 70-89 years) were randomized to a moderate intensity PA intervention or an education-based “successful aging” health program. Resting pulse rate was assessed at baseline, 6 months, and 12 months. Longitudinal differences in RPR were evaluated between treatment groups using generalized estimating equation models, reporting unstandardized β coefficients with robust SEs.
Results Increased frequency and duration of aerobic training were observed for the PA group at 6 and 12 months as compared with the successful aging group (P = 0.001). In both groups, RPR remained unchanged over the course of the 12-month study period (P = .67). No significant improvement was observed (β [SE] = 0.58 [0.88]; P = .51) for RPR when treatment groups were compared using the generalized estimating equation method. Comparable results were found after omitting participants with a pacemaker, cardiac arrhythmia, or who were receiving β-blockers.
Conclusions Twelve months of moderate intensity aerobic training did not improve RPR among older adults. Additional studies are needed to determine whether PA of longer duration and/or greater intensity can slow RPR in older persons.

Autonomic regulation and maze-learning performance in older and younger dults

Karen J. Mathewson, J Dywan, PJ Snyder, WJ Tays, SJ Segalowitz
Biological Psychology 88 (2011) 20– 27
http://dx.doi.org:/10.1016/j.biopsycho.2011.06.003

There is growing evidence that centrally modulated autonomic regulation can influence performance on complex cognitive tasks but the specificity of these influences and the effects of age-related decline in these systems have not been determined. We recorded pre-task levels of respiratory sinus arrhythmia (RSA; an index of phasic vagal cardiac control) and rate pressure produce (RPP; an index of cardiac workload) to determine their relationship to performance on a cumulative maze learning task. Maze performance has been shown to reflect executive error monitoring capacity and non-executive visuomotor processing speed. Error monitoring was predicted by RSA in both older and younger adults but by RPP only in the older group. Non-executive processes were unrelated to either measure. These data suggest that vagal regulation is more closely associated with executive than nonexecutive aspects of maze performance and that, in later life, pre-task levels of cardiac workload also influence executive control.

Sympathovagal Imbalance Contributes to Prehypertension Status and Cardiovascular Risks Attributed by Insulin Resistance, Inflammation, Dyslipidemia and Oxidative Stress in First Degree Relatives of Type 2 Diabetics

Gopal Krushna Pal, C Adithan, P Hariharan Ananthanarayanan, Pravati Pal, et al.
PLoS OME 2013; 8(11), e78072 http://dx.doi.org:/10.1371/journal.pone.0078072

Background: Though cardiovascular (CV) risks are reported in first-degree relatives (FDR) of type 2 diabetics, the pathophysiological mechanisms contributing to these risks are not known. We investigated the association of sympathovagal imbalance (SVI) with CV risks in these subjects.
Subjects and Methods: Body mass index (BMI), basal heart rate (BHR), blood pressure (BP), rate-pressure product (RPP), spectral indices of heart rate variability (HRV), autonomic function tests, insulin resistance (HOMA-IR), lipid profile, inflammatory markers, oxidative stress (OS) marker, rennin, thyroid profile and serum electrolytes were measured and analyzed in subjects of study group (FDR of type 2 diabetics, n = 72) and control group (subjects with no family history of diabetes, n = 104).
Results: BMI, BP, BHR, HOMA-IR, lipid profile, inflammatory and OS markers, renin, LF-HF (ratio of low-frequency to high frequency power of HRV, a sensitive marker of SVI) were significantly increased (p,0.0001) in study group compared to the control group. SVI in study group was due to concomitant sympathetic activation and vagal inhibition. There was significant correlation and independent contribution of markers of insulin resistance, dyslipidemia, inflammation and OS to LF-HF ratio. Multiple-regression analysis demonstrated an independent contribution of LF-HF ratio to prehypertension status (standardized beta 0.415, p,0.001) and bivariate logistic-regression showed significant prediction (OR 2.40, CI 1.128–5.326, p = 0.002) of LF-HF ratio of HRV to increased RPP, the marker of CV risk, in study group.
Conclusion: SVI in FDR of type 2 diabetics occurs due to sympathetic activation and vagal withdrawal. The SVI contributes to prehypertension status and CV risks caused by insulin resistance, dyslipidemia, inflammation and oxidative stress in FDR of type 2 diabetics.

Exercise prescription for patients with type 2 diabetes and pre-diabetes: A position statement from Exercise and Sport Science Australia

Matthew D. Hordern, DW Dunstan, JB Prins, MK Baker, et al.
Journal of Science and Medicine in Sport 15 (2012) 25–31
http://dx.doi.org:/10.1016/j.jsams.2011.04.005

Type 2 diabetes mellitus (T2DM) and pre-diabetic conditions such as impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) are rapidly increasing in prevalence. There is compelling evidence that T2DM is more likely to develop in individuals who are insufficiently active. Exercise training, often in combination with other lifestyle strategies, has beneficial effects on preventing the onset of T2DM and improving glycaemic control in those with pre-diabetes. In addition, exercise training improves cardiovascular risk profile, body composition and cardiorespiratory fitness, all strongly related to better health outcomes. Based on the evidence, it is recommended that patients with T2DM or pre-diabetes accumulate a minimum of 210 min per week of moderate-intensity exercise or 125 min per week of vigorous intensity exercise with no more than two consecutive days without training. Vigorous intensity exercise is more time efficient and may also result in greater benefits in appropriate individuals with consideration of complications and contraindications. It is further recommended that two or more resistance training sessions per week (2–4 sets of 8–10 repetitions) should be included in the total 210 or 125 min of moderate or vigorous exercise, respectively. It is also recommended that, due to the high prevalence and incidence of comorbid conditions in patients with T2DM, exercise training programs should be written and delivered by individuals with appropriate qualifications and experience to recognise and accommodate comorbidities and complications.

Estimation of the Ejection Fraction in Patients with Myocardial Infarction Obtained from the Combined Index of Systolic and Diastolic Left Ventricular Function: A New Method

Jorge A. Lax, Alejandra M. Bermann, Tomás F. Cianciulli, Luis A. Morita, et al.
J Am Soc Echocardiogr 2000;13:116-23.

The index of myocardial performance combining systolic and diastolic time intervals (Index) is a useful method, already explained in past studies, that offers new values that have not been widely known among clinical cardiologists. The aim of this study is to obtain from this Index a measurement of the ejection fraction (EF), which is a very well-known value.
The study involved 97 patients with myocardial infarction, 55 of whom were studied retrospectively (group A, aged 46-62 years, 50 men) to obtain and test the formula EF = 60 – (34 × Index). The second group (group B, aged 47-63 years, 40 men) included 42 patients who were evaluated prospectively. The EF obtained was compared with that reached through the use of radionuclide angiography (EF-RNA).
The Index was obtained through the use of the formula (a – b)/b, where a is the interval between cessation and onset of the mitral inflow, and b is the ejection time. In group A the EF obtained by the Index (EF-Index) was 37.5% ± .8%, and the EF-RNA was 37.7% ± 11% (r = 0.76). In group B the EF-Index was 41.6% ± 7%, and the EF-RNA was 41.2% ± 10% (r = 0.75).
Conclusion: Through the new formula described here it is possible to obtain a reliable measurement of the EF in patients with myocardial infarction, a well known and extremely useful value, especially for those patients with poor acoustic windows.

HCN channels: new roles in sinoatrial node function

Christian Wahl-Schott, Stefanie Fenske and Martin Biel
Current Opinion in Pharmacology 2014, 15:83–90
http://dx.doi.org/10.1016/j.coph.2013.12.005

Hyperpolarization-activated cyclic nucleotide gated (HCN) channels pass a cationic current (Ih/If) that crucially contributes to the slow diastolic depolarization (SDD) of sinoatrial pacemaker cells and, hence, is a key determinant of cardiac automaticity and the generation of the heart beat. There is growing evidence, that HCN channel functions in the sinoatrial node (SAN) are not restricted to impulse formation but are also required for impulse propagation. In addition, HCN channels are involved in coordination and maintenance of sinoatrial network activity and, hence, are crucial for stabilizing cardiac rhythmicity. In the present review we will outline these new concepts.

In this review we will focus on HCN channel functions in the sinoatrial node beyond the established concepts described above. We will outline recent advances involving the characterization of the HCN1-deficient mouse line (HCN1-/- mouse) which have provided evidence that HCN channels are required for impulse propagation and the precision of the heart beat [19**]. Furthermore, we show how these properties can be generalized across the other HCN channel subtypes in the sinoatrial node.

19** Fenske S, Krause SC, Hassan SI, Becirovic E, Auer F, Bernard R, Kupatt C, Lange P, Ziegler T, Wotjak CT et al.: Sick sinus syndrome in HCN1-deficient Mice. Circulation 2013. Epub 2013 Nov 11.
First demonstration of a functional relevance of HCN1 channels in the murine sinoatrial node. The authors demonstrate that mice lacking the pacemaker channel HCN1 display congenital sinoatrial node dysfunction characterized by bradycardia, sinus dysrhythmia, prolonged sinoatrial node recovery time, increased sinoatrial conduction time and recurrent sinus pauses. As a consequence of sinoatrial node dysfunction HCN1-deficient mice display a severely reduced cardiac output.

Recent studies indicate that the role of cardiac HCN channels extends well beyond generation of pacemaker potentials. In addition to being merely ‘pacemaker channels’, HCN channels are important for sinoatrial impulse propagation, cardiac excitability and for the precision of the heartbeat. Furthermore, cardiac HCN channels are involved in the repolarization process of heart ventricles [56**,57]. It will be important to consider the full spectrum of these diverse cardiac functions when exploring agents acting on HCN channels for a specific clinical purpose such as reduction of heart rate.

56.** Fenske S, Mader R, Scharr A, Paparizos C, Cao-Ehlker X, et al.: HCN3 contributes to the ventricular action potential waveform in the murine heart. Circ Res 2011, 109:1015-1023.
First study demonstrating a functional role of HCN3 channels in the heart. Using HCN3-deficient mouse line the authors show that HCN3 together with other members of the HCN channel family confers a depolarizing background current that regulates ventricular resting potential and counteracts the action of hyperpolarizing potassium currents in late repolarization.
57. Fenske S, Krause S, Biel M, Wahl-Schott C: The role of HCN channels in ventricular repolarization. Trends Cardiovasc Med 2011, 21:216-220.

Roles of HCN1 channels for sinoatrial impulse conduction (source-sink relation) The primary impulse initiating the heart beat is generated in the leading pacemaker cell(s) of the sinoatrial node. Once the leading pacemaker cell(s) reaches the threshold for L-type Ca2+ channels an action potential is generated. Since pacemaker cells are interconnected via gap junctions, the impulse is conducted through the sinoatrial network and to the atrium. During impulse propagation the source cell (the cell which first reached AP threshold and is firing the action potential) charges the neighboring cell (sink), in which the membrane potential is below threshold (Figure 1) [24*]. Impulse propagation depends on the source-sink relation [24*, 25–29]. HCN1 deletion increases the sinoatrial conduction time suggesting the existence of a source sink mismatch in the HCN1-deficient mouse [19**].

Role of HCN1 channels for impulse formation and impulse conduction in the sinoatrial node. Schematic pacemaker potential in sinoatrial node cells of wild type (a) and HCN1-/- mice.
(b) HCN channels contribute to the slow diastolic depolarization. In the absence of HCN1 the slope of SDD isdecreased and the time to threshold for an action potential increased. HCN channels decrease the maximal diastolic potential (MDP). In the absence of HCN1 the MDP is increased. This results in an increased distance and time to threshold for an action potential and a decrease in impulse propagation.  [SDD: slow diastolic depolarization; MDD: maximal diastolic depolarization; Vthr: threshold potential for the generation of an action potential.]
(c) Direction of intracellular and extracellular current flow during propagation of an action potential from depolarized (source) to resting cells (sink).
(d)Source sink relationship in propagation. Charge from excited cells (source) flows into unexcited cell (sink) and provides the charge to depolarize them to activation threshold. Arrows and dotted lines indicate changes observed in HCN1-/- mice of parameter indicated leading to source sink mismatch and prolonged sinoatrial conduction. Modified from [24*].

24.* Spector P: Principles of cardiac electric propagation and their implications for re-entrant arrhythmias. Circ Arrhythm Electrophysiol 2013, 6:655-661.
The authors provide an excellent review of the principles of impulse propagation in relation to arrhythmia.

HCN1 channels increase the temporal and spatial precision of impulse formation in sinoatrial node

HCN1 channels increase the temporal and spatial precision of impulse formation in sinoatrial node

HCN1 channels increase the temporal and spatial precision of impulse formation in sinoatrial node.
(a) Schematic of the sinoatrial node. Atrial cells invaginate into the central sinoatrial node. Putative localization of HCN1 channels at contact interface between strands of atrial myocytes which extend into the central SAN and sinoatrial node pacemaker cells. Green: autonomous innervation. HCN1 channels dampen network noise generated by neighboring pacemaker cells in the sinoatrial network, by invading hyperpolarization of atrial cells and by autonomous regulation. SAN: sinoatrial node, RA: right atrium, CT: crista terminalis.
(b) Model of sinoatrial node function (for detail see text). Note that individual cells display different phases and slightly different periods.

Pharmacological inhibition of cardiac HCN channels

HCN channels have emerged as interesting targets for the development of drugs that lower the heart rate. Ivabradine is the first and currently the only clinically approved compound that specifically targets HCN channels. The therapeutic indication of ivabradine is the symptomatic treatment of chronic stable angina pectoris in patients with coronary artery disease with a normal sinus rhythm (for details see [48], the international trial on the treatment of angina with ivabradine vs. atenolol (INITIATIVE) trial (n = 939) [49] and the antianginal efficacy and safety of the association of the Ih/If current inhibitor ivabradine with a beta-blocker (ASSOCIATE) study (n = 889) [50]).

The Role of HCN Channels in Ventricular Repolarization

Stefanie Fenske, Stefanie Krause, Martin Biel, and Christian Wahl-Schott
Trends Cardiovasc Med 2011; 21:216-220
PII S1050-1738(12)00143-0

Hyperpolarization-activated cyclic nucleotide gated (HCN) channels pass a cationic current (Ih/If) that crucially contributes to the slow diastolic depolarization (SDD) of sinoatrial pacemaker cells and, hence, is a key determinant of cardiac automaticity and the generation of the heartbeat. However, there is growing evidence that HCN channels are not restricted to the spontaneously active cells of the sinoatrial node and the conduction system but are also present in ventricular cardiomyocytes that produce an action potential lacking SDD. This observation raises the question of the principal function(s) of HCN channels in working myocardium. Our recent analysis of an HCN3-deficient (HCN3–/–) mouse line has shed new light on this central question.

We propose that HCN channels contribute to the ventricular action potential waveform, specifically during late repolarization. In this review, we outline this new concept.

In the late 1970s, the hyperpolarization activated current (Ih/If) was discovered and characterized in sinoatrial node cells (Brown and Difrancesco 1980). This current displays several unique biophysical properties: activation upon hyperpolarization and deactivation by depolarization, with a small but substantial degree of activation at resting potentials typically observed in sinoatrial node pacemaker cells (–60 to –50 mV) and ventricular cells (–85 to –75 mV); shift of the activation curve to more positive potentials by cAMP;  block by millimolar concentrations of external Cs+; and permeability for Na+ and K+ions with a reversal potential near –35 mV.

  • HCN3 Is a Component of Ventricular Ih
  • HCN Channels Prolong Action Potentials During Late Repolarization
  • HCN3 Forms Background Channels That Do Not Deactivate During the Action Potential
  • HCN channels need to be open at the resting membrane potential;
    (2) HCN channels remain open during the entire time course of the action potential—de novo opening of HCN channels during the AP does not occur because these channels are activated by hyperpolarization and depolarization decreases open probability; and
    (3) a driving force is needed to sustain an HCN-mediated current during the AP. A detailed analysis of the functional properties of heterologously expressed HCN3 channels revealed that these three prerequisites are met.

Neurophysiology of HCN channels: From cellular functions to multiple regulations

Chao He, Fang Chen, Bo Li, Zhian Hu
Progress in Neurobiology 112 (2014) 1–23
http://dx.doi.org/10.1016/j.pneurobio.2013.10.001

Hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels are encoded by HCN1-4 gene family and have four subtypes. These channels are activated upon hyperpolarization of membrane potential and conduct an inward, excitatory current Ih in the nervous system. Ih acts as pacemaker current to initiate rhythmic firing, dampen dendritic excitability and regulate presynaptic neurotransmitter release. This review summarizes recent insights into the cellular functions of Ih and associated behavior such as learning and memory, sleep and arousal. HCN channels are excellent targets of various cellular signals to finely regulate neuronal responses to external stimuli. Numerous mechanisms, including transcriptional control, trafficking, as well as channel assembly and modification, underlie HCN channel regulation. In the next section, we discuss how the intracellular signals, especially recent findings concerning protein kinases and interacting proteins such as cGKII, Ca2+/CaMKII and TRIP8b, regulate function and expression of HCN channels, and subsequently provide an overview of the effects of neurotransmitters on HCN channels and their corresponding intracellular mechanisms. We also discuss the dysregulation of HCN channels in pathological conditions. Finally, insight into future directions in this exciting area of ion channel research is provided.

The hyperpolarization-activated current, Ih, was first observed in sino-atrial node tissue in 1976 and later was identified in rod photoreceptors and hippocampal pyramidal neurons (Noma and Irisawa, 1976). Due to its unique properties, particularly the activation upon hyperpolarization of the membrane potential, Ih has been also termed If (f for funny) or Iq (q for queer). The hyperpolarization-activated cyclic nucleotide-gated (HCN) cation ion channels underlying Ih were discovered in the late 1990s and subsequently, the genes encoding these channels were identified, which enable the expression of HCN channels in heterologous systems.

HCN channels belong to the superfamily of voltage-gated pore loop channels with four pore-forming subunits (HCN1-4) encoded by the HCN1-4 gene family in mammals (Robinson and Siegelbaum, 2003). Each subunit has six transmembrane helices (S1–S6), with the positively charged voltage sensor (S4) and the pore region carrying the GYG motif between S5 and S6, which forms the ion selectivity filter (Macri et al., 2012). Following S6 is the 80-residue C-linker comprising six a-helices (A0–F0) and the cyclic nucleotide binding domain (CNBD). The CNBD consists of three a-helices (A–C) and a b-roll between the A- and B-helices (Fig. 1) (Biel et al., 2009; Wahl-Schott and Biel, 2009; Wicks et al., 2011). Together, the C-linker and CBND can be referred to as the ‘‘cAMP-sensing domain’’ (CSD) because they are of functional importance for the cAMP-induced positive shift of the voltage-dependent activation of HCN channels. The crystal structure of CSD has been elucidated at an atomic resolution, but a high-resolution structure of the transmembrane core remains unsolved.

Structure of HCN channels

Structure of HCN channels

Structure of HCN channels. Left: one subunit is composed of six transmembrane segments (S1–S6), with the positive charged voltage sensor (S4) and the pore region carrying the GYG motif between S5 and S6. The C-terminal of HCN channels is composed of the C-linker and the cyclic nucleotide-binding domain (CNBD) which mediates their responses to cAMP. The C-linker consists of six a-helices: A0 to F0 . The CNBD follows the C-linker domain and consists of a-helices A–C with a b-roll between the A- and B-helices. Right: the four subunits assemble in homomeric or heteromeric tetramer configurations in vivo.

Regulatory mechanisms of Ih function by the small molecules, protein kinases and interacting proteins.

Regulatory mechanisms of Ih function by the small molecules, protein kinases and interacting proteins.

Regulatory mechanisms of Ih function by the small molecules, protein kinases and interacting proteins. Black arrows indicate known sites of HCN channels interaction with small molecules, protein kinases and interacting proteins. Broken lines indicate the speculated interaction sites. Filamin A interacts with HCN1 via a region of 22 amino acids located downstream from the CNBD. Tamalin and Mint2 bind to the CNBD-downstream sequence of HCN2. The binding of the PDZ domain of S-SCAM occurs at the cyclic nucleotide-binding domain (CNBD) and the CNBD downstream sequence of the carboxy-terminal tail. CNBD, cyclic nucleotide binding domain; SNL, C-terminal tripeptide of HCN1, HCN2 and HCN4.

modulation of HCN channels by neurotransmitters and associated intracellular signal pathways

modulation of HCN channels by neurotransmitters and associated intracellular signal pathways

The modulation of HCN channels by neurotransmitters and associated intracellular signal pathways. Glutamate (Glu) activates N-methyl-D-aspartate receptors (NMDARs) and a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) which results in the Ca2+ influx and subsequently activates calcium calmodulin kinase (CaMKII). CaMKII increases channels surface expression through the interacting protein TRIP8b (1a-4) or reduces the HCN1 gene transcription via Neuronal Restrictive Silencing Factor (NRSF) in pathological conditions. Glu, norepinephrine (NE, in rats), 5-hydroxytryptamine (5-HT) and triphosphate (ATP) bind to specific G-coupled receptors and modulate the activity of HCN channels via the PLC-PKC or p38-MAPK signaling pathways. Activation of PKC suppresses the activation of HCN channels, whereas p38-MAPK causes a positive shift of HCN channels voltage-dependent activation. Adenosine, NE (in monkey), 5-HT, dopamine (DA) and Ach (acetylcholine) bind to Gs- or Gi coupled receptors. Gs or Gi oppositely control the activity of adenylate cyclase (AC), which catalyzes the ATP to cAMP. cAMP could shift the HCN channels voltage-dependent activation to positive direction and accelerate the kinetics of channels activation. Nitric oxide (NO) interacts with soluble guanylyl cyclase (GC) and thus increases the intracellular concentration of cGMP, which induces a positive shift of HCN channels voltage-dependent activation. Sharp and blunted arrows represent the positive and negative regulation, respectively. Broken lines indicate the speculated signal pathway.

Ultimately, the study of the HCN channels will provide an overall picture underlying the real-time in vivo regulation of the function and expression of HCN channels to fulfill complex functions in different contexts.

Oxygen uptake kinetics during high-intensity arm and leg exercise

Katrien Koppo, Jacques Bouckaert, Andrew M. Jones
Respiratory Physiology & Neurobiology 133 (2002) 241-250
PII: S1569 – 9048 ( 02 ) 00184 – 2

The purpose of the present study was to examine the oxygen uptake kinetics during heavy arm exercise using appropriate modelling techniques, and to compare the responses to those observed during heavy leg exercise at the same relative intensity. We hypothesized that any differences in the response might be related to differences in muscle fiber composition that are known to exist between the upper and lower body musculature. To test this, ten subjects completed several bouts of constant-load cycling and arm cranking exercise at 90% of the mode specific ˙VO2 peak. There was no difference in plasma [lactate] at the end of arm and leg exercise. The time constant of the fast component response was significantly longer in arm exercise compared to leg exercise (mean ­+ S.D., 489 +12 vs. 219 + 5 sec; P < 0.01), while the fast component gain was significantly greater in arm exercise (12.19 + 1.0 vs. 9.29 + 0.5 ml min-1 W-1; P < 0.01). The ˙VO2 slow component emerged later in arm exercise (1269 + 27 vs. 959 + 20 sec; P < 0.01) and, in relative terms, increased more per unit time (5.5 vs. 4.4% min-1; P < 0.01). These differences between arm crank and leg cycle exercise are consistent with a greater and/or earlier recruitment of type II muscle fibers during arm crank exercise.

Probability and magnitude of response to cardiac resynchronization therapy according to QRS duration and gender in nonischemic cardiomyopathy and LBBB

Niraj Varma, Mahesh Manne, Dat Nguyen, …, Patrick Tchou
Heart Rhythm 2014; 11: 1139–1147
http://dx.doi.org/10.1016/j.hrthm.2014.04.001

BACKGROUND QRS morphology and QRS duration (QRSd) determine cardiac resynchronization therapy (CRT) candidate selection but criteria require refinement.
OBJECTIVE To assess CRT effect according to QRSd, treated by dichotomization vs a continuous function, and modulation by gender.
METHODS Patients selected were those with New York Heart Association classIII/IV heart failure and with left bundle branch block and nonischemic cardiomyopathy (totest “pure” CRT effect) with pre-and post- implant echocardiographic evaluations. Positive response was defined as increased left ventricular ejection fraction (LVEF) post-CRT.
RESULTS In 212 patients (LVEF 19% +  7.1%; QRSd 160 + 23 ms; 105 (49.5%) women), CRT increased LVEF to 30% + 15% (P < .001) during a median follow-up of 2 years. Positive response occurred in 150 of 212 (71%) patients. Genders did not differ for QRSd, pharmacotherapy, and comorbidities, but response to CRT among women was greater: incidence 84% (88of105) in women vs 58% (62of107) in men (P < .001); increase in LVEF 15%+ 14% vs 7.2% + 13%, respectively (P < .001). Overall, the response rate was 58% when QRSd <150 ms and 76% when QRSd > 150 ms (P <.009). This probability differed between genders: 86% in women vs 36% in men (P < .001) when QRSd <150 ms and 83% vs 69%, respectively, when QRSd >150 ms (P < .05). Thus, female response rates remained high whether QRSd was < 150 ms >150 ms (86% vs 83%; P = .77) but differed in men (36% vs 69%; P < .001). With QRSd as a continuum, the CRT-response relationship was nonlinear and significantly different between genders. Female superiority at shorter QRSd inverted with prolongation > 180 ms.
CONCLUSION The QRSd-CRT response relationship in patients with heart failure and with left bundle branch block and non-ischemic cardiomyopathy is better  described by a sex-specific continuous function and not by dichotomization by 150ms, which excludes a large proportion of women with potentially favorable outcome.

Comparison of eterminants Myocardial Oxygen Consumption During Arm and Leg Exercise in Normal Persons

Gary J. Balady, et al.  Am J Cardiol 1985; 57: 1385-87.

The effects of arm exercise on myocardiai oxygen consumption are not well understood; they may differ from the effects of leg exercise. Previous studies have shown that the ischemic threshold is higher in patients performing arm exercise and leg exercise at the same heart rate-blood pressure product. The contribution of other determinants of myocardiai oxygen consumption-left ventricular (LV) peak meridional systolic wail stress and contractility-to these observed differences were studied.
Thirty healthy subjects exercised to the same peak rate-pressure product during dynamic upper- and lower-extremity exercise. Peak workload was lower
during arm exercise (100 + 16 W) leg exercise (170 + 21 W, p < 0.001). LV wail stress did not differ during either form of exercise (197 + 44 vs 204 + 33 dynes/cm2 X 103, arm vs leg, respectively). This was also true of contractility as assessed by the velocity of circumferential fiber shortening (2.6 + 0.6 vs 2.5 + 0.4 circ/s, arm vs leg, respectively) and the preejection period/LV ejection time ratio (0.33 + 0.11 vs 0.31 + 0.07, arm vs leg, respectively). Normal subjects exercising to a similar rate-pressure product showed the same levels at LV wail stress and contractility for arm and leg exercise despite the lower rkioad performed with arm exercise.

Anti-hypertensive effect of radiofrequency renal denervation in spontaneously hypertensive rats

Takeshi Machino, N Murakoshi, A Sato, …, T Hoshi, T Kimura, K Aonuma
Life Sciences 110 (2014) 86–92 http://dx.doi.org/10.1016/j.lfs.2014.06.015

Aims: We aimed to investigate the anti-hypertensive effect of radiofrequency (RF) renal denervation (RDN) in an animal model of hypertension.           Materials and methods: RF energy was delivered to bilateral renal arteries through a 2 Fr catheter with opening abdomen in 8 spontaneously hypertensive rats (SHRs) and 8 Wistar–Kyoto rats (WKYs). Sham operation was performed in other 8 SHRs and 8 WKYs. Blood pressure (BP), heart rate (HR), and urinary norepinephrine excretion were followed up for 3 months. Plasma and renal tissue concentrations of norepinephrine and plasma renin activity were measured 3 months after the procedure. The RDN was confirmed by a decrease in renal tissue norepinephrine.
Key findings: RF-RDN restrained a spontaneous rise in systolic BP (46 ± 12% increase from 158 ± 8 to 230 ± 14 mmHg vs. 21 ± 18% increase from 165 ± 9 to 197 ± 20 mmHg, p= 0.01) and diastolic BP (55 ± 27% increase from 117 ± 9 to 179 ± 23 mmHg vs. 28 ± 13% increase from 120 ± 7 to 154 ± 13 mm Hg, p= 0.04) in SHRs; however, WKYs were not affected. Although there were no changes in HR and systemic norepinephrine, the renal tissue norepinephrine was decreased by RF-RDN in both SHR (302±41 vs. 159±44 ng/g kidney, p b 0.01) and WKY (203 ± 33 vs. 145 ± 26 ng/g kidney, p= 0.01). Plasma renin activity was reduced by the RF-RDN only in SHR (35.3 ± 9.5 vs. 21.4 ±  8.6 ng/mL/h, p < 0.01).
Significance: RF-RDN demonstrated an anti-hypertensive effect with a reduction of renal tissue norepinephrine and plasma renin activity in SHR.

Effectiveness of Renal Denervation Therapy for Resistant Hypertension: A Systematic Review and Meta-Analysis

Mark I. Davis, KB Filion, D Zhang, MJ Eisenberg, …, EL Schiffrin, D Joyal
J Am Coll  Cardiol 2013; 62(3): 231-241.
http://dx.doi.org/10.1016/j.jacc.2013.04.010

Objectives This study sought to determine the current effectiveness and safety of sympathetic renal denervation (RDN) for resistant hypertension.               Background RDN is a novel approach that has been evaluated in multiple small studies.
Methods We performed a systematic review and meta-analysis of published studies evaluating the effect of RDN in patients with resistant hypertension. Studies were stratified according to controlled versus uncontrolled design and analyzed using random-effects meta-analysis models.                                    Results We identified 2 randomized controlled trials, 1 observational study with a control group, and 9 observational studies without a control group. In controlled studies, there was a reduction in mean systolic and diastolic blood pressure (BP) at 6 months of –28.9 mm Hg (95% confidence interval [CI]: –37.2 to –20.6 mm Hg) and –11.0 mm Hg (95% CI: –16.4 to –5.7 mm Hg), respectively, compared with medically treated patients (for both, p < 0.0001). In uncontrolled studies, there was a reduction in mean systolic and diastolic BP at 6 months of –25.0 mm Hg (95% CI: –29.9 to –20.1 mm Hg) and –10.0 mm Hg (95% CI: –12.5 to –7.5 mm Hg), respectively, compared with pre-RDN values (for both, p < 0.00001). There was no difference in the effect of RDN according to the 5 catheters employed. Reported procedural complications included 1 renal artery dissection and 4 femoral pseudoaneurysms.
Conclusions RDN resulted in a substantial reduction in mean BP at 6 months in patients with resistant hypertension. The decrease in BP was similar irrespective of study design and type of catheter employed. Large randomized controlled trials with long-term follow-up are needed to confirm the sustained efficacy and safety of RDN.

Effects of renal denervation on the development of post-myocardial infarction heart failure and cardiac autonomic nervous system in rats

Jialu Hu, Yan Yan, Qina Zhou, Meng Ji, Conway Niu, Yuemei Hou, Junbo Ge
Intl J Cardiol 172 (2014) e414–e416 http://dx.doi.org/10.1016/j.ijcard.2013.12.254

Prior studies indicated that radiofrequency renal denervation (RD) had beneficial effects on post-myocardial infarction (MI) heart failure (HF) in rats. In this study we aimed to assess its effects on cardiac autonomic nervous system (CANS) which might be one of the most important mechanisms of RD’s therapeutic effect on post-MI HF and determine the best timing for RD.

One hundred Wistar rats were randomly assigned into five experimental groups: MI group (n = 20), RD group (n = 20), MI-1d + RD group (RD performed one day post-MI, n = 20), MI-4w + RD group (RD performed four weeks post-MI, n = 20), and N group (control group, n = 20).MI was produced through ligation of the anterior descending artery. RD was performed through stripping of the renal nerves. The experimental design and implementation were conducted in accordance with animal welfare guidelines.

Eight weeks post-MI, significant improvements were observed in both MI-1d + RD and MI-4w + RD groups compared to the MI group, that include

(1) improved left ventricular (LV) function and hemodynamics with increased water and sodium excretion;
(2) decreased plasma and renal tissue norepinephrine levels while tissue norepinephrine content increased in myocardium;
(3) increased β1-receptor in myocardium and improved heart rate variability;  (4) decreased plasma renin, angiotensin II, aldosterone, BNP and endothelin levels.

More therapeutic effects were found in the MI-1d + RD group than the MI-4w + RD group.

Firstly, our study showed that RD attenuated the remodeling of CANS and modulated its activities. RD leads to preservation of β1 receptors content along with the β1 mRNA expression in noninfarcted cardiac tissue in this HF model (Fig. 1). This correlated with an improvement in heart function and cardiac remodeling. HRV is a sensitive marker for the CANS. RD led to a slower HR and higher SDNN in both intervention groups.

Secondly, we found that RD blocked both peripheral and central RAAS and sympathetic nervous system (SNS) at the same time. And this may answer the question how RD exerted effect on CANS. In our study RD restores renin, angiotensin II, and aldosterone to near normal levels. This not only explains the increase in sodium and water excretion, but also confirms that RD blocks renal RAAS via blockage of the efferent renal sympathetic nerves which is consistent with our previous study.

Thirdly, early RD, performed one day post-MI, resulted in greater excretion of urinary sodium, lower circulating BNP and ET-1 levels compared to late interventions (four weeks post-MI). This suggests that RD performed in the acute phase of MI may not only reverse cardiac remodeling but also has a preventive effect against the development of HF, as what was observed with β-blockers. RD alleviated cardiac preload and afterload by increasing water and sodium retention, blocking cardiac sympathetic activation and decreasing a variety of vasomotor factors which may lead to alleviated acute and chronic ischemia of the heart.

RD improves hemodynamics, decreases neuro-hormonal activations, modulates cardiac autonomic activities, and attenuates LV remodeling in HF. Early intervention appears to have greater beneficial effects on cardiac functional recovery and reverse remodeling after myocardial injury. Circulating neuro-hormones may be effective indicators to evaluate the therapeutic effect of RD on HF. Our data suggested that RD is a safe, non-pharmaceutical treatment of HF after cardiac injury, with unique benefits in stabilizing cardiac autonomic activity and remodeling post-MI.

The cardiac pacemaker current

Mirko Baruscotti, Andrea Barbuti, Annalisa Bucchi
Journal of Molecular and Cellular Cardiology 48 (2010) 55–64
http://dx.doi.org:/10.1016/j.yjmcc.2009.06.019

In mammals cardiac rate is determined by the duration of the diastolic depolarization of sinoatrial node (SAN) cells which is mainly determined by the pacemaker If current. f-channels are encoded by four members of the hyperpolarization-activated cyclic nucleotide-gated gene (HCN1–4) family. HCN4 is the most abundant isoform in the SAN, and its relevance to pacemaking has been further supported by the discovery of four loss-of-function mutations in patients with mild or severe forms of cardiac rate disturbances. Due to its selective contribution to pacemaking, the If current is also the pharmacological target of a selective heart rate-reducing agent (ivabradine) currently used in the clinical practice. Albeit to a minor extent, the If current is also present in other spontaneously active myocytes of the cardiac conduction system (atrioventricular node and Purkinje fibres). In working atrial and ventricular myocytes f-channels are expressed at a very low level and do not play any physiological role; however in certain pathological conditions over-expression of HCN proteins may represent an arrhythmogenic mechanism. In this review some of the most recent findings on f/HCN channels contribution to pacemaking are described.

Cardiac pacemaking originates in the sinoatrial node (SAN) as a consequence of spontaneous firing of rhythmic action potentials generated by specialized myocytes. Although the electrical behavior of a typical SAN cell differs in several aspects from that of a working myocyte, the functional hallmark can be precisely identified in the events that take place during the diastolic interval. During this phase atrial and ventricular myocytes rest in a standby-like condition at a stable voltage (∼−80 mV); a quite different situation characterizes SAN cells, where the cell potential slowly creeps up from the
maximum diastolic potential of about −60 mV to the threshold for the ignition of a new action potential. Since this time interval sets the pace of the heart, this phase is named “pacemaker depolarization”. Given the large spectrum of heart rates observed in mammals the duration of this phase can vary substantially, however the voltage range encompassed is extremely constant and roughly extends from −60 to−40 mV . To sustain this phase several ionic currents and pumps enter in action at variable times and voltages, and this complexity allows for a highly flexible system since the chronotropic fine tuning operated by neuro-hormonal regulators can target different effectors.

In this review we will focus on the If current which is responsiblefor initiating the diastolic depolarization of SAN cells. Due to its fundamental role and its unusual characteristics of being activated in hyperpolarization, this current was named “pacemaker current” or “funny” (If) current. The unique property of a reverse voltage dependence, together with the inward nature of the current at diastolic potentials, makes this current apt to initiate and support the diastolic depolarization. In addition, the direct modulation of the current operated by the second messenger cAMP, represents one of the main pathways by which the autonomic nervous system controls cardiac chronotropism. Two recent clinical findings further confirm the role of f-channels in setting the cardiac rate: one is the evidence of a causative link between the presence of loss-of-function mutations found in these channels and the arrhythmic state of individuals carrying the mutations, and the other is the specific heart rate reduction observed in patients treated with ivabradine, a drug that at therapeutic doses selectively reduces the If current (see specific sections in this review).

Although originally discovered in the heart, the If current is also abundantly present in a large fraction of neuronal elements, where it contributes to rhythmic firing, synaptic integration, and dendritic integration.

Molecular and functional properties of SAN myocytes

Molecular and functional properties of SAN myocytes

Molecular and functional properties of SAN myocytes. (A) Spontaneous action potentials (left) and If current traces (right) recorded from typical rabbit SANmyocytes; currents were elicited by hyperpolarizing voltage steps in the range−45 to −75 mV. (B) Immunofluorescence analysis of rabbit SAN tissue slice labelled with anti-connexin 43 (Cx43, red) and anti-HCN4 (green) antibodies. HCN4 is strongly expressed in the central region of the SAN, while the opposite staining is observed for Cx43; crista terminalis (CT), interatrial septum (IS). (C) HCN4 labelling of single myocytes isolated from CT, SAN and IS (top), and  representative current traces recorded at−125mV frommyocytes isolated from the same regions (bottom). Both If current density and HCN4 labelling are more abundant in the central nodal area. (Panels B and C from [61] with permission).

[61] Brioschi C, Micheloni S, Tellez JO, Pisoni G, Longhi R, Moroni P, et al. Distribution of the pacemaker HCN4 channel mRNA and protein in the rabbit sinoatrial node. J Mol Cell Cardiol 2009;47:221–7.

The search of new therapeutic tools consisting of gene- and/or cell-based intervention aimed to restore compromised cardiac functions has prompted researchers to exploit the use of HCN channels to alter cellular electrical activity in order to generate, in normally quiescent substrates, stable rhythmic activity similar to that of native pacemaker myocytes. The specific features of pacemaker channels and in particular the fact that they are activated only at diastolic potentials and do not contribute to other phases of the action potentials, make them particularly suitable for such purpose. Early in vitro studies demonstrated that virus-mediated over-expression of HCN2 channels induced a significant increase in the rate of spontaneously beating neonatal ventricular myocytes by causing an If-mediated increase of the diastolic depolarization slope. This approach was later confirmed in vivo by showing that direct injection of the HCN2-adenovirus in the left atrium or into the ventricular conduction system of dogs, was able to induce ectopic regular spontaneous activity after AV block. Similarly, adenovirus-mediated over-expression of HCN1 or HCN4 was sufficient to induce a regular rhythm in quiescent cardiomyocyte. Alternative cell-based strategies, aimed to avoid the use of viruses, have been developed by engineering cells in order to express high levels of HCN channels. Engineered human mesenchymal stem cells (hMSCs) expressing either HCN2 or HCN4 have been shown in vitro to properly connect to neonatal cardiomyocytes and to increase their intrinsic spontaneous rhythm. HCN2-expressing hMSCs have also been successfully transplanted in canine left ventricular wall where they were able to induce stable ectopic beats.

Currently, ivabradine is marketed for treatment of chronic stable angina in patients with normal sinus rhythm who have a contraindication or intolerance to β-blockers; clinical studies of patients with chronic stable angina have shown that ivabradine acts as a pure heart rate-reducing agent and has anti-ischemic and anti-anginal properties equivalent to β-blockers and Ca2+ channel blockers and presents a good safety and tolerability profile even during long-term treatment. Mild visual symptoms (phosphenes) were occasionally reported, but were generally well tolerated. Additional information comes from results from a recent large clinical trial (BEAUTIFUL) which indicate that ivabradine treatment of patients with stable coronary artery disease (CAD) and heart rate ≥70 bpm can reduce the incidence of some CAD outcomes such as hospitalization for myocardial infarction and coronary revascularization.

The beat goes on: Cardiac pacemaking in extreme conditions

Christopher M.Wilson, Georgina K. Cox, Anthony P. Farrell
Comparative Biochemistry and Physiology, Part A xxx (2014) xxx–xxx
http://dx.doi.org/10.1016/j.cbpa.2014.08.014

In order for an animal to survive, the heart beat must go on in all environmental conditions, or at least restart its beat. This review is about maintaining a rhythmic heartbeat under the extreme conditions of anoxia (or very severe hypoxia) and high temperatures. It starts by considering the primitive versions of the protein channels that are responsible for initiating the heartbeat, HCN channels, divulging recent findings from the ancestral craniate, the Pacific hagfish (Eptatretus stoutii). It then explores how a heartbeat can maintain a rhythm, albeit slower, for hours without any oxygen, and sometimes without autonomic innervation. It closes with a discussion of recent work on fishes, where the cardiac rhythm can become arrhythmic when a fish experiences extreme heat.

Sympathetic renal denervation: Hypertension beyond SYMPLICITY

Israel M. Barbash, Ron Waksman
Cardiovascular Revascularization Medicine 14 (2013) 229–235
http://dx.doi.org/10.1016/j.carrev.2013.02.004

Despite a wide range of drug treatment for hypertension, resistant hypertension rates remain high. The Symplicity™ Renal Denervation System (Medtronic, Santa Rosa, CA), which creates renal nerve denervation, has shown initial success in lowering blood pressure among patients with resistant  hypertension. Given the enormous market for this treatment approach, an estimated two dozen other companies are pursuing technologies with alternative approaches. Despite this fact, very little has been published on preclinical and clinical experience with these new devices. The current review summarizes the most prominent technologies in the pipeline and provides insight into the mechanism of action, preclinical, and clinical experience with these new devices

A large body of evidence has established the central role of the kidneys in hypertension, both as an affector and effector of the central sympathetic system [9]. Renal efferent sympathetic activity initiates processes towards fluid retention, such as the release of renin and increased tubular sodium reabsorption. Moreover, afferent sympathetic activity increases central sympathetic drive, which plays a major role in sustaining hypertension. In fact, historic studies of surgical sympathectomy in patients with resistant hypertension or malignant hypertension uncontrolled by pharmacotherapy were shown to be effective in reducing blood pressure, albeit with severe side effects. Thus, with the introduction of more effective medications, this procedure was abandoned. Renal sympathetic nerves run alongside the renal artery adventitia to enter the hilus of the kidney. Thereafter, they divide into smaller nerve bundles following the anatomic course of the renal blood vessels, penetrating the cortical and juxtamedullary areas inside the kidneys. Based on these anatomic features, it was postulated that creating local nerve injury along the renal arteries may achieve effective denervation.

A key issue in accomplishing effective RDN is to target the sympathetic nerve bundles lying in the adventitia of the renal arteries. Because the vast majority of devices currently under development are percutaneous, RDN is performed from within the vessel lumen. Thus, one of the most important features of such a device is the ability to minimize the damage to the renal artery wall.

Ultrasound energy consists of high-frequency sound waves emitted by a transducer within the catheter. This high energy can pass through surrounding fluids and can generate frictional heating in tissues resulting in a temperature increase that is sufficient to cause injury to the surrounding tissue, specifically the renal nerves. Based on these principles, several systems were developed and are currently being evaluated. ReCor Medical’s (Ronkonkoma, NY) PARADISE™ Percutaneous Renal Denervation System is based on delivery of high ultrasonic energy to induce nerve tissue injury. The PARADISE system is composed of two components: a 6 F-compatible balloon catheter with a cylindrical ultrasound transducer that emits ultrasound energy circumferentially (Fig. 2A)[ Ultrasound based renal denervation systems: (A) Percutaneous Renal Denervation System (PARADISE™); (B) TIVUS system]  and a portable generator which controls automated balloon inflation and deflation, and energy delivery. Energy is delivered in 3 different locations along the artery with 50 s inflation and delivery of ultrasound energy at each site. This device received CE mark in February 2012. For RDN, the PARADISE balloon catheter is positioned inside the renal artery and the generator automatically inflates the balloon, delivers the ultrasonic energy, and deflates the balloon. Endothelial thermal damage is prevented by cooled fluid in the balloon.

Radiofrequency based renal denervation systems

Radiofrequency based renal denervation systems: (A) Symplicity Renal Denervation System; (B) EnligHTN Renal Denervation System; (C) V2 bipolar balloon catheter; (D) OneShot Balloon catheter

Sample Entropy and Traditional Measures of Heart Rate Dynamics Reveal Different Modes of Cardiovascular Control During Low Intensity Exercise

Matthias Weippert, Martin Behrens, Annika Rieger and Kristin Behrens
Entropy 2014, 16, 5698-5711; http://dx.doi.org:/10.3390/e16115698

Biological time series like the normal heartbeat-to-heartbeat fluctuation demonstrate complex dynamics. Based on their potential to give additional information beyond traditional heart rate variability (HRV) indices, nonlinear parameters have been applied for investigating short and long term effects of exercise on heart rate (HR) control. However, despite their diagnosticity and their clinical significance, the physiological background of their behavior is not very well established. It is assumed that complexity and regularity measures are fundamentally different from traditional HRV indices and show no correlation to these measures. However, many researchers found at least modest correlations for some nonlinear measures and traditional HRV indices under different conditions. It has also been shown that complexity of short-term HRV is under control of the autonomic nervous system. Currently, there are only few studies available that compared the cardiovascular response pattern to different exercise modes at similar HR. Lindquist et al. found a stronger increase of systolic (SBP) and diastolic arterial blood pressure (DBP) during isometric handgrip compared to cycling at comparable HR of 90 bpm.

Nonlinear parameters of heart rate variability (HRV) have proven their prognostic value in clinical settings, but their physiological background is not very well established. We assessed the effects of low intensity isometric (ISO) and dynamic (DYN) exercise of the lower limbs on heart rate matched intensity on traditional and entropy measures of HRV. Due to changes of afferent feedback under DYN and ISO a distinct autonomic response, mirrored by HRV measures, was hypothesized. Five-minute inter-beat interval measurements of 43 healthy males (26.0 ± 3.1 years) were performed during rest, DYN and ISO in a randomized order. Blood pressures and rate pressure product were higher during ISO vs. DYN (p < 0.001). HRV indicators SDNN as well as low and high frequency power were significantly higher during ISO (p < 0.001 for all measures). Compared to DYN, sample entropy (SampEn) was lower during ISO (p < 0.001). Concluding, contraction mode itself is a significant modulator of the autonomic cardiovascular response to exercise. Compared to DYN, ISO evokes a stronger blood pressure response and an enhanced interplay between both autonomic branches. Non-linear HRV measures indicate a more regular behavior under ISO. Results support the view of the reciprocal antagonism being only one of many modes of autonomic heart rate control. Under different conditions; the identical “end product” heart rate might be achieved by other modes such as sympathovagal co-activation as well.

ANOVA revealed a significant effect of experimental condition on all cardiovascular measures and autonomic indices. Average HR raised moderately from 65 ± 9 bpm at baseline to 85 ± 9 bpm during both types of exercise. HR during the first exercise perfectly matched HR of the subsequent exercise; average difference was only 0.3 ± 1.5 bpm (range: −2.6 to 4.3 bpm). Accordingly, HR and average R-R interval did not differ between DYN and ISO. The traditional vagal modulation HRV measure RMSSD was also not affected by the exercise mode, whereas SDNN was. Natural log-transformed HRV spectral indices HFP and LFP, the normalized powers LF n. u. and HF n. u. as well SampEn (Figure 1) were significantly different between DYN and ISO. Interestingly, SampEn did not differ between REST and DYN. There was no difference of the LF/HF ratio between REST and ISO, whereas comparison of REST vs. DYN showed a statistical trend (p = 0.077). Further, there was a small effect of condition on the HF peak frequency (F(2; 84) = 4.959, p < 0.01, η² = 0.106). While HF peak significantly shifted from 0.22 ± 0.07 Hz during REST to 0.26 ± 0.09 Hz during DYN (p < 0.05), no difference was found between REST and ISO (0.23 ± 0. 07 Hz). Post-hoc pair wise comparison between DYN and ISO showed a statistical trend for the HF peak shift (p = 0.063). SBP and RPP were moderately, DBP and MAP largely affected by the type of exercise. In comparison to DYN, myocardial oxygen consumption, reflected by RPP, was about 5% higher under ISO. Correlation analysis revealed only modest associations between traditional HRV indices and entropy measures during the different experimental conditions. Consistent correlation coefficients across all conditions were found for SampEn and R-R length only.

Mean ± SD of sample entropy during REST, ISO, and DYN; N = 43.

Mean ± SD of sample entropy during REST, ISO, and DYN; N = 43.
*** = significantly different from rest on a p-level < 0.001;
§§§ = significantly different from the respective exercise condition on a p-level < 0.001.

Role of neurotensin and opioid receptors in the cardiorespiratory effects of [Ile9]PK20, a novel antinociceptive chimeric peptide

Katarzyna Kaczynska, M Szereda-Przestaszewska, P Kleczkowska, AW Lipkowski European Journal of Pharmaceutical Sciences 63 (2014) 8–13 http://dx.doi.org/10.1016/j.ejps.2014.06.018

Ile9PK20 is a novel hybrid of opioid–neurotensin peptides synthesized from the C-terminal hexapeptide of neurotensin and endomorphin-2 pharmacophore. This chimeric compound shows potent central and peripheral antinociceptive activity in experimental animals, however nothing is known about its influence on the respiratory and cardiovascular parameters.

The present study was designed to determine the cardiorespiratory effects exerted by an intravenous injection (i.v.) of [Ile9]PK20. Share of the vagal afferentation and the contribution of NTS1 neurotensin and opioid receptors were tested.

Intravenous injection of the hybrid at a dose of 100 lg/kg in the intact, anaesthetized rats provoked an increase in tidal volume preceded by a prompt short-lived decrease. Immediately after the end of injection brief acceleration of the respiratory rhythm appeared, and was ensued by the slowing down of breathing. Changes in respiration were concomitant with a bi-phasic response of the blood pressure: an immediate increase was followed by a sustained hypotension. Midcervical vagotomy eliminated the increase in tidal volume and respiratory rate responses. Antagonist of opioid receptors – naloxone hydrochloride eliminated only [Ile9]PK20-evoked decline in tidal volume response. Blockade of NTS1 receptors with an intravenous dose of SR 142,948, lessened the remaining cardiorespiratory effects. This study depicts that [Ile9]PK20 acting through neurotensin NTS1 receptors augments the tidal component of the breathing pattern and activates respiratory timing response through the vagal pathway. Blood pressure effects occur outside vagal afferentation and might result from activation of the central and peripheral vascular NTS1 receptors. In summary the respiratory effects of the hybrid appeared not to be profound, but they were accompanied with unfavorable prolonged hypotension.

Integrative regulation of human brain blood flow

Christopher K.Willie, Yu-Chieh Tzeng, Joseph A. Fisher and Philip N. Ainslie
J Physiol 2014; 592(5): pp 841–859
http://dx.doi.org:/10.1113/jphysiol.2013.268953

Herein, we review mechanisms regulating cerebral blood flow (CBF), with specific focus on humans. We revisit important concepts from the older literature and describe the interaction of various mechanisms of cerebrovascular control. We amalgamate this broad scope of information into a brief review, rather than detailing any one mechanism or area of research. The relationship between regulatory mechanisms is emphasized, but the following three broad categories of control are explicated:

  • the effect of blood gases and neuronal metabolism on CBF;
  • buffering of CBF with changes in blood pressure, termed cerebral autoregulation; and
  • the role of the autonomic nervous system in CBF regulation.

With respect to these control mechanisms, we provide evidence against several canonized paradigms of CBF control. Specifically, we corroborate the following four key theses:

(1) that cerebral autoregulation does not maintain constant perfusion through a mean arterial pressure range of 60–150 mmHg;
(2) that there is important stimulatory synergism and regulatory interdependence of arterial blood gases and blood pressure on CBF regulation;

(3) that cerebral autoregulation and cerebrovascular sensitivity to changes in arterial blood gases are not modulated solely at the pial arterioles; and
(4) that neurogenic control of the cerebral vasculature is an important player in autoregulatory function and, crucially, acts to buffer surges in perfusion pressure.
Finally, we summarize the state of our knowledge with respect to these areas, outline important gaps in the literature and suggest avenues for future research.

Integrative physiological and computational approaches to understand autonomic control of cerebral autoregulation

Can Ozan Tan and J. Andrew Taylor
Exp Physiol 99.1 (2014) pp 3–15 http://dx.doi.org:/10.1113/expphysiol.2013.072355

New Findings

  1. What is the topic of this review?

This review focuses on the autonomic control of the cerebral vasculature in health and disease from an integrative physiological and computational perspective.

  1. What advances does it highlight?

This review highlights recent studies exploring autonomic effectors of cerebral autoregulation as well as recent advances in experimental and analytical approaches to understand cerebral autoregulation.

The brain requires steady delivery of oxygen and glucose, without which neurodegeneration occurs within minutes. Thus, the ability of the cerebral vasculature to maintain relatively steady blood flow in the face of changing systemic pressure, i.e. cerebral autoregulation, is critical to neurophysiological health. Although the study of autoregulation dates to the early 20th century, only the recent availability of cerebral blood flow measures with high temporal resolution has allowed rapid, beat-by-beat measurements to explore the characteristics and mechanisms of autoregulation. These explorations have been further enhanced by the ability to apply sophisticated computational approaches that exploit the large amounts of data that can be acquired. These advances have led to unique insights. For example, recent studies have revealed characteristic time scales wherein cerebral autoregulation is most active, as well as specific regions wherein autonomic mechanisms are prepotent. However, given that effective cerebral autoregulation against pressure fluctuations results in relatively unchanging flow despite changing pressure, estimating the pressure–flow relationship can be limited by the error inherent in computational models of autoregulatory function. This review focuses on the autonomic neural control of the cerebral vasculature in health and disease from an integrative physiological perspective. It also provides a critical overview of the current analytical approaches to understand cerebral autoregulation.

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Reversal of Cardiac mitochondrial dysfunction

Curator: Larry H Bernstein, MD, FACP

This article is the FOURTH in a four-article Series covering the topic of the Roles of the Mitochondria in Cardiovascular Diseases. They include the following;

  • Mitochondria and Cardiovascular Disease: A Tribute to Richard Bing, Larry H Bernstein, MD, FACP

https://pharmaceuticalintelligence.com/2013/04/14/chapter-5-mitochondria-and-cardiovascular-disease/

  • Mitochondrial Metabolism and Cardiac Function, Larry H Bernstein, MD, FACP

https://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-metabolism-and-cardiac-function/

  • Mitochondrial Dysfunction and Cardiac Disorders, Larry H Bernstein, MD, FACP

https://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-dysfunction-and-cardiac-disorders/

https://pharmaceuticalintelligence.com/2013/04/14/reversal-of-cardiac-mitochondrial-dysfunction/

 

Mitochondrial metabolism and cardiac function

There is sufficient evidence to suggest that, even with optimal therapy, there is an

  • attenuation or loss of effectiveness of neurohormonal antagonism as heart failure worsens.

The production of oxygen radicals is increased in the failing heart, whereas

  • normal antioxidant enzyme activities are preserved.

Mitochondrial electron transport is an enzymatic source of oxygen radical generation and

  • can be a therapeutic target against oxidant-induced damage in the failing myocardium.

Therefore, future therapeutic targets

  • must address the cellular and molecular mechanisms that contribute to heart failure.

Furthermore, since  fundamental characteristics of the failing heart are 

  • defective mitochondrial energetics and
  • abnormal substrate metabolism

we might expect that substantial benefit may be derived from the development of therapies aimed at

  • preserving cardiac mitochondrial function and
  • optimizing substrate metabolism.

Nutrition and physiological function

Blockade of electron transport in isolated, perfused guinea pig hearts –
before ischaemia with the reversible complex I inhibitor amobarbital
  • decreased superoxide production and
  • preserved oxidative phosphorylation in cardiac mitochondria,
  • decreased myocardial damage.
But when ascorbic acid was administered orally to chronic heart failure patients, there were improvements
  • in endothelial function but
  • no improvement in skeletal muscle energy metabolism.
Angiotensin I-converting enzyme (ACE) inhibitors with trandolapril treatment  in models of heart failure
  • appear to preserve mitochondrial function
  • improving cardiac energy metabolism and
  • function in rats with chronic heart failure.
Similarly perindopril treatment   – in rat skeletal muscle after myocardial infarction -restored :
  • levels of the mitochondrial biogenesis transcription factors PPARg coactivator-1a and
  • nuclear respiratory factor-2a, and
  • prevented mitochondrial dysfunction
Tissue effects of ACE inhibition, such as
might activate intracellular signalling cascades that
  • stimulate mitochondrial biogenesis and
  • improve energy metabolism.
Clearly, the mechanisms of metabolic regulation by
  • existing cardioprotective agents require further investigation.

Substrate metabolism in the failing heart

Increased sympathetic drive in heart failure patients causes adipose tissue lipolysis, thus
  • elevating plasma FFA concentrations.
Myocardial FFA uptake rates are largely determined by circulating FFA concentrations.
In addition to being a major fuel in heart,
  • fatty acids are ligands for the peroxisome proliferator-activated receptors (PPARs),
    •  members of the nuclear hormone receptor (NHR) family.
One PPAR subtype, PPARa, is highly expressed in heart and skeletal muscle. PPARs regulate gene expression by
binding to response elements in the promoter region of target genes that control fatty acid metabolism, including
It has been known for many years that high plasma FFA concentrations are detrimental to the heart,
  • increasing oxygen consumption for any given workload.
Decreased myocardial oxygen efficiency could result, in part,
  • from the inherent stoichiometric inefficiency of fatty acid oxidation,
  • which accounts for the consumption of 12% more oxygen per ATP synthesized than glucose oxidation.

High levels of plasma FFAs have been associated with increased cardiac UCP3 levels in patients undergoing CABG(Fig) and

  • are believed to activate the uncoupling action of UCP3.

http://htmlimg1.scribdassets.com/8o5pfgywg0lyerj/images/4-244729cb6a.jpg

Fig .  Metabolic modulation of the failing heart can be achieved by inhibiting mitochondrial beta-oxidation with trimetazidine, or
  • free fatty acid (FFA) uptake via the carnitine palmitoyltransferase (CPT) system with perhexiline,
    • giving rise to more oxygen-efficient glucose oxidation.
Alternatively, CPT is inhibited by malonyl-coenzyme A (CoA),
  • synthesized from cytosolic acetyl-CoA by acetyl-CoA  carboxylase.
Pharmacological inhibition, or mutation, of
  • malonyl-CoA decarboxylase, which normally converts malonyl-CoA back to acetyl-CoA,
  • elevates malonyl-CoA levels, inhibiting mitochondrial FFA uptake and thus protects the failing heart.

Nutritional Support for the Mitochondria

Human Studies                                       Animal or In Vitro Studies

Alpha lipoic acid                                                    Resveratrol
Co-Enzyme Q10                                                      EgCG
Acetyl-L-Carnitine                                                Curcumin

Lipoic Acid & Acetyl-L-Carnitine

Alpha lipoic acid is known to be a mitochondrial antioxidant that preserves or improves mitochondrial function.

  •  lipoic acid can prevent arterial calcification, and
  • arterial calcification may be related to mitochondrial dysfunction
  • methods are under study to increase lipoic acid synthase production, the enzyme responsible for making lipoic acid in the body.

Co-Enzyme Q10

It is well known that statin drugs taken for high cholesterol severely reduce CoQ10 levels, and causes other negative cardiovascular side effects.
A  study on CAD patients has shown that over 8 weeks of supplementing with 300mg of CoQ10 reversed

  • mitochondrial dysfunction (as measured by a reduced lactate:pyruvate ratio) and
  • improved endothelial function (as measured by increased flow-mediated dilation)

Other Mitochondrial Antioxidants

Other natural compounds that have been shown to have antioxidant effects in the mitochondria include

  • resveratrol, found in wine and grapes,
  • curcumin from turmeric and
  • EGCG, found abundantly in green tea extract.

But no studies have been conducted for these compounds in CVD.

Metabolic syndrome and serum carotenoids: findings of a cross-sectional study
in Queensland, Australia

Metabolic syndrome and serum carotenoids.

T Coyne, TI Ibiebele, PD Baade, CS McClintock and JE Shaw.
Viertel Center for Research in Cancer Control, Cancer Council Queensland, and School of Public Health,
Queensland University of Technology and University of Queensland, Brisbane, Australia
Several components of the metabolic syndrome are known to be oxidative stress-related conditions
  1. diabetes and
  2. cardiovascular disease,
Carotenoids are compounds derived primarily from plants and several have been shown to be potent antioxidant nutrients.
Both diabetes and cardiovascular disease are known to be oxidative stress-related conditions such that
  • antioxidant nutrients may play a protective role in these conditions.
Several cross–sectional surveys have found lower levels of serum carotenoids among those with impaired glucose metabolism or type 2 diabetes.
Carotenoids are compounds derived primarily from plants, several of which are known to be potent antioxidants.
Epidemiological evidence indicates that some serum carotenoids may play a protective role against the development of chronic diseases such as
  1. atherosclerosis,
  2. stroke,
  3. hypertension,
  4. certain cancers,
  5. inflammatory diseases and
  6. diabetic retinopathy.

The primary carotenoids found in human serum are

  1. α-carotene
  2. β-carotene
  3. β-cryptoxanthin
  4. lutein/zeaxanthin
  5. lycopene.
The aim of this study was to examine the associations between metabolic syndrome status and major serum carotenoids in adult Australians.
Data on the presence of the metabolic syndrome, based on International Diabetes Federation 2005 criteria, were collected from 1523 adults
aged 25 years and over in six randomly selected urban centers in Queensland, Australia, using a cross sectional study design.
The following were determined:
  1. Weight
  2. height
  3. BMI
  4. waist circumference
  5. blood pressure
  6. fasting and 2-34 hour blood glucose
  7. lipids
  8. five serum carotenoids.
Criteria used to assess the number of metabolic syndrome components present in a 171 participant using the
2005 International Diabetes Federation definition are as follows:
Components = 0 -none of the metabolic syndrome components (i.e. abdominal obesity, raised triglyceride,
reduced HDL-cholesterol, raised blood pressure, and impaired fasting plasma glucose) are present;
  1. Components = any 1 one of the five metabolic syndrome components is present ;
  2. Components = 2 – any two of the five components are present;
  3. Components = 3 any three of the components are present;
  4. Components = 4 – any four of the components are present;
  5. Components = 5 = all five metabolic syndrome components are present.
This study investigated the relationships between these five primary serum carotenoids and the metabolic syndrome
in a cross-sectional population-based study in Queensland, Australia.  Distributions of serum carotenoids were skewed
and therefore natural logarithmically transformed to better approximate the normal distribution for regression analyses.
Association between log transformed serum carotenoids as dependent variables and metabolic syndrome status were
assessed using multiple linear regression analysis. Results are reported as back transformed geometric means.
Analysis was performed for each serum carotenoid separately, and the sum of the five carotenoids,
adjusting for the following potential confounders:
  1. age
  2. sex
  3. education
  4. BMI
  5. smoking
  6. alcohol intake
  7. physical activity
  8. vitamin use.
Mean serum alpha-carotene, beta-carotene and the sum of the five carotenoid concentrations were significantly lower (p<0.05)
in persons with the metabolic syndrome (after adjusting for age,sex, education, BMI status, alcohol intake, smoking, physical activity
status and vitamin/mineral use) than persons without the syndrome. Alpha, beta and total carotenoids also decreased significantly
(p<0.05) with increased number of components of the metabolic syndrome, after adjusting for these confounders. These differences
were significant among former smokers and non-smokers, but not in current smokers. Low concentrations of serum
  • alpha-carotene,
  • beta carotene and
  • the sum of five carotenoids
appear to be associated with metabolic syndrome status.
The overall prevalence of the syndrome was 24% and was significantly higher among males than females. As would be expected, significant
differences in prevalence of the syndrome were seen with
  • body mass index
  • waist circumference
  • systolic and diastolic blood pressure
  • blood lipids.
Significant differences were also evident by
  • age group, smoking status, educational status and income.
Income was marginally inversely associated. The prevalence increased with age, and was lower in those with post graduate education.
No significant differences were seen by alcohol intake, physical activity levels,  vitamin usage, or fruit intake. There was actually an
  • inverse relationship between vegetable intake (not fruit) and serum carotenoids.
Those who consumed 4 serves or more of vegetable were less likely to have the metabolic syndrome
  • compared to those who consumed 1 serve or less of vegetables.
The mean concentrations of serum alpha-carotene, beta-carotene and the sum of the five carotenoids were significantly lower for participants
  • with the metabolic syndrome present compared with those without the syndrome, after adjusting for potential confounding variables.
Concentrations of alpha-carotene, beta-carotene and the sum of the five carotenoids decreased significantly as
  • the number of components of the metabolic syndrome increased after adjusting for potential confounding variables.
Similarly there was an inverse association between quartiles of
  • individual and total serum carotenoids and metabolic syndrome status and each of its components.
This study was designed to investigate the association between several serum carotenoids and the metabolic syndrome.
The data from the present population study suggest that several serum carotenoids are inversely related to the metabolic syndrome.
The study showed significantly lower concentrations present among those with the metabolic syndrome of
  1. α-carotene,
  2. β-carotene and
  3. the sum of the five carotenoids
 compared to those without.We also found decreasing concentrations of all the carotenoids tested as

  • the number of the metabolic syndrome components increased.
This was significant for
  1. α-carotene,
  2. β-carotene,
  3. β-cryptoxanthin
  4. total carotenoids.
    (not lycopenes)
These findings are consistent with data reported from the third National Health and Nutrition Examination Survey (NHANES III).
In the NHANES III study, significantly lower concentrations of all the carotenoids, except lycopene, were found among persons
with the metabolic syndrome compared with those without, after adjusting for confounding factors similar to those in our study.

Carnitine: A novel health factor-An overview. 

CD Dayanand, N Krishnamurthy, S Ashakiran, KN Shashidhar
Int J Pharm Biomed Res 2011; 2(2): 79-89.  ISSN No: 0976-0350
Carnitine comprises L-carnitine, acetyl –L-carnitine and Propionyl –L-carnitine. Carnitine is
  • obtained in greater amount from animal dietary sources than from plant sources.
The endogenous synthesis of carnitine takes place in animal tissues like
  • liver
  • kidney
  • brain
using precursor amino acids lysine and methionine by a pathway
  • dependent on iron, vitamin C, niacin, pyridoxine .
This is the basis of vegans generally depending on carnitine in larger proportion
  • through in vivo synthesis than omnivorous subjects.
The concentration of tri-methyl lysine residues and the tissue specificity of  butyro-betaine dehydrogenase
  • plays a significant role in regulating the carnitine biosynthesis.
Carnitine transport from the site of synthesis to target tissue occurs via blood.
The measurement of plasma carnitine concentration represents –
  • the balance between the rate of synthesis and rate of excretion
    • through specific transporter proteins.
The cellular functional role of carnitine depends on the uptake into cells through
  1. carnitine transport proteins and
  2. transport into mitochondrial matrix.
The function of carnitine is to traverse Long-chain Fatty Acids across inner mitochondrial membrane
  • for β-oxidation, thereby, generating ATP.
Carnitine deficiency results in muscle disorders.  The deficiency states are primary and secondar.
The primary is of systemic or myopathic, characterized by a defect of high affinity organic cation transporter protein (CTP)
  • present on the plasma membrane of liver and kidney and
  • also due to dysfunction of carnitine reabsorbtion through
    • similar transport proteins in renal tubules.
Secondary carnitine deficiency is associated with
  1. mitochondrial disorders and also
  2. defective β-oxidation such as CPT-II and acyl CoA dehydrogenase.
In recent times, carnitine has been extensively studied in various research activities to explore the therapeutic benefit.
Thus, carnitine justifies as a novel health factor.

Propionyl-L-carnitine Corrects Metabolic and Cardiovascular Alterations in
Diet-Induced Obese Mice and Improves Liver Respiratory Chain Activity

C Mingorance,  L Duluc, M Chalopin, G Simard, et al.
PLC improved the insulin-resistant state and reversed the increased total cholesterol
but not the increase in free fatty acid, triglyceride and HDL/LDL ratio induced by high-fat diet.
Vehicle-HF exhibited a reduced

  • cardiac output/body weight ratio,
  • endothelial dysfunction and
  • tissue decrease of NO production,

all of them being improved by PLC treatment.
The decrease of hepatic mitochondrial activity by high-fat diet was reversed by PLC.

Oral administration of PLC improves the insulin-resistant state developed by obese animals and
decreases the cardiovascular risk associated with the metabolically impaired mitochondrial function.

Omega-3 Fatty Acid and cardioprotection

The Benefits of Flaxseed    

By Elaine Magee, MPH, RD    WebMD Expert Column
Some call it one of the most powerful plant foods on the planet. There’s some evidence it may help reduce your risk of

  • heart disease, cancer, stroke, and diabetes.

That’s quite a tall order for a tiny seed that’s been around for centuries.

Flaxseed was cultivated in Babylon as early as 3000 BC. In the 8th century, King Charlemagne believed so strongly in the
health benefits of flaxseed that he passed laws requiring his subjects to consume it. Now, thirteen centuries later, some
experts say we have preliminary research to back up what Charlemagne suspected.

http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/article_
thumbnails/features/benefits_of_flaxseed_features/375x321_benefits_of_flaxseed_features.jpg

Not only has consumer demand for flaxseed grown, agricultural use has also increased.
Flaxseed is what’s used to feed all those chickens that are laying eggs with higher levels of omega-3 fatty acids.
Although flaxseed contains all sorts of healthy components, it owes its primary healthy reputation to three of them:

  1. Omega-3 essential fatty acids, have been shown to have heart-healthy effects.  1.8 grams of plant omega-3s/tablespoon ground.
  2. Lignans, which have both plant estrogen and antioxidant qualities.  75 to 800 times more lignans than other plant foods.
  3. Fiber. Flaxseed contains both the soluble and insoluble types.

Omega-3 Polyunsaturated Fatty Acids and Cardiovascular Diseases

CJ Lavie, RV Milani, MR Mehra, and HO Ventura.
J. Am. Coll. Cardiol. 2009;54;585-594.   http://dx.doi.org/10.1016/j.jacc.2009.02.084
Fish oil is obtained in the human diet by eating oily fish, such as
  • herring, mackerel, salmon, albacore tuna, and sardines, or
  • by consuming fish oil supplements or cod liver oil.
Fish do not naturally produce these oils, but obtain them through the ocean food chain from the marine microorganisms
  • that are the original source of the omega-3 polyunsaturated fatty acids (ω-3 PUFA) found in fish oils.
Numerous prospective and retrospective trials from many countries, including the U.S., have shown that moderate
  • fish oil consumption decreases the risk of major cardiovascular (CV) events, such as
  1. myocardial infarction (MI),
  2. sudden cardiac death (SCD),
  3. coronary heart disease (CHD),
  4. atrial fibrillation (AF), and most recently,
  5. death in patients with heart failure (HF).
Most of the evidence for benefits of the ω-3 PUFA has been obtained for
  • eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the long-chain fatty acids in this family.
There is support for a benefit from alpha-linolenic acid (ALA),
  • the plant-based precursor of EPA.
The American Heart Association (AHA) has currently endorsed the use of ω-3 PUFA in patients with documented CHD

  • at a dose of approximately 1 g/day of combined DHA and EPA, either in the form of fatty fish or fish oil supplements
The health benefits of these long chain fatty acids are numerous and remain an active area of research.
Omega-3 polyunsaturated fatty acid (ω-3 PUFA) therapy continues to show great promise in primary and,
  • particularly in secondary prevention of cardiovascular (CV) diseases.
This portion of discussion summarizes the current scientific data on the effects of the long chain ω-3 PUFA
  • in the primary and secondary prevention of various CV disorders.
The most compelling evidence for CV benefits of ω-3 PUFA comes from 4 controlled trials
  • of nearly 40,000 participants randomized to receive eicosapentaenoic acid (EPA)
  • with or without docosahexaenoic acid (DHA) in studies of patients
    • in primary prevention,
    • after myocardial infarction, and
    • with heart failure (HF).
The evidence from retrospective epidemiologic studies and from large randomized controlled trials
show the benefits of ω-3 PUFA, specifically EPA and DHA, in primary and secondary CV prevention
and provide insight into potential mechanisms of these observed benefits.

Background Epidemiologic Evidence

During the past 3 decades, numerous epidemiologic and observational studies have been published on the CV benefits of ω-3 PUFA.
As early as 1944, Sinclair described the rarity of CHD in Greenland Eskimos, who consumed a diet high in whale, seal, and fish.
More than 30 years ago, Bang and Dyberg reported that despite a diet low in fruit, vegetables, and complex carbohydrates but
high in saturated fat and cholesterol, serum cholesterol and triglycerides were lower in Greenland Inuit than in age-matched residents
of Denmark, and the risk of MI was markedly lower in the Greenland population compared with the Danes. These initial observations raised
speculation on the potential benefits of ω-3 PUFA (particularly EPA and DHA) as the protective “Eskimo factor”.
Potential EPA and DHA Effects   
  1. Antiarrhythmic effects
  2. Improvements in autonomic function
  3. Decreased platelet aggregation
  4. Vasodilation
  5. Decreased blood pressure
  6. Anti-inflammatory effects
  7. Improvements in endothelial function
  8. Plaque stabilization
  9. Reduced atherosclerosis
  10. Reduced free fatty acids and triglycerides
  11. Up-regulated adiponectin synthesis
  12. Reduced collagen deposition
The target EPA + DHA consumption should be at least 500 mg/day for individuals without underlying overt CV disease
  • and at least 800 to 1,000 mg/day for individuals with known coronary heart disease and HF.
Further studies are needed to determine optimal dosing and the relative ratio of DHA and EPA ω-3 PUFA that
  • provides maximal cardioprotection in those at risk of CV disease
  • as well in the treatment of atherosclerotic, arrhythmic, and primary myocardial disorders.
Lavie et al.  Omega-3 PUFA and CV Diseases  J Am Coll Cardiol 2009; 54(7): 585–94

Assessing Appropriateness of Lipid Management Among Patients With Diabetes Mellitus

Moving From Target to Treatment.   AJ Beard, TP Hofer, JR Downs, et al. and Diabetes Clinical Action Measures Workgroup
Performance measures that emphasize only a treat-to-target approach may motivate ove-rtreatment with high-dose statins,
  • potentially leading to adverse events and unnecessary costs.
We developed a clinical action performance measure for lipid management in patients with diabetes mellitus that is designed
  • to encourage appropriate treatment with moderate-dose statins while minimizing over-treatment.
We examined data from July 2010 to June 2011 for 964 818 active Veterans Affairs primary care patients ≥18 years of age with diabetes mellitus.
We defined 3 conditions as successfully meeting the clinical action measure for patients 50 to 75 years old:
  1.  having a low-density lipoprotein (LDL) <100 mg/dL,
  2. taking a moderate-dose statin regardless of LDL level or measurement, or
  3. receiving appropriate clinical action (starting, switching, or intensifying statin therapy) if LDL is ≥100 mg/dL.
We examined possible over-treatment for patients ≥18 years of age by examining the proportion of patients
  • without ischemic heart disease who were on a high-dose statin.
We then examined variability in measure attainment across 881 facilities using 2-level hierarchical multivariable logistic models.
Of 668 209 patients with diabetes mellitus who were 50 to 75 years of age, 84.6% passed the clinical action measure:
  1. 67.2% with LDL <100 mg/dL,
  2. 13.0% with LDL ≥100 mg/dL and either on a moderate-dose statin (7.5%) or with appropriate clinical action (5.5%), and
  3. 4.4% with no index LDL on at least a moderate-dose statin. Of the entire cohort ≥18 years of age, 13.7% were potentially over-treated.
Use of a performance measure that credits appropriate clinical action indicates that almost 85% of diabetic veterans 50 to 75 years of age
  • are receiving appropriate dyslipidemia management.

Exercise training and mitochondria in heart failure

The beneficial effects of exercise in the rehabilitation of patients with heart failure are well established,
with improvements observed in
  • exercise capacity,
  • quality of life,
  • hospitalization rates and
  • morbidity/mortality.
There is no evidence of training-induced
improvements in cardiac energy metabolism or
  • mitochondrial function, and
  • no modification of myocardial oxidative capacity,
  • oxidative enzymes, or
  • energy transfer enzymes
in exercising rats with experimental heart failure, but there is  evidence of
There are also improvements in
  • skeletal muscle oxidative capacity with
  • increased mitochondrial density
following endurance training in heart failure patients associated with alleviation of symptoms such as
  • exercise intolerance and
  • chronic fatigue.
The mechanism underlying improvements in mitochondrial function may perhaps be a result of
  • more effective peripheral oxygen delivery following training,
  • alleviating tissue hypoxia and oxidative stress.

Treating Type 2 diabetes, and lowering cardiovascular disease risk

Treating Diabetes and Obesity with an FGF21-Mimetic Antibody
Activating the βKlotho/FGFR1c Receptor Complex

IN Foltz, S Hu, C King, Xinle Wu, et al.  Amgen and Texas A&M HSC, Houston, TX.
Sci Transl Med  Nov 2012; 4(162), p. 162ra153
http://dx.doi.org/10.1126/scitranslmed.3004690

Fibroblast growth factor 21 (FGF21) is a distinctive member of the FGF family with potent beneficial effects on

  1. lipid
  2. body weight
  3. glucose metabolism

A monoclonal antibody, mimAb1, binds to βKlotho with high affinity and specifically

  • activates signaling from the βKlotho/FGFR1c (FGF receptor 1c) receptor complex.

Injection of mimAb1 into obese cynomolgus monkeys led to FGF21-like metabolic effects:

  1. decreases in body weight,
  2. plasma insulin,
  3. triglycerides, and
  4. glucose during tolerance testing.

Mice with adipose-selective FGFR1 knockout were refractory to FGF21-induced improvements

  • in glucose metabolism and body weight.

mimAb1 depends on βKlotho to activate FGFR1c, but

  • it is not expected to induce side effects caused by activating FGFR1c alone.

The results in obese monkeys (with mimAb1) and in FGFR1 knockout mice (with FGF21) demonstrated

  • the essential role of FGFR1c in FGF21 function and
  • suggest fat as a critical target tissue for the cytokine and antibody.

This antibody activates FGF21-like signaling through cell surface receptors, and  provided

  • preclinical validation for an innovative therapeutic approach to diabetes and obesity.

Influencing Factors on Cardiac Structure and Function Beyond Glycemic Control
in Patients With Type 2 Diabetes Mellitus (T2DM)

R Ichikawa, M Daimon, T Miyazaki, T Kawata, et al.     Cardiovasc Diabetol. 2013;12(38)

We studied 148 asymptomatic patients with T2DM without overt heart disease.
Early (E) and late (A) diastolic mitral flow velocity and early diastolic mitral annular velocity (e’)

  • were measured for assessing left ventricular (LV) diastolic function.

In addition

  • insulin resistance,
  • non-esterified fatty acid,
  • high-sensitive CRP,
  • estimated glomerular filtration rate,
  • waist/hip ratio,
  • abdominal visceral adipose tissue (VAT),
  • subcutaneous adipose tissue (SAT)

In T2DM (compared to controls),

  • E/A and e’ were significantly lower, and
  • E/e’, left atrial volume and LV mass were significantly greater

VAT  and age were independent determinants of

  • left atrial volume (β =0.203, p=0.011),
  • E/A (β =−0.208, p=0.002), e’ (β =−0.354, p<0.001) and
  • E/e’ (β=0.220, p=0.003).

Independent determinants of LV mass were

  • systolic blood pressure,
  • waist-hip ratio (β=0.173, p=0.024)
  • VAT/SAT ratio (β=0.162, p=0.049)

Excessive visceral fat accompanied by adipocyte dysfunction may play a greater role than

  • glycemic control in the development of diastolic dysfunction and LV hypertrophy in T2DM

Inhibition of oxidative stress and mtDNA damage

Novel pharmacological agents are needed that

  • optimize substrate metabolism and
  • maintain mitochondrial integrity,
  • improve oxidative capacity in heart and skeletal muscle, and
  • alleviate many of the clinical symptoms associated with heart failure.

The evidence for the attenuation or loss of effectiveness of neurohormonal antagonism as heart failure worsens

  • indicates future therapeutic targets must address the cellular and molecular mechanisms that contribute to heart failure.

Pharmacological Targets of oxidative stress and mitochondrial damage

Defective mitochondrial energetics and abnormal substrate metabolism are fundamental characteristics of CHF.

A significant benefit may be derived from developing therapies aimed at

  • preserving cardiac mitochondrial function and
  • optimizing substrate metabolism.
Oxidative stress is enhanced in myocardial remodelling and failure. The increased production of oxygen radicals in the failing heart
  • with preserved antioxidant enzyme activities suggests
  • mitochondrial electron transport as a source of oxygen radical generation
  • can be a therapeutic target against oxidant-induced damage in the failing myocardium.
Chronic increases in oxygen radical production in the mitochondria
  • leads to mitochondrial DNA (mtDNA) damage,
  • functional decline,
  • further oxygen radical generation, and
  • cellular injury.
MtDNA defects may thus play an important role in the
  • development and progression of myocardial remodelling and failure.
Reactive oxygen species induce
  1. myocyte hypertrophy,
  2. apoptosis, and
  3. interstitial fibrosis
  4. by activating matrix metallo-proteinases,
  5. promoting the development and
  6. progression of maladaptive myocardial remodelling and failure.
Oxidative stress has direct effects on cellular structure and function and
  • may activate integral signalling molecules in myocardial remodelling and failure (Figure).
ROS result in a phenotype characterized by
  • hypertrophy and apoptosis in isolated cardiac myocytes.
Therefore, oxidative stress and mtDNA damage are good therapeutic targets.
Overexpression of the genes for
  • peroxiredoxin-3 (Prx-3), a mitochondrial antioxidant, or
  • mitochondrial transcription factor A (TFAM),
    • could ameliorate the decline in mtDNA copy number in failing hearts.
Consistent with alterations in mtDNA, the
  • decrease in mitochondrial function was prevented,
  • proving that the activation of Prx-3 or TFAM gene expression
  • could ameliorate the pathophysiological processes seen
  1. in mitochondrial dysfunction and
  2. myocardial remodelling.
Inhibition of oxidative stress and mtDNA damage
  • could be novel and effective treatment strategies for heart failure.
Proposed mechanisms through which overexpression of the
  • mitochondrial transcription factor A (TFAM) gene prevents
  • mitochondrial DNA (mtDNA) damage,
  • oxidative stress, and
  • myocardial remodelling and failure.
In wild-type mice, mitochondrial transcription factor A
  • directly interacts with mitochondrial DNA to form nucleoids.
Stress such as ischaemia causes mitochondrial DNA damage, which
  1. increases the production of reactive oxygen species (ROS)
  2. leading to a catastrophic cycle of mitochondrial electron transport impairment,
  3. further reactive oxygen species generation, and mitochondrial dysfunction.
TFAM overexpression may protect mitochondrial DNA from damage by
  1. directly binding and stabilizing mitochondrial DNA and
  2. increasing the steady-state levels of mitochondrial DNA
ameliorating mitochondrial dysfunction and thus the development and progression of heart failure.

Conclusion

Heart failure is a multifactorial syndrome that is characterized by
  • abnormal energetics and substrate metabolism in heart and skeletal muscle.
Although existing therapies have been beneficial, there is a clear need for new approaches to treatment.
Pharmacological targeting of the cellular stresses underlying mitochondrial dysfunction, such as
  • elevated fatty acid levels,
  • tissue hypoxia and oxidative stress and
  • metabolic modulation of heart and skeletal muscle mitochondria,
    • appears to offer a promising therapeutic strategy for tackling heart failure.
Murray AJ, Anderson RE, Watson GC, et al. Uncoupling proteins in human heart. Lancet 2004; 364:1786.
Delarue J, Magnan C. Free fatty acids and insulin resistance. Curr Opin ClinNutr Metab Care 2007; 10:142
Lee L, Campbell R, Scheuermann-Freestone M, et al. Metabolic modulation with perhexiline in chronic heart failure: a randomized, controlled trialof short-term use of a novel treatment. Circulation 2005; 112:3280
Tsutsui H, Kinugawa S, Matsushima S. Mitochondrial oxidative stress and dysfunction in myocardial remodelling. Cardiovasc Res. 2009;81(3):449-56. http://dxdoi.org/10.1093/cvr/cvn280.
C Maack, M Böhm. Targeting Mitochondrial Oxidative Stress in Heart Failure. J Am Coll Cardiol. 2011;58(1):83-86. http://dx.doi.org/10.1016/j.jacc.2011.01.032

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Mitochondrial dynamics and cardiovascular diseases    Ritu Saxena
https://pharmaceuticalintelligence.com/2012/11/14/mitochondrial-dynamics-and-cardiovascular-diseases/

Mitochondrial Damage and Repair under Oxidative Stress   larryhbern
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Mitochondria: Origin from oxygen free environment, role in aerobic glycolysis, metabolic adaptation   larryhbern
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Ca2+ signaling: transcriptional control     larryhbern
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MIT Scientists on Proteomics: All the Proteins in the Mitochondrial Matrix identified  Aviva Lev-Ari
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Nitric Oxide has a ubiquitous role in the regulation of glycolysis -with a concomitant influence on mitochondrial function    larryhbern
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Ubiquinin-Proteosome pathway, autophagy, the mitochondrion, proteolysis and cell apoptosis  larryhbern
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Low Bioavailability of Nitric Oxide due to Misbalance in Cell Free Hemoglobin in Sickle Cell Disease – A Computational Model   Anamika Sarkar
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The rationale and use of inhaled NO in Pulmonary Artery Hypertension and Right Sided Heart Failure    larryhbern
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Mitochondria and Cardiovascular Disease: A Tribute to Richard Bing, Larry H Bernstein, MD, FACP
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Clinical Trials Results for Endothelin System: Pathophysiological role in Chronic Heart Failure, Acute Coronary Syndromes and MI – Marker of Disease Severity or Genetic Determination? Aviva Lev-Ari, PhD, RN 10/19/2012
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Structure of the human mitochondrial genome.

Structure of the human mitochondrial genome. (Photo credit: Wikipedia)

English: Treatment Guidelines for Chronic Hear...

English: Treatment Guidelines for Chronic Heart Failure (Photo credit: Wikipedia)

English: Oxidative stress process Italiano: Pr...

English: Oxidative stress process Italiano: Processo dello stress ossidativo (Photo credit: Wikipedia)

Diagram taken from the paper "Dissection ...

Diagram taken from the paper “Dissection of mitochondrial superhaplogroup H using coding region SNPs” (Photo credit: Asparagirl)

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Endothelial Function and Cardiovascular Disease

Pathologist and AuthorLarry H Bernstein, MD, FCAP 

 

This discussion is a continuation of a series on Nitric Oxide, vascular relaxation, vascular integrity, and systemic organ dysfunctions related to inflammatory and circulatory disorders. In some of these, the relationships are more clear than others, and in other cases the vascular disorders are aligned with serious metabolic disturbances. This article, in particular centers on the regulation of NO production, NO synthase, and elaborates more on the assymetrical dimethylarginine (ADMA) inhibition brought up in a previous comment, and cardiovascular disease, including:

Recall, though, that in SIRS leading to septic shock, that there is a difference between the pulmonary circulation, the systemic circulation and the portal circulation in these events. The comment calls attention to:
Böger RH. Asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, explains the ‘L-arginine paradox’ and acts as a novel cardiovascular risk factor. J Nutr 2004; 134: 2842S–7S.

This observer points out that ADMA inhibits vascular NO production at concentrations found in pathophysiological conditions (i.e., 3–15 μmol/l); ADMA also causes local vasoconstriction when it is infused intra-arterially. ADMA is increased in the plasma of humans with hypercholesterolemia, atherosclerosis, hypertension, chronic renal failure, and chronic heart failure.

Increased ADMA levels are associated with reduced NO synthesis as assessed by impaired endothelium-dependent vasodilation. We’ll go into that more with respect to therapeutic targets – including exercise, sauna, and possibly diet, as well as medical drugs.

It is remarkable how far we have come since the epic discovery of 17th century physician, William Harvey, by observing the action of the heart in small animals and fishes, proved that heart receives and expels blood during each cycle, and argued for the circulation in man. This was a huge lead into renaissance medicine. What would he think now?

Key Words: eNOS, NO, endothelin, ROS, oxidative stress, blood flow, vascular resistance, cardiovascular disease, chronic renal disease, hypertension, diabetes, atherosclerosis, MI, exercise, nutrition, traditional chinese medicine, statistical modeling for targeted therapy.

Endothelial Function
The endothelium plays a crucial role in the maintenance of vascular tone and structure by means of eNOS, producing the endothelium-derived vasoactive mediator nitric oxide (NO), an endogenous messenger molecule formed in healthy vascular endothelium from the amino acid precursor L-arginine. Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. The generation and actions of NO under physiological and pathophysiological conditions are exquisitely regulated and extend to almost every cell type and function within the circulation. While the molecule mediates many physiological functions, an excessive presence of NO is toxic to cells.

The enzyme NOS, constitutively or inductively, catalyses the production of NO in several biological systems. NO is derived not only from NOS isoforms but also from NOS-independent sources. In mammals, to date, three distinct NOS isoforms have been identified:

  1. neuronal NOS (nNOS),
  2. inducible NOS (iNOS), and
  3. endothelial NOS (eNOS).

The molecular structure, enzymology and pharmacology of these enzymes have been well defined, and reveal critical roles for the NOS system in a variety of important physiological processes. The role of NO and NOS in regulating vascular physiology, through neuro-hormonal, renal and other non-vascular pathways, as well as direct effects on arterial smooth muscle, appear to be more intricate than was originally thought.

Vallance et al. described the presence of asymmetric dimethylarginine (ADMA) as an endogenous inhibitor of eNOS in 1992. Since then, the role of this molecule in the regulation of eNOS has attracted increasing attention.
Endothelins are 21-amino acid peptides, which are active in almost all tissues in the body. They are potent vasoconstrictors, mediators of cardiac, renal, endocrine and immune functions and play a role in bronchoconstriction, neurotransmitter regulation, activation of inflammatory cells, cell proliferation and differentiation.

Endothelins were first characterised by Yanagisawa et al. (1988). The three known endothelins ET-1, -2 and -3 are structurally similar to sarafotoxins from snake venoms. ET-1 is the major isoform generated in blood vessels and appears to be the isoform of most importance in the cardiovascular system with a major role in the maintenance of vascular tone.

The systemic vascular response to hypoxia is vasodilation. However, reports suggest that the potent vasoconstrictor endothelin-1 (ET-1) is released from the vasculature during hypoxia. ET-1 is reported to augment superoxide anion generation and may counteract nitric oxide (NO) vasodilation. Moreover, ET-1 was proposed to contribute to increased vascular resistance in heart failure by increasing the production of asymmetric dimethylarginine (ADMA).

A study investigated the role of ET-1, the NO pathway, the potassium channels and radical oxygen species in hypoxia-induced vasodilation of large coronary arteries and found NO contributes to hypoxic vasodilation, probably through K channel opening, which is reversed by addition of ET-1 and enhanced by endothelin receptor antagonism. These latter findings suggest that endothelin receptor activation counteracts hypoxic vasodilation.

Endothelial dysfunction
Patients with Raynaud’s Phemonenon had abnormal vasoconstrictor responses to cold pressor tests (CPT) that were similar in primary and secondary RP. There were no differences in median flow-mediated and nitroglycerin mediated dilation or CPT of the brachial artery in the 2 populations. Patients with secondary RP were characterized by abnormalities in microvascular responses to reactive hyperemia, with a reduction in area under the curve adjusted for baseline perfusion, but not in time to peak response or peak perfusion ratio.

Plasma ET-1, ADMA, VCAM-1, and MCP-1 levels were significantly elevated in secondary RP compared with primary RP. There was a significant negative correlation between ET-1 and ADMA values and measures of microvascular perfusion but not macrovascular endothelial function. Secondary RP is characterized by elevations in plasma ET-1 and ADMA levels that may contribute to alterations in cutaneous microvascular function.

ADMA inhibits vascular NO production within the concentration range found in patients with vascular disease. ADMA also causes local vasoconstriction when infused intra-arterially, and increases systemic vascular resistance and impairs renal function when infused systemically. Several recent studies have supplied evidence to support a pathophysiological role of ADMA in the pathogenesis of vascular dysfunction and cardiovascular disease. High ADMA levels were found to be associated with carotid artery intima-media-thickness in a study with 116 clinically healthy human subjects. Taking this observation further, another study performed with hemodialysis patients reported that ADMA prospectively predicted the progression of intimal thickening during one year of follow-up.

In a nested, case-control study involving 150 middle-aged, non-smoking men, high ADMA levels were associated with a 3.9-fold elevated risk for acute coronary events. Clinical and experimental evidence suggests elevation of ADMA can cause a relative L-arginine deficiency, even in the presence of “normal” L-arginine levels. As ADMA is a competitive inhibitor of eNOS, its inhibitory action can be overcome by increasing the concentration of the substrate, L-arginine. Elevated ADMA concentration is one possible explanation for endothelial dysfunction and decreased NO production in these diseases.
Metabolic Regulation of L-arginine and NO Synthesis 
Methylation of arginine residues within proteins or polypeptides occurs through N-methyltransferases, which utilize S-adenosylmethionine as a methyl donor. After proteolysis of these proteins or polypeptides, free ADMA is present in the cytoplasm. ADMA can also be detected in circulating blood plasma. ADMA acts as an inhibitor of eNOS by competing with the substrate of this enzyme, L-arginine. The ensuing reduction in nitric oxide synthesis causes vascular endothelial dysfunction and, subsequently, atherosclerosis. ADMA is eliminated from the body via urinary excretion and via metabolism by the enzyme DDAH to citrulline and dimethylamine.
Supplementation with L-arginine in animals with experimentally-induced vascular dysfunction atherosclerosis improves endothelium-dependent vasodilation. Moreover, L-arginine supplementation results in enhanced endothelium-dependent inhibition of platelet aggregation, inhibition of monocyte adhesion, and reduced vascular smooth muscle proliferation. One mechanism that explains the occurrence of endothelial dysfunction is the presence of elevated blood levels of asymmetric dimethylarginine (ADMA) – an L-arginine analogue that inhibits NO formation and thereby can impair vascular function. Supplementation with L-arginine has been shown to restore vascular function and to improve the clinical symptoms of various diseases associated with vascular dysfunction.

Beneficial Effects of L-Arginine

  • Angina
  • Congestive Heart Failure
  • Hypertension
  • Erectile dysfunction
  • Sickle Cell Disease and Pulmonary Hypertension

The ratio of L-arginine to ADMA is considered to be the most accurate measure of eNOS substrate availability. This ratio will increase during L-arginine supplementation, regardless of initial ADMA concentration. Due to the pharmacokinetics of oral L-arginine and the positive results from preliminary studies, it appears supplementation with a sustained-release L-arginine preparation will achieve positive therapeutic results at lower dosing levels.

Many prospective clinical trials have shown that the association between elevated ADMA levels and major cardiovascular events and total mortality is robust and extends to diverse patient populations. However, we need to define more clearly in the future who will profit from ADMA determination, in order to use this novel risk marker as a more specific diagnostic tool.
Elimination of ADMA by way of DDAH
Asymmetric dimethylarginine (ADMA) and monomethyl arginine (L-NMMA) are endogenously produced amino acids that inhibit all three isoforms of nitric oxide synthase (NOS). ADMA accumulates in various disease states, including renal failure, diabetes and pulmonary hypertension, and its concentration in plasma is strongly predictive of premature cardiovascular disease and death. Both LNMMA and ADMA are eliminated largely through active metabolism by dimethylarginine dimethylaminohydrolase (DDAH) and thus DDAH dysfunction may be a crucial unifying feature of increased cardiovascular risk. These investigators ask whether ADMA is the underlying issue related to the pathogenesis of the vascular disorder.
They identified the structure of human DDAH-1 and probed the function of DDAH-1 both by deleting the Ddah1 gene in mice and by using DDAH-specific inhibitors that is shown by crystallography, bind to the active site of human DDAH-1. The loss of DDAH-1 activity leads to accumulation of ADMA and reduction in NO signaling. This in turn causes vascular pathophysiology, including endothelial dysfunction, increased systemic vascular resistance and elevated systemic and pulmonary blood pressure. The results suggest that DDAH inhibition could be harnessed therapeutically to reduce the vascular collapse associated with sepsis.
Methylarginines are formed when arginine residues in proteins are methylated by the action of protein arginine methyltransferases (PRMTs), and free methylarginines are liberated following proteolysis. Clear demonstration of an effect of endogenous ADMA and L-NMMA on cardiovascular physiology would be of importance, not only because of the implications for disease, but also because it would expose a link between post-translational modification of proteins and signaling through a proteolytic product of these modified proteins.
Which is it? ADMA or DDHA: Intrusion of a Genetic alteration.
The study showed that loss of DDAH expression or activity causes endothelial dysfunction, we believe that DDAH inhibition could potentially be used therapeutically to limit excessive NO production, which can have pathological effects. They then showed treated cultured isolated blood vessels with lipopolysaccharide (LPS) induced expression of the inducible isoform of NO synthase (iNOS) and generated high levels of NO, which were blocked by the iNOS-selective inhibitor 1400W and by DDAH inhibitors. Treatment of isolated blood vessels with DDAH inhibitors significantly increased ADMA accumulation in the culture medium. Treatment of isolated blood vessels with bacterial LPS led to the expected hyporeactivity to the contractile effects of phenylephrine, which was reversed by treatment with a DDAH inhibitor. The effect of the DDAH inhibitor was large and stereospecific, and was reversed by the addition of L-arginine.
In conclusion, genetic and chemical-biology approaches provide compelling evidence that loss of DDAH-1 function results in increased ADMA concentrations and thereby disrupts vascular NO signaling. A broader implication of this study is that post-translational methylation of arginine residues in proteins may have downstream effects by affecting NO signaling upon hydrolysis and release of the free methylated amino acid. This signaling pathway seems to have been highly conserved through evolution.

The crucial role of nitric oxide (NO) for normal endothelial function is well known. In many conditions associated with increased risk of cardiovascular diseases such as hypercholesterolemia, hypertension, abdominal obesity, diabetes and smoking, NO biosynthesis is dysregulated, leading to endothelial dysfunction. The growing evidence from animal and human studies indicates that endogenous inhibitors of endothelial NO synthase such as asymmetric dimethylarginine (ADMA) and NG-monomethyl-L-arginine (L-NMMA) are associated with the endothelial dysfunction and potentially regulate NO synthase.

Nitric Oxide Synthase

Asymmetric dimethylarginine (ADMA) is one of three known endogenously produced circulating methylarginines (i.e. ADMA, NG-monomethyl-L-arginine (L-NMMA) and symmetrically methylated NG, NG-dimethyl-L-arginine). ADMA is formed by the action of protein arginine methyltransferases that methylate arginine residues in proteins and after which free ADMA is released. ADMA and L-NMMA can competitively inhibit NO elaboration by displacing L-arginine from NO synthase (NOS). The amount of methylarginines is related to overall metabolic activity and the protein turnover rate of cells. Although methylarginines are excreted partly by the kidneys, the major route of elimination of ADMA in humans is metabolism by the dimethylarginine dimethylaminohydrolase enzymes[ dimethylarginine dimethylaminohydrolase-1 and -2 (DDAH)] enzymes. Inhibition of DDAH leads to the accumulation of ADMA and consequently to inhibition of NO-mediated endothelium dependent relaxation of blood vessels.
The potential role of ADMA in angina pectoris has been evaluated by Piatti and co-workers, who reported ADMA levels to be higher in patients with cardiac syndrome X (angina pectoris with normal coronary arteriograms) than in controls. According to preliminary results from the CARDIAC (Coronary Artery Risk Determination investigating the influence of ADMA Concentration) study, patients with coronary heart disease (n 816) had a higher median ADMA plasma concentration than age and sex matched controls (median 0.91 vs. 0.70 mol/l; p 0.0001). Further, in a prospective Chinese study, a high plasma ADMA level independently predicted subsequent cardiovascular adverse events (cardiovascular death, myocardial infarction, and repeated revascularization of a target vessel).

Protein detoxification pathway.

Protein detoxification pathway. (Photo credit: Wikipedia)

There are only few published findings concerning variations in human DDAH. However, polymorphisms in other genes potentially related to risk factors for endothelial dysfunction and cardiovascular events have been studied. Reduced NO synthesis has been implicated in the development of atherosclerosis. For example, there are some functionally important variants of the NOS that could affect individual vulnerability to atherosclerosis by changing the amount of NO generated by the endothelium.
There are probably several functional variations in genes coding DDAH enzymes in different populations. Some of them could confer protection against the harmful effects of elevated ADMA and others impair enzyme function causing accumulation of ADMA in cytosol and/or blood.
In a study of 16 men with either low or high plasma ADMA concentrations were screened to identify DDAH polymorphisms that could potentially be associated with increased susceptibility to cardiovascular diseases. In that study a novel functional mutation of DDAH-1 was identified; the mutation carriers had a significantly elevated risk for cardiovascular disease and a tendency to develop hypertension. These results confirmed the clinical role of DDAH enzymes in ADMA metabolism. Furthermore, it is possible that more common variants of DDAH genes contribute more widely to increased cardiovascular risk.
We found a rare variation in the DDAH-1 gene, which is associated with elevated plasma concentrations of ADMA in heterozygous mutation carriers. There was also an increased prevalence of CHD and a tendency to hypertension among individuals with this DDAH-1 mutation. These observations highlight the importance of ADMA as a possible risk factor and emphasize the essential role of DDAH in regulating ADMA levels.

ADMA Elevation and Coronary Artery Disease
Endothelial dysfunction may be considered as a systemic disorder and involves different vascular beds. Coronary endothelial dysfunction (CED) precedes the development of coronary. Endothelial dysfunction is characterized by a reduction in endogenous nitric oxide (NO) activity, which may be accompanied by elevated plasma asymmetric dimethylarginine (ADMA) levels. ADMA is a novel endogenous competitive inhibitor of NO synthase (NOS), an independent marker for cardiovascular risk.

English: Structure of asymmetric dimethylargin...

English: Structure of asymmetric dimethylarginine; ADMA; N,N-Dimethylarginine Deutsch: Asymmetrisches Dimethylarginin; N,N-Dimethyl-L-arginin; Guanidin-N,N-dimethylarginin (Photo credit: Wikipedia)

In a small study fifty-six men without obstructive coronary artery disease (CAD) who underwent coronary endothelial function testing were studied. Men with CED had significant impairment of erectile function (P ¼ 0.008) and significantly higher ADMA levels (0.50+0.06 vs. 0.45+0.07 ng/mL, P ¼ 0.017) compared with men with normal endothelial function. Erectile function positively correlated with coronary endothelial function. This correlation was independent of age, body mass index, high-density lipoprotein, C-reactive protein, homeostasis model assessment of insulin resistance index, and smoking status, suggesting that CED is independently associated with ED and plasma ADMA concentration in men with early coronary atherosclerosis.

ADMA and Chronic Renal Failure in Hepatorenal Syndrome
The concentration of SDMA was significantly higher in the patients with HRS compared to the patients without HRS and it was also higher than the values obtained from the healthy participants (1.76 ± 0.3 μmol/L; 1.01 ± 0.32 and 0.520 ± 0.18 μmol/L, respectively; p < 0.01). The concentrations of ADMA were higher in the cirrhotic patients with HRS than in those without this serious complication of cirrhosis. The concentration of ADMA in all the examined cirrhotic patients was higher than those obtained from healthy volunteers (1.35 ± 0.27 μmol/L, 1.05 ± 0.35 μmol/L and 0.76 ± 0.21 μmol/L, respectively). In the patients with terminal alcoholic liver cirrhosis, the concentrations
of ADMA and SDMA correlated with the progress of cirrhosis as well as with the development of cirrhosis complications. In the patients with HRS there was a positive correlation between creatinine and SDMA in plasma (r2 = 0.0756, p < 0.001) which was not found between creatinine and ADMA. The results demonstrate that the increase in SDMA concentration is proportionate to the progression of chronic damage of the liver and kidneys. Increased ADMA concentration can be a causative agent of renal insufficiency in patients with cirrhosis.

In patients with cirrhosis, ADMA, as well as SDMA could be markers for kidney insufficiency development. Accumulation of ADMA in plasma causes kidney
vasoconstriction and thereby retention of SDMA. Considering that ADMA has several damaging effects, it can be concluded that modulation of the activity of enzyme which participates in ADMA catabolism may represent a new therapeutic goal which is intended to reduce the progress of liver and kidney damage and thus the development of HRS.

ADMA Therapeutic Targets
Elevated plasma concentrations of the endogenous nitric oxide synthase
inhibitor asymmetric dimethylarginine (ADMA) are found in various clinical settings, including

  • renal failure,
  • coronary heart disease,
  • hypertension,
  • diabetes and
  • preeclampsia.

In healthy people acute infusion of ADMA promotes vascular dysfunction,
and in mice chronic infusion of ADMA promotes progression of atherosclerosis.
Thus, ADMA may not only be a marker but also an active player in cardiovascular disease, which makes it a potential target for therapeutic interventions.

This review provides a summary and critical discussion of the presently available data concerning the effects on plasma ADMA levels of cardiovascular drugs, hypoglycemic agents, hormone replacement therapy, antioxidants, and vitamin supplementation.
We assess the evidence that the beneficial effects of drug therapies on vascular function can be attributed to modification of ADMA levels. To develop more specific ADMA-lowering therapies, mechanisms leading to elevation of plasma ADMA concentrations in cardiovascular disease need to be better understood.

ADMA is formed endogenously by degradation of proteins containing arginine residues that have been methylated by S-adenosylmethionine-dependent methyltransferases (PRMTs). There are two major routes of elimination: renal excretion and enzymatic degradation by the dimethylarginine dimethylaminohydrolases (DDAH-1 and -2).

Oxidative stress causing upregulation of PRMT expression and/or attenuation of DDAH activity has been suggested as a mechanism and possible drug target in clinical conditions associated with elevation of ADMA. As impairment of DDAH activity or capacity is associated with substantial increases in plasma ADMA concentrations, DDAH is likely to emerge as a prime target for specific therapeutic interventions.

Cardiovascular diseases (CVD) in diabetic patients have endothelial dysfunction as a key pathogenetic event. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), plays a pivotal role in endothelial dysfunction. Different natural polyphenols have been shown to preserve endothelial function and prevent CVD. Another study assessed the effect of silibinin, a widely used flavonolignan from milk thistle, on ADMA levels and endothelial dysfunction in db/db mice.

Plasma and aorta ADMA levels were higher in db/db than in control lean mice. Silibinin administration markedly decreased plasma ADMA; consistently, aorta ADMA was reduced in silibinin-treated animals. Plasma and aorta ADMA levels exhibited a positive correlation, whereas liver ADMA was inversely correlated with both plasma and aorta ADMA concentrations. Endothelium-(NO)-dependent vasodilatation to ACh was impaired in db/db mice and was restored in the silibinin group, in accordance with the observed reduction of plasma and vascular levels of ADMA. Endothelium-independent vasodilatation to SNP was not modified by silibinin administration.

Endothelin Inhibitors
Endothelins are potent vasoconstrictors and pressor peptides and are important mediators of cardiac, renal andendocrine functions. Increased ET-1 levels in disease states such as congestive heart failure, pulmonary hypertension, acute myocardial infarction, and renal failure suggest the endothelin system as an attractive target for pharmacotherapy. A non-peptidic, selective, competitive endothelin receptor antagonist with an affinity for the ETA receptor in the subnanomolar range was administered by continuous intravenous infusion to beagle dogs, rats, and Goettingen minipigs. It caused mild arteriopathy characterised by segmental degeneration in the media of mid- to large-size coronary arteries in the heart of dog, but not rat or minipig.

The lesions only occurred in the atrium and ventricle. Frequency and severity of the vascular lesions was not sex or dose related. No effects were noted in blood vessels in other organs or tissue. Plasma concentrations at steady state, and overall exposure in terms of AUC(0–24h) were higher in minipig and rat than the dog but did not cause cardiac arteriopathy. These findings concur with those caused by other endothelin anatagonists, vasodilators and positive inotropic: vasodilating drugs such as potassium channel openers, phosphodiesterase inhibitors and peripheral vasodilators.

Results by echocardiography indicate treatment-related local vasodilatation in the coronary arteries. These data suggest that the coronary arteriopathy may be the result of exaggerated pharmacology. Sustained vasodilatation in the coronary vascular bed may alter flow dynamics and lead to increased shear stress and tension on the coronary wall with subsequent microscopic trauma. In our experience with a number of endothelin receptor antagonists, the cardiac arteriopathy was only noted in studies with multiple daily or continuous intravenous infusion inviting speculation that sustained high plasma levels are needed for development of the lesions.

Up-regulation of vascular endothelin type B (ETB) receptors is implicated in the
pathogenesis of cardiovascular disease. Culture of intact arteries has been shown to induce similar receptor alterations and has therefore been suggested as a suitable method for, ex vivo, in detail delineation of the regulation of endothelin receptors. We hypothesize that mitogen-activated kinases (MAPK) and protein kinase C (PKC) are involved in the regulation of endothelin ETB receptors in human internal mammary arteries.

The endothelin-1-induced contraction (after endothelin ETB receptor desensitization) and the endothelin ETA receptor mRNA expression levels were not altered by culture. The sarafotoxin 6c contraction, endothelin ETB receptor protein and mRNA expression levels were increased. This increase was antagonized by;

PKC inhibitors (10 μM bisindolylmaleimide I and 10 μM Ro-32-0432), and
inhibitors of the p38, extracellular signal related kinases 1 and 2 (ERK1/2) and C-jun terminal kinase (JNK) MAPK pathways
Endothelin Receptor Antagonist Tezosentan
The effects of changes in the mean (Sm) and pulsatile (Sp) components of arterial wall shear stress on arterial dilatation of the iliac artery of the anaesthetized dog were examined in the absence and presence of the endothelin receptor antagonist tezosentan (10 mg kg_1 I.V.; Ro 61-0612; [5-isopropylpyridine-2-sulphonic acid 6-(2-hydroxy-ethoxy)-5-(2-methoxy-phenoxy)-2-(2-1H-tetrazol-5-ylpyridin-4-yl)-pyrimidin-4-ylamide]).

Changes in shear stress were brought about by varying local peripheral resistance and stroke volume using a distal infusion of acetylcholine and stimulation of the left ansa subclavia. An increase in Sm from 1.81 ± 0.3 to 7.29 ± 0.7 N m_2 (means ± S.E.M.) before tezosentan caused an endothelium-dependent arterial dilatation which was unaffected by administration of tezosentan for a similar increase in Sm from 1.34 ± 0.6 to 5.76 ± 1.4 N m_2 (means ± S.E.M.).

In contrast, increasing the Sp from 7.1 ± 0.8 to a maximum of 11.5 ± 1.1 N m_2 (means ± S.E.M.) before tezosentan reduced arterial diameter significantly. Importantly, after administration of tezosentan subsequent increases in Sp caused arterial dilatation for the same increase in Sp achieved prior to tezosentan, increasing from a baseline of 4.23 ± 0.4 to a maximum of 9.03 ± 0.9 N m_2 (means ± S.E.M.; P < 0.001). The results of this study provide the first in vivo evidence that pulsatile shear stress is a stimulus for the release of endothelin from the vascular endothelium.

Exercise and Diet
Vascular endotheliumis affected by plasma asymmetric dimethylarginine (ADMA), and it is induced by inflammatory cytokines of tumour necrosis factor (TNF)-a in vitro. Would a tight glycemic control restore endothelial function in patients with type-2 diabetes mellitus (DM) with modulation of TNF-a and/or reduction of ADMA level? In 24 patients with type-2 DM, the flow-mediated, endothelium-dependent dilation (FMD: %) of brachial arteries during reactive hyperaemia was determined by a high-resolution ultrasound method. Blood samples for glucose, cholesterol, TNF-a, and ADMA analyses were also collected from these patients after fasting. No significant glycemic or FMD changes were observed in 10 patients receiving the conventional therapy.

In 14 patients who were hospitalized and intensively treated, there was a significant decrease in glucose level after the treatment [from 190+55 to 117+21 (mean+SD) mg/dL, P , 0.01]. After the intensive control of glucose level, FMD increased significantly (from 2.5+0.9 to 7.2+3.0%), accompanied by a significant (P , 0.01) decrease in TNF-a (from 29+16 to 11+9 pg/dL) and ADMA (from 4.8+1.5 to 3.5+1.1 mM/L) levels. The changes in FMD after treatment correlated inversely with those in TNF-a (R ¼ 20.711, P , 0.01) and ADMA (R ¼ 20.717, P , 0.01) levels.
The exaggerated blood pressure response to exercise (EBPR) is an independent predictor of hypertension. Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide inhibitor and higher plasma levels of ADMA are related to increased cardiovascular risk. The aim of this study is to identify the relationship between ADMA and EBPR.

A total of 66 patients (36 with EBPR and 30 as controls) were enrolled in the study. EBPR is defined as blood pressure (BP) measurements ≥200/100 mmHg during the treadmill test. All the subjects underwent 24-h ambulatory BP monitoring. L-arginine and ADMA levels were measured using a high performance lipid chromatography technique.

The serum ADMA levels were increased in the EBPR group compared to the healthy controls (4.0±1.4 vs 2.6±1.1 μmol/L respectively, P=0.001), but L-arginine levels were similar in the 2 groups (P=0.19). The serum ADMA levels were detected as an independent predictor of EBPR (odds ratio 2.28; 95% confidence interval 1.22–4.24; P=0.002). Serum ADMA levels might play a role in EBPR to exercise.

Endothelial dysfunction occurs early in atherosclerosis in response to cardiovascular risk factors. The occurrence of endothelial dysfunction is primarily the result of reduced nitric oxide (NO) bioavailabilty. It represents an independent predictor of cardiovascular events and predicts the prognosis of the patient. Therefore, endothelial function has been identified as a target for therapeutic intervention. Regular exercise training is a nonpharmacological option to improve endothelial dysfunction in patients with cardiovascular disease by increasing NO bioavailability.

Peripheral Arterial Disease (PAD) is a cause of significant morbidity and mortality in the Western world. risk factor modification and endovascular and surgical revascularisation are the main treatment options at present. However, a significant number of patients still require major amputation. There is evidence that nitric oxide (NO) and its endogenous inhibitor asymmetric dimethylarginine (ADMA) play significant roles in the pathophysiology of PAD.

This paper reviews experimental work implicating the ADMA-DDAH-NO pathway in PAD, focusing on both the vascular dysfunction and both the vascular dysfunction and effects within the ischaemic muscle, and examines the potential of manipulating this pathway as a novel adjunct therapy in PAD.

In patients with CHF, the peripheral vascular resistance is increased via activation of the neurohormonal system, namely by autonomous sympathetic nervous system, rennin -angiotensin- aldosterone system (RAAS), and endothelin system. The vascular endothelial function in patients with CHF, mainly represented by the endothelium-dependent vasodilation, is altered.

Such alteration leads to increased vascular tone and remodeling of the blood vessels, reducing the peripheral blood flow. Hence, the amount of oxygen for the skeletal muscles is compromised, with progressive exercise intolerance. The vascular endothelial dysfunction in the CHF is mainly due to the decrease of the nitric oxide production induced by the reduced gene expression of eNOS and increased oxidative stress.

The endothelium-dependent vasodilation alteration has been virtually reported in all cardiovascular diseases. Using sauna bath as therapeutic option for CHF is not very recent, since in the 1950’s the first studies with CHF patients were conducted and the potential beneficial effect of sauna was suggested. However, some time later the studies emphasized especially its risks and recommended caution in its use for cardiac patients.

Frequently, sports medicine physicians are invited to evaluate the impact of the sauna on diseases and on health in general. Sauna can be beneficial or dangerous depending on its use. In the past few years the sauna is considered beneficial for the cardiovascular diseases’ patients, as the heart failure and lifestyle-related diseases, mainly by improving the peripheral endothelial function through the increase in cardiac output and peripheral vasodilation.

It is widely known that the vasodilators, such as angiotensin converting enzyme inhibitors, improve the CHF and increase the peripheral perfusion. Since the endothelial function is altered in CHF, the endothelium is considered as a new therapeutic target in heart failure. Hence, the angiotensin converting enzyme inhibitors and physical training improve the endothelial function in CHF patients. One of the proposed mechanisms for the alteration of the endothelium-dependent vasodilation would be through the decrease of the NO production in the peripheral vessels in CHF patients. The decrease of peripheral perfusion would decrease the shear stress. The shear stress is an important stimulus for NO production and eNOS expression. On the other hand, the heat increases the cardiac output and improves the peripheral perfusion in CHF patients. Consequently, with the cardiac output improvement in CHF patients, an increase of the shear stress, NO production and eNOS expression are expected.

Sauna bath
The sauna bath represents a heat load of 300-600 W/m2 of body surface area. The skin temperature rapidly increases to ± 40o-41oC and the thermoregulatory mechanisms are triggered. Evaporative heat transfer by sweating is the only effective body heat loss channel in dry sauna. The sweating begins rapidly and reaches its maximum level in ± 15 min. The total sweat secretion represents a heat loss of about 200 W/m2 of the body surface area. The body cannot compensate for the heat load and causing elevation of internal temperature. The skin circulation increases substantially. The skin blood flow, in the thermo-neutral condition (± 20oC) and in rest corresponding to ± 5-10% of the cardiac output, can reach ± 50-70% of the cardiac output.

Thermal therapy in 60oC produced systemic arterial, pulmonary arterial and venous vasodilation, reduced the preload and afterload and improved the cardiac output and the peripheral perfusion, clinical symptoms, life quality, and cardiac arrhythmias in CHF patients. In infants with severe CHF secondary to ventricular septal defect, the sauna therapy decreased the systemic vascular resistance and increased the cardiac output. The sauna benefits in CHF patients are possibly caused by the improvement of the vascular endothelial function and normalization of the neurohormonal system .

Ikeda et al. discovered that the observed improvements in the sauna therapy are due to the eNOS expression increase in the arterial endothelium. They later showed that the thermal therapy with sauna improves the survival of the TO-2 cardiomyopathic hamsters with CHF and, more recently, showed that the repetitive therapy with sauna increases the eNOS expression and the nitric oxide production in artery endothelium of TO-2 cardiomyopathic hamsters with CHF.
Whether n-3 polyunsaturated fatty acid (PUFA) supplementation and/or diet intervention might have beneficial influence on endothelial function was assessed using plasma levels of ADMA and L-arginine. A male population (n = 563, age 70 ± 6 yrs) with long-standing hyperlipidemia, characterized as high risk individuals in 1970–72, was included, randomly allocated to receive placebo n-3 PUFA capsules (corn oil) and no dietary advice (control group), dietary advice (Mediterranean type), n-3 PUFA capsules, or dietary advice and n-3 PUFA combined and followed for 3 years. Fasting blood samples were drawn at baseline and the end of the study.

Compliance with both intervention regimens were demonstrated by changes in serum fatty acids and by recordings from a food frequency questionnaire. No influence of either regimens on ADMA levels were obtained. However, n-3 PUFA supplementation was accompanied by a significant increase in L-arginine levels, different from the decrease observed in the placebo group (p < 0.05). In individuals with low body mass index (<26 kg/m2), the decrease in L-arginine on placebo was strengthened (p = 0.01), and the L-arginine/ADMA ratio was also significantly reduced (p = 0.04). In this rather large randomized intervention study, ADMA levels were not influenced by n-3 PUFA supplementation or dietary counselling. n-3 PUFA did, however, counteract the age related reduction in L-arginine seen on placebo, especially in lean individuals, which might be considered as an improvement of endothelial function.

Traditional Chinese Medicine

Traditional Chinese Medicine (TCM) involves a broad range of empirical testing and refinement and plays an important role in the health maintenance for people all over the world. However, due to the complexity of Chinese herbs, a full understanding of TCM’s action mechanisms is still unavailable despite plenty of successful applications of TCM in the treatment of various diseases, including especially cardiovascular diseases (CVD), one of the leading causes of death.

An integrated system of TCM has been constructed to uncover the underlying action mechanisms of TCM by incorporating the chemical predictors, target predictors and network construction approaches from three representative Chinese herbs, i.e., Ligusticum chuanxiong Hort., Dalbergia odorifera T. Chen and Corydalis yanhusuo WT Wang widely used in CVD treatment, by combined use of drug absorption, distribution, metabolism and excretion (ADME) screening and network pharmacology techniques. These studies have generated 64 bioactive ingredients and identified 54 protein targets closely associated with CVD, to clarify some of the common conceptions in TCM, and provide clues to modernize such specific herbal medicines.

Ligusticum chuanxiong Hort., Dalbergia odorifera T. Chen and Corydalis yanhusuo WT Wang
Twenty-two of 194 ingredients in Ligusticum chuanxiong demonstrate good bioavailability (60%) after oral administration. Interestingly, as the most abundant bioactive compound of Chuanxiong, Ligustilide (M120) only has an adequate OB of 50.10%, although it significantly inhibits the vasoconstrictions induced by norepinephrine bitartrate (NE) and calcium chloride (CaCl2). Indeed, this compound can be metabolized to butylidenephthalide, senkyunolide I (M156), and senkyunolide H (M155) in vivo.

The three natural ingredients produce various pharmacological activities in cerebral blood vessels, the general circulatory system and immune system including spasmolysis contraction effects, inhibitory effects of platelet aggregation and anti-proliferative activity, and thus improve the therapeutic effect on patients. Cnidilide (M93, OB = 77.55%) and spathulenol (M169, OB = 82.37%) also closely correlate with the smooth muscle relaxant action, and thereby have the strongest spasmolytic activity. Carotol (M8) and Ferulic acid (M105) with an OB of 149.03% and 86.56%, respectively, demonstrate better bioavailability compared with cnidilide and spathulenol, which show strong antifungal, antioxidant and anti-inflammatory activity.

The pharmacological activity of ferulic acid results in the improvement of blood fluidity and the inhibition of platelet aggregation, which may offer beneficial effects against cancer, CVD, diabetes and Alzheimer’s disease. As for 3-n-butylphthalide (M85, OB = 71.28%), this compound is not only able to inhibit platelet aggregation, but also decreases the brain infarct volume and enhances microcirculation, thus benefiting patients with ischemic stroke. Platelet aggregation represents a multistep adhesion process involving distinct receptors and adhesive ligands, with the contribution of individual receptor-ligand interactions to the aggregation process depending on the prevailing blood flow conditions, implying that the rheological (blood flow) conditions are an important impact factor for platelet aggregation. Moreover, thrombosis, the pathological formation of platelet aggregates and one of the biggest risk factors for CVD, occludes blood flow causing stroke and heart attack. This explains why the traditional Chinese herb Ligusticum chuanxiong that inhibits platelet aggregates forming and promotes blood circulation can be used in treatment of CVD.

Twenty-six percent (24 of 93) of the ingredients in Dalbergia odorifera meet the OB > 60% criterion irrespective of the pharmacological activity. Relatively high bioavailability values were predicted for the mainly basic compounds odoriflavene (M275, OB = 84.49%), dalbergin (M247, OB = 78.57%), sativanone (M281, OB = 73.01%), liquiritigenin (M262, OB = 67.19%), isoliquiritigenin (M259, OB = 61.38%) and butein (M241, OB = 78.38%). Interestingly, all of the six ingredients show obvious anti-inflammatory property. Butein, liquiritigenin and isoliquiritigenin inhibit cell inflammatory responses by suppressing the NF-κB activation induced by various inflammatory agents and carcinogens, and by decreasing the NF-κB reporter activity. Inflammation occurs with CVD, and Dalbergia odorifera, one of the most potent anti-cardiovascular and anti-cerebrovascular agents, exerts great anti-inflammatory activity.

Corydalis yanhusuo has gained ever-increasing popularity in today’s world because of its therapeutic effects for the treatment of cardiac arrhythmia disease, gastric and duodenal ulcer and menorrhalgia. In our work, 21% (15 of 73) of chemicals in this Chinese herb display good OB (60% or even high), and the four main effective ingredients are natural alkaloid agents.

Dehydrocorydaline blocks the release of noradrenaline from the adrenergic nerve terminals in both the Taenia caecum and pulmonary artery, and thereby inhibits the relaxation or contraction of adrenergic neurons. As for dehydrocavidine with an OB of 47.59%, this alkaloid exhibits a significant spasmolytic effect, which acts via relaxing smooth muscle.

In recent years, CVD has been at the top list of the most serious health problems. Many different types of therapeutic targets have already been identified for the management and prevention of CVD, such as endothelin and others. The key question asked is

  • what the interactions of the active ingredients of the Chinese herbs are with their protein targets in a systematic manner and
  • how do the corresponding targets change under differential perturbation of the chemicals?

The study used an unbiased approach to probe the proteins that bind to the small molecules of interest in CVD on the basis of the Random Forest (RF) and Support Vector Machine (SVM) methods combining the chemical, genomic and pharmacological information for drug targeting and discovery on a large scale. Applied to 64 ingredients derived from the three traditional Chinese medicines Dalbergia odorifera, Ligusticum chuanxiong and Corydalis yanhusuo, which show good OB, 261 ligand-target interactions have been constructed, 221 of which are enzymes, receptors, and ion channels. This indicates that chemicals with multiple relative targets are responsible for the high interconnectedness of the ligand-target interactions. The promiscuity of drugs has restrained the advance in recent TCM, because they were thought to be undesirable in favor of more target-specific drugs.

Target Identification and Validation
To validate the reliability of these target proteins, the researchers performed a docking analysis to select the ligand-protein interactions with a binding free energies of ≤−5.0 kcal/mol, which leads to the sharp reduction of the interaction number from 5982 to 760. These drug target candidates were subsequently subject to PharmGkb (available online: http://www.pharmgkb.org; accessed on 1 December 2011), a comprehensive disease-target database, to investigate whether they were related to CVD or not, and finally, 54 proteins were collected and retained.

Fourty-two proteins (76%) were identified as the targets of Ligusticum chuanxiong, such as dihydrofolate reductase (P150), an androgen receptor (P210) and angiotensin-converting enzyme (P209) that were involved in the development of CVD. Of the proteins, seven and two were recognized as those of Dalbergia odorifera and Corydalis yanhusuo, respectively. For Dalbergia odorifera, this Chinese herb has 48 potential protein targets, 13 of which have at least one link to other drugs.

The three herbs share 29 common targets, accounting for 52.7% of the total number. Indeed, as one of the most important doctrines of TCM
abstracted from direct experience and perception, “multiple herbal drugs for one disease” has played an undeniable role. These studies explored the targets of the three Chinese herbs, indicating that these drugs target the same targets simultaneously and exhibit similar pharmacological effects on CVD. This is consistent with the theory of “multiple herbal drugs for one disease”.

The three Chinese herbs possess specific targets. The therapeutic efficacy of a TCM depends on multiple components, targets and pathways. The complexity becomes a huge obstacle for the development and innovation of TCM. For example, the Chinese herb Ligusticum chuanxiong identifies the protein caspase-3 (P184), a cysteinyl aspartate-specific protease, as one of its specific targets, and exhibits inhibitory effects on the activity of this protease. In fact, connective tissue growth factor enables the activation of caspase-3 to induce apoptosis in human aortic vascular smooth muscle cells.

Thus, modulation of the activity of caspase-3 with Ligusticum chuanxiong suggests an efficient therapeutic approach to CVD. The Chinese herb Dalbergia odorifera has the α-2A adrenergic receptor (P216) as its specific target and probably blocks the release of this receptor, and thus influences its action. As for Corydalisyanhusuo, the protein tyrosine-protein kinase JAK2 (P9) is the only specific target of this Chinese herb. The results indicate different specific targets possessed by the three Chinese herbs.

Ligand-Candidate Target and Ligand-Potential Target Networks
Previous studies have already reported the relationships of the small molecules with CVD, which indicates the reliability of our results [45,46]. Regarding the candidate targets, we have found that prostaglandin G/H synthase 2 (P46) and prostaglandin G/H synthase 1 (P47) possess the largest number of connected ingredients. Following are nitric-oxide synthase, endothelial (P66) and tyrosine-protein phosphatase non-receptor type 1 (P8), which have 62 and 61 linked chemicals, respectively.
The 29 targets shared by the three traditional Chinese herbs exhibit a high degree of correlations with CVD, which further verifies their effectiveness for the treatment of CVD. These results provide a clear view of the relationships of the target proteins with CVD and other related diseases, which actually link the Chinese herbs and the diseases via the protein targets. This result further explains the theory of “multiple herbal drugs for one disease” based on molecular pharmacology.

Target-Pathway Network
Cells communicate with each other using a “language” of chemical signals. The cell grows, divides,or dies according to the signals it receives. Signals are generally transferred from the outside of the cell. Specialized proteins are used to pass the signal—a process known as signal transduction. Cells have a number of overlapping pathways to transmit signals to multiple targets. Ligand binding in many of the signaling proteins in the pathway can change the cellular communication and finally affect cell growth and proliferation. The authors extracted nine signal pathways closely associated with CVD in PharmGkb (available online: http://www.pharmgkb.org; accessed on 1 December 2011).

As the main components in the VEGF system, proto-oncogene tyrosine-protein kinase Src, eNOS, and hsp90-α is also recognized as common targets of Dalbergia odorifera, Ligusticum chuanxiong and Corydalis yanhusuo, which are efficient for the treatment of CVD. This implies that the candidate drugs can target different target proteins involved in the same or different signal pathways, and thereby have potential effects on the whole signal system.

Target Prediction
In search of the candidate targets, the model that efficiently integrates the chemical, genomic and pharmacological information for drug targeting and discovery on a large scale is based on the two powerful methods Random Forest (RF) and Support Vector Machine (SVM). The model is supported by a large pharmacological database of 6511 drugs and 3999 targets extracted from the DrugBank database (available online: http://drugbank.ca/; accessed on 1 June 2011), and shows an impressive performance of prediction for drug-target interaction, with a concordance of 85.83%, a sensitivity of 79.62% and a specificity of 92.76%. the candidate targets were selected according to the criteria that the possibility of interacting with potential candidate targets was higher than 0.6 for the RF model and 0.7 for the SVM model. The obtained candidate targets were finally reserved and were further predicted for their targets.

Target Validation
Molecular docking analysis was carried out using the AutoDock software (available online: http://autodock.scripps.edu/; accessed on 1 February 2012). This approach performs the docking of the small, flexible ligand to a set of grids describing the target protein. During the docking process, the protein was considered as rigid and the molecules as flexible. The crystal structures of the candidate targets were downloaded from the RCSB Protein Data Bank (available online: http://www.pdb.org/; accessed on 1 December 2011), and the proteins without crystal structures were performed based on homology modeling using the Swiss-Model Automated Protein Modelling Server (available online: http://swissmodel.expasy.org/; accessed on 1 February 2012).

TCM is a heritage that is thousands of years old and is still used by millions of people all over the world—even after the development of modern scientific medicine. Chinese herbal combinations generally include one or more plants and even animal products.

The study identified 54 protein targets, which are closely associated with CVD for the three Chinese herbs, of which 29 are common targets (52.7%), which clarifies the mechanism of efficiency of the herbs for the treatment of CVD.

Activation of NFkB

Extracellular stimuli for NFkB activation and NFkB regulated genes
Extracellular stimuli                       Regulated genes
TNFa                                         Growth factors (G/M-CSF)
Interleukin 1                            G/M CSF, M CSF, G CSF
ROS                                              Cell adhesion molecules
UV light                            ICAM-1, VCAM, E-Selectin, P-selectin
Ischaemia                                   Cytokines
Lipopolysaccharide               TNFa, IL-1, IL-2, IL-6, interferon
Bacteria                                        Transcription regulators
Viruses                                         P53, IkB, c-rel, c-myc
Amyloid                                      Antiapoptotic proteins
Glutamate                              TRAF-1, TRAF-2, c-IAP1, c-IAP2
Pathophysiology
Reactive oxygen species (ROS) are toxic and in conditions of a dysbalance between their overproduction and the diminished activity of various antioxidant enzymes and other molecules induce cellular injury termed oxidative stress. ROS are often related to a number of diseases like atherosclerosis. However, the mechanism is not clear at all. Latest years of research have brought the idea of connection between ROS and NFkB. And indeed, in vitro studies showed a rapid activation of NFkB after exposure of certain cell types to ROS. Today, no specific receptor for ROS has been found, thus, the details of the ROS induced activation of NFkB are missing.

Natural occurring agents which actions are still a matter of debate in the theory and nouvelle small molecular derivates activate or inhibit the transcriptional factor. Synthetic oligo and polypeptide inhibitors of NFkB can penetrate the cell membrane and directly act on the Rel proteins. The most sophisticated approaches towards inhibiting the activation and translocation of NFkB into the nucleus represent gene deliveries, using plasmids or adenoviruses containing genes for various super repressors—modified IkB proteins, or so called NFkB decoys, which interact with activated NFkB and thus, inhibit the interaction between the transcription factor and nuclear DNA enhancers.

A simplified scheme of the activation of NFkB by the degradation of IkB. IkB is phosphorylated by IKK and ubiquinatated by the ubiquitine ligase system (ULS). IkB is further degradated by the 26S proteasome (26S).Activated NFkB can pass the nuclear membrane and interact with kB binding sequences in enhancers of NFkB regulated genes. LPS, lipopolysaccharide; ROS, reactive oxygen species; FasL, Fas ligand; TRAF, TNFa receptor associated factor; NIK, NFkB inducing kinase; MEKK, mitogen activated protein kinase/extracellular signal regulated kinases kinases.

The medicine of this century is a medicine of molecules, the diagnostic procedure and the therapy moves further from the “clinical picture” to the use of achievements in molecular biology and genetics. However, sober scepticism and awareness are indicated. Especially the role of NFkB in multiple signal transducing pathways and the tissue dependent variability of responses to alternations in NFkB pathway may be the reasons for unwanted side effects of the therapy that are after in vitro or in vivo experiments hardly to expect in the clinical use.

Therapeutic Targets
Modern drug discovery is primarily based on the search and subsequent testing of drug candidates acting on a preselected therapeutic target. Progress in genomics, protein structure, proteomics, and disease mechanisms has led to a growing interest in an effort for finding new targets and more effective exploration of existing targets. The number of reported targets of marketed and investigational drugs has significantly increased in the past 8 years. There are 1535 targets collected in the therapeutic target database.
Knowledge of these targets is helpful for molecular dissection of the mechanism of action of drugs and for predicting features that guide new drug design and the
search for new targets. This article summarizes the progress of target exploration and investigates the characteristics of the currently explored targets to analyze their sequence, structure, family representation, pathway association, tissue distribution, and genome location features for finding clues useful for searching for new targets. Possible “rules” to guide the search for druggable proteins and the feasibility of using a statistical learning method for predicting druggable proteins directly from their sequences are discussed.

Current Trends in Exploration of Therapeutic Targets
There are 395 identifiable targets described in 1606 patents. Of these targets, 264 have been found in more than one patent and 50 appear in more than 10 patents. The number of patents associated with a target can be considered to partly correlate with the level of effort and intensity of interest currently being directed to it. Approximately one third of the patents with an identifiable target were approved in the past year. This suggests that the effort for the exploration of these targets is ongoing, and there has been steady progress in the discovery of new investigational agents directed to these targets.

Various degrees of progress have been made toward discovery and testing of agents directed at these targets. However, for some of these targets, many difficulties remain to be resolved before viable drugs can be derived. The appearance of a high number of patents associated with these targets partly reflects the intensity of efforts for finding effective drug candidates against these targets.

There are 62 targets being explored for the design of subtype-specific drugs, which represents 15.7% of the 395 identifiable targets in U.S. patents approved in 2000 through 2004. Compared with the 11 targets of FDA approved subtype-specific drugs during the same period, a significantly larger number of targets are being explored for the design of subtype-specific drugs.

What Constitutes a Therapeutic Target?
The majority of clinical drugs achieve their effect by binding to a cavity and regulating the activity, of its protein target. Specific structural and physicochemical properties, such as the “rule of five” (Lipinski et al., 2001), are required for these drugs to have sufficient levels of efficacy, bioavailability, and safety, which define target sites to which drug-like molecules can bind. In most cases, these sites exist out of functional necessity, and their structural architectures accommodate target-specific drugs that minimally interact with other functionally important but structurally similar sites.
These constraints limit the types of proteins that can be bound by drug-like molecules, leading to the introduction of the concept of druggable proteins (Hopkins and Groom, 2002; Hardy and Peet, 2004). Druggable proteins do not necessarily become therapeutic targets (Hopkins and Groom, 2002); only those that play key roles in diseases can be explored as potential targets.

 Prediction of Druggable Proteins by a Statistical Learning Method

Currently, the support vector machine (SVM) method seems to be the most accurate statistical learning method for protein predictions. SVM is based on the structural risk minimization principle from statistical learning theory. Known proteins are divided into druggable and nondruggable classes; each of these proteins is represented by their sequence-derived physicochemical features.

These features are then used by the SVM to construct a hyperplane in a higher dimensional hyperspace that maximally separates druggable proteins and nondruggable ones. By projecting the sequence of a new protein onto this hyperspace, it can be determined whether this protein is druggable from its location with respect to the hyperplane. It is a druggable protein if it is located on the side of druggable class.
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 Nitric Oxide and Sepsis, Hemodynamic Collapse, and the Search for Therapeutic Options

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Reveals from ENCODE project will invite high synergistic collaborations to discover specific targets

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Upending the cliché of muscleheads, scientists at the Laboratory of Neuroscience at the National Institute on Aging recently set out to examine whether changes in muscles prompted by exercise might subsequently affect and improve the brain’s ability to think.

Lab animals and people generally perform better on tests of cognition after several weeks of exercise training, and studies have shown that over time, running and other types of endurance exercise increase the number of neurons in portions of the brain devoted to memory and learning. But the mechanisms that underlie this process remain fairly mysterious. Do they start within the brain itself? Or do messages arrive from elsewhere in the body to jump-start the process?

The researchers were especially interested in the possibility that the action starts outside the brain – and specifically in the muscles. “We wondered whether peripheral triggers might be activating the cellular and molecular cascades in the brain that led to improvements in cognition,” says Henriette van Praag, the investigator at the National Institute on Aging who led the study.

Muscles are, of course, greatly influenced by exercise. Muscle cells respond to exercise by pumping out a variety of substances that result in larger, stronger muscles. Some of those compounds might be entering the bloodstream and traveling to the brain, Dr. van Praag says.

The problem is that exercise is such a complicated physiological stimulus that it’s very difficult to isolate which compounds are involved and what their effects might be. So she and her colleagues decided to study “fake” exercise instead, using two specialized drugs that had been tested several years ago by scientists at the Salk Institute in San Diego. The drugs had been shown to induce the same kinds of changes in sedentary animals’ muscles that exercise would cause, so that even though the mice didn’t exercise, they physiologically responded as if they had.

One of the drugs that they used, known as Aicar, increases the muscles’ output of AMPK, an enzyme that affects cellular energy and metabolism. Regular endurance exercise, like running or cycling, increases the muscles’ production of this enzyme. In the Salk experiments, Aicar enabled untrained mice to run 44 percent farther during treadmill tests than other, sedentary animals that hadn’t received the drug.

The second compound, GW1516, a cholesterol drug, also stimulates biochemical changes in muscle cells like those caused by endurance exercise. But in the Salk studies, it had amplified endurance primarily in animals that also ran, allowing them to run farther than another set of running mice that didn’t get the drug. But it hadn’t done much muscle-wise for animals that remained sedentary.

By using these drugs in unexercised animals under well-controlled conditions, the scientists from the National Institute on Aging sought to determine whether changes in muscles then initiated changes in the brain.

And as it turned out, muscles did affect the mind. After a week of receiving either of the two drugs (and not exercising), the mice performed significantly better on tests of memory and learning than control animals that had simply remained quiet in their cages. The effects were especially pronounced for the animals taking Aicar.

The results, published in the journal Learning and Memory, showed that the drugged animals’ brains also contained far more new neurons in brain areas central to learning and memory than the brains of the control mice, an effect found by microscopic examination.

Because the two drugs “don’t cross the blood-brain barrier much, if at all,” Dr. van Praag says, “we could be fairly confident that the changes we were seeing were related to an exercise-type reaction in the muscles” and not to brain responses to the drugs.

The message of this finding, she continues, is that “improvements in cognition” that follow exercise “would seem to involve changes throughout the body and not just in the brain.”

Although the exact process isn’t clear, Dr. van Praag speculates that some of the AMPK enzyme created during exercise enters the bloodstream and travels to the brain, setting off a series of new reactions there.

http://well.blogs.nytimes.com/2012/05/09/how-working-the-muscles-may-boost-brainpower/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3032576/Endurance factors improve hippocampal neurogenesis and spatial memory in mice

Tali Kobilo, Chunyan Yuan, and Henriette van Praag
Reporter: Prabodh Kandala, PhD

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