The role of endogenous opioids in congestive heart failure: effects of nalmefene on systemic and regional hemodynamics in dogs

Chronic Naltrexone Therapy Is Associated with Improved Cardiac Function in Volume Overloaded Rats

PURPOSE

Myocardial opioid receptors were demonstrated in animals and humans and seem to colocalize with membranous and sarcolemmal calcium channels of the excitation-contraction coupling in the left ventricle (LV). Therefore, this study investigated whether blockade of the cardiac opioid system by naltrexone would affect cardiac function and neurohumoral parameters in Wistar rats with volume overload-induced heart failure.

METHODS

Volume overload in Wistar rats was induced by an aortocaval fistula (ACF). Left ventricular cardiac opioid receptors were identified by immunohistochemistry and their messenger ribonucleic acid (mRNA) as well as their endogenous ligand mRNA quantified by real-time polymerase chain reaction (RT-PCR). Following continuous delivery of either the opioid receptor antagonist naltrexone or vehicle via minipumps (n = 5 rats each), hemodynamic and humoral parameters were assessed 28 days after ACF induction. Sham-operated animals served as controls.

RESULTS

In ACF rats mu-, delta-, and kappa-opioid receptors colocalized with voltage-gated L-type Ca2+ channels in left ventricular cardiomyocytes. Chronic naltrexone treatment of ACF rats reduced central venous pressure (CVP) and left ventricular end-diastolic pressure (LVEDP), and improved systolic and diastolic left ventricular functions. Concomitantly, rat brain natriuretic peptide (rBNP-45) and angiotensin-2 plasma concentrations which were elevated during ACF were significantly diminished following naltrexone treatment. In parallel, chronic naltrexone significantly reduced mu-, delta-, and kappa-opioid receptor mRNA, while it increased the endogenous opioid peptide mRNA compared to controls.

CONCLUSION

Opioid receptor blockade by naltrexone leads to improved LV function and decreases in rBNP-45 and angiotensin-2 plasma levels. In parallel, naltrexone resulted in opioid receptor mRNA downregulation and an elevated intrinsic tone of endogenous opioid peptides possibly reflecting a potentially cardiodepressant effect of the cardiac opioid system during volume overload.

Opioids in Cardiovascular Disease: Therapeutic Options

The World Health Organization suggests that the cardiovascular diseases (CVDs) are the major cause of mortality and account for two-thirds of the deaths all over the world. These diseases kill about 17 million people every year and 3 in every 10 deaths are due to these diseases. The past decade has seen considerable improvements in diagnosis as well as treatment of various heart diseases. Various new therapeutic targets are being identified through in-depth knowledge of the disease mechanisms which has favored the testing of new strategies leading to newer treatment options. Opioid peptides and G-protein-coupled opioid receptors (ORs) have been previously studied widely in terms of central nervous system actions in mitigating the pain and drug abuse. The OR agonism or antagonism induces cytoprotective states in the myocardium, rendering these receptors as an attractive target for protection of heart from the fatal heart diseases. The opioids can provide an extended window of protection of the heart from various diseases. Although the mechanisms may not be fully understood, they seem to play a crucial role in various CVDs such as hypertension, hyperlipidemia, ischemic heart disease myocardial ischemia, and congestive heart failure. Since these compounds are already being used in acute and chronic pain, soon these compounds might be approved for use as cardioprotective agents. The following review focuses on the new information acquired on the role of the ORs in various CVDs.

Proenkephalin in Heart Failure

The opioid system is activated in heart failure, which may be cardioprotective but may also be counter-regulatory. Recently, systemic proenkephalin activation has been investigated in various conditions predicting mortality and kidney injury. In acute heart failure, proenkephalin independently predicts mortality and heart failure rehospitalization in addition to traditional risk markers. It also predicts worsening renal function, increasingly recognized as an important risk predictor for poor outcome in heart failure. This article explores the role of enkephalins and delta-opioid receptors in the heart, then reviews studies measuring proenkephalin levels in the circulation and their associations with prognosis.

Cellular localization and adaptive changes of the cardiac delta opioid receptor system in an experimental model of heart failure in rats

The role of the cardiac opioid system in congestive heart failure (CHF) is not fully understood. Therefore, this project investigated the cellular localization of delta opioid receptors (DOR) in left ventricle (LV) myocardium and adaptive changes in DOR and its endogenous ligand, the precursor peptide proenkephalin (PENK), during CHF. Following IRB approval, DOR localization was determined by radioligand binding using [H(3)]Naltrindole and by double immunofluorescence confocal analysis in the LV of male Wistar rats. Additionally, 28 days following an infrarenal aortocaval fistula (ACF) the extent of CHF and adaptions in left ventricular DOR and PENK expression were examined by hemodynamic measurements, RT-PCR, and Western blot. DOR specific membrane binding sites were identified in LV myocardium. DOR were colocalized with L-type Ca(2+)-channels (Cav1.2) as well as with intracellular ryanodine receptors (RyR) of the sarcoplasmatic reticulum. Following ACF severe congestive heart failure developed in all rats and was accompanied by up-regulation of DOR and PENK on mRNA as well as receptor proteins representing consecutive adaptations. These findings might suggest that the cardiac delta opioid system possesses the ability to play a regulatory role in the cardiomyocyte calcium homeostasis, especially in response to heart failure.

Endogenous cardiac opioids: enkephalins in adaptation and protection of the heart

Opiates have been used for thousands of years in the form of opium for relief of pain or fever and to induce sleep. However, it was only in the 1970s that the endogenous ligands for the opiate receptors were identified and termed opioid peptides. Opioid peptides activate G protein-coupled receptors in the central and autonomic nervous system, with marked effects on the regulation of pain perception, body temperature, respiration, heart rate and blood pressure. Cardiovascular regulatory effects of endogenous opioids were initially considered to originate from neural centres in the central nervous system, facilitating a regulatory role in neuro-transmission, as demonstrated by the presynaptic co-release from sympathetic neurones of norepinephrine with enkephalin or acetylcholine with enkephalin. However, opioid peptides of myocardial origin have also recently been shown to play a key role in local regulation of the heart. This brief review highlights the key features of the enkephalin opioids in the heart and the current understanding of their role in development, ageing, cardioprotection, hypertension, hypertrophy, and heart failure.

Opioids

Opioids are the most effective and widely used drugs in the treatment of severe pain. They act through G protein-coupled receptors. Four families of endogenous ligands (opioid peptides) are known. The standard exogenous opioid analgesic is morphine. Opioid agonists can activate central and peripheral opioid receptors. Three classes of opioid receptors (mu, delta, kappa) have been identified. Multiple pathways ofopioid receptor signaling (e.g., G(i/o) coupling, cAMP inhibition, Ca++ channel inhibition) have been described. The differential regulation of effectors, preclinical pharmacology, clinical applications, and side effects will be reviewed in this chapter.

Vagotonic effects of enkephalin are not mediated by sympatholytic mechanisms

This study examined the hypothesis that vagotonic and sympatholytic effects of cardiac enkephalins are independently mediated by different receptors. A dose-response was constructed by administering the delta-receptor opioid methionine-enkephalin-arginine-phenylalanine (MEAP) by microdialysis into the interstitium of the canine sinoatrial node during vagal and sympathetic stimulation. The right cardiac sympathetic nerves were stimulated as they exited the stellate ganglion at frequencies selected to increase heart rate approximately 35 bpm. The right cervical vagus was stimulated at frequencies selected to produce a two-step decline in heart rate of 25 and 50 bpm. A six-step dose-response was constructed by recording heart rates during nerve stimulation as the dose of MEAP was increased between 0.05 pmol/min and 1.5 nmol/min. Vagal transmission improved during MEAP at 0.5 pmol/min. However, sympathetically mediated tachycardia was unaltered with any dose of MEAP. In Study 2, a similar dose-response was constructed with the kappa-opioid receptor agonist trans(+/-)-3-4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide-HCl (U-50488H) to illustrate an independent sympatholytic effect and to verify its kappa-receptor character. U-50488H gradually suppressed the sympathetic tachycardia, with a significant effect obtained only at the highest dose (1.5 nmol/min). U-50488H had no effect on vagally mediated bradycardia. Surprisingly, the sympatholytic effect was not reversed by withdrawing U-50488H or by the subsequent addition of the kappa-antagonist 17,17'-(dichloropropylmethyl)-6,6',7,7'-6,6'-imino-7,7'-binorphinan-3,4',14,14'-tetroldi-hydrochloride (norBNI). Study 3 was conducted to determine whether the sympatholytic effect of U-50488H could be prevented by norBNI. NorBNI blocked the sympatholytic effect of the U50488H for 90 mins. When norBNI was discontinued afterward and U-50488H was continued alone, a sympatholytic effect emerged within 30 mins. Collectively these observations support the hypothesis that the vagotonic influence of MEAP is not dependent on a sympatholytic influence. Furthermore, the sympatholytic effect is mediated independently by kappa-receptors. The sympatholytic effect of sustained kappa-receptor stimulation appears to evolve gradually into a functional state not easily reversed.

Myocardial and peripheral concentrations of beta-endorphin before and following myocardial ischemia and reperfusion during coronary angioplasty

There is substantial evidence indicating that endogenous opioid peptides are involved in the pathophysiology of myocardial ischemia and reperfusion. We measured the myocardial and peripheral concentrations of beta-endorphin before and following myocardial ischemia and reperfusion during coronary angioplasty. The results indicate that in patients with coronary artery disease, there was an augmented myocardial concentration of beta-endorphin. Moreover, there was an increased peripheral concentration of beta-endorphin following myocardial ischemia and reperfusion. The data support the previous notion that endogenous opioid peptides are involved in the pathophysiology of ischemic heart disease.

Chronic mu-opioid receptor stimulation alters cardiovascular regulation in humans: differential effects on muscle sympathetic and heart rate responses to arterial hypotension

In opioid addicted patients, respiratory regulation adapts allowing intake of otherwise lethal dosages of opioids. In contrast, little is known about cardiovascular regulation during chronic opioid receptor stimulation. We previously demonstrated that chronic mu-opioid receptor stimulation by methadone decreases resting muscle sympathetic activity (MSA). However, for short-term control of arterial blood pressure autonomic responses to arterial hypotension may be of greater importance. Accordingly, we tested the hypothesis that chronic opioid receptor stimulation attenuates muscle sympathetic and heart rate responses to arterial hypotension. Ten young patients (mean +/- SD, 30 years +/- 6) with a long history of mono-opioid addiction and under oral methadone substitution therapy (54 mg d(-1) +/- 31) for 12 months (+/-20) were studied. Peroneal MSA (microneurography) and heart rate responses to hypotensive challenges (sodium nitroprusside) were assessed in the awake state and compared with those of 10 matched healthy subjects. Effects of mu-opioid receptor blockade by naloxone (12.4 mg i.v.) were determined during propofol anesthesia. Chronic mu-opioid receptor stimulation markedly decreased the MSA response to hypotension (-0.5 units mm Hg(-1) +/- 0.2 vs. -2.0 +/- 1.8; p = 0.01) compared with healthy subjects despite similar arterial blood pressure and heart rate at rest. In contrast, the heart rate response to hypotension did not differ between addicted patients (6 ms mm Hg(-1) +/- 2) and healthy subjects (7 ms mm Hg(-1) +/-4). Opioid receptor blockade during propofol anesthesia markedly increased the MSA response to hypotension even beyond awake values (-1.2 units mm Hg(-1) +/- 1.1; p = 0.02 vs. awake) while the heart rate response remained unchanged. Thus, chronic mu-opioid receptor stimulation 1) results in uncompensated depression of cardiovascular sympathetic neural regulation, and 2) exerts differential effects on efferent sympathetic nerve activity to muscle and on heart rate control in response to arterial hypotension.

The diverse molecular mechanisms responsible for the actions of opioids on the cardiovascular system

The actions of opioid agonist and antagonist drugs have not been well characterized in the heart and cardiovascular system. This stems from the limited role opioid receptors have been perceived to have in the regulation of the cardiovascular system. Instead, the focus of opioid receptor research, for many years, relates to the characterization of the actions of opioid drugs in analgesia associated with receptor activation in the CNS. However, recent studies suggest that opioid receptors have a role in the heart and cardiovascular system. While some of these actions may be mediated by activation of peripheral opioid receptors, others are not, and may result from direct or receptor-independent actions on cardiac tissue and the peripheral vascular system. This review will outline some of the diverse molecular mechanisms that may be responsible for the cardiovascular actions of opioids, and will characterize the role opioid receptors have in several cardiovascular pathophysiological disease states, including hypertension, heart failure, and ischaemic arrhythmogenesis. In many instances, it would appear that the effects of opioid agonists (and antagonists) in cardiovascular disease models may be mediated by opioid receptor-independent actions of these drugs.

Plasma beta-endorphin and adenosine concentration in pulmonary hypertension

To determine whether beta-endorphin plays a role in the regulation of pulmonary vascular tone in patients with pulmonary hypertension, we investigated the relations between hemodynamics and beta-endorphin and adenosine concentrations in 3 clinical situations: (1) normal hemodynamics (7 subjects, mean pulmonary artery [PA] pressure 18.5 +/- 1 mm Hg); (2) moderate pulmonary hypertension secondary to chronic obstructive pulmonary disease (COPD) (8 patients, mean PA pressure 31 +/- 3 mm Hg); and (3) severe primary pulmonary hypertension (PPH) (8 patients, mean PA pressure 70 +/-5 mm Hg). Plasma beta-endorphin and adenosine were measured in a distal PA and in the femoral artery in room air and during oxygen inhalation. Beta-endorphin levels were similar in the pulmonary and systemic circulations. No difference was observed between patients with COPD and PPH, but relative to controls, both had significantly higher beta-endorphin levels. Pulmonary adenosine was significantly lower in patients with pulmonary hypertension than in controls (-60% in COPD [p <0.005] and -70% in PPH [p <0.001]). Pure oxygen administration significantly decreased adenosine and beta-endorphin levels, much more so in patients with COPD and PPH. We found a negative correlation between beta-endorphin and adenosine concentrations (r = -0.751, p <0.001): the higher the adenosine, the lower the beta-endorphin level. These observations suggest that because adenosine release by pulmonary vascular endothelium is reduced in pulmonary hypertension, the resulting worsened hypoperfusion and tissue oxygenation may cause increased beta-endorphin release.

Enkephalin inhibits vagal control of heart rate, contractile force and coronary blood flow in the canine heart in vivo

The following studies were conducted to determine if the ability of the intrinsic cardiac opioid, met-enkephalin-arg-phe to interrupt vagal bradycardia can be generalized to include the disruption of vagal effects on atrial contraction and coronary blood flow. Anesthetized dogs were instrumented to measure heart rate and left atrial contractile force or heart rate and coronary blood flow. The response of each variable was recorded at rest and during vagal stimulation. During the evaluation of vagal effects on contractile activity and coronary blood flow, heart rate was maintained constant by electrically pacing the hearts above their resting heart rate. In the first protocol, vagal stimulation reduced both heart rate and atrial contractile force in a frequency dependent fashion. When met-enkephalin-arg-phe (MEAP) was infused systemically for three min at 3 nmol min(-1) kg(-1), there were no observed changes in resting heart rate or atrial contraction. However, when the vagal stimuli were reapplied during the peptide infusion, the previously observed vagal effects on rate and contractile force were reduced in magnitude by one-half to two-thirds. The ability of MEAP to interrupt the vagal control of heart rate and contractile activity involves opiate receptors since the effect was eliminated in both cases by prior opiate receptor blockade with the high affinity antagonist, diprenorphine. In the second protocol, vagal stimulation produced a transient increase in coronary blood flow and an accompanying increase in myocardial oxygen consumption. These effects were reduced by approximately 80% during the systemic infusion of MEAP. A similar increase in coronary blood flow mediated by the direct acting muscarinic agonist, methacholine, was unaltered by the infusion of peptide. In summary, these data suggest that the intrinsic cardiac enkephalin, MEAP, is capable of inhibiting the vagal control of heart rate, contractile force and coronary blood flow and probably does so through a common opiate receptor located prejunctionally on vagal nerve terminals or within nearby parasympathetic ganglia.

Effects of mu-, delta- and kappa-opioid antagonists in atrial preparations from nonfailing and failing human hearts

1. We examined the effects of naloxone (preferentially mu-antagonist), naltrindole (selective delta-antagonist) or nor-binaltorphimine (nor-BNI, selective kappa-antagonist) on auricular myocardium tissue from nonfailing and failing human hearts. 2. The opioid antagonists used in this study induced inhibitory effects in auricular strips from failing and nonfailing human hearts. In addition, the maximal effect, the IC50, and the slope of concentration-response curves obtained with mu-, delta-, and kappa-opioid antagonists were similar in failing and nonfailing human heart tissues. 3. The kappa-antagonist was more effective than naltrindole or naloxone. Moreover, the IC50 for nor-BNI (0.25 +/- 0.01 x 10(-5) M) was lower than the IC50 for naloxone (26.5 +/- 5.0 x 10(-5) M) and naltrindole (13.8 +/- 2.0 x 10(-5) M). Similar results were obtained in auricular strips from failing human hearts. 4. Our results demonstrate that the failing heart does not modify the inhibitory cardiac effects obtained with selective opioid antagonists.

Plasma beta-endorphin response to exercise in patients with congestive heart failure

OBJECTIVE

To determine whether the net release of beta-endorphin during exercise, similar to that of norepinephrine, is related to functional disability in patients with congestive heart failure.

BACKGROUND

Plasma beta-endorphin and norepinephrine levels are elevated at rest in patients with heart failure, reflecting a functional disability. The net release of beta-endorphin during exercise in patients with heart failure is unknown.

METHODS

We measured plasma beta-endorphin and norepinephrine levels (respectively: radioimmune and radioenzymatic assay) at rest and during graded exercise testing in 28 patients with congestive heart failure (Weber's class A, 10; B, 9; and C, 9) and in 9 normal subjects.

RESULTS

At rest, plasma beta-endorphin levels were higher in patients in classes B and C than in normal subjects (p < 0.05 and < 0.01, respectively). At peak exercise, patients in different functional classes and normal subjects reached similar beta-endorphin levels. However, the net release of beta-endorphin during exercise was lower in patients in classes B and C than in those in class A and normal subjects (p < 0.01 for both). At rest, plasma norepinephrine levels were significantly higher in patients than in normal subjects (p < 0.01). At peak exercise, norepinephrine levels were significantly lower in class C patients than in normal subjects (p < 0.05), and tended to be lower in patients in classes A and B (p = NS). The net release of norepinephrine during exercise was lower in patients than in normal subjects (p < 0.01). In patients, releases of both beta-endorphin and norepinephrine during exercise were related to peak oxygen consumption and duration of exercise, but not to resting left ventricular ejection fraction.

CONCLUSIONS

In patients with congestive heart failure, the net release of plasma beta-endorphin during exercise is decreased, like norepinephrine, and reflects a functional disability.

Sympathetic dysregulation in heart failure: mechanisms and therapy

Heart failure is accompanied by sympathetic over-activity, which contributes to the pathophysiology and to poor prognosis. This paper reviews the mechanisms and potential therapy for sympathetic dysregulation in heart failure (HF). Several points are emphasized: (1) There is increased sympathetic activity to skeletal muscle, kidney, and heart, but not to skin, in HF. This information challenges the concept of generalized sympathetic activation in HF and suggests that the factors responsible for sympathetic activation result in a partitioning of excess sympathetic outflow to some but not all tissues and organs. (2) The sympathetic dysregulation appears to result from impairment in cardiac and arterial baroreceptor restraint on sympathetic activity, but this abnormality in baroreceptor function may result from abnormal humoral and/or ionic influences acting on baroreceptor endings or in the central nervous system and not from intrinsic structural abnormalities in baroreceptors. This distinction has potential therapeutic importance because abnormalities in humoral or ionic mechanisms would more likely lend themselves to therapeutic modulation. (3) Digitalis sensitizes cardiac and arterial baroreceptors and inhibits sympathetic nerve activity in patients with HF. This sympathoinhibitory influence of digitalis is maintained during chronic therapy. These observations support the concept that the therapeutic effects of digitalis include autonomic modulation in addition to positive inotropism. In a broader concept, these observations suggest that sympathetic modulation may represent an important target for drugs for treatment of heart failure.

Activation and inhibition of the endogenous opioid system in human heart failure

BACKGROUND

In a canine model of congestive heart failure beta endorphin concentrations were high and opioid receptor antagonists exerted beneficial haemodynamic effects. In humans previous studies have suggested that opioid peptides may modify the perception of breathlessness and fatigue in heart failure.

METHODS

Plasma concentrations of beta endorphin were measured in patients with acute and chronic heart failure and cardiogenic shock. A subgroup of eight patients with New York Heart Association (NYHA) class III-IV heart failure was assessed for acute haemodynamic effects of naloxone, an opioid receptor antagonist. A separate group of 10 patients with class II-III heart failure, was randomised to a double blind placebo controlled study of the effects of intravenous naloxone on cardiopulmonary exercise performance.

RESULTS

Plasma concentrations of beta endorphin were usually normal in patients with chronic heart failure and did not correlate with severity as assessed by NYHA class. In 29% of patients with acute heart failure and 71% of those with cardiogenic shock beta endorphin concentrations were high. The median concentration in the cardiogenic shock group was significantly higher than in either of the two heart failure groups and there was some evidence of a relation between beta endorphin concentrations and survival. At the doses tested, naloxone was unable to modify systemic haemodynamics, exercise performance, or symptoms in patients with chronic congestive heart failure.

CONCLUSIONS

Circulating concentrations of beta endorphin are usually normal in patients with chronic congestive heart failure. Inhibition of the endogenous opioid system is unlikely to have therapeutic potential in heart failure.

Short-term effects of naloxone on hemodynamics and baroreflex function in conscious dogs with pacing-induced congestive heart failure

OBJECTIVES

The purpose of this study was to determine the effects of naloxone on systemic hemodynamics and reflex function in dogs with congestive heart failure induced by rapid pacing.

BACKGROUND

We have shown previously that naloxone, an opiate receptor antagonist, improves cardiac output, aortic blood pressure, systolic performance and the baroreflex function in conscious dogs with chronic right-sided congestive heart failure. However, whether endogenous opioids also play a role n mediating the reduction of myocardial and baroreflex function in animals with left heart failure remains controversial.

METHODS

We administered naloxone (1 mg/kg body weight) and normal saline solution to 15 dogs with pacing-induced congestive heart failure (225 beats/min for 8 weeks) and 11 control dogs. In addition to systemic hemodynamic measurements, the slope of pressure-area relation obtained from echocardiography with intravenous bolus injection of phenylephrine was taken as a load-independent index of myocardial contractility. Baroreflex function was estimated by the slope of the regression line relating systolic aortic pressure and RR interval.

RESULTS

Plasma beta-endorphin levels were elevated in dogs with congestive heart failure. Naloxone administration increased heart rate, mean aortic pressure, first derivative of left ventricular pressure, cardiac output and myocardial contractility in pacing-induced congestive heart failure. These changes correlated significantly with basal plasma beta-endorphin levels and were accompanied by increases in plasma beta-endorphin and catecholamines after naloxone administration. However, unlike the hemodynamic and cardiac effects of naloxone, baroreflex function did not change after naloxone in dogs with congestive heart failure.

CONCLUSIONS

The increase in basal plasma beta-endorphin suggests that the endogenous opiate system is activated in left-sided congestive heart failure. Because naloxone improves the systemic hemodynamics and myocardial contractile function under this condition, the endogenous opioids appear to play an important role in mediating the myocardial depression that occurs in heart failure. However, the endogenous opiate system has no apparent effect on the regulation of baroreflex control in heart failure induced by rapid pacing.

Beta endorphin release in patients after spontaneous and provoked acute myocardial ischaemia

BACKGROUND

In animal models of circulatory shock and heart failure concentrations of the endogenous opioid peptide beta endorphin are raised and opioid receptor blockade improves haemodynamic variables and survival. This study was performed to identify whether acute myocardial ischaemia provokes the release of beta endorphin in humans.

METHODS

Observational study in a university cardiology centre. Serial measurements of beta endorphin made by specific radioimmunoassay were correlated with other clinical and neuroendocrine variables that were measured prospectively. Fifty five patients with acute myocardial ischaemia and 26 patients undergoing elective coronary angioplasty of the left anterior descending coronary artery were studied.

RESULTS

beta endorphin concentrations were raised above the upper limit of normal in 31/42 (74%) patients with confirmed myocardial infarction, 3/13 (23%) patients with unstable angina, and 10/24 (42%) patients after coronary angioplasty. There was no evidence of myocardial release of beta endorphin. There were significant positive correlations between beta endorphin and the concentrations of adrenocorticotrophic hormone, cortisol, and arginine vasopressin. In patients with acute myocardial ischaemia there was a significant positive correlation between the peak concentrations of creatine kinase and beta endorphin but no correlation with visual analogue scores of the intensity of chest pain. The highest beta endorphin concentrations were seen in patients whose clinical course was complicated by the development of heart failure.

CONCLUSIONS

beta endorphin release is a component of the neuroendocrine activation associated with myocardial ischaemia/infarction.

Administration of slow-release nifedipine does not affect lactate threshold, hormone release during exercise, and quality of life in normal subjects

In a double-blind crossover study of 10 normal healthy subjects, we examined the effects of slow-release nifedipine (nifedipine-SR, 10 mg b.i.d) administration on exercise capacity, hormone levels during exercise, and quality of life (QOL) after a 2-week treatment. Two exercise tests, a progressive exercise test and a constant work-rate exercise test, were performed. Maximal oxygen uptake (VO2max) and blood lactate concentration were measured during the progressive exercise test and the exercise intensity corresponding to half lactate threshold (LT), LT, and 4 mmol/l of lactate concentration was determined. Subjects underwent 20 minutes of constant work-rate exercise at each work load, and blood lactate, plasma epinephrine, plasma norepinephrine, plasma renin activity, plasma aldosterone, atrial natriuretic peptide, plasma beta-endorphin, and met-enkephalin were measured. Taking nifedipine-SR had no effect on the responses of blood pressure, heart rate, VO2max, maximal work load, and LT compared to taking placebo. Blood lactate, plasma catecholamine, plasma renin activity, aldosterone, atrial natriuretic peptide, and beta-endorphin levels increased during exercise, and there was no difference between nifedipine-SR and placebo. Met-enkephalin did not increase with either treatment. In the QOL questionnaires, no differences were noted between the two treatments. These findings suggest nifedipine-SR to be a potentially useful drug in view of the lack of effect on exercise capacity, hormone release, and QOL.

Elevated plasma beta-endorphin levels in patients with congestive heart failure

Recent experimental studies show that the opioid system is important to the pathophysiology of cardiovascular impairment in congestive heart failure. Plasma beta-endorphin levels were measured in 37 patients with congestive heart failure and compared with those of 21 age- and gender-matched normal subjects. The relation of plasma beta-endorphin levels and cardiac function at rest and exercise capacity was assessed in 17 of the patients with dilated cardiomyopathy. Exercise capacity was determined by symptom-limited maximal treadmill exercise with expired gas analysis. Plasma beta-endorphin levels were elevated and correlated with the patients' New York Heart Association functional cardiac status (control: 14.0 +/- 4.4 pg/ml; class II: 17.9 +/- 3.6 pg/ml; class III: 28.3 +/- 8.8 pg/ml; class IV: 46.7 +/- 14.6 pg/ml, mean +/- SD). No relation was found between plasma beta-endorphin levels and left ventricular systolic performance as assessed by M-mode and Doppler echocardiography. Plasma beta-endorphin levels were negatively correlated with cardiac output determined by Doppler echocardiography and positively correlated with systemic vascular resistance (r = -0.733, r = 0.747, respectively, both p less than 0.001), but not correlated with calf blood flow as measured by a plethysmography. A good correlation was found between plasma beta-endorphin levels at rest and exercise capacity. The correlations with peak oxygen consumption, anaerobic threshold, and peak rate-pressure product were r = -0.721, -0.672, and -0.674, respectively (p less than 0.01). The data show that plasma beta-endorphin levels are elevated in patients with congestive heart failure and reflect, to some degree, the severity of the disease.

Compensation and overcompensation in congestive heart failure

The compensatory mechanisms that develop in response to heart failure have been well defined. In this review, it is argued that each compensatory mechanism leads to overcompensation and that there is no way to distinguish between the beneficial aspects of the former and the harmful effects of the latter. Therapeutic agents that maintain rather than decrease blood pressure might perhaps be more beneficial because of the crucial role of hypotension in initiating both compensation and overcompensation.

Decreased adrenergic neuronal uptake activity in experimental right heart failure. A chamber-specific contributor to beta-adrenoceptor downregulation

The reduction of myocardial beta-adrenoceptor density in congestive heart failure has been thought to be caused by agonist-induced homologous desensitization. However, recent evidence suggests that excessive adrenergic stimulation may not produce myocardial beta-receptor downregulation unless there is an additional defect in the local norepinephrine (NE) uptake mechanism. To investigate the association between beta-adrenoceptor regulation and NE uptake activity, we carried out studies in 30 dogs with right heart failure (RHF) produced by tricuspid avulsion and progressive pulmonary artery constriction and 23 sham-operated control dogs. We determined NE uptake activity by measuring accumulation of [3H]NE in tissue slices, NE uptake-1 carrier density by [3H]mazindol binding and beta-adrenoceptor density by [3H]dihydroalprenolol binding. Compared with sham-operated dogs, RHF dogs showed a 26% decrease in beta-adrenoceptor density, a 51% reduction in NE uptake activity, and a 57% decrease in NE uptake-1 carrier density in their right ventricles. In addition, right ventricle beta-receptor density correlated significantly with NE uptake activity and NE uptake-1 carrier density. In contrast, neither NE uptake activity nor beta-receptor density in the left ventricle and renal cortex was affected by RHF. Thus, the failing myocardium is associated with an organ- and chamber-specific subnormal neuronal NE uptake. This chamber-specific loss of NE uptake-1 carrier could effectively reduce local NE clearance, and represent a local factor that predisposes the failing ventricle to beta-adrenoceptor downregulation.

The neuroanatomy, neurophysiology, and neurochemistry of pain, stress, and analgesia in newborns and children

Beginning with a brief description of mature anatomic pathways and neurotransmitters in the "pain system," this article details their development in the human fetus, neonate, and child. Special emphasis is given to the basic mechanisms and physiologic effects of opioid analgesia. The clinical implications of these data are described, particularly with regard to the maintenance of cardiovascular stability and hormonal-metabolic homeostasis in newborns and children undergoing surgery or other forms of stress.

Endogenous opiates: 1987

This paper is the tenth installment of our annual review of the research during the past year involving the endogenous opiate system. It covers the nonanalgesia and behavioral studies of the opiate peptides published in 1987. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal activity; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical activity; locomotor activity; sex, pregnancy, and development; immunology and cancer; and other behavior.

Modulation of peripheral sympathetic nerve transmission

The past 15 years have been witness to a remarkable growth in knowledge regarding the modulation of "sympathetic traffic" to neuroeffector organs, including vascular tissue. The release of norepinephrine from peripheral sympathetic neurons is now known to be under both negative and positive feedback control. Norepinephrine, when released from peripheral neurons, acts on presynaptic alpha 2-receptors to inhibit further neurotransmission. Vascular postsynaptic alpha 2-receptors, sensitive to circulating catecholamines, subserve vasoconstriction. The antihypertensive agents clonidine, guanabenz and guanfacin likely reduce blood pressure by acting centrally on alpha 2 postsynaptic neurons to limit sympathetic transmission to blood vessels. Clonidine can produce venoconstriction and thereby improve orthostatic hypotension by activating venous alpha 2-receptors. Additional presynaptic dopaminergic receptors (DA2), muscarinic receptors (acetylcholine), opioid receptors, prostaglandin receptors, adenosine receptors (A1) and histamine (H2) receptors are present on sympathetic nerve membranes and, when engaged with the appropriate ligand, can limit the exocytotic process. Gamma-aminobutyric acid and serotonin demonstrate similar roles in reducing sympathetic nerve activity. In contrast to these inhibitory presynaptic mechanisms, facilitation of norepinephrine release appears to occur by way of neuronal angiotensin II receptor activation and perhaps through stimulation of sympathetic nerve membrane beta 2-receptors. An appreciation of these inhibitory and facilitator mechanisms is useful in the treatment of a variety of clinical conditions, including hypertension, heart failure, orthostatic hypotension, septic shock and a number of common withdrawal syndromes.

Alterations in cardiac beta-adrenoceptor responsiveness and adenylate cyclase system by congestive heart failure in dogs

The effects of congestive heart failure on the physiological and biochemical functions of the cardiac beta-adrenoceptor-coupled adenylate cyclase system were studied in dogs with right heart failure produced by progressive pulmonary artery constriction and tricuspid avulsion. The cardiac inotropic response to dobutamine was attenuated in congestive heart failure, as determined by the right and left ventricular dP/dt responses. Adrenergic beta-receptor density, measured by [3H]dihydroalprenolol binding, was reduced in membrane fractions of the failing right ventricle, but not in the left ventricle. The functional activity of the adenylate cyclase system was studied in vitro by measuring the net cyclic AMP production following additions of isoproterenol, 5'-guanylylimidodiphosphate (Gpp(NH)p), forskolin, or manganese chloride, which act either directly on the beta-adrenergic receptors or on one of the post-receptor components of the adenylate cyclase system. Congestive heart failure reduced the net production of cyclic AMP by isoproterenol, Gpp(NH)p, and forskolin in both the right and left ventricles, but did not alter the effect of manganese chloride. Thus, beta-receptor down-regulation is chamber-specific, occurring only in the hemodynamically stressed right ventricle. In contrast, the post-receptor defect of the adenylate cyclase system occurred in both ventricles of the heart failure dogs. This decreased activation of adenylate cyclase by beta-agonists may be responsible, at least in part, for the diminished cardiac inotropic response to catecholamines in congestive heart failure.