Endogenous opioid peptides and cardiac arrhythmias

Prospects for Creation of Cardioprotective and Antiarrhythmic Drugs Based on Opioid Receptor Agonists

It has now been demonstrated that the μ, δ1 , δ2 , and κ1 opioid receptor (OR) agonists represent the most promising group of opioids for the creation of drugs enhancing cardiac tolerance to the detrimental effects of ischemia/reperfusion (I/R). Opioids are able to prevent necrosis and apoptosis of cardiomyocytes during I/R and improve cardiac contractility in the reperfusion period. The OR agonists exert an infarct-reducing effect with prophylactic administration and prevent reperfusion-induced cardiomyocyte death when ischemic injury of heart has already occurred; that is, opioids can mimic preconditioning and postconditioning phenomena. Furthermore, opioids are also effective in preventing ischemia-induced arrhythmias.

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.

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.

Cardiac opioids

Opioid peptides have long been considered as neuropeptides or neurotransmitters. The more recent discovery of these same peptides in non-neuronal tissue suggests that the peptides may have autocrine, paracrine, or endocrine functions as well. The opioid peptides, enkephalins, dynorphins, and endorphins, have been found in isolated cardiac myocytes and heart tissue. This review will cover the recent literature on opioid peptides in respect to cardiac distribution, biochemistry, and function.

Opioids in cardiac surgery: cardiopulmonary bypass and inflammatory response

After a brief overview of the history of narcotic use in anesthesia, the various opiates are reviewed mainly from a stress-reducing, antiinflammatory and hemodynamic perspective. The emphasis is placed on cardiac anesthesia.

Exercise effect on canine and miniswine cardiac catecholamines and enkephalins

Chronic exercise changes cardiac function and responsiveness to autonomic control. Catecholamines and enkephalins are neuroendocrine transmitters involved in autonomic regulation and signaling. We hypothesized that intermittent increased sympathetic stimulation caused by exercise training would decrease cardiac catecholamine and enkephalin content. Dogs and miniswine were exercise trained and hearts extracted for catecholamine and enkephalin measurements. Atrial catecholamine content is greater than ventricular content in dog heart which is in keeping with the greater atrial neuronal density. In contrast, porcine epinephrine content was evenly distributed across heart sections and norepinephrine content was greater on the right side than the left. Changes in miniswine and dog heart catecholamine content after exercise training were different. Canine cardiac norepinephrine content decreased and porcine norepinephrine content increased. This indicates a difference in cardiac adrenergic control in miniswine versus canines. Methionine-enkephalin (met-enk) distribution across canine heart is uniform, unlike the miniswine, where the atria contain more than the ventricles. Proenkephalin processing produces four met-enk sequences and one met-enk-arg-phe; despite this, ventricles of both species contain more met-enk-arg-phe immunoreactivity than met-enk. Therefore, proenkephalin processing is incomplete in heart tissue. Exercise training in the dog resulted in decreased cardiac met-enk, decreased left atrial met-enk-arg-phe, and increased ventricular met-enk-arg-phe. Porcine cardiac enkephalin concentration was unchanged by training. The changes in the enkephalins may be explained by changes in proenkephalin processing and/or release. Met-enk-arg-phe is particularly good at modulating vagal stimulation of the canine heart. The changes in tissue content seen after exercise training may be a result of the exercise-induced change in autonomic tone to the heart. These data suggest species dependent changes in autonomic regulation.

Stereospecific blocking effects of naloxone against hemodynamic compromise and ventricular dysfunction due to myocardial ischemia and reperfusion

Endogenous opioid peptides subserve regulatory roles in cardiovascular function and are released upon myocardial ischemia contributing to the development of ischemic arrhythmias and cardiogenic shock, which are reversed by the opioid antagonist naloxone. Since the hallmark of myocardial infarction is the impairment of hemodynamics and ventricular function, we evaluated further if blockade of opioids reverses the ischemia induced hemodynamic compromise, and if the effects are mediated by opioid receptors. Thirty-two mongrel dogs were anesthetized and artificially ventilated. Median thoracotomy was performed, the heart exposed, and the left anterior descending coronary artery isolated for subsequent occlusion and reperfusion. All cardiac parameters were recorded on an Electronics for Medicine recorder through the intracardiac catheters advanced from femoral vessels. Results indicate that naloxone significantly reversed the ischemic and reperfusion induced reduction in aortic, left ventricular and pulmonary arterial pressures, and left ventricular dp/dt. The inactive (+) stereoisomer of naloxone was without effect. These data demonstrate that opioids may have a role in the pathophysiology of myocardial infarction, mediated by opioid receptors, and provide new insight and strategies for the understanding and treatment of ischemic heart disease.

Methionine-enkephalin-Arg-Phe immunoreactivity in heart tissue

Previous findings of enkephalins in cardiac tissue led us to investigate enkephalin distribution in animal models used for cardiovascular research. Canine cardiac methionine-enkephalin (ME) concentrations are low and evenly distributed between atria (4.2 +/- 0.6 fmol/mg protein, n = 30) and ventricles (4.4 +/- 0.5). In contrast, methionine-enkephalyl-arginyl-phenylalanine (MEAP) immunoreactivity (IR) is higher and preferentially concentrated in the ventricle (112 +/- 12) vs. the atria (23.2 +/- 2.6 fmol/mg protein). HPLC analysis suggests the atrial/ventricular difference is partly due to altered posttranslational processing. Nearly 90% of ventricular IR is comprised of MEAP (46%) and peptide B (40%) whereas these peptides represent less than half of the atrial content. A nonneuronal localization is indicated because the peptide distribution does not correspond to the catecholamine distribution. Canine left ventricular tissue sections were processed for immunohistochemistry with the MEAP antibody. Fluorescence was distributed throughout the myocytes and concentrated in ordered lines perpendicular to the myocyte longitudinal axis corresponding to the area of the intercalated disc. This suggests opioids may be important in communication between cardiomyocytes, and possibly the presence of a unique peptide secretory mechanism utilizing the intercalated disc. The relative peptide content in cat and pig hearts was similar to the dog; however, the distribution was different. Feline cardiac ME content was distributed 2:1 in favor of the ventricles and corresponded with a preferential ventricular norepinephrine distribution. The MEAP-IR pattern gave a ventricular/atrial ratio lower (3.5:1) in cat heart vs. dog (5:1). In contrast, pig heart ME and MEAP-IR ventricular/atrial ratios were reversed for both ME (1:10) and MEAP (1:2). HPLC of pig left ventricle showed that MEAP and peptide B represented 33% and 39% of the MEAP-IR, respectively. These species variations may correlate to the differences observed in cardiac function.

Stereospecific antiarrhythmic effects of naloxone against myocardial ischaemia and reperfusion in the dog

1. The effects of both the (-)- and (+)-stereoisomers of naloxone in anaesthetized dogs with arrhythmias induced by acute coronary artery occlusion followed by reperfusion were investigated. 2. Following coronary artery occlusion and reperfusion, all dogs in the control group developed ischaemia- and reperfusion-induced cardiac arrhythmias, bradycardia and hypotension. 3. The opiate antagonist (-)-naloxone prevented the arrhythmias, bradycardia and hypotension due to myocardial ischaemia and reperfusion. 4. The (+)-stereoisomer of naloxone, which is inactive as an opiate antagonist, was without beneficial effects. 5. These results indicate a possible involvement of endogenous opioid peptides in the cardiac effects due to myocardial ischaemia and reperfusion, mediated by opiate receptors through opiate antagonism.

Demonstration by in situ hybridization of the proopiomelanocortin gene in the rat heart

A biotinylated oligonucleotide probe was used to demonstrate the presence in the heart of the portion of the proopiomelanocortin messenger RNA which contains the sequence for beta-endorphin. The probe indicated the presence of beta-endorphin messenger RNA in cardiac tissue and specifically in the cardiac muscle cell. The probe also confirmed the well-documented presence of messenger RNA for beta-endorphin in the anterior and neurointermediate lobes of the pituitary. These findings indicate that in addition to the pituitary, beta-endorphin is produced in situ in the heart.

Electrophysiologic effects of blocking and stimulating the opioid system in patients with unexplained heart palpitations

The opioid system plays a role in the regulation of the cardiovascular system. Endogenic as well as egzogenic administration of opioids influences the heart rhythm. This work was undertaken in order to assess the influence of crossover activity of the heart opioid system on the heart conduction system in patients with various disturbances of rhythm having an efficient circulatory system and a normal 12-lead stationary ECG. Subjects were 20 patients (9 men and 11 women of mean age of 38.7 years) reporting sudden heart palpitations. They were subjected to invasive programmable electrophysiological studies (PES). Naloxone was administered intravenously to 10 patients. Pentazocine was administered in the same way. In the remaining 10 patients the order of drug administration was reversed. PES was done in the basic state and after the administration of each drug. Study results were subjected to statistical analysis with no-parameter Wilcoxon test assuming differences to be significant at p less than 0.05. Blocking of the opioid system resulted in significant lengthening of the sinoatrial (SACT), intra-atrial (PA), and atrioventricular node (AH) conduction times, while no changes were induced in conduction in the His-Purkinje system (HV) and automation of the sinus node. Naloxone lengthened the atrial (ERPA) and atrioventricular node (ERPA AVN) effective refractory periods. Stimulation of the opioid system resulted in decreases of the following values: SACT, PA, AH, ERPA, ERPA AVN, while no effect was exerted on the SNRT, HV, ERPV. Neither drug influenced the QRS time, although naloxone lengthened QTc period significantly. Opioids did not influence the time of conduction in concealed extranodal atrioventricular pathways.(ABSTRACT TRUNCATED AT 250 WORDS)