Opioid antagonist modulation of ischaemia-induced ventricular arrhythmias: a peripheral mechanism

Long-acting opioids and cardiovascular diseases: Help or hindrance!

Opioids are widely being used for chronic pain management, cough and diarrhea suppressants, anesthetic agents, and opioid de-addiction therapy. Opioid receptors, present in the central nervous system and peripheral tissues, are documented to regulate several cardiac functions through different signaling pathways. Long-acting opioids (LAO) have been successfully evaluated for their beneficial effects in various cardiovascular diseases viz. myocardial infarction, ischemic reperfusion injuries, atherosclerosis etc. However, on the other hand, several research studies pointed towards the harmful effects of LAOs which are mainly associated with QTc prolongation, torsade de pointes, ventricular arrhythmias, and cardiac arrest. This review shall familiarize readers with the benefits as well as the harmful effects of long-acting opioids in cardiovascular diseases. We have also provided an overview of cardiac opioid receptors, endogenous cardiac opioid peptides, and regulation of cardiovascular functions by central and cardiac opioid receptors.

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.

Activation of peripheral delta opioid receptors increases cardiac tolerance to arrhythmogenic effect of ischemia/reperfusion

OBJECTIVES

The objective of this study was to investigate the role of peripheral μ, δ1, δ2, and nociceptin opioid receptors agonists in the regulation of cardiac tolerance to the arrhythmogenic effect of ischemia/reperfusion in rats.

METHODS

Anesthetized open-chest male Wistar rats were subjected to either 45 minutes of left coronary artery occlusion (phase 1a 10 minutes and phase 2b 35 minutes) and 2 hours of reperfusion in Experiment 1 or 10 minutes of ischemia and 10 minutes of reperfusion in Experiment 2. In Experiment 1, saline or vehicle controls and the mu-specific opioids dermorphin-H (Derm-H) and ([d-Ala2, N-Me-Phe4, Gly-ol5] enkephalin (DAMAGO); the delta-1-specific opioid d-Pen2,5enkephalin (DPDPE); nociceptin; and the delta-2-specific opioids deltorphin-II (Delt-II), Delt-Dvariant (Delt-Dvar), and deltorphin-E (Delt-E) were infused 15 minutes prior to ischemia. In Experiment 2, DPDPE, Delt-D, Delt-Dvar, and Delt-E were infused at 15 minutes prior to ischemia. The universal opioid receptor antagonist naltrexone, the peripherally acting antagonist naloxone methiodide, the selective δ1 antagonist 7-benzylidene naltrexone maleate, and the specific δ2 antagonist naltriben mesylate were infused 25 minutes prior to ischemia.

RESULTS

In Experiment 1, pretreatment with the μ opioids Derm-H and DAMGO, DPDPE, and nociceptin at all doses tested did not reduce the incidence of ischemia-induced arrhythmias compared to controls during 45 minutes of ischemia. The δ2 opioids Delt-II (0.12 mg/kg), Delt-Dvar (0.3 mg/kg), and Delt-E (0.18 mg/kg) all demonstrated significant antiarrhythmic effects at the 150 nmol/kg dose compared to saline or vehicle controls. Nine of 19 animals treated with Delt-II were tolerant without ventricular arrhythmias to the arrhythmogenic effect of ischemia during the first 10 minutes of ischemia (phase 1a) and 11 of 19 were without ventricular arrhythmias during the following 35 minutes of ischemia (phase 1b). Delt-II also decreased the incidence of premature ventricular contractions and ventricular tachycardia by almost half during phase 1a. Delt-II did not affect the incidence of ventricular fibrillation (VF). Pretreatment with Delt-Dvar and Delt-E completely blocked the incidence of VF in phase 1b. Delt-E also decreased premature ventricular contractions by 50%, and the incidence of ventricular tachycardia decreased over twofold in phase 1b of ischemia. There was no enhanced tolerance by any of the delta-2 opioids to the arrhythmogenic effect of reperfusion after long-term ischemia. In Experiment 2, after 10 minutes of ischemia and 10 minutes of reperfusion, Delt-II (0.12 mg/kg) reduced the incidence of premature ventricular contractions and ventricular tachycardia compared to controls, and completely blocked the incidence of VF following 10 minutes of reperfusion. Delt-Dvar and Delt-E were without effect, as was DPDPE following 10 minutes of reperfusion. The antiarrhythmic effect of Delt-II during 10 minutes of ischemia and 10 minutes of reperfusion was completely blocked by the peripherally acting opioid receptor inhibitor naloxone methiodide and the selective delta-2 opioid receptor inhibitor naltriben mesylate, but not by the selective delta-1 inhibitor 7-benzylidene naltrexone maleate. The antagonists alone had no effect on arrhythmogenesis.

CONCLUSIONS

Peripheral delta-2 opioid receptor activation by Delt-II, Delt-Dvar, and Delt-E enhanced cardiac tolerance to the arrhythmogenic effects of ischemia.

Combination of opium smoking and hypercholesterolemia augments susceptibility for lethal cardiac arrhythmia and atherogenesis in rabbit

Opium consumption is increasing in some eastern societies, where it is grown. We investigated the effect of opium smoking on plasma atherogenic index and incidence of lethal cardiac arrhythmia, i.e. ventricular tachycardia (VT) and ventricular fibrillation (VF) in rabbits. Animals were divided into two-, normo- and hyper-cholesterolemic main groups fed with normal or high cholesterol diet prior and during short-term and long-term exposure to opium smoke. Then, isoproterenol (3mg/kg, i.p.) was injected to induce cardiac ischemia and animals were followed for 3h for counting of lethal arrhythmia incidence. Long-term opium smoking significantly increased the plasma atherogenic index. In ischemic hearts, opium smoking along with hypercholesterolemia significantly enhanced the incidence of fatal arrhythmia. This vulnerability was not mediated by changes in QT interval. These data suggest that opium smoking, especially in hypercholesterolemic conditions, can be a predisposing factor for atherogenesis and lethal arrhythmia.

Differential involvement of 3′, 5′-cyclic adenosine monophosphate-dependent protein kinase in regulation of Fos and tyrosine hydroxylase expression in the heart after naloxone induced morphine withdrawal

We previously demonstrated that morphine withdrawal induced hyperactivity of the heart by the activation of noradrenergic pathways innervating the left and right ventricle, as evaluated by noradrenaline (NA) turnover and Fos expression. We investigated whether cAMP-dependent protein kinase (PKA) plays a role in this process by estimating changes in PKA immunoreactivity and the influence of inhibitor of PKA on Fos protein expression, tyrosine hydroxylase (TH) immunoreactivity levels and NA turnover in the left and right ventricle. Dependence on morphine was induced by a 7-day s.c. implantation of morphine pellets. Morphine withdrawal was precipitated on day 8 by an injection of naloxone (5 mg/kg). When opioid withdrawal was precipitated, an increase in PKA immunoreactivity and phospho-CREB (cyclic AMP response element protein) levels were observed in the heart. Moreover, morphine withdrawal induces Fos expression, an enhancement of NA turnover and an increase in the total TH levels. When the selective PKA inhibitor HA-1004 was infused, concomitantly with morphine pellets, it diminished the increase in NA turnover and the total TH levels observed in morphine-withdrawn rats. However, this inhibitor neither modifies the morphine withdrawal induced Fos expression nor the increase of nonphosphorylated TH levels. The present findings indicate that an up-regulated PKA-dependent transduction pathway might contribute to the activation of the cardiac catecholaminergic neurons in response to morphine withdrawal and suggest that Fos is not a target of PKA at heart levels.

Cardioprotective action of fentanyl in a model of central sympathetic overactivity in rabbits: antiarrhythmic and anti-ischemic effects

BACKGROUND

Sympathetic overactivity resulting from perioperative noxious stimuli elicits hyperdynamic cardiovascular responses that may lead to myocardial ischemia and/or ventricular arrhythmia, especially in patients presenting with coronary artery disease. In the present study we investigated the cardioprotective effects of clinically relevant doses of fentanyl in an experimental model of sympathetic overactivity associated with myocardial ischemia in anesthetized rabbits.

METHODS

Central sympathetic stimulation was achieved through intracerebroventricular (i.c.v.) injection of L-glutamate (10 micro mol), with simultaneous inhibition of nitric oxide (NO) synthesis through i.v. administration of N(omega)-nitro-l-arginine methyl ester (L-NAME; 40 mg kg(-1)).

RESULTS

L-glutamate triggered ventricular arrhythmia and electrocardiographic alterations indicative of myocardial ischemia. The intravenous administration of fentanyl (5, 10 or 50 micro g kg(-1)) reduced the incidence of ST-segment shift (70, 20 and 10%, respectively, vs. 66.7% in controls) as well as of T-wave inversion from 58.3% to 30, 20 and 10%, respectively. The total number of ventricular premature complexes per minute fell from 65.2 +/- 16 in the control group to 6.8 +/- 3, 3.5 +/- 2 and 2.6 +/- 1.5, respectively. The occurrence of ventricular tachycardia and bigeminy was completely abolished by fentanyl. Finally, the i.v. administration of fentanyl did not induce significant hemodynamic effects (except for dP/dt(max) in the 50 micro g kg(-1)-dose).

CONCLUSION

Fentanyl elicits significant cardioprotective effects in a model of arrhythmia resulting from the association of central sympathetic overactivity with myocardial ischemia in rabbits, independently from its systemic hemodynamic actions.

Morphine withdrawal-induced c-fos expression in the heart: a peripheral mechanism

We previously demonstrated that hyperactivity of cardiac noradrenergic pathways observed during morphine withdrawal is mediated by peripheral mechanisms. In the present study, naloxone methiodide (quaternary derivative of naloxone that does not cross the blood-brain barrier) and naloxone were administered to morphine-dependent rats and Fos immunostaining was used as a reflection of neuronal activity. Dependence on morphine was induced by 7-day chronic subcutaneous (s.c.) implantation of six morphine pellets (75 mg). Morphine withdrawal was precipitated by administration of naloxone methiodide (5 mg/kg, s.c.) or naloxone (5 mg/kg, s.c.) on day 8. Using immunohistochemical staining of Fos, present results indicate that the administration of naloxone methiodide or naloxone to morphine-dependent rats induced marked Fos immunoreactivity within the cardiomyocyte nuclei. Moreover, Western blot analysis revealed a peak expression of c-fos in the right and left ventricles after naloxone methiodide- or naloxone-precipitated withdrawal. In addition, in the hypothalamic paraventricular nucleus (PVN), Fos expression was increased after naloxone-but not after naloxone methiodide-administration to morphine-dependent rats. These results suggest that the activation of c-fos expression observed during morphine withdrawal in the heart is due to intrinsic mechanisms outside the central nervous system (CNS).

Electrophysiological effects of morphine in an in vitro model of the 'border zone' between normal and ischaemic-reperfused guinea-pig myocardium

BACKGROUND

Morphine is commonly used in clinical practice in pain management. Although morphine has been shown to precondition the myocardium, its effects on action potential parameters and ischaemia-reperfusion-induced arrhythmias and conduction blocks remain unknown.

METHODS

In a double-chamber bath, guinea-pig right ventricular muscle strips were subjected partly to normal conditions and partly to 30 min of simulated ischaemia (hypoxia, hyperkalaemia, acidosis, and lack of nutritional substrate) followed by 30 min of reperfusion. Action potential parameters were recorded continuously in the normal zone and in the ischaemic- reperfused zone. Spontaneous arrhythmias and conduction blocks were noted. The electro physiological effects of morphine were studied at 0.01 and 0.1 micro M.

RESULTS

In control conditions, morphine did not modify action potential parameters of resting membrane potential, maximal upstroke velocity (V(max)), action potential amplitude (APA) and action potential duration at 50 and 90% of repolarization. Morphine reduced ischaemia-induced depolarization and lessened the ischaemia-induced decrease in APA and V(max). Morphine significantly decreased the occurrence of conduction block during simulated ischaemia (20% at 0.01 and 0.1 micro M vs 67% in the control group, P<0.05) and reperfusion-induced arrhythmias (40% at 0.01 micro M and 30% at 0.1 micro M vs 92% in the control group, P<0.05).

CONCLUSIONS

In ischaemic-reperfused guinea-pig myocardium, morphine at clinically relevant concentrations decreased ischaemia-induced conduction blocks and reperfusion-induced ventricular arrhythmias.

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.

Pharmacological delayed preconditioning against ischaemia-induced ventricular arrhythmias: effect of an adenosine A(1)-receptor agonist

1. The goal of this study was to investigate the effects of the delayed pharmacological preconditioning produced by an adenosine A(1)-receptor agonist (A(1)-DPC) against ventricular arrhythmias induced by ischaemia and reperfusion, compared to those of ischaemia-induced delayed preconditioning (I-DPC). 2. Eighty-nine instrumented conscious rabbits underwent a 2 consecutive days protocol. On day 1, rabbits were randomly divided into four groups: 'Control' (saline, i.v.), 'I-DPC' (six 4-min coronary artery occlusion/4-min reperfusion cycles), 'A(1)-DPC(100)' (N(6)-cyclopentyladenosine, 100 microg kg(-1), i.v.), and 'A(1)-DPC(400)' (N(6)-cyclopentyladenosine, 400 microg kg(-1), i.v.). On day 2, i.e., 24 h later, the incidence and severity of ventricular arrhythmias during a 30-min coronary artery occlusion and subsequent reperfusion were analysed in all animals, using an arrhythmia score. 3. I-DPC, A(1)-DPC(100) and A(1)-DPC(400) significantly reduced the infarct size (34+/-5, 42+/-3 and 43+/-7% of the area at risk, respectively) as compared to Control (55+/-3% of the area at risk). 4. During both ischaemia and reperfusion, neither the incidence nor the severity of ventricular arrhythmias were altered by A(1)-DPC(100), A(1)-DPC(400) or I-DPC as compared to Control. 5. Thus, despite reduction of infarct size induced by delayed preconditioning, A(1)-DPC as well as I-DPC failed to exert any anti-arrhythmic effect in the conscious rabbit model of ischaemia-reperfusion.

Endogenous opiates: 1999

This paper is the twenty-second installment of the annual review of research concerning the opiate system. It summarizes papers published during 1999 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunologic responses.