C-reactive protein in acute and delayed preconditioning of the rat heart.

UNLABELLED: The involvement of C-reactive protein (CRP) in early (acute) and delayed ischaemic (IPC) and pharmacological (chemical) (CPC) preconditioning in an in vivo model of rat myocardial infarction is presented. Acute IPC was produced by three 5-min occlusion (ischaemia) periods interspersed with 5 min reperfusion, followed by 30-min occlusion of the left coronary artery and 2 h reperfusion injury. Acute CPC was produced by a Kappa-opioid receptor agonist U50488H (5 mg/kg) applied i.v. 15 min before 30-min ischaemia/2-h reperfusion. Delayed preconditioning was produced by 30-min ischaemia/2-h reperfusion, induced 24 h after either ischaemic or pharmacological preconditioning. The myocardial ischaemia/reperfusion injury was evaluated on the basis of total and cardiac creatine kinase isoenzyme activity, functional recovery of the heart (ECG), infarct size (% IS/RA) and mortality at the end of the experiments. The results obtained showed that: . The Kappa-opioid receptor agonist U50488H mimics both the acute and delayed IPC in the above experimental protocol. .Both acute IPC and CPC produce effects by opening of the KATP channels (the effects were blocked by nonspecific ATP-sensitive K channel blocker glybenclamide), and via activation of protein kinase C (a selective protein kinase C inhibitor chelerythrine blocked the effects). .C-reactive protein was significantly elevated by 54% in non-preconditioned acute ischaemia/reperfusion injury. The elevation was more pronounced (82% increase) 24 h after non-preconditioned ischaemia/ reperfusion injury. It reflected very well the increase in cardiac isoenzymes, infarct size and mortality of the rats, and can be used as a marker of the severity of myocardial injury in this model. . The increase of CRP was prevented by both IPC and CPC in early, and especially in late preconditioning. This shows the involvement of CRP, not only as a marker, but as a causative factor in cardiac ischaemic/reperfusion injury. CONCLUSION: In addition to the established involvement of adenosine, bradykinin, opioid and other receptors, a suppression of myocardial CRP/complement production might be involved in the biological mechanism of preconditioning. This could be a promising perspective in clinical interventions against ischaemia/reperfusion injuries of the heart.

The role of C-reactive protein in ischemia/reperfusion injury and preconditioning in a rat model of myocardial infarction.

For the first time the involvement of C-Reactive protein (CRP) in early (acute) and delayed ischemic (IPC) and pharmacological (chemical) preconditioning (CPC) in an in vivo model of rat myocardial infarction was presented. Acute IPC was produced by three 5 minute occlusion (ischemia) periods interspersed with 5 minute reperfusion, followed by 30 minute occlusion of the left coronary artery and 2 hour reperfusion injury. Acute CPC was produced by a k-opioid receptor agonist U50488H (5 mg/kg) applied i.v. 15 minutes before 30 minute ischemia/ 2 hour reperfusion. Delayed preconditioning was produced by 30 minute ischemia/ 2 hour reperfusion, induced 24 hour after either ischemic or pharmacological preconditioning. The myocardial ischemia/reperfusion injury was evaluated on the basis of total and cardiac creatine kinase isoenzyme activity, functional recovery of the heart (ECG), infarct size (% IS/RA) and mortality at the end of the experiments. The results obtained showed that: k-opioid receptor agonist U50488H mimics both the acute and delayed IPC in the above experimental protocol; Both acute IPC and most probably CPC act by opening of K(ATP) channels (the effects were blocked by nonspecific ATP-sensitive K channel blocker glybenclamide), and via activation of protein kinase C (a selective protein kinase C inhibitor chelerythrine blocked the efects); C-reactive protein (CRP) was significantly elevated by 54% in non-preconditioned acute ischemia/reperfusion injury. The elevation was more pronounced (82% increase) 24 hour after non-preconditioned ischemia/reperfusion injury. It reflected very well the increase in cardiac isoenzymes, infarct size and mortality of the rats, and can be used as a marker of the severity of myocardial injury in this model; The increase of CRP was prevented by both IPC and CPC in early, and especially in late preconditioning. This confirms the involvement of CRP as a marker in cardiac ischemic/reperfusion injury. It was concluded that in addition to the established involvement of adenosine, bradykinin, opioid and other receptors, a suppression of myocardial CRP/complement production might be involved in the biological mechanism of preconditioning. This could be a promising perspective in clinical interventions against ischemia/reperfusion injuries of the heart.

Evaluation of the antidysrhythmic effects of delta- and kappa-opioid receptor agonists and antagonists on calcium chloride-, adrenaline- and ischemia/reperfusion-induced arrhythmias in rats.

This study was undertaken to evaluate the involvement of delta- and kappa-opioid receptors in both ischemia- and reperfusion-induced arrhythmias, and to elucidate some of the plausible mechanisms conferring antidysrhythmic effects on opioid delta- and kappa-receptor agonists and antagonists. Different models of arrhythmia (calcium chloride [CaCl(2)]-, adrenaline-, and ischemia/reperfusion-induced arrhythmias) were employed. The following opioid agonists, antagonists and blockers were used in the study: [D-Ala(2), D-Leu(5)]enkephalin (DADLE), a selective delta-receptor agonist; trans-3,4-Dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide (U-50488H), a selective kappa-receptor agonist; Naltriben Methanesul-fonate (NTB), a selective delta(2)-antagonist with kappa-receptor agonist-like activity; natrindole, a non-selective delta(1)- and delta(2)-receptor antagonist; nor-binaltorphimine dehydrochloride (nor-BNI), a selective kappa-receptor antagonist; chelerythrine, a selective protein kinase C inhibitor, and glibenclamide, a selective blocker of ATP-sensitive K channel. Although results of the morphometric, enzymatic, hemodynamic, electrocardiographic and pharmacodynamic studies undertaken suggest that both opioid delta(1)- and kappa-receptors are involved in the phenomenon of ischemic heart preconditioning (IPC), the antidysrhythmic effects of the opioids seem to be mediated mainly via kappa-receptors. The antidysrhythmic effect of U50488H was found to be a consequence of its beta-blocking activity (which is comparable to that of propranolol, a Class II antiarrhythmic drug) and its ability to prolong myocardial action potential (QT-interval prolongation, which is comparable to that of amiodarone, a Class III antiarrhythmic drug). The antidysrrhythmic effects of the opioid compounds examined were almost completely abolished by glibenclamide or chelerythrine pretreatment. No calcium-channel blocking activity was observed in this investigation. The present observations suggested that opioid receptors displaying well known analgesic properties may have the potential to protect the myocardium during cardiac ischemia at the early stages of myocardial infarction (when early arrhythmias are the most common causes of death).

Mechanisms of opioid delta (delta) and kappa ( kappa) receptors' cardioprotection in ischaemic preconditioning in a rat model of myocardial infarction.

It has been demonstrated that brief periods of coronary artery occlusion before a prolonged period of sustained occlusion paradoxically protect the myocardium against infarction. The mechanisms involved in this phenomenon, termed "ischaemic preconditioning" (IPC) are still not clear, although it has been established that opioid receptors are involved. The aim of this study was to probe some of the plausible mechanisms involved in the phenomenon by using an in vivo model of myocardial infarction in intact rat, a model that allows electro-cardiographic and enzymatic in addition to morphometric evaluation of the development of 24-hour myocardial infarction. Selective opioid delta-receptor agonist (DADLE) and antagonist (natrindole), and opioid kappa-receptor agonist (U-50488H) and antagonist (nor-BNI) were used. To clarify some of the mechanisms of IPC, we used selective inhibitors of the anticipated cellular systems involved. Pertussis toxin (inhibitor of adenylate cyclase G(I/o) protein), glibenclamide (inhibitor of K(ATP ) channel) and chelerythrine (inhibitor of PKC) were used. Results obtained showed that: Both opioid delta- and kappa-receptors were involved in the beneficial effect of IPC, although we were unable to differentiate between opioid receptor subtypes (delta1, delta2 and kappa1, kappa2). Opioid delta- and kappa-receptors displayed different effects in IPC. After 30 minutes of left coronary occlusion and 2-hour reperfusion, opioid delta-receptor agonist DADLE significantly decreased (p < 0.05) the infarct size (by 66%--from % IS/AAR 59.80 in the control, untreated infracted rats to % 20.40), without a significant effect (p > 0.05) on the occurrence of early arrhythmias. Opioid kappa-receptor agonist U-50488H produced mainly antiarrhythmic effects. It decreased % IS/AAR by 44%, reduced the occurrence of early arrhythmias by 77%, and decreased ventricular ectopic beats by 80%. Both opioid delta- and kappa-receptor agonists significantly reduced (p < 0.05 ) early (2-hour) mortality by 22% and 19% respectively. The above opioid delta- and kappa-receptor cardiac effects were abolished by the use of respective specific opioid delta- and kappa-receptor antagonists. The beneficial effects of opioid delta- and kappa-receptor agonists persisted for at least 24 hours post-infarction. It is most likely that both opioid delta- and kappa-receptors act via common cellular mechanisms involving: activation of ATP-sensitive (sarcolemmal) K+ channel via G(I/o) proteins (based on the results of our experiments with K(ATP) channel antagonist, glibenclamide); phosphatidylinositol pathway via activation of protein kinase C (judging from the results of our experiments with the inhibitor of PKC, chelerythrine); and the recently proposed "cross talk" between beta (1)-adrenergic and opioid receptors in cardiac myocytes (involving inhibition of adenylate cyclase by G(I/o) proteins). Exploring the possibility of this signaling pathway will be the next step in our experimental studies.

Involvement of opioid delta (delta)- and kappa (kappa)-receptors in ischemic preconditioning in a rat model of myocardial infarction.

There is controversy in the literature regarding the involvement of opioid delta (DOP, OP1)- and kappa (KOP,OP2)-receptors in ischemic preconditioning (IPC). Previous studies on this subject in our laboratories and elsewhere have been performed on either isolated heart muscles of experimental animals, or in open-heart surgery rats. To highlight this problem, we introduced an in vivo model of myocardial infarction in rats, which not only allowed electrocardiographic and enzymatic evaluation, but also morphometric assessment of myocardial infarction. In addition to these parameters, a direct receptor ligand study was undertaken, using [3H]-DPDPE, a specific opioid delta-receptor ligand. In our pharmacodynamic studies, we used the selective opioid delta-receptor agonist D-Ala2,D-Leu5 enkephalin (DADLE) and antagonist natrindole. For the evaluation of opioid kappa-receptors, the selective opioid agonist U-50488H and antagonist nor-BNI were employed. Ischemic preconditioning showed the best beneficial effect, compared with pharmacological stimulation of either opioid delta- or kappa-receptors. In normal rat myocytes, two types of opioid delta-receptors exist, namely, low-affinity and high-affinity opioid receptors. In acute myocardial infarction (30-min ischemia), the low-affinity type opioid receptors disappeared, most likely as a result of receptor downregulation due to an excessive release of enkephalins. There was no change in the density of the high-affinity opioid receptor type, but their affinity significantly increased (p < 0.05) by 58%. The radioligand receptor studies showed that opioid delta 1-receptor type was involved not only in triggering, but also in maintaining, the preconditioned state. On the basis of our pharmacodynamic studies, we suggest that both opioid delta 1- and kappa-receptors are involved in the phenomenon of IPC, but with different effects. After 30 min of left coronary artery occlusion, opioid delta-receptor agonist DADLE decreased the infarct size/area at risk from 59.80% in control, untreated, infarcted rats, to 20.40% in treated rats, without a significant effect (p > 0.05) on the occurrence of early cardiac arrhythmias. Opioid kappa-receptor agonist U-50488H produced an opposite effect on the myocardium. It decreased the infarct size/area at risk by 44%, decreased occurrence of early arrhythmias by 77% and also decreased ventricular ectopic beats by 80%. The opioid delta- and kappa-receptor agonists used in this study significantly reduced (p < 0.05) early (2 h) postinfarction mortality by 22% and 19%, respectively. Further studies are in progress to differentiate between the role of opioid kappa 1- and kappa 2-receptors and the molecular mechanisms of the effects of both opioid delta- and kappa-receptors.