[Agonists of opioid receptors may aggravate ischemic and reperfusion damages of the heart].

Authors analyzed articles that opioids may aggravate ischemic and reperfusion damages of the heart but the opioid receptor antagonists may prevent these damages. Authors concluded the it is existed opioid receptor pool an activation of its decreases cardiac tolerance to an impact of ischemia-reperfusion.

[Protein kinases role in adaptive phenomenon of heart ischemic postconditioning development].

Authors submitted an analysis of papers given up an involvement of protein kinases in heart ischemic postconditioning. This analysis of literature source allowed to authors affirms that signaling system of postconditioning can involve kinases: PKC, PI3K, Akt, MEKl/2, ERK1/2, MTOR, p70s6K, GSK3b, PKG and also eNOS, NO, GC, motoKATP channel, ROS, MPT pore. At the same time it is unclear a real contributions of kinases mTOR, p70s6, AMPK and GSK3b in the mechanism of infarct limiting impact of postconditioning. It is required a further study of the chain of signaling events following JAK2 and p38 kinase activation. The knowledge of Ras and Raf-1 role in postconditioning has hypothetical character. The tyrosine kinase significance in postcondi-tioning is unclear, particular Src kinase, which plays an important role in the regulation of cardiac tolerance to an impact of ischemia and reperfusion.

[Signaling mechanism of cardioprotective effects of opioids].

It has been established that G(i/o)-proteins are an intermediate link that provides intracellular signaling between opioid receptors and protein kinases. Our investigations have shown that protein kinase C is involved in realization of the anti-necrotic and anti-apoptotic effects of opioids. PI3 and Akt kinases are involved in the cardioprotective effect of opioids. MEK1/2, ERK1/2, Src and JAK2 kinases play an important role in the cardioprotective effect of opioids. Further study of the participation of JNK, p70s6K and GRK2 in the opioid-induced increase of cardiac tolerance to ischemia and reperfusion is required. NO-synthase plays an important role in the cardioprotective action of opioids. Transactivation of opioid and adenosine receptors is an important element in the development of cardiac tolerance to ischemia and reperfusion. Opioid transactivation of EGF receptor is a connecting link between opioid receptors and ERK1/2 and PI3 kinase cascades.

[Receptor and signalling mechanisms of antiarrhythmic effects of ischemic pre-conditioning].

It has been established that ischemic preconditioning (IP) exerts significant antiarrhythmic effects, as revealed in experiments both in vivo and in vitro. Consequently, processes arising within the myocardium play a key role in adaptive tolerance to ischemia/reperfusion. Preconditioning enhances cardiac electrical stability both in animals and humans. The antiarrhythmic effect of preconditioning is transient, with enhanced tolerance to ischemia-reperfusion triggered arrhythmogenesis dissipating 2-3 after the IP stimulus. The basis of the antiarrhythmic and cardioprotective effects of IP may differ. Preconditioning improves conduction of the cardiac electrical impulse, thereby preventing occurrence of re-entrant arrhythmias. NO-synthase and peroxynitrite play an important role in evolution of the antiarrhythmic effects of IP. Furthermore, intracellular Ca2+ may be a trigger of improved cardiac electrical stability after IP. It has been established that G(i/o)-protein coupled receptors are not involved in antiarrhythmic effects of IP, whereas bradykinin B2 and alpha1 adrenergic receptor activities are involved in IP-dependent improvements in cardiac electrical stability. Adenosine receptors contribute only partially to these effects. In terms of signalling mechanisms, protein kinase C appears essential to the antiarrhythmic effects of IP, whereas PI3-kinase and cyclooxygenase do not appear to be significantly involved. It has also been established that cardiac mast cells are involved in IP effects. Some data indicate that increased cardiac electrical stability with preconditioning depends upon mitoK(ATP) channel opening. Other data provide evidence that antiarrhythmic effects of preconditioning depends upon sarcK(ATP) channel opening. Some data indicate that an increase in electrical stability of heart after preconditioning depends upon mitoK(ATP) channel opening. Other data are evidence that antiarrhythmic effect of preconditioning depends upon sarCK(ATP) channel opening. Further work is needed to fully delineate the mechanistic basis of antiarrhythmic effects of IP.

[Preconditioning impact on coronary perfusion during ischemia and reperfusion of heart].

Recent studies have confirmed that ischemic preconditioning prevents appearance of reperfusion endothelial dysfunction. However, the issue of preconditioning impact on no-reflow phenomenon remains unresolved. The receptor mechanisms involved in the cardioprotective and vasoprotective effects of preconditioning are different. The ability of preconditioning in preventing reperfusion endothelial dysfunction is dependent upon bradykinin B2-receptor activation and not dependent upon adenosine receptor stimulation. The vasoprotective effect of preconditioning is mediated via mechanisms relying in part on activation of protein kinase C, NO-synthase, cyclooxygenase, mitochondrial K(ATP)-channel opening and an enhancement of antioxidative protection of the heart. The delayed preconditioning also exerts endothelium-protective effect. Peroxynitrite, NO* and O2* are the triggers of this effect but a possible end-effector involves endothelial NO-synthase.

[Role of receptor transactivation in the cardioprotective effects of preconditioning and postconditioning].

Analysis of published data indicates that the activity of receptors for adenosine, opioids, bradykinin, calcitonin-gene related peptides (CGRP) and epidermal growth factor (EGF) play important role in triggering the cardioprotective effects of ischemic preconditioning. Cannabinoids mimic the infarct-sparing effects of preconditioning. Endogenous adenosine, opioids, bradykinin and CGRP have also been implicated in infarct-reduction with ischemic postconditioning. Again, cannabinoids also mimic the protective effect of postconditioning. Recent works support heterodimerization of G-protein coupled receptors (GPCRs), and GPCR transactivation of EGF receptors. It was found that cross-talk between delta(j)-opioid receptors and adenosine A(1)-receptors is essential to cardiac protection. Furthermore, evidence implicates EGF receptor transactivation in cardioprotective effect of multiple GPCrs including adenosine, acetylcholine, bradykinin, and opioid receptors. Such findings support a convergent pathway in which multiple GPCRs may interact (or function independently) to transactivate EGF receptor-dependent kinase signaling and cytoprotection.

[Trigger mechanism of adaptive phenomenon of ischemic heart postconditioning].

Analysis of published data indicates on trigger role of protons, adenosine, opioids, bradykinin, calcitonin gene-related peptide, nitric oxide, epoxyeicosatrienoic acid, reactive oxygen species, hydrogen sulfide in ischemic heart postconditioning. It is shown that B-type natriuretic peptide, transforming growth factor-beta1, cardiotrophin-1, urocortin, acetylcholine, insulin and carbon monoxide can mimic postconditioning phenomenon.

Opioid peptide deltorphin II simulates the cardioprotective effect of ischemic preconditioning: role of δ2-opioid receptors, protein kinase C, and K(ATP) channels.

The cardioprotective properties of a δ2-opioid receptor agonist deltorphin II were studied in rats with coronary occlusion and reperfusion. Opioid receptor ligands and inhibitors (glybenclamide, chelerythrine, and 5-hydroxydecanoate) were injected intravenously before ischemia and reperfusion. A δ2-opioid receptor agonist deltorphin II significantly decreased the infarction zone/risk zone index. This effect was abolished by naltrexone, naloxone methiodide, and δ2-opioid receptor antagonist naltriben, but not by a δ1-opioid receptor antagonist BNTX. The infarct-limiting effect of deltorphin II was not observed after inhibition of protein kinase C or blockade of mitochondrial K(ATP) channels.

[Significance of opioid receptors in regulation of cardiac tolerance in pathogenic impact of long-term ischemia-reperfusion in vivo].

The study aimed at investigation of the role of opioid receptor (OR) in regulation of cardiac tolerance to ischemia-reperfusion. Opioid receptor ligands and inhibitors were administered in vivo prior to coronary artery occlusion (45 min) and reperfusion (2 hrs). Occurring infraction size/area at risk (IS/AAR) ratio was determined. Pretreatment with the micro-OR agonists DAMGO and dermorphin H exerted no effect on the IS/AAR ratio. Activation of delta 1-OR by DPDPE did not alter cardiac tolerance in ischemia-reperfusion either. Pretreatment with the delta 2-OR agonists deltorphin D and deltorphin E or ORL1 receptor agonist nociceptin exerted no effect on the IS/AAR ratio. Stimulation of K-OR by selective agonists did not modify cardiac tolerance to ischemia-reperfusion. The delta 2-OR agonist deltorphin II significantly reduced the IS/AAR index. This effect was prevented by treatment with naltrexone, naloxone methiodide and the delta 2-OR antagonist naltriben but not by the delta 1-OR antagonist BNTX. The infarction-limiting effect of deltorphin II was also abolished by inhibition of protein kinase C (PKC) and mitochondrial Katp channels. Thus, the agonists of micro, delta 1, kappa, and ORL1 receptors in used doses did not affect cardiac tolerance in ischemia-reperfusion injury in vivo. The peripheral delta 2-OR activation induces infarction size reduction. Its infarction-reducing effect of deltorphin II is mediated via PKC activation and mitochondrial Katp, channel opening.

[Signaling mechanism of NO-induced increase in cardiac tolerance to ischemia-reperfusion].

In the review it is analyzes published data on the signaling mechanism of cardioprotective impact of nitric oxide. It was shown that nitric oxide exhibited a rapid and a delayed cardioprotective effects. In the rapid effect, endothelial NO-synthase (NOS) is involved was involved as well as guanylate cyclase, cGMP, kinase G, kinase C, PI3-kinase, Akt-kinase, mitochondrial ATP-sensitive K+-channel, reactive oxygen species, MPT-pore. Delayed cardioprotective effect of NOS required synthesis of proteins de novo. In this process, transcription factors NF-KB, STAT1/3, HIF-1 are involved. Some published data state that peroxynitrite, cGMP, kinase G, kinase C, Src kinase, p38 kinase, ERK-kinase can be involved in delayed cardioprotective effect of NOS. The cardioprotective impact of nitric oxide was shown to depend on enhancement in expression of NOS, cyclooxygenase-2 and Blc-2 protein which inhibits MPT-pore.

[Cardiovascular effects of D-ALA2, LEU5, ARG6-enkephalin (dalargin) are mediated by peripheral mu-opioid receptor activation].

It has been established that intravenous administration of dalargin at a dose of 0.1 mg/kg induced hypotensive, positive inotropic, and positive chronotropic response in patients with myocardial infarction, while not producing the "steal syndrome." The positive chronotropic effect of dalargin was mediated by peripheral mu-opioid receptors. Increase in the heart rate induced by dalargin had a reflex nature. Direct action of dalargin on the heart was accompanied by a decrease in the heart rate and a delay in the cardiac conductance in the atrioventricular junction region.

[Significance of cardiac cannabinoid receptors in regulation of cardiac rhythm, myocardial contractility, and electrophysiologic processes in heart].

Intravenous administration of cannabinoid (CB) receptor agonists (HU-210, 0.1 mg/kg; ACPA, 0.125 mg/kg; methanandamide, 2.5 mg/kg; and anandamide, 2.5 mg/kg) induced bradycardia in chloralose-anesthetized rats irrespective of the solubilization method. Methanandamide, HU-210, and ACPA had no effect on the electrophysiological activity in the heart, while anandamide increased the duration of the QRS complex. The negative chronotropic effect of HU-210 was due to CB1 receptor activation since is was not observed after CB1 receptor blockade by SR141716A (1 mg/kg intravenously) but was present after pretreatment with CB2 receptor antagonist SR144528 (1 mg/kg intravenously). CB receptor antagonists SR141716A and SR144528 had no effect on cardiac rhythm or ECG indices. Hence, in the intact heart, endogenous CB receptor agonists are not involved in the regulation of cardiac rhythm and electrophysiological processes. The chronotropic effect of CBs was independent of the autonomic nervous system because it remained significant after autonomic ganglion blockade by hexamethonium (1 mg/kg intravenously). CB receptor activation by HU-210 (0.1 and 1 microM) in vitro decreased the rate and force of isolated heart contractions, the rates of contraction and relaxation, and end diastolic pressure. The negative chronotropic effect of HU-210 was less pronounced in vitro than in vivo. The maximum inotropic effect of HU-210 was reached at the concentration of 0.1 microM.

[Activity of lipid peroxidation and functional state of the myocardium in remodeling of rat heart after experimental myocardial infarction].

It was shown in experiments on Wistar rats that the processes of postinfarction remodeling of the heart in animals that survived myocardial infarction were characterized by lowering of excitability of cardiac muscle, impairment of ability of sarcoplasmic reticulum to accumulate calcium ions. High level of content of lipid peroxidation products both in blood serum and myocardial tissue, and lowering of activity of antioxidant enzymes were also noted. A conclusion was made that high level of lipid peroxidation, lowering of defense properties of endogenous antioxidants and impairment of myocardial contractile function induced by myocardial infarction were sustained minimally for subsequent 45 days. This could serve as a factor, capable to significantly affect the process of postinfarction remodeling and development of heart failure.

Negative inotropic and chronotropic effects of delta-opioid receptor antagonists are mediated via non-opioid receptors.

Ten-minute perfusion of intact isolated rat heart with Krebs-Henseleit solution containing delta-opioid receptor agonists (DPDPE, (-)-TAN-67) or delta-opioid receptor antagonists (naltrindole, TIPP[psi], ICI 174,864) at a final concentration of 0.1 mg/liter decreased HR, blood pressure in the left ventricle, and the rates of myocardial contraction and relaxation. Intravenous injection of delta-agonists (DPDPE, (-)-TAN-67, deltorphin II) or delta-antagonists (naltrindole, TIPP[psi], ICI 174,864) decreased HR in narcotized rats. Naloxone and naltrexone produced no effect on contractility and HR both in vivo and in vitro. Preliminary injection of naloxone and naltrexone did not prevent the negative chronotropic effect of ICI 174,864 in vitro. The negative inotropic and chronotropic effects of delta-opioid receptor antagonists are mediated by unknown non-opioid receptors in the heart.

[Paticipation of cannabinoid receptors in the regulation of cardiac rhythm and cardiac contractility].

It has been found that i. v. administration of cannabinoid receptor (CB) agonists (HU-210, ACPA, anandamide, methanandamide) induced a decrease in the heart rate (HR) in anesthetized rats. Pretreatment with CB1 receptor antagonist SR141716A completely abolished a negative chronotropic effect of CB receptor agonist HU-210. The CB2 receptor antagonist SRI 44528 did not prevent a HU-210-induced decrease in the HR. Pretreatment with the ganglion blocker hexamethonium had no effect on the negative chronotropic action of HU-210. Addition of HU-210 (100 nM) to perfusion solution induced a decrease in the HR, left ventricular development pressure, rate of contractility and relaxation of isolated perfused rate heart without change in end diastolic pressure. These data suggest that cardiac CBI receptor activation induces a decrease in the HR both in vivo and in vitro. An occupancy of the same receptors mediates a negative inotropic effects of cannabinoids.

Negative chronotropic effect of cannabinoids and their water-soluble emulsion is related to activation of cardiac CB1 receptors.

Intravenous injection of cannabinoids dissolved in cremophore EL:ethanol:NaCl mixture and water-soluble emulsion of the same cannabinoids caused identical negative chronotropic effects in chloralose-narcotized rats. Selective CB1 and CB2 receptor antagonist HU-210 also induced a negative chronotropic effect in rats, while pre-injection of CB1 receptor antagonist SR 141716A completely abolished this effect of HU-210. Selective CB2 receptor antagonist SR 144528 had no effect on HU-210-induced bradycardia. Preinjection of ganglioblocker hexamethonium also did not abolish the negative chronotropic effect of HU-210 and ACPA. Perfusion of isolated rat heart with Krebs-Henseleit solution containing HU-210 in a final concentration of 100 nM reduced heart rate. It was shown that the negative chronotropic effect of cannabinoids is mediated through activation of cardiac CB1 receptors.

[Contribution of the endogenous opioid system to regulation of heart resistance to the arrhythmogenic effect of short-term ischemia and reperfusio].

Preliminary selective blockade of micro, delta1, delta2, kappa1, and kappa2 opioid receptors proved to have no effect on the incidence of ventricular arrhythmias during a 10-min coronary occlusion and subsequent reperfusion in ketamine-anesthetized rats. We propose that the endogenous opioid system has no considerable role in regulation of heart resistance to the arrhythmogenic effect of short-term local ischemia and subsequent reperfusion.

Role of endogenous opioid receptor agonists in regulation of heart resistance to the arrhythmogenic action of short-term ischemia and reperfusion.

Preliminary selective block of mu-, delta1-, delta2-, and kappa-opioid receptors had no effect on the incidence of ventricular arrhythmias during 10-min coronary occlusion-reperfusion in ketamine-narcotized rats. Repetitive short-term immobilization of rats for 2 weeks improved heart resistance to the arrhythmogenic action of coronary occlusion and reperfusion. Selective mu-opioid receptor antagonist CTAP completely abolished, while selective delta- and kappa-opioid receptor antagonists did not modulate the antiarrhythmic effect of adaptation. Probably, endogenous agonists of mu-opioid receptors play an important role in the adaptive improvement of heart resistance to arrhythmogenic factors, but are insignificant for the modulation of heart resistance to the arrhythmogenic action of short-term local ischemia-reperfusion in non-adapted animals.

Chronotropic effect of D-Ala2,Leu5,Arg6-enkephalin (dalargin) is associated with activation of peripheral kappa-opioid receptors.

Intravenous infusion of D-Ala2,Leu5,Arg6-enkephalin (dalargin) caused bradycardia in narcotized rats. This effect was not observed during opioid receptor blockade with naloxone, naloxone methiodide, and norbinaltorphimine. Dalargin and (-)-U-50,488 added to Krebs-Henseleit perfusion solution for isolated rat heart decreased heart rate. Ganglionic blocker hexamethonium potentiated the negative chronotropic effect of dalargin. The negative chronotropic effect of dalargin is probably associated with activation of cardiac kappa-opioid receptors. It should be noted that dalargin caused tachycardia in some animals. This reaction was not observed after treatment with hexamethonium. The positive chronotropic effect of dalargin is probably related to modulation of the parasympathetic autonomic nervous system. Agonists and antagonists of delta-opioid receptors caused persistent bradycardia. We hypothesized that selective delta-opioid antagonists exhibit properties of partial delta-receptor agonists.