The Mechanism Of Protective Effects Induced By Intracerebroventricular Morphine Preconditioning On Postischemia Mycardial Injury In Rats

Objective Morphine is a kind of non-selective opioid receptor agonist and widely used as analgesic drug in clinical practice. Recently, it has been demonstrated that small doses of intracerebroventricular or intrathecal morphine could confer protection against injury induced by ischemia in the intact rat heart. The purpose of this study was to investigate the mechanism of protective effects induced by intracerebroventricular morphine preconditioning(MPC) on postischemia mycardial injury in rats.Methods After intracerebroventricular catheter placement, the open chest anesthetized male SD rats were subject to 30 min ischemia and 120 min reperfusion to set up ischemia and reperfusion model and ischemia-reperfusion was elicited by occlusion and open of left coronary artery(LCA). Before ischemia and reperfusion, MPC was elicited by three 5 minute infusions interspersed with 5 min drug-free periods, to determine whether MPC limited myocardial infarct size. This study consisted of two series of experiments. Series 1: The objective of this series experiments is to determine which opioid receptor(OR) subtypes is mediated the effects of MPC. The experiments were performed with nor-Binaltorphimine(nor-BNI), naltrindole(NTD) or CTOP opioid receptor antagonists intracerebroventricular administered 10 min before MPC respectively in vivo. Series 2: The objective of this series experiments is to study the signal mechanism of this cardioprotection. By observing the expression of substance P(SP) in hypothalamic paraventricular nucleus(PVN), ischemia and non-ischemia myocardial, we assessed whether analgesic effects played a key role in this effect. Additionally, trifluoperazine, a selective calmodulin(CaM) antagonist, was employed to ascertain whether calcitonin gene related peptide(CGRP) regulating by CaM mediated this effect. Indicators to be observed were composed of MAP, HR and RPP(MAP×HR); the volume of area at risk(AAR) and infarct size(IS); and the area of myocardial infarction, which was demonstrated by IS/AAR. Meanwhile, lactate dehydrogenase(LDH), creatine kinase(CK) and the CGRP in the blood plasma were respectively tested by colorimetric method and radioimmunity protocol; the epression of CaM in the hippocampus was determined by Western blotting; the expression of SP in the PVN, ischemia and non-ischemia myocardium area was determined by immunohistochemical method. All data were expressed as mean±SD and data analysis was performed with Prism 4.0,a statistical software . Data of different groups were analyzed using one-way analysis of variance(ANOVN) with Newman-Keuls test for multiple comparisons,and Sigmoid dose-response nonlinear regression was used for intrathecal morphine-treated rats. Statistical differences were considered significant if the P value was < 0.05.Results Series 1: MPC significantly reduced the IS/AAR, LDH and CK and enhanced the release of CGRP compared to CON group.δ,κandμ-OR antagonists NTD, nor-BNI and CTOP reserved the cardioprotective effect of MPC on ischemia and reperfusion injury rat heart. Series 2: MPC inhibited the increase effect of SP in PVN, ischemia and non-ischemia myocardial caused by myocardial ischemia and reperfusion injury. Trifluoperazine abolished the effects of decreasing infarct size, increasing CGRP in blood plasma and expression of calmodulin in the hippocampus induced by MPC. Hemodynamic data: two series both indicated that HR, MAP and RPP did not differ among groups at baseline, after preconditioning, 30 minutes after ischemia and 2 hours after reperfusion. But HR, MAP and RPP at the time points of 30 minutes after ischemia and 2 hours after reperfusion decreased from baseline in all groups.Conclusion Cerebralδ,κandμ-OR mediated the cardioprotection induced by MPC. CGRP regulating by CaM of center nervous system and analgesic effects probablely contribute to the cardioprotection.