The Effect Of Endomorphin-1(EM-1) Postconditioning On Myocardial Ischemia Reperfusion Injury And Its Mechanism

Background:The incidence of acute myocardial infarction(AMI) is increasing with years and myocardial ischemia and reperfusion injury(MIRI) also becomes a problem.Many scholars have carried out many researches on the soutions of ischemia and reperfusion injury. Pharmacological postconditioning becomed a more feasible measure compared with the time limit of ischemic preconditioning(IPC) and the invasive operation of ischemic postconditioning(IPO). Previous studies have suggested that exogenous opioids resisted MIRI and exerted myocardial protection,Endomorphin as a newly endogenous opioid have important function and a broad application prospect. Endomorphin included endomorphin-1(EM-1) and endomorphin-2(EM-2). EM-1 was widely distributed in brain and may be have a certain correlation with cardiovascular regulating function. However, the effect of Endomorphin on myocardial ischemia and reperfusion injury is still not relevant reported. Therefore, We copy myocardial ischemia and reperfusion injury model in this study, to investigate the effect of endomorphin-1(EM-1) postconditioning on myocardial ischemia and reperfusion injury in rat model and assess its possible mechanism.Objective:To investigate the effect of endomorphin-1(EM-1) postconditioning i n rat with myocardial ischemia and reperfusion injury(IR) in vivo and to asse ss its mechanism. Methods:Male Sprague Dawley rats were randomly divided into 10 groups: sham group(S group), ischemia and reperfusion group(IR grou p), ischemia postconditioning group(IPO group), EM-1 postconditioning groups(10, 20, 50μg/kg)(EM10, EM20, EM50), EM-1 50μg/kg+Naloxone 3mg/kg post conditioning(EM50+Nal group), Naloxone 3mg/kg postconditioning group(Nal g roup), EM-1 50μg/kg+15μg/kg Wort postconditioning(EM50+Wort group), Wort15μg/kg postconditioning group(Wort group). The myocardial ischemia and repe rfusion injury model was established through occluding the left anterior descen ding branch of coronary artery for 30 min and reperfusing for 120 min in viv o.Heart rate(HR),mean arterial Pressure(MAP), and a leadⅡ1electrocardiogr am were continuously monitored during the process. At the end of reperfusion,arterial blood sample was obtained to measure plasma lactate dehydrogenase(L DH), reatine kinase(CK-MB) and(cardiac troponin I)CTn I, interleukin-6(IL-6) a nd tumor necrosis factor-α(TNF-α), malondialdehyde(MDA) and superoxide dis mutase(SOD) contents or activities. The rats were sacrificed for assessment ce ll morphology of light microscopy. The infarct size was determined by TTC. T he expression levels of Bcl-2 and Bax at the m RNA level and cleaved caspase-3 at the protein level in the left anterior myocardium were assessed by RT-PC R and western-blot. Results: Compared to S group, the heart rate, mean arteria l pressure and RPP were decreased in IR group(P<0.05~P<0.01); LDH activity,CK-MB and CTn I, IL-6 and TNF-α, MDA contents were significantly increas ed and SOD activity was significantly decreased in IR group(P<0.05~P<0.01); i n cell morphology of light microscopy,the damage of myocardial structure wa s significantly increased in IR group. Compared with IR group, the heart rate,mean arterial pressure and RPP were increased in IPO and EM-1 groups(P<0.05~P<0.01). LDH activity, CK-MB and CTn I, IL-6 and TNF-α, MDA content s were significantly decreased and SOD activity was significantly increased in IPO and EM-1 groups(P<0.05~P<0.01), EM-1 produces a dose-related effect on CK-MB, CTn I, IL-6, TNF-α and MDA contents and SOD activity. In cell mo rphology of light microscopy,the damage of myocardial structure was significa ntly decreased in IPO and EM-1 groups. The infarct size was reduced in IPO and EM-1 groups(P<0.05~P<0.01). Compared with EM50 group, the heart rate,mean arterial pressure and RPP were decreased in EM50+Nal and EM50+Wor t groups(P<0.05~P<0.01). LDH activity, CK-MB and CTn I, IL-6 and TNF-α,MDA contents were significantly increased and SOD activity was significantly decreased in EM50+Nal and EM50+Wort groups(P<0.05~P<0.01). The infarct size was increased in EM50+Nal and EM50+Wort groups(P<0.05~P<0.01). Co mpared with IR group, the level of Bcl-2/Bax was increased and the expressio n level of cleaved caspase-3 protein was decreased in EM50 group(P<0.05~P<0.01). Compared with EM50 group, the level of Bcl-2/Bax was decreased and the expression level of cleaved caspase-3 protein was increased in EM50+Wor t group(P<0.05~ P<0.01). Conclusion: Endomorphin-1 postconditioning may re duce ischemia and reperfusion injury and inhibit myocardial cell apoptosis. End omorphin-1 postconditioning may produce a cardioprotection by reducing the M DA, increasing the SOD; decreasing IL-6 and TNF-α, and by activating opioi d receptor, and PI3K/Akt signaling pathway may mediate the cardioprotection.