Effects Of Ischemic Postconditioning On Myocardial Protection In Isolated Rat Hearts

The effect of ischemic preconditioning on myocardial protection has been demonstrated in many experimental studies. Recently some studies have indicated that ischemic postconditioning also has shown the protection in ischemia/reperfusion hearts. The present study is aimed to observe the protective effect of ischemic postconditioning and morphine postconditioning on ischemia/reperfusion myocardium in isolated rat hearts and its mechanism.Test 1 Effects of ischemic preconditioning and postconditioning on myocardial protection in isolated rat heartsObjective: To observe the protective effect of ischemic preconditioning and postconditioning on ischemia/reperfusion myocardium in isolated rat hearts and its mechanism. Methods: 40 SD rats were divided into 4 groups randomly with 10 in each group: (1) ischemia/reperfusion (I/R) group; (2) ischemic preconditioning (IPC) group; (3) ischemic postconditioning (Post-con) group; (4) preconditioning plus postconditioning (IPC+Post-con) group. All hearts underwent 30min global ischemia and following 60min reperfusion in Langendorff mode. Hemodynamic data (±dP/dtmax) was monitored before and after ischemia. Myocardial infarct size, concentrations of lactate dehydrogenase(LDH) and creatine phosphokinase (CK) in the liquid of coronary, myocardial superoxide dismutase (SOD) activity and malonaldehyde (MDA) concentration were measured. Myocardial ultrastruture was observed. Myocardial apoptosis, expression of antiapoptotic protein Bcl-2 and proapoptotic protein Bax were detected. Results: Compared with I/R group, IPC, Post-con and IPC+Post-con all remarkablely improved hemodynamic data; reduced infarct size; decreased concentrations of LDH and CK in the liquid of coronary; increased activity of SOD and reduced concentration of MDA in myocardium; reduced the injury of myocardial ultrastruture and apoptosis of myocardium; increased the protein expression of Bcl-2 gene, reduced the protein expression of Bax gene. Those data showed no significant differences among the three experimental groups. Conclusion: Our findings suggest IPC and Post-con both can improve cardiac function, reduce infarct size and inhibit apoptosis. But IPC+Post-con cannot provide better protection for myocardium than IPC or Post-con. IPC and Post-con maybe provide the protective effect of myocardium via the same mechanism in part.Test 2 Opioid Receptors Mediated the Effects of Ischemic Postconditioning on myocardial protection in the Isolated Rat HeartsObjective To investigate the possible role of opioid receptors in ischemic postconditioning in the isolated rat hearts. Methods 60 SD rats were divided into 6 groups randomly with 10 in each group.(1) Ischemia/reperfusion (I/R) group; (2) Naloxone (NAL) group; (3) Postconditioning (Post-con) group; (4) Naloxone plus postconditioning (NAL+ Post-con) group; (5) morphine (MOR) group; (6)morphine plus naloxone (MOR+NAL) group. All hearts underwent 30min global ischemia and following 60min reperfusion in Langendorff mode. Hemodynamic data (±dP/dtmax), myocardial infarct size, concentrations of lactate dehydrogenase(LDH) and creatine phosphokinase (CK) in the liquid of coronary, and myocardial ultrastruture were assessed before and after ischemia. Results Postconditioning and morphine remarkablely improve heart function and reduce infarct size, which could be weakened or abolished by Naloxone. Conclusion These findings suggest that the effect of postconditioning on ischemic myocardial protection may be mediated in part by activation of opioid receptors and morphine may offer cardiac protection when it is used at the beginning of reperfusion.