Protective Effects Of Ischemic Preconditioning And Hypoxic Postconditioning On Long-term Myocardial Preservation

Objective: This study was designed to assess the protective effects of ischemic preconditioning and hypoxic postconditioning on long-term myocardial preservation in isolated rat hearts by using the Langendorff Model.Method: 27 isolated rat hearts were perfused with oxygen-bicarbonated Krebs-Henseleit buffer in the Langendorff mode for 20 minutes. These hearts were then randomly divided into three groups : Group A(n=9, sham controls, SC), the hearts were perfused continuously for another 15 min; Group B(n=9, ischemic preconditioning, IP) the hearts were delt with 5 min of global ischemia and 10 min of buffer-perfusion, both group A and group B were then arrested and preserved for 6 h with St.Thoma's solution II at 4℃, followed by 60 min of reperfusion; Group C(n=9, hypoxic postconditioning, HP), the isolated hearts were perfused and preserved in the same way as group A, but during the reperfusion period the hearts were treated with hypoxic postconditioning, they were induced with repeated ischemia and reperfusion four times and followed by 35 min of reperfusion. Observed indexes include: 1)recovery of cardiac function; 2) coronary flow; 3)myocardial QCK—MB leakage; 4)myocardial water content; 5) incidence of serious arrhythmia; 6)myocardial ultrastructure observation.Results: The results demonstrated that ischemic preconditioning significantly improved myocardial contractility and relaxation as compared with sham control group during reperfusion period(P<0.01),so was the hypoxic postconditioning group (P<0.05). But the hearts that underwent IP showed better recovery of cardial function than those underwent HP(P<0.05). IP group showed a lower left ventricular end-diastolic pressure level(P<0.05). Both IP and HP group showed less CK-MB leakage(P<0.05), but there was no statistical difference between IP group and HP group. The serious arrhythmia incidence of both groups was less than SC group. Myocardial water content in HP group was less than SC group. Myocardial electron microscope observation showed that myocardial ultrastructure of IP group and HP group was better than that of SC group.Conclusion: These data suggested that ischemic preconditioning can significantly enhance cardio-protective effects on long-term myocardial preservation. Hypoxic postconditioning can also improve the ventricular function in some degree. Ischemic preconditioning and hypoxic postconditioning might be effective methods for clinical myocardial protection in myocardial preservation for heart transplantation.