Cardioprotective effect of ischemic preconditioning on cyanotic myocardium and its relation to Heat Shock Protein

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BACKGROUND/AIMS : Ischemic preconditioning (IP) has been suggested to protect the heart against ischemic and reperfusion injury. However, the mechanism of this phenomenon remains unknown. We thus examined the myocardial protective effect of IP and its relation to cGMP in the isolated perfused working heart model.METHODS : Eighteen hearts from male Wister rats were placed in the Langendorff circuit and subjected to 10 minutes of perfusion with a modified Krebs-Henseleit solution, 15 minutes of normothermic global ischemia, and 15 minutes of reperfusion. IP was performed in the pre-ischemic Langendorff period with 2 minutes' global ischemia and 8 minutes' reperfusion in six hearts (IP 2 group), 5 minutes' ischemia and 5 minutes' reperfusion in six hearts (IP 5 group). The other six hearts (control) were perfused without IP.Functional recovery, total creatin kinase leakage, cGMP leakage and myocardial water ratio were compared among the groups using ANOVA and Bonferroni/Dunn test.RESULTS : Five minutes of IP significantly improved post-ischemic cardiac function. Percent recovery of cardiac output in IP 5 was significantly greater than in control group (88.8% ± 2.8% versus 66.7% ± 4.3%, respectively, mean ± SEM, p < 0.01). There was no significant difference in percent recovery of coronary sinus flow, heart rate, and myocardial water ratio among the groups. After IP, there was no significant difference in cGMP and creatin kinase leakage compared with control group. However, cGMP leakage in IP 5 after 15 minutes' ischemia tended to be lower than other groups (p= NS).CONCLUSION : These data suggest that 5 minutes of IP has myocardial protective effect against ischemic and reperfusion injury. Cyclic GMP may play a role in this effect.