The cardioprotective effect of diazoxide preconditioning in immature rabbits

Objective To investigate whether diazoxide preconditioning can exert protective effect on myocardium against ischemia-reperfusion injury in immature rabbits and the possible mechanism. Methods Twenty-one healthy 3-4 week old white rabbits of either sex were randomly divided into 3 groups : group Ⅰ control ( n = 8) ; group Ⅱ diazoxide preconditioning ( n = 8) and group Ⅲ diazoxide + 5-HD preconditioning ( n = 5) . The animals were anesthetized with intraperitoneal pentobarbital 50 mg·kg-1 and heparized (150 IU·kg-1). The hearts were excised and connected to Langendorff apparatus and passively perfused with normothermic (37℃), oxygenated (95% O2 , 5% CO2) Krebs-Henseleit buffer (KHB) at a constant perfusion pressure of 70cmH2O. A latex balloon was inserted via left atrium into left ventricle and filled with water. The left ventricular end-diastolic pressure (LVEDP) was maintained at 10 mm Hg. In group I cardiac arrest was induced with St Thomas Ⅱ solution after the heart was perfused with KHB for 30 min. In group 11 after being perfused with KHB for 15 min, the hearts were perfused with diazoxide 100μmol·L-1 for 5 min followed by 10 min wash-out with KHB , then cardiac arrest was induced as in group Ⅰ . In group Ⅲ after being perfused with KHB for 15 min, the hearts were perfused with diazoxide 100μmol·L-1 and 5-HD 100μmol·L-1 for 5 min, followed by 10 min wash-out with KHB, then the cardiac arrest was induced as in group Ⅰ and Ⅱ . All hearts were subjected to 30 min ischemia followed by 45 min reperfusion after cardiac arrest. Coronary flow (CF), HR, left ventricular developed pressure (LVDP) and dp / dt max were measured after the hearts were perfused with KHB for 15 min (baseline) and at 5, 10, 15, 30, 45 min after reperfusion was resumed. Coronary effluent was collected at 5 min after reperfusion was resumed for determination of myocardial enzymes, CK, LDH and AST. At the end of experiment myocardial specimen was obtained for determination of ATP content and ultrastructure examination. Results There was no significant difference in the baseline hemodynamic parameters among the three groups. The rates of recovery of LVDP and ± dp / dt max after reperfusion were significantly higher in group Ⅱ than those in group I and Ⅲ ( P 0.05 or 0.01). Myocardial enzyme leakage was least and myocardial ATP content was highest in group Ⅱ ( P 0.01) . Mitochondria score was significant lower in group Ⅱ as compared with that in group Ⅰ , but there was no significant difference in mitochondria score between group Ⅰ and Ⅲ( P 0.05 ) , Conclusion Diazoxide can protect myocardium from ischemia-reperfusion injury by opening the mitochondrial KATP channel in immature rabbits.