Effect of astragalus membranaceus pretreatment agaist myocardial ischemia/reperfusion injury in immature rabbit hearts

Objective To investigate if mitochondrial KATP channels are involved in the cardioprotective effects of astragalus membranaceus in immature rabbit hearts. Methods Twenty-four New Zealand white rabbits of both sexes aged 14-21 days weighing 300-350 g were anesthetized and heparinized. The hearts were rapidly removed after thoracotomy and mounted on a Langendorff apparatus via ascending aorta and perfused with oxygenated (95% O2-5% CO2) Krebs-Hensleit buffer (KHB) solution at 60 cm H2O (perfusion pressure) and 38 ℃ . A fluid-filled latex balloon was inserted into left ventricle via left atrium for measurement of left ventricular developed pressure ( LVDP) , Global myocardial ischemia was induced by suspension of perfusion for 30 min followed by 45 min reperfusion. The animals were randomly divided into 3 groups with 8 animals in each group : group A control;group B astragalus and group C astragalus +- 5-HD (a selective inhibitor of the mitochondrial KATP channel). In group B the hearts were perfused with astragalus 40 g· L-1 for 15 min before ischemia. In group C the hearts were perfused with 5-HD 100μmol·L-1 for 5 min followed by 10 min astragalus perfusion before ischemia. In control group the hearts were perfused with only KHB before ischemia. Coronary flow (CF), HR, LVDP and ± dp/dtmax, were measured at 5, 10, 15, 30 and 45 min of reperfusion and recorded. Coronary effluent was collected at 10 min of reperfusion for determination of CK-MB, LDH and CK levels . At the end of 45 min reperfusion the isolated heart was removed for determination of myocardial ATP and iNOS levels and electron microscopic examination.Results In astragalus group (B) LVDP ± dp/dtmax and CF recovered significantly better and myocardial ATP content was significantly higher as compared with group A and C (P 0.05 or 0.01). The myocardial levels of CK-MD, LDH and CK were significantly lower and the myocardial iNOS level was significantly higher in astragalus group than in the other two groups ( P 0.05 or 0.01). Conclusion Astragalus can protect myocardium from ischemia-reperfusion injury by opening the mitochondrial KATP channel in isolated immature rabbit heart.