| Object:To study the early protective effect of rhBNP and postischemia adapation on rabbit's acute myocardial ischemia/reperfusion (I/R) injury and the mechanism.Methods: All rabbits enrolled in this study were randomly divided into 4 groups (n=8 in each group): (1)Control group;(2)rhBNP group;(3) postischemia adapation group;(4)rhBNP+postischemia adaption group.Myocardial ischemic postconditioning (IP):reperfusion was initiated for 180 min followed by 40min of left ventricle branch occlusion.(1)Control group was started to give intravenous injection of normal saline when left ventricle branch was ligated until 180 min reperfusion;(2) rhBNP group was started to give intravenous injection of rhBNP when left ventricle branch was ligated, until 180 min reperfusion;(3)postischemia adapation group was started to give intravenous injection of normal saline as the control group in dose when left ventricle branch was ligated, until 180 min reperfusion; moreover, three cycles of repefusion(30s) and myocardial ischemia (30s) were performed when reperfusion was initiated in one min, followed by the recovery of coronary blood flow. (3)rhBNP + postischemia adaption group was started to give intravenous injection of rhBNP (the same as rhBNP group in dose) when left ventricle branch was ligated, until 180 min reperfusion; and three cycles of repefusion(30s) and myocardial ischemia(30s) were performed when reperfusion was initiated in one min, followed by the recovery of coronary blood flow. ECG,degression of ST segment and arrhythmia scores were observed during the first 2 hr's reperfusion and plasma MB isoenzyme of creatine kinase (CK-MB) activity,cardiac troponin-I (Tn-I) activity,malondialdehyd(eMDA)activity and superoxide dismutase(SOD) activity were measured ahead of ischemia,before reperfusion and the end of reperfusion respectively. At the end of the experiment, the rabbits of all groups were randomly divided into half(4 rabbits) respectively. The 4 rabbits of each group were made death to determine myocardial infarct size by dual staining with Evan'S blue and tetrazolium chloride dye. The other rabbits of each group were tested cardiac structure and function change(Wall wth of PLV, LVEF, LVFS) by transthoracic echocardiography (TTE) after four weeks.Results: 1.Compare with the control group , at the end of 120 min reperfusion the average values of S-T segment elevation in leadâ…¡,â…¢,AVF displayed on the ECG were smaller, and the rate of arrhythmia occurrence were decreased, and the level of CK-MB,TnI activity at the end of 180min reperfusion and myocardial infarct size were significantly reduced in the rhBNP group,postischemia adaption group and rhBNP+postischemia adaption group than that in the control group(P<0.05). Compared to the control group ,the concentration of MDA at the end of 180min reperfusion were significantly lower(P <0.05),and the activity of SOD were higher in postischemia adaption group and rhBNP+postischemia adaption group(P<0.05), and there was no significant difference between the control group and rhBNP group (P>0.05).Four weeks later TTE shows that the thickness of posterior left ventricular (PLV) wall,LVFS and LVEF in the other groups were all significantly reduced than that in the control group (P<0.05).2.In postischemia adaption group, the concentration of MDA at the end of 180min reperfusion was lower and the activity of SOD was higher than that in rhBNP group. There were no differences between the two groups on other indexes.3.At the end of 120 min reperfusion the average values of ST segment elevation in the rhBNP+postischemia adaption group were lower than that in the rhBNP group and postischemia adaption group. The level of CK-MB,TnI and myocardial infarct size at the end of 180min reperfusion and all indexes tested by transthoracic echocardiography (TTE) after four weeks of myocardial infarction were significantly reduced in the rhBNP +postischemia adaption group than that the rhBNP group and the postischemia adaption group(P<0.05). It shared no differences between the rhBNP+postischemia adaption group and the postischemia adaption group on the concentration of MDA and the activity of SOD at the end of 180min reperfusion(P>0.05);Contrarily, there were significantly difference between the rhBNP+postischemia adaption group and the rhBNP group(P<0.05).Conclusions:1.Ischemic postconditioning has protective effect on acute myocardial ischemia /reperfusion injury and could reduce myocardial infarct size,improve heart reconstition in the near future of myocardial infarction and protect heart function by inhibiting oxyradical activation and reducing lipid peroxidation injury and increasing the induce of SOD and at the beginning of reperfusion.Applica-tion of rhBNP in nonage of reperfusion could reduce myocardial infarct size and protect heart function,it's possibile to be a drug choice to protecte acute myocardial ischemia /reperfusion injury.2.Associated application of rhBNP and ischemic postconditioning may further relieve acute myocardial ischemia/reperfusion injury and protect heart function.
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