Effects And Mechanisms Of B-type Natriuretic Peptide Post-conditioning On Myocardial Reperfusion Injury In Rabbit

Objective:1. In the present study, by using rabbit models of acute myocardial infarction, we tested the hypothesis that BNP postconditioning exert cardioprotection against ischemia reperfusion injury.2. Ischemia reperfusion injury, results in myocardial apoptosis and necrosis. This study investigates cardioprotection provided by BNP postconditioning is associated with inhibition of apoptosis following myocardial ischemia reperfusion injury.Method:A left lateral thoracotomy was performed. Rabbits were randomly divided into three groups (9 animals for each group):sham-operated group, ischemia-reperfusion group and BNP postconditionning group. Occlusion of the left circumflex coronary for 45 min was followed by 3-h reperfusion with infusion of physiological saline or BNP starting 5 min before reperfusion and throughout the whole reperfusion. Hemodynamic, ECG monitor were obtained. Evans blue/TTC staining identified the area-at-risk (AAR) and infarction. Serum CK and LDH were assayed. Tissue concentration of MDA and SOD activity were assayed. Myocardial apoptosis was detected by histological TUNEL staining. Expression of Bcl-2, Bax and pGSK-3β/GSK-3βproteins was analyzed using Western blot assay. Cardiac tissue caspase-3 activity was measured by spectrophotometric analysis.Result:The serum levels of creatine kinase and lactate dehydrogenase were markedly increased in ischemia reperfusion group (P<0.05) compared with the sham-operated group. BNP significantly attenuated the elevation of creatine kinase and lactate dehydrogenase. The infarct size was significantly smaller in BNP group than in ischemia reperfusion group (9.0±2.2%vs.16.2±3.1%, P<0.01). Decreased SOD activity in ischemia reperfusion group was significantly increased in BNP group. MDA concentration was increased in ishchemia reperfusion group and was decreased in BNP group. We observed obvious apoptotic myocytes during reperfusion detected by histological TUNEL staining in both ischemia reperfusion group and BNP group. Administed BNP at reperfusion significantly inhibited myocardial index of apoptosis (4.7±1.9 vs.12.9±2.5). Reperfusion increased the expression of Bax and decreased the expression of Bcl-2. Administed BNP at reperfusion significantly increased the expression of downregulated Bcl-2, and attenuated expression of upregulated Bax. Increased caspase-3 activity in ischemic reperfusion group also inhibited by BNP postconditioning. Ratio of pGSK-3β/GSK-3βwas increased significantly in BNP group compared with ischemia reperfusion group.Conclusion:The present study suggests that BNP postconditoning reduced infarct size, attenuated oxidative stress, provided myocardial protection. Inhibition of apoptosis by BNP at reperfusion involves alteration in anti-apoptotic Bcl-2 and pro-apoptotic Bax proteins and caspase-3 activity, primarily mediated by cGMP induced GSK-3βphosphorylation.