| Objective: To investigate the acute cardioprotection of 17b-estradiol (E2) on severe myocardial ischemia/reperfusion (I/R) injury in anesthetized rabbits and to compare the effects administered on two different times.Methods: To establish the model of myocardial I/R in vivo by occluding the left anterior descending coronary artery(LAD) in 36 male white rabbits, which were randomly assigned to 3 groups (n=12 each group) and treated intravenously with either ethanol 1ml (Control group) , E2 (10μg/kg) 15 min before coronary occlusion (Early group),or 3 min prior to coronary reperfusion following myocardium ischemia (Late group).All the groups were subjected to 40 min occlusion of LAD followed by 3 h of reperfusion. During the experiment,blood was collected from artery at different times and was assessed,including the concentration of serum E2, the activities of superoxide dismutase (SOD),lactate dehydrogenase (LDH) ,creatine kinase (CK) and creatine kinase isoenzyme-MB (CK-MB) and the content of maleic dialdehyde (MDA). At the end of reperfusion,infarct size was assessed by weight after Evans blue-TTC staining, and apoptosis cadiocytes were identified by TUNEL staining.Results:During the reperfusion , either in early or late group, the rise of MDA and LDH,CK and CK-MB and the reduction of SOD were greatly inhibited compared with control group ( P < 0.05 ), and there were no difference between these changes in the early and late group(P >0.05). Rabbits treated with E2, either early or late, showed significant reduction of infarct size [(30.57±3.20)﹪and (32.01±4.07)﹪, respectively versus(54.36±3.91)﹪in control group, P<0.01,both] and apoptotic index [(11.01±3.67)﹪and (9.85±3.79)﹪versus (21.78±4.33)﹪,P<0.01,both],and there were no difference between these changes in the early and late group(P >0.05).Conclusion: It is at the time of reperfusion that E2 protect the myocardium against I/R injury, and this effect of E2 may associate with its role of antioxidant, anti-apoptotic and reduced myocardium necrosis. |
