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Objective:To study the protective effects of different doses of Cyclosporin A (CsA) on rat heart after myocardial ischenmic/reperfusion injury(MIRI). To explore the dose-response curve and the best protection dose of CsA on rat heart after ischenmic/reperfusion injuryMethods:32 male SD rats were randomly divided into 4 groups:Control group as sodium chloride group (n= 8),low dose group (the dose of CsA is lmg/kg, n=8), middle dose group (the dose of CsA is 2.5mg/kg, n=8), high dose group (the dose of CsA is 5mg/kg, n=8), We made rat MIRI model through left anterior decending coronary artery ligation reversibly. Reperfusion took place after the left anterior decending coronary artery occlusion 30min, the time of reperfusion is 120min. Different doses of CsA was injected intravenously into low dose group、middle dose group and high dose group at 5min before reperfusion. sodium chloride was injected intravenously into Control group at 5min before reperfusion. mean arterial blood pressure(MAP)^ left ventricular systolic pressure (LVSP) and heart rate (HR) was measured before occlusion and after reperfusion Omin、30min、60min、90min and 120min. Creatine kinase-MB and cardiac troponin hypersensitive was measured after reperfusion 120min.Rats were killed and remove the hearts. Given Evans Blue-TTC staining and use weighting method to determine the myocardial infarction.Results:(1)For CK-MB values, low dose group, middle dose group and high dose group compared with the control group were decreased, the difference was statistically significant (P<0.05). middle dose group and high dose group compared with the low dose group, the CK-MB values were decreased, the difference was statistically significant (P<0.05). But middle dose group compared with high dose group, although the CK-MB values were different, the difference was no statistical significance (P> 0.05). (2) For cTnI values, low dose group, middle dose group and CsA3 group compared with the control group were decreased and the difference was statistically significant (P<0.05). Although the cTnI values among low dose group, middle dose group and high dose group were differences, but the cTnI values among each groups was no significant difference (P> 0.05). (3) For heart rate, before coronary artery ligation in rats, the base value of heart rate is similar, there were no significant differences (P> 0.05). Although the heart rate after ligation compared with the base heart rate were decreased among each group, but heart rate compared between every two groups at each time point, the heart rate were no significant difference (P> 0.05), therefore, CsA have no effect on heart rate in rats. (4) For MAP and LVSP values, the base values before reperfusion among each group were no significant differences (P> 0.05).But the values after reperfusion of 0min、30min、60min、90min and 120min were decreased over time among each group but only middle dose group compared with high dose group the values at all time points between the two groups was no significant difference(P> 0.05),the other group compared with each other at all time points the values were statistically significant differences (P<0.05). Also the control group and low dose group compared with middle dose group and high dose group, the values of LVSP and MAP were decreased, and low dose group compared the control group the values were decreased, the difference of values were statistically significant (P<0.05). (5) For myocardial infarction, the sizes of low dose group, middle dose group, high dose group compared with the control group were reduced and the differences were statistically significant (P<0.05). middle dose group and high dose group compared with the low dose group, the myocardial infarction sizes were more smaller and the differences were statistically significant (P<0.05). The middle dose group compared with high dose group, although the sizes were different, the differences were no statistical significance (P> 0.05).Conclusion:(1) The protective effects of different doses CsA is different on rat MIRI model, The protective effects of middle dose group and high dose group is greater than low dose group, but the protective effects of middle dose group and high dose group has no significant difference. (2) the best protection dose of CsA is about 2.5mg/kg on rat MIRI model
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