Objective:To determine the effect of acidic reperfusion on myocardial ischemia/reperfusion injury by cardiopulmonary bypass(CPB) and choose the optimum pH of perfusion fluid.Methods:thirty adult New Zealand white rabbits of both sexes weighing 2.5～3.0 kg were randomly divided into 5 groups(n=6 each).In control group

CPB was executed for 180 min without aortic clamping.In the other groups

hearts were subjected to ischemia for 40 min followed by 120 min of reperfusion

and were respectively perfused with Krebs-Henseleit bicarbonate buffer solution at pH 7.4

7.1

6.9 and 6.7 in the first 2 min of referfusion.After 2 h reperfusion

the lactate dehydrogenase(LDH) activity was tested with colorimetric method

cardiac troponin I(cTnI) concentration was determined with ELISA and myocardial tissues were observed by light microscopy and transmission electron microscope.Results:In the other groups

the LDH activity and cTnI concentration were significantly increased as compared with in the control group(P<0.05).Compared with pH 7.4 group

the LDH activity and cTnI concentration were significantly lower in acidic reperfusion groups(P<0.05)

and were lowest in pH 6.9 group.The pH 7.4 group showed the most serious injury while the pH 6.9 group showed the least damage in the acidic reperfusion groups by pathological examination.Conclusion:Acidic reperfusion can attenuate the myocardial ischemia/reperfusion injury by CPB in rabbits and the reperfusion of Krebs-Henseleit bicarbonate buffer solution of pH 6.9 provides best protective effect.