Effects Of Ischemic Postconditioning On Myocardial Cell Apoptosis During The Short Periods Of Ischemia/reperfusion In Rabbit

Object ischemia and reperfusion injury (IRI)is an urgent problem that must be soluted in clinic. The mechanism about IRI is not fully illustrated except for the production of oxygen free radicles, calcium overload and neutrophil infiltration. In 1980' s Murry reported that ischemic preconditioning(IP) has robust cardio-protection in IRI. however, this method is hard to be applied in clinic due to the characteristic of the preconditioning itself and the difficulty of indicating the moment of ischemia in clinic. At the same time, some people reported that controlling the condition of reperfusion could also have protection effects; also this method is hard to be applied due to the different results between different labs and the difficulty of controlling the reperfusion conditions. In the early of this century, some people provided the conception of postconditioning (Post), i.e. multiple, brief coronary occlusions during the early time (onset) of reperfusion has the same robust myocardial protection as preconditioning in IR. In this study, we investigated whether postconditioning has myocardial protection in rabbits in IR, and the effects of ischemic preconditioning and ischemic postconditioning on myocardial cell apoptosis and expression of Bcl-2 and Bax protein during ischemia/reperfusion period in rabbits.Methods All studies were performed on 30 healthy new Zealand rabbits, which are randomly allocated to five groups(n=6):sham operation group(S Group), ischemia/reperfusion group(IR Group) , ischemic preconditioning group(Group IP),ischemic postconditioning group(Post Group) and Group IP+Post. Group IR and Group Post were subjected to 15 minutes of left anterior descending coronary artery occlusion followed for 30 minutes of reperfusion. Ischemic preconditioning was achieved by three 5 minutes cycles of ischemia, each followed by 5 minutes of reperfusion. Ischemic postconditioning was achieved by three 30 seconds cycles of reperfusion, each followed by 30 seconds ischemia. Cardiomyocyte apoptosis was determined by in situ TDT-mediated dUTP nick end labeling(TUNEL) and DNA electrophoresis . The expression of Bcl-2 and Bax proteins were detected by immunohistochemiscal method.Results A total of 30 rabbits were involved in the analysis of results.①DNA electrophoresis showed that there were two ladder-shaped straps of 200 bp and 400 bp in the myocardium of ischemic region in the IR group ,whereas no ladder-shaped strap was found in other group.②TUNEL detection showed that the apoptotic index in IP group(32.13%),Post group (28.06%)and IP +Post group(32.91%) were obviously lower than that in the IR group(55.70%,P<0.01), there is no difference between the IP group ,Post group and IP+ Post group(P>0.05)..③The expression of Bcl-2 protein in IP group(9.33±1.37), Post group(10.00±0.89) and IP + Post group(10.17±0.75) higher than that in the IR group(7.83±1.47,P<0.05), there is no difference between the IP group ,Post group and IP+ Post group(P>0.05).④The expression of Bax protein in IP group(8.00±1.26), Post group(7.50±0.84) and IP + Post group(7.17±0.94) were lower than that in the IR group(9.83±0.98,P<0.05), there is no difference between the IP group, Post group and IP + Post group(P>0.05).Conclusion①IP and Post has robust myocardial protection in rabbits in IRI .②IP and Post significantly decreases the ratio of apoptosis and protects myocardial cells from IRI by increasing Bcl-2 expression and decreasing Bax expression.③Myocardial protection with Post is not enhanced by IP.