Protective Effects Of Postconditioning Combined With Erythropoietin On The Rat Heart Ischemia-reperfusion Injury

Objective:Previous studies have shown that a brief period of repetitive coronary oc-clusion applied at the onset of reperfusion, postconditioning (postcond), attenuates myocar-dial injury. This study tested the hypothesis that coincident application of EPO and postcond would provide more cardioprotection than either intervention alone after ischemia and reperfusion.Methods: Four groups of open-chest rats endured 30 minutes coronary occlusion fol-lowed by 3 hours reperfusion: control (n=10), no intervention; postcond (n = 10), 3 cycles of 10 seconds reperfusion-10 seconds reocclusion were imposed immediately upon reperfusion; EPO (n = 10), recombinant human erythropoietin (rhEPO)(5000U/kg) was injected intrap-eritoneally at the beginning of coronary occlusion; postcond +EPO (n= 10), postcond and EPO algorithms were combined. The hemodynamic parameters, infracted size of hearts, ar-rhythmia caused by reperfusion and plasma troponin level were observed in all rats. The apoptotic index of cardiomyocytes was investigated by TUNEL method. The expression and distribution of P-selectin and E-selectin were observed by immunohistochemical staining. The levels of myocardial malonaldehyole (MDA),myeloperoxidase(MPO),superoxide dismutase ( SOD),Na⁺ -K⁺ -ATPase and Ca²⁺ -Mg²⁺-ATPase were measured at reperfu-sion 180 min. The phosphorylation states of Akt, endothelial nitric oxide synthase (eNOS) were determined by ELISA and western-blot respectively.Results:â‘ Compared to control group, infarct size, ventricular arrhythmia and plasma troponin level were comparably reduced in postcond, EPO and postcond +EPO, consistent with an improvement in hemodynamic parameters in these groups(p<0.05); plasma tro-ponin level was further reduced by postcond +EPO and hemodynamic parameters were also futher improved by postcond +EPO(p<0.05).â‘¡The results of the myocardial TUNEL staining revealed that the TUNEL positive cardiomyocytes were decreased dramatically in all intervention groups, especially in the EPO treated groups(P<0.01). After 3-hour reperfusion, immunohistochemical analysis showed that the expression of P-selectin and E- selectin on coronary vascular endothelium were also reduced in the intervention groups.â‘¢The levels of myocardial MDA,MPO were comparably reduced and the activity of SOD,ATPase were promoted in all intervention groups relative to control(P<0.05). ATPase ac-tivity was further promoted by EPO(P<0.05).â‘£ELISA and western blot analysis demonstrated that a significant increase in phosphorylation of Akt and eNOS were induced in all intervention groups, especially in the postcond +EPO groups(P<0.05).Conclusion :Postconditioning combined with erythropoietin can protect the rat heart against ischemia-reperfusion injury by activating the prosurvival kinases PI-3K.