Role of ERK1/2 signaling pathway in mitigation of myocardial ischemia-reperfusion injury by diazoxide postconditioning in rats

Objective To evaluate the role of ERK1/2 signaling pathway in mitigation of myocardial ischemia-reperfusion (I/R) injury by diazoxide postconditioriing in rats.Methods Sixty adult male SpragueDawley rats,aged 3 months,weighing 240-260 g,were randomly divided into 5 groups (n =12 each) using a random number table:sham operation group (S group),I/R group,vehicle group (Ⅴ group),diazoxide postconditioning group (D group),and ERK1/2 signaling pathway inhibitor U0126 group (U group).Myocardial I/R was produced by occlusion of left anterior descending branch of coronary artery for 30 min followed by 120 min reperfusion.In V and D groups,0.4％ DMSO and diazoxide 7 mg/kg (in 1 ml 0.4％ DMSO) were administrated,respectively,through the femoral vein at the onset of the reperfusion.In U group,U0126 was given through the femoral vein at 10 min before reperfusion,and the following procedures were similar to those previously described in group D.At 120 min of reperfusion,myocardial specimens were obtained for detection of myocardial infarct size,cell apoptosis (using TUNEL),and expression of ERK1/2 mRNA (by RT-PCR),total ERK1/2 (t-ERK1/2) and phosphorylated ERK1/2 (p-ERK1/2) (by Western blot).Apoptosis index was calculated.Results Compared with S group the myocardial infarct size and apoptosis index were significantly increased in the other groups,the expression of ERK1/2 mRNA and p-ERK1/2 was down-regulated in I/R,V and U groups,and no significant change was found in the expression of ERK1/2 mRNA and p-ERK1/2 in Dgroup.Compared with I/R group,the myocardial infarct size and apoptosis index we re significantly decrcaed,and the expression of ERK1/2 mRNA and p-ERK1/2 was up-regulated in D group,and no significant change was foundin the parameters mentioned above in V and U groups.Compared with D group,the myocardial infarct sizeand apoptosis index were significantly increased,and the expression of ERK1/2 mRNA and p-ERK1/2 was down-regulated in U group.There was no significant difference in t-ERK1/2 expression between five groups.Conclusion Diazoxide postconditioning mitigates myocardial I/R injury possibility through activating ERK1/2 signaling pathway in rats. Key words: Extracellular signal-regulated MAP kinases ;  Diazoxide ;  Ischemic postconditioning; Myocardial reperfusion injury