Objective To evaluate the role of the phosphatidylinositol 3-kinase(PI3K)/protein kinase B(Akt)or Janus kinase(JAK)/signal transducer and activator of transcription 3(STAT-3)signaling pathways in reduction of myocardial ischemia-reperfusion(I/R)injury by combination of limb ischemic and morphine postconditioning in rats.Methods Eighty SPF healthy male Sprague-Dawley rats,aged 8 weeks,weighing 280-320 g,were used in the study.Myocardial I/R was induced by occlusion of the left anterior descending branch of the coronary artery for 30 min followed by 120 min reperfusion.The rats were divided into 8 groups(n=10 each)using a random number table:I/R group,limb ischemic postconditioning group(LIP group),morphine postconditioning group(group MP),combination of limb ischemic and morphine postconditioning group(LIP+MP group)and signaling pathway blocker groups(I/Rb group,LIPb group,MPb group,LIP+MPb group).In I/R,LIP,MP and LIP+MP groups,the animals were sacrificed at the end of reperfusion,and myocardial specimens in ischemic and non-ischemic regions were obtained for determination of phosphorylated STAT-3(p-STAT-3),STAT-3,phosphorylated Akt(p-Akt)and Akt expression(by Western blot)and STAT-3 and Akt mRNA expression(by polymerase chain reaction).In I/Rb,LIPb,MPb and LIP+MPb groups,PI3K/Akt signaling pathway blocker LY294002 0.3 mg/kg was intravenously injected in 5 rats of each group,and JAK/STAT-3 signaling pathway blocker AG490 5 mg/kg was intravenously injected in the other 5 rats of each group.The animals were sacrificed at the end of reperfusion,and myocardial specimens in the ischemic region were obtained for determination of myocardial infarct size.Results Compared with I/R group,the p-STAT-3/STAT-3 ratio in LIP,MP and LIP+MP groups and p-Akt/Akt ratio in LIP+MP group were significantly increased,and the expression of STAT-3 and Akt mRNA was up-regulated in LIP+MP group(P<0.05).Compared with LIP and MP groups,the p-STAT-3/STAT-3 and p-Akt/Akt ratios were significantly increased,and the expression of STAT-3 and Akt mRNA was up-regulated in LIP+MP group(P<0.05).There was no significant difference in myocardial infarct size between the four groups when PI3K inhibitor LY294002 was applied(P>0.05).When JAK2 inhibitor AG490 was applied,the myocardial infarct size was significantly smaller in LIP+MPb group than in I/Rb,LIPb and MPb groups(P<0.05),and there was no significant difference in myocardial infarct size between I/Rb,LIPb and MPb groups(P>0.05).Conclusion Combination of limb ischemic and morphine postconditioning can enhance the activation of PI3K/Akt or JAK/STAT-3 signaling pathways,and the cardioprotection is dependent on the integrity of the PI3K/Akt signaling pathway and partially dependent on the integrity of the JAK/STAT-3 signaling pathway when applied in combination in rats.