Role of PI3K/Akt or JAK/STAT-3 signaling pathways in reduction of myocardial ischemia-reperfusion injury by combination of limb ischemic and morphine postconditioning in rats

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). 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). 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. Key words: 1-Phosphatidylinositol 3-kinase; Protein-tyrosine kinases; Extremities; Morphine; Myocardial reperfusion injury; Postconditioning