Mechanism underlying inhibition of inflammatory responses induced by α7nAChR agonist postconditioning alone or in combination with remote limb ischemic postconditioning during myocardial I/R in rats: the relationship with GSK-3β

Abstract

Objective To evaluate the relationship between the mechanism underlying inhibition of inflammatory responses induced by α7 nicotinic acetylcholine receptor(α7nAChR)agonist postconditioning alone or in combination with remote limb ischemic postconditioning during myocardial ischemia-reperfusion(I/R)and glycogen synthase kinase-3β(GSK-3β)in rats. Methods Eighty adult male Sprague-Dawley rats, aged 8 weeks, weighing 290-320 g, were divided into 4 groups(n=20 each)using a random number table: I/R group, α7nAChR agonist postconditioning group(group P), remote limb ischemic postconditioning group(group L)and α7nAChR agonist postconditioning plus remote limb ischemic postconditioning group(group P+ L). Myocardial I/R was induced by 30 min occlusion of the left anterior descending branch of coronary artery followed by 120 min reperfusion.Specific α7nAChR agonist PNU282987 2 mg/kg was intravenously injected immediately before reperfusion in group P. In group L, limb ischemia was induced by tourniquet occlusion of bilateral hind paws for 10 min starting from 20 min of myocardial ischemia, and the tourniquet was released at the beginning of reperfusion.Combination of intervention measures previously described in P and L groups was performed in group P+ L.Venous blood samples were taken at 120 min of reperfusion for determination of serum troponin I(TnI)and creatine kinase-MB(CK-MB)concentrations, myocardial infarct size(IS)and expression of phosphorylated GSK-3β [p-GSK-3β(Ser536)], NF-κBp65 and phosphorylated nuclear factor-κBp65(p-NF-κBp65)in myocardial tissues(by Western blot). Results Compared with group I/R, myocardial IS and serum cTnI and CK-MB concentrations were significantly decreased, the expression of p-GSK-3β(Ser9)in ischemic area was up-regulated, and the expression of p-NF-κBp65 in ischemic area was down-regulated in P, L and P+ L groups(P<0.05). Compared with group L, myocardial IS and serum cTnI and CK-MB concentrations were significantly decreased, the expression of p-GSK-3β(Ser9)in ischemic area was up-regulated, and the expression of p-NF-κBp65 in ischemic area was down-regulated in group P+ L(P<0.05). Conclusion The mechanism by which α7nAChR agonist postconditioning alone or in combination with remote limb ischemic postconditioning inhibits inflammatory responses during myocardial I/R may be related to inhibiting GSK-3β activity in rats. Key words: Myocardial reperfusion injury; Inflammation; Glycogen synthase kinase 3; Cholinergic agonists; Extremities; Ischemic postconditioning