Hepatic Ischemia-reperfusion Injury On The Upstream Of The Insulin Signal Transduction Pathway And The Intervention Of Propofol

Part One Effects of hepatic ischemia-reperfusion on early steps of insulin-signaling in ratsObjectiveEffects of hepatic ischemia-reperfusion(I/R)on insulin signaling remain unclear.We observed the changes of insulin secretion and signal protein expression in the early steps of insulin signaling after hepatic I/R in rats.MethodsEighty healthy Sprague-Dawley rats were randomly divided into I/R group and control group(C)with 40 rats each.After hepatic hilum was exposed,ischemia was induced by clamping off the hepatic artery and portal vein for 30 min.The liver then was reperfused for 2h in group I/R,which was not in group C.Blood samples were taken after the exposure of hepatic hilum(T1)and at 2 h after reperfusion(T2)in I/R group and 2.5 h after T1(T2)in C group.Blood glucose(BG)and serum insulin(Ins)concentrations were measured.The insulin secretion index (ISI)and resistance index(HOMA-IR)were calculated.Expressions of insulin-signaling proteins including insulin receptor(IR)βunit(IRβ),IR substrate 1(IRS-1),IR substrates 2(IRS-2),and p85 in phosphatidylinositol 3-kinase(PI3K)were detected with Western blot method.Tyrosine phosphorylation of these proteins in the liver and skeletal muscles were determined with immune precipitation.ResultsCompared with that at T₁,BG concentrations were significantly increased at T₂ in both groups(P＜0.01).BG was higher in I/R group than that in group C at T₂(P＜0.01).No differences were seen between T₁ and T₂ with respect to Ins concentrations in group I/R.Insulin concentrations at T₂ were higher than those at T₁ in group C(P＜0.05).Compared with those at T₁,the values of ISI in group I/R were obviously lower at T₂(P＜0.01). Compared with those at T₁,the values of HOMA-IR in both groups increased significantly at T₂(P＜0.01).Expressions of insulin signal proteins had no significant difference between two groups in the liver and skeletal muscles.Compared with those in group C,tyrosine phosphorylation of IRβ,IRS-2 and the interaction between IRS-2 and PI3K at T₂ in the liver decreased by 32.2%(P＜0.01),47.7%(P＜0.01) and 55.6%(P＜0.01),respectively.Tyrosine phosphorylation of IRβ, IRS-1,and the interaction between IRS-1 and PI3K at T₂ in the skeletal muscles were decreased by 79%(P＜0.01),49%(P＜0.01)and 38% (P＜0.01),respectively.ConclusionHepatic ischemia-reperfusion inhibits insulin secretion and induces insulin resistance via down-regulation of the early steps in insulin-signaling in rats. Part Two Effects of propofol on the down-regulations of early steps in insulin-signaling after hepatic ischemia-reperfusion injury in ratsObjectiveTo observe the effects of propofol on the expressions and phosphorylations of early steps in insulin-signaling after hepatic ischemia-reperfusion injury(HIRI)in rats.MethodsA total of 80 healthy Sprague-Dawley rats were divided randomly into propofol group(P)and ischemia-reperfusion group(I/R)with 40 rats each.HIRI was produced by clamping the hepatic hilum for 30 min, and then the clamp was removed for 120 min reperfusion.In group P, propofol was infused at a rate of 10 mg·kg^-1·h^-1from 20 min before ischemia to 120 min after reperfusion.In group I/R,equal volume of normal saline was infused at an equal speed.Blood samples were takened before hepatic ischemia(T₁)and at 2h after reperfusion(T₂)to determine the levels of plasma glucose(BG)and insulin(Ins).The insulin secretion index(ISI)and resistance index(HOMA-IR)were calculated. Expressions of insulin-signaling proteins including insulin receptor(IR)βunit(IRβ),IR substrate 1(IRS-1),IR substrates 2(IRS-2),and p85 in phosphatidylinositol 3-kinase(PI3K)were measured with Western blot method.Tyrosine phosphorylation of these proteins in the liver and skeletal muscles were determined with immune precipitation.ResultsThe BG levels were higher at T₂ than those at T₁ in both groups(P＜0.01). Compared with that in group P,there was no significant difference in BG at T₁.BG in group I/R was higher than that in group P at T₂ (P＜0.05).Ins concentrations in both groups did not changed significantly at T₁ and T₂.The concentration of Ins in group I/R at T₂ was lower than that in group P(P＜0.05).Compared with those at T₁,the values of ISI at T₂ in both groups declined obviously(P＜0.01).The value of ISI in group I/R was significantly lower than that in group P at T₂(P＜0.01).The value of HOMA-IR rose significantly at T₂ compared with that at T₁ in both groups(P＜0.01).Compared with those in group P,total protein expressions of IRβ,IRS-2 and p85 in the liver did not vary significantly in group I/R.However,the phosphotyrosine state of IRβ,IRS-2 and p85 was decreased by 22.8%(P＜0.01),24.1%(P＜0.01)and 23.9%(P＜0.01),respectively. Compared with those in group P,total protein expressions of IRβ,IRS-1 and p85 in skeletal muscles did not vary significantly in group I/R. However,the phosphotyrosine state of IRβ,IRS-1 and p85 were decreased by 34.9%(P＜0.01),24.2%(P＜0.01)and 20.2%(P＜0.01), respectively. Conclusion Propofol improved the expression of the phosphotyrosine state of IRβ,IRS-1,IRS-2 and p85 in the liver and skeletal muscles,so as to alleviate the elevation of plasma glucose and insulin resistance after HIRI.