Mechanisms of hemorrhage-induced hepatic insulin resistance: role of tumor necrosis factor-alpha.

Hemorrhage, sepsis, burn injury, surgical trauma and critical illness all induce insulin resistance. Recently we found that trauma and hemorrhage acutely induced hepatic insulin resistance in the rat. However, the mechanisms of this hemorrhage-induced acute hepatic insulin resistance are unknown. Here we report on the mechanisms of this hepatic insulin resistance. Protein levels and phosphorylation of the insulin receptor and insulin receptor substrate-1/2 (IRS-1/2) were measured, as was the association between IRS-1/2 and phosphatidylinositol 3-kinase (PI3K). Also examined were the hepatic expression of TNFalpha and TNFalpha-induced serine phosphorylation of IRS-1. Insulin receptor and IRS-1/2 protein levels and insulin-induced tyrosine phosphorylation of the insulin receptor were unaltered. In contrast, insulin-induced tyrosine phosphorylation of IRS-1/2 and association between IRS-1/2 and PI3K were dramatically reduced after hemorrhage. Hepatic levels of TNFalpha mRNA and protein were increased as was phosphorylation of IRS-1 serine 307 after hemorrhage. Our data provide the first evidence that compromised IRS-1/2 tyrosine phosphorylation and their association with PI3K contribute to hemorrhage-induced acute hepatic insulin resistance. Increased local TNFalpha may play a role in inducing this hepatic insulin resistance after trauma and hemorrhage.