ENDOTOXIN-INDUCED ALTERATIONS IN INSULIN-STIMULATED PHOSPHORYLATION OF INSULIN-RECEPTOR, IRS-1, AND MAP KINASE IN SKELETAL-MUSCLE

Sepsis and endotoxin (LPS) have been demonstrated to impair insulin-me diated glucose uptake in skeletal muscle. However, the intracellular m echanism responsible for this defect is not fully defined. The purpose of the present study was to determine whether specific elements of th e insulin receptor OR) signaling pathway in skeletal muscle are altere d by LPS. In vivo injection of Escherichia coli LPS resulted in a 44% reduction in whole body glucose disposal under euglycemic hyperinsulin emic conditions, which was largely accounted for by a decreased rate o f glycogen synthesis. Scatchard analysis indicated that the number and affinity of the high-affinity insulin binding sites in muscle were si milar between control and LPS-treated rats. Western blot analysis indi cated that under basal conditions, the levels of total and phosphoryla ted IR, insulin receptor substrate (IRS)-1, and mitogen-activated prot ein (MAP) kinase were not significantly different between control and endotoxic rats. In control animals, muscle obtained 2 min after intrav enous injection of a maximally stimulating dose of insulin demonstrate d a marked increase in the amount of phosphorylated IR (similar to 5-f old), IRS-1 (similar to 10-fold), and MAP kinase (similar to 10-fold). insulin-stimulated phosphorylation of IR, IRS-1, and MAP kinase was m arkedly diminished (similar to 75%, 90%, and 78%, respectively) in LPS -treated rats. However, there was no concomitant reduction in the tota l abundance of these proteins under hyperinsulinemic conditions. These data demonstrate that LPS alters multiple steps in the insulin signal transduction pathway, but not insulin binding, in skeletal muscle tha t may mediate the observed impairment in glucose uptake.