Whole body insulin resistance has been demonstrated in sepsis, and is primarily referable to a decrease in insulin-mediated glucose uptake (IMGU) by skeletal muscle. The reduction in IMGU results from a decrease in insulin responsiveness and/or sensitivity, suggesting that sepsis may impair insulin action by both a receptor and postreceptor defect. Therefore, the long-term goal of the proposed studies is to elucidate the cellular mechanism by which gram-negative infection produces insulin resistance in skeletal muscle. The working hypothesis to be tested is that the sepsis-induced insulin resistance is mediated primarily by the elevation in plasma epinephrine levels which alters insulin binding as well as the intracellular disposition of the glucose by muscle. This hypothesis will be addressed by three specific aims. The first specific aim will determine: (a) insulin binding characteristics, (b) tyrosine kinase activity, (c) abundance of glucose transporters GLUT-1 and -4, (d) intracellular glucose disposal via oxidative and nonoxidative pathways, and (e) the activity of rate-controlling enzymes of glycogen synthesis and glycolysis, under basal and hyperinsulinemic conditions in septic and nonseptic rats. Our preliminary studies indicate that the insulin- antagonistic effects of sepsis are prevented by the concurrent infusion of a beta-adrenergic antagonist. Therefore, the experiments designed to answer the second specific aim will determine the mechanism by which beta- blockade prevents the sepsis-induced insulin resistance. The proposed experiments to answer these first two aims will be performed in rats in which a gram-negative hypermetabolic sepsis is induced. Since our data indicates that an increase in the plasma epinephrine concentration accompanying sepsis is primarily responsible for the decrease in IMGU and that a chronic infusion of epinephrine can produce peripheral insulin resistance, the third specific aim will determine whether the infusion of epinephrine into nonseptic control animals impairs IMGU in muscle by the same mechanism as sepsis. The various experimental protocols proposed closely integrate both in vivo measurements of IMGU and glucose disposal with in vitro studies designed to elucidate molecular mechanisms. These studies will provide novel and important information on the cellular mechanism by which gram-negative infection produces insulin resistance, and will substantially aid our understanding of the factors which modulate carbohydrate flux in this disease state.
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