Enhanced responsiveness to insulin in sheep exposed to cold

The effects of cold exposure on tissue sensitivity and responsiveness to insulin were determined by the euglycemic insulin clamp technique. Insulin was infused at rates of 0.2, 0.5, 1.0, 6.0, and 30.0 mU x kg-1 x min-1 into five adult sheep in a warm environment and after cold exposure (0 degree C) from 7 to 23 days. Cold exposure increased basal plasma glucose concentration and basal glucose irreversible loss. Glucose metabolic clearance rate (MCR) was significantly increased by cold exposure at all rates of insulin infusion, with increases ranging from 44 to 72%. The insulin concentration causing half-maximal stimulation of glucose MCR was unchanged by environment (warm, 42 microU/ml; cold, 36 microU/ml). Combined alpha + beta-adrenergic blockade did not affect the increased response to insulin during cold exposure. Endogenous (hepatic) glucose production was inhibited by insulin to a similar extent in the two environments and was less sensitive to insulin than was glucose utilization or MCR. The results suggest that cold exposure increases the responsiveness to insulin of a postreceptor event in peripheral tissues.