Endogenous release of epinephrine after stress as well as exogenous epinephrine infusion are known to result in impaired glucose tolerance. Previous studies of man and animals have demonstrated that this effect of epinephrine results from inhibition of insulin secretion and augmentation of hepatic glucose production. However, the effect of epinephrine on tissue sensitivity to insulin, and the relative contributions of peripheral vs. hepatic resistance to impaired insulin action, have not been defined. Nine young normal-weight subjects were studied with the insulin clamp technique. Plasma insulin was raised by ∼100 μU/ml while plasma glucose concentration was maintained at basal levels by a variable glucose infusion. Under these conditions of euglycemia, the amount of glucose metabolized equals the glucose infusion rate and is a measure of tissue sensitivity to insulin. Subjects received four studies: (a) insulin (42.6 mU/m2·min), (b) insulin plus epinephrine (0.05 μg/kg·min), (c) insulin plus epinephrine plus propranolol (1.43 μg/kg·min), and (d) insulin plus propranolol. During insulin administration alone, glucose metabolism averaged 5.49±0.58 mg/kg·min. When epinephrine was infused with insulin, glucose metabolism fell by 41% to 3.26 mg/kg·min (P < 0.001). After insulin alone, hepatic glucose production declined by 92% to 0.16±0.08 mg/kg·min. Addition of epinephrine was associated with a delayed and incomplete suppression of glucose production (P < 0.01) despite plasma insulin levels >100 μU/ml. When propranolol was administered with epinephrine, total glucose metabolism was restored to control values and hepatic glucose production suppressed normally. Propranolol alone had no effect on insulin-mediated glucose metabolism. These results indicate that epinephrine, acting primarily through a β-adrenergic receptor, markedly impairs tissue sensitivity to an increase in plasma insulin levels, and that this effect results from both peripheral and hepatic resistance to the action of insulin.
David C. Deibert, Ralph A. Defronzo