Selective alterations of insulin actions by glucagon in isolated rat epididymal adipocytes

Abstract

Previously we demonstrated that glucagon inhibits high affinity insulin binding without influence on low affinity binding in rat adipocytes in vitro. In this study we investigated the effects of glucagon on insulin actions in adipocytes in vitro. Glucagon modified neither glucose oxidation nor lipogenesis stimulated by insulin. The antilipolytic action of insulin was decreased by preincubation of the cells with glucagon. Glucose transport enhanced by insulin was diminished by preincubation of the cells with glucagon. The decrease in antilipolysis was a lowering of the maximal response to insulin, whereas the decrease in glucose transport was a lowering of the sensitivity to insulin. These results suggested that glucagon does not necessarily inhibit all of the insulin actions, and that the mechanism of insulin stimulation of glucose transport, which is supposed to be mediated by glucagon-sensitive insulin receptor, is different from those of insulin-induced antilipolysis, glucose oxidation, and lipogenesis.