Insulin action and resistance in obesity and noninsulin-dependent type II diabetes mellitus.

Resistance to the action of insulin can result from a variety of causes, including the formation of abnormal insulin or proinsulin molecules, the presence of circulating antagonists to insulin or the insulin receptor, or defects in insulin action at the target tissue level. Defects of the latter type are characteristic of obesity and of noninsulin-dependent diabetes mellitus. Analysis of the nature of the insulin resistance in those disorders has been investigated in intact subjects with the use of the euglycemic glucose clamp technique, and both insulin receptors and insulin-mediated glucose metabolism have been studied in adipocytes and monocytes from affected individuals. In both conditions, the cause of insulin resistance is heterogeneous. In some, insulin resistance appears to be due to a defect in the insulin receptor, whereas others have a defect both in the receptor and at the postreceptor level. In both groups, more severe insulin resistance is due to the postreceptor lesion and is correctable with appropriate therapy.