Effect of trypsin treatment of rat adipocytes on biological effects and binding of insulin and insulin-like growth factors: further evidence for the action of insulin-like growth factors through the insulin receptor.

Trypsin-treatment of isolated rat adipocytes abolishes the metabolic effects not only of insulin, but also of the insulin-like growth factors: in trypsin-treated cells, concentrations of these hormones that are otherwise maximally effective no longer stimulate 3-O-methylglucose transport and lipogenesis or inhibit epinephrine induced lipolysis. Concomitantly, the trypsin-treated adipocytes no longer display specific insulin binding. In contrast, the characteristics of the binding of the insulin-like growth factors are not grossly affected by prior trypsinization of the adipocytes. These findings add further support to the concept that the insulin-like growth factors act on glucose metabolism and antilipolysis via the insulin receptor of the adipocyte.