"Bound" insulin: in vivo and in vitro biologic activity

Partially purified preparations of human serum "bound" insulin were injected intraperitoneally or intravenously into intact fed, fasted or fasted-refed rats, or incubatedin vitro with their isolated epididymal adipose tissue. The biologic activity of "bound" insulin on muscle and adipose tissue,in vivo andin vitro, was compared with the activity of crystalline insulin standards. "Bound" and crystalline insulin injected intraperitoneally into rats stimulated the incorporation of glucose-u-(14)C into the glycogen of muscle and into the glycogen and fat of adipose tissue. The activities of both "bound" and crystalline insulin were affected by the nutritional state of the animals. Intravenous administration of partially purified "bound" insulin or crystalline insulin stimulated the incorporation of glucose-u-(14)C into the muscle glycogen of intact fed, fasted or fasted-refed rats and into the fat of the adipose tissue of fed or fasted-refed rats. "Bound" insulin, but not crystalline insulin stimulated fat synthesis in the adipose tissue of fasted rats. "Bound" or crystalline insulin, at the concentration used, failed to stimulate glycogen synthesis in adipose tissue. "Bound" insulin stimulated the oxidation of glucose into CO2 in isolated rat adipose tissue and the incorporation of glucose-u-(14)C into the glycogen and fat of the adipose tissue. The effect of "bound" or crystalline insulin on isolated adipose tissue was also affected by the nutritional state of the animal.