Enhancement by hypophysectomy of insulin effect on extrahepatic galactose transfer

¹ Department of Physiology, University of California Medical School, San Francisco, California

Fasted, normal, and hypophysectomized rats were eviscerated and nephrectomized under light pentobarbital anesthesia. Glucose was infused intravenously at rates that maintained a nearly constant blood glucose concentration. Single injections of galactose were given that produced an equilibrium concentration at 60 min of 247 ± 30 mg%. The galactose level was not significantly different at 90 min. Thus insulin could be administered at 60 min and the 60–90 min blood galactose change used as an index of insulin action. The extrahepatic uptake of galactose in hypophysectomized rats was demonstrated to be hypersensitive to insulin by two criteria: a) significant decreases in blood galactose concentration of hypophysectomized rats were produced by 0.01 unit of insulin/kg, a dose that had no effect on normal rats; b) after 0.02 unit of insulin/kg, changes in blood levels of galactose were greater in hypophysectomized rats than in their normal controls. Hypophysectomy did not alter galactose distribution volume. In neither normal nor hypophysectomized rats did prior administration of growth hormone alter either volume distribution of galactose or insulin hypersensitivity.