Insulin and glucagon as determinants of body weight set point and microregulation in rats.

Abstract

Seven adult male Long-Evans rats were observed for body weight and microregulation (feeding, drinking, and running patterns) after manipulation of insulin and glucagon levels. They received 3 injections/day for 3 days/wk of 3 U of protamine zinc insulin, .25 mg of zinc glucagon, 50 μg of protamine zinc somatostatin (SRIF), or protamine zinc vehicle. Diabetes was then induced with an iv injection of streptozotocin (65 mg/kg), and the injection schedule was repeated after the full diabetic syndrome emerged. In all Ss whose insulin levels were increased relative to glucagon levels, body weight increased; in those whose glucagon levels were increased relative to insulin levels, body weight decreased. All injections except vehicle reduced meal sizes in both normal and diabetic rats, but only insulin increased the frequency of feeding. These effects could be predicted by the glucostatic theory of food intake regulation and are thus interpreted as supporting this theory. Results also support the hypothesis that the relative concentration of insulin to glucagon is a regulator of body weight set point. (PsycINFO Database Record (c) 2006 APA, all rights reserved)