ADRENALECTOMY INCREASES SENSITIVITY TO CENTRAL INSULIN

When infused into the third ventricle of rats, insulin dose-dependentl y reduces food intake and body weight, with doses of 1 mU/day and lowe r being ineffective. Because corticosterone functionally antagonizes m any of insulin's peripheral actions, and because corticosterone acts i n the brain to enable hyperphagia under some conditions, a subthreshol d dose of insulin (1 mU/day), or its saline vehicle, was infused into the third ventricle of adrenalectomized (ADX) and sham-ADX male Long-E vans rats. Sham-ADX rats that received insulin or saline had no signif icant change of food intake or body weight over a 2-week interval. Lik ewise, saline-infused ADX were unaffected. In contrast, ADX rats recei ving insulin had a significant reduction of food intake and body weigh t. These results suggest that the absence of circulation glucocorticoi ds increases the brain's sensitivity to insulin, and that insulin in t he brain acts to lower food intake and body weight via a glucocorticoi d-sensitive mechanism. (C) 1997 Elsevier Science Inc.