Food intake and serum insulin responses to intraventricular infusions of insulin and IGF-I.

Previous studies reported that intracerebroventricular (ICV) infusion of insulin decreased food intake in rats and baboons. Insulin can bind to insulin-like growth factor I (IGF-I) receptors and mimic the response of IGF-I. Our objective was to determine the effects of ICV infused-insulin or IGF-I on food intake in sheep. In the present study, a 6-day ICV infusion of insulin (123 ng/kg of body weight/day) but not of IGF-I (123 ng/kg of body weight/day) decreased food intake by 40% (p less than 0.003) and body weight (p less than 0.015) compared with control sheep. In addition, sheep that received ICV insulin or IGF-I had only half the concentration of insulin in serum as compared with controls. Our results support the hypothesis that ICV insulin does not decrease food intake through IGF-I receptors. Nevertheless, apparently both insulin and IGF-I in the brain can influence the concentration of insulin in blood.