Intracerebroventricular insulin-like growth factor-1 decreases feeding in diabetic rats

Insulin-like growth factor-1 (IGF-1) is a hormone that is important in the regulation of growth processes and additionally has been demonstrated to mo dulate metabolic and autonomic responses. Some of its effects are mediated by the central nervous system (CNS), and there are IGF-1 receptors disperse d throughout the CNS. Both IGF-1 and insulin alter peripheral metabolic and autonomic nervous activity by a central mechanism, and the well-defined ro le of insulin in the regulation of feeding, especially in diabetes, led us to investigate the effect of chronic central administration of IGF-1 on met abolic and feeding parameters in normal and diabetic rats. Normal and diabe tic rats with intracerebroventricular cannulas were given IGF-1, insulin (0 .5 nmol/animal), or artificial cerebrospinal fluid via cannula twice daily for 4 d. Blood samples were collected on d 2 and 4, and the body weights an d food intake were recorded daily. IGF-1 administered intracerebroventricul arly did not alter plasma glucose, insulin, body weight, or food intake in normal rats. However, in diabetic animals, IGF-1 decreased food intake but did not alter blood glucose or plasma insulin. In correlated studies, intra cerebroventricular insulin decreased food intake in both normal and diabeti c animals. From these studies, we conclude that IGF-1 may act centrally to decrease food intake in the hyperphagic diabetic animals but not in normal animals. This suggests that diabetic animals have an increased sensitivity to CNS IGF-1.