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 modulate metabolic and autonomic responses. Some of its effects are mediated by the central nervous system (CNS), and there are IGF-1 receptors dispersed throughout the CNS. Both IGF-1 and insulin alter peripheral metabolic and autonomic nervous activity by a central mechanism, and the well-defined role of insulin in the regulation of feeding, especially in diabetes, led us to investigate the effect of chronic central administration of IGF-1 on metabolic and feeding parameters in normal and diabetic rats. Normal and diabetic 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 and food intake were recorded daily. IGF-1 administered intracerebroventricularly 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, intracerebroventricular insulin decreased food intake in both normal and diabetic 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.