The Role of Insulin in the Development of Obesity in Hypothalamic Deafferented Rats

Studies of the Effects of Insulin on Feeding Behavior

Abstract

The effects of exogenous insulin on food intake were investigated in medial basal hypothalamic deafferented rats which were newly developed as experimental obese animals by Ohshima et al.
Female Wistar rats weighing 190-210 g were injected with streptozotocin (60 mg/kg) to deplete endogenous insulin. Medial basal hypothalamic deafferentation (8 rats) and sham-operation (12 rats) were performed with a Halasz's knife 8 days after the streptozotocin treatments. One week after the operation we injected 4 U of N PH insulin per rat subcutaneously daily for 8 days and 8U/rat for the following 8 days. Daily food intake and body weight were measured every day. Increased food intake and body weight were observed in the hypothalamic deafferented rats immediately after the operation despite the lack of insulin. However, both of them gradually decreased to the same level as in the sham-operated rats.
Food intake in the hypothalamic deafferented rats was significantly increased by administration of insulin in a dose-dependent manner in association with a significant increase in body weight. Incontrast, in the sham-operated rats food intake was decreased significantly by administration of insulin.
These results indicate that medial basal hypothalamic deafferentation modulates the effects of insulin on feeding behavior. It is suggested that not only hyperinsulinemia itself but also this enhancing effect of insulin on food intake contribute to the development of obesity in hypothalamic deafferented obese rats by acceleration of hyperphagia.