Long-term effects of insulin in weanling rats with dorsomedial hypothalamic hypophagia: Food intake,efficiency of food utilization,body weight and composition

Twenty-five day-old Sprague-Dawley rats received electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats); sham-operated rats served as controls. Two weeks after the operation the DMNL rats showed reduced (p<0.001) body weight and food intake but normal body composition (Lee Index) and efficiency of food utilization (EFU). During the following 32 days subcutaneous administration twice daily of intermediary-acting insulin in increasing doses (mean daily dose 2.64 IU/kg) caused highly significant increases in food intake in both groups. Injection for the subsequent 14 days of higher doses of insulin (mean daily dose 5.64 IU/kg) caused dramatic increase in both food intake and Lee Index and equalized the rate of weight gain with that of the controls. However, in absolute terms the DMNL rats remained consistently hypophagic and weighed significantly less than the controls. Both DMNL rats and controls showed the same EFU during both periods of insulin administration. On discontinuation of hormone treatment during the subsequent 20 days, food intake and body weight gains returned to pretreatment values and the insulin-induced increased Lee Index returned into the low-normal range. However, EFU was significantly (p<0.05) decreased during this period. At sacrifice, plasma glucose, glycerol, free fatty acids and total protein and carcass lipid and protein were normal in the DMNL rats. Absolute and relative (per 100 g body weight and per metabolic size) weight of epididymal fat pads, pituitaries, adrenals and kidneys were normal in the DMNL rats but testes weight per 100 g body weight was higher (p<0.05) in the DMNL rats. Although DMN lesions may remove some glucose-sensitive elements within the hypothalamus, the animals are still capable of responding to the food intake and weight-promoting properties of insulin, as do intact animals.