INSULIN AND SATIETY FROM FEEDING IN PANCREATIC-NORMAL AND DIABETIC RATS

Insulin's role in food ingestion and satiety was investigated in strep tozotocin-diabetic and pancreatic-normal rats. Markedly diabetic rats (60-65 mg/kg b.wt. streptozotocin with mean glycemia of 380 mg/dl) wer e observed for daily food/water intake and body weight changes and mea l pattern in a standard operant chamber. Diabetic animals showed an im mediate hypophagia (days 1-4) by decreasing meal size (MS). As animals lost weight, a significant hyperphagia appeared, accomplished by an e levation in MS. Treatment with insulin infused via osmotic minipump at a stable rate (6.0 U/24 h) reduced polyuria and glycemia, eliminated glycosuria, and restored weight gain. MS did not, however, return to b aseline immediately. In a second experiment with milder diabetes (20-2 2 mg/rat streptozotocin, which produced glycemia ranging from 148 to 3 04 mg/dl), significant hyperphagia appeared, again attributable to an increase in MS. Minipumps infusing 2.4-4.0 U insulin/24 h reversed thi s hyperphagia. In pancreatic-normal rats, pumps infusing insulin at 1. 2 or 2.4 U/24 h produced a modest hypophagia accomplished by a primary decrease in nocturnal intake (11% suppression in dark feeding). Subdi aphragmatically vagotomized rats showed an attenuation of this suppres sion (no significant effects on food or water intake produced by insul in infused). Insulin appears to participate in satiety by limiting MS, without significantly shortening latency to take the next meal.