HEPATIC PORTAL INSULIN ANTIBODY INFUSION INCREASES, BUT INSULIN DOES NOT ALTER, SPONTANEOUS MEAL SIZE IN RATS

To investigate the acute effects of pancreatic insulin on spontaneous feeding in rats fed adlibitum, insulin or insulin antibodies were infu sed into the hepatic portal vein during the first meal of either the l ight or dark phase. Infusions (3 min, 0.033 ml/min) were remotely cont rolled, and a computerized system recorded meal patterns. In separate crossover tests, 1, 2, 4, 8, and 16 mU insulin/meal did not affect mea l size or subsequent intermeal interval (P > 0.10). In one test, noctu rnal meal duration was decreased by 2 mU insulin/meal (19%, P < 0.05). Infusions of polyclonal antibodies to human insulin with in vitro rat insulin binding capacity of 20 or 50 mU increased the size of the fir st nocturnal meal by 24 and 29% (P < 0.05), respectively. Meal duratio n was reliably increased only by the smaller antibody dose. Subsequent intermeal interval was unaffected by either antibody dose. The stimul atory effect of insulin antibody infusion on meal size indicates that antagonism of circulating insulin during meals interferes with the con trol of meal termination. Thus insulin appears to play a role in the p hysiological control of nocturnal spontaneous feeding in rats. Exogeno us insulin may have failed to decrease meal size because of a ceiling effect.