Caloric and noncaloric controls of food intake.

Hunger and satiety appear to reflect the postabsorptive and absorptive phases of caloric homeostasis, respectively. However, only some of the signals that inhibit food intake can be related to caloric homeostasis. For example, decreases in food intake also are observed after administration of nauseogenic chemical agents, treatment with cholecystokinin (CCK), or dehydration. In each case, inhibition of food intake is correlated with induced decreases in gastric motility and increases in secretion of pituitary oxytocin in rats; in primates, including humans, vasopressin but not oxytocin is secreted. In contrast, meal-induced satiety increases gastric contractions and has little or no effect on neurohypophyseal hormone secretion in rats or human subjects. Nauseogenic toxins, CCK, and dehydration stimulate very different subjective states from satiety: LiCl elicits abdominal cramps, nausea, and vomiting, as does exogenous CCK in high doses, whereas dehydration elicits thirst. Thus, inhibition of eating may not be associated with satiety or reflect changes in caloric flux; noncaloric controls of food intake exist and may be accompanied by distinctive increases in neurohypophyseal hormone secretion and loss of gastric function.