The regulation of food intake by peptides.

Historically, nutrients and related metabolic signals were considered to control the onset and offset of meals. Recent research has focused upon the roles of peptides found in the gastrointestinal tract and brain as alternate controllers of these processes. During a meal, the gut secretes a variety of peptides as part of the digestive process. Some of these substances, acting as hormonal or as local signals, may also provide information which is relayed to the central nervous system, causing eating to stop and producing the sense of satiety. When administered to animals or people before a meal, exogenous cholecystokinin (CCK), the most studied of the putative satiety peptides, reduces food intake in a dose-dependent manner. Recent findings support the concept that endogenous CCK acts during meals to limit meal size, and evidence is reviewed suggesting a possible pathophysiological role for CCK in bulimia. Adiposity is also regulated via peptide hormones, especially insulin. Insulin is secreted in direct proportion to adiposity, and blood-borne insulin gains access to brain areas important in the regulation of feeding. The administration of insulin into the brain causes reduced eating and weight loss.