Role of peptides from gastrointestinal cells in food intake regulation

Many peptides are contained in specific cells distributed throughout the gastrointestinal tract. Some are known to be released by the presence of specific components of food and to affect specific gastrointestinal functions related to digestion and absorption of nutrients. For many of the more recently identified peptides, however, stimuli for release and physiological functions are unknown. Improved radioimmunoassay techniques have allowed measurement of serum concentration changes of peptides that act via endocrine but not neurocrine or paracrine modes of action. Peptides that may play a role in the control of food intake include cholecystokinin (CCK), bombesin (BBS) and pancreatic polypeptide (PP) as possible satiety components and opiates as possible hunger components. All four have been found in the brain as well as in the gastrointestinal tract. Systemic administration of each has been shown to affect food intake, but whether doses used produced changes that normally occur during a meal awaits further development of radioimmunological assays. In the obese, the decreased sensitivities to, or decreased concentrations of the satiety components CCK, BBS and PP and the increased concentrations of the hunger component, B-endorphin, may contribute to the imbalance of food intake and energy expenditure, which leads to the accumulation of adipose tissue.