[The role of cholecystokinin as a regulator of gastrointestinal functions]

Cholecystokinin (CCK), a peptide synthesized in the small bowel, is secreted into the blood stream after food intake. Its effects are primarily hormonal but of equal significance is that of a neurotransmitter. Its central role as a digestive peptide is illustrated by the following sequence: Mostly fat and protein of a consumed meal liberate CCK which triggers the contraction of the gallbladder and stimulates secretion of pancreatic enzymes. At the same time CCK slows down gastric emptying leading to an optimal ratio of foodstuff and digestive secreta. Via activation of afferent nerves CCK induces the sensation of saturation and thus limits food intake. Many questions remain open or undefined in this context but two conclusions may be drawn. 1. The significance of Pawlowian neural regulation of digestive functions is supported by new evidence, although hormones may support or modulate these functions. 2. It has become clear that a peptide may assume diverse regulatory functions be it as a hormone or as a neurotransmitter. Dear old concepts have therefore to be revised.