Cholecystokinin

Cholecystokinin (CCK) is a peptide hormone discovered in the small intestine. Together with secretin and gastrin, CCK constitutes the classical gut hormone triad. In addition to gallbladder contraction, CCK also regulates pancreatic enzyme secretion and growth, intestinal motility, satiety signaling and the inhibition of gastric acid secretion. CCK is, however, also a transmitter in central and intestinal neurons. Notably, CCK is the most ubiquitously found neuropeptide in the human brain. Owing to difficulties in developing accurate assays for the hormone, knowledge about CCK secretion in disease is limited. Available data indicate, however, that proCCK is expressed in certain malignant neuroendocrine tumors and sarcomas, whereas the secretion of CCK is affected in celiac disease and the eating disorder bulimia nervosa. Stimulation with exogenous CCK has proved this protein useful in diagnostic imaging of gallbladder and pancreatic diseases, as well as testing of medullary thyroid carcinomas.

Cholecystokinin, a natural polypeptide which is formed in the amine precursor uptake and decarboxylation (APUD) cells of the proximal mucosa of the small intestine, promotes contraction of the gallbladder muscle, resulting in the reduction of gallbladder size and the expression of bile. Cholecystokinin stimulates secretion of pancreatic digestive enzymes and secretion from the glands of Brunner.

CCK is composed of a five amino acid sequence at the carboxyl terminus that is identical to that of gastrin. The carboxyl terminus confers the biologic activity of CCK; as a result, gastrin has CCK-mimicking activity and CCK has gastrin-mimicking activity. The amino acid sequence similarity has made the creation of assays for CCK cumbersome, due to the fact that antibodies specific for the biologically active portion the molecule often cross-react with gastrin. This hormone circulates in the blood at concentrations 10 to 100 times greater than that of CCK.