Cholecystokinin (CCK) is synthesized as a preprohormone, which is then converted into multiple isoforms. The sulphated octapeptide amide CCK-8 exists as the predominant form of CCK in neurons.
CCK is widely distributed in several brain regions, including hypothalamus, hippocampus, amygdala nuclei, and cortical regions. In the periphery, CCK peptides are mainly produced in small intestinal endocrine I-cells and in neurons of the enteric nervous system.
CCK plays important physiological roles both as a neuropeptide in the central nervous system and as a peptide hormone in the gut. It is released rapidly into the circulation in response to a meal. The greatest stimulator of CCK release is the presence of fatty acids and/or certain amino acids in the chyme entering the duodenum. CCK peptides stimulate pancreatic enzyme secretion and growth, gallbladder contraction, gut motility, and inhibit gastric acid secretion.
In the central nervous system, CCK acts as a neurotransmitter and neuromodulator regulating both the electrical activity of neurons and the release of other neuropeptides. It is involved in feeding, satiety, pain, anxiety, and memory processes.