This peptide hormone induces gall bladder contraction and the release of pancreatic enzymes in the gut. Its function in the brain is not clear. Expressed in brain, lung, testis and throughout the length of the small intestine. In the brain, expressed predominantly in the optic tectum and brain stem. The precursor is cleaved by proteases to produce a number of active cholecystokinins. Frog brain contains CCK-octapeptide (CCK8) and CCK7; whereas the gut contains intact CCK33 and CCK58. Belongs to the gastrin/cholecystokinin family.