<b>CHOLECYSTOKININ: A HORMONE AND A NEUROTRANS</b><b>MITTER </b>

Abstract

Various molecular forms 'of cholecystokinin (CCK) sharing the same C-terminal sequences exist in the digestive tract, peripheral circulation and within the cells of the central nervous system. In the periphery, CCK fulfills most of the characteristics for definition as a hormone. It is localized in specialized cells of the intestinal mucosa, is released into the blood in response to the presence of certain foodstuffs in the gut, and acts on a number of target organs including the pancreas, gallbladder, and gut. It exerts its actions by means of specific receptors which are highly sensitive to certain structural features of the CCK molecule. In the nervous system CCK is localized within neurons and fulfills most of the criteria for a neurotransmitter or neuromodulator. The physiological importance of this CCK is, however, not well understood. In the nervous system, CCK also acts on specific receptors but these are less selective, thus this CCK action may depend primarily on release at the right location. Further work is needed to understand both the neural and the hormonal role of CCK.