Localization of cholecystokinin A and cholecystokinin B/gastrin receptors in the canine upper gastrointestinal tract.

Abstract

Cholecystokinin (CCK) is a neuropeptide that exerts numerous effects in the gut. To determine the sites of action of CCK, the distribution and properties of CCK receptor subtypes were studied. CCK receptors were localized by autoradiographic analysis of 125I-CCK binding to frozen sections of the canine upper gastrointestinal tract. In the cardiac and fundic stomach, CCK-B/gastrin receptors were found in the mucosa and in a subpopulation of neuronal elements in the circular muscle. The antrum expressed CCK-B/gastrin receptors in a few neurons in the circular muscle and in the entire myenteric plexus; no receptors were observed in the antral mucosa or esophagus. The duodenum showed a high concentration of CCK-B/gastrin receptors in the myenteric plexus. The cardiac and fundic basal mucosae expressed CCK-A receptors. Two nonpeptide CCK receptor antagonists were unable to differentiate between the receptor subtypes. The differential expression of CCK receptor subtypes in the gastric mucosa provides a morphological basis for the separate regulatory roles of CCK and gastrin in gastric function. CCK-B/gastrin receptor expression in a subset of neurons in gastric circular muscle suggests a novel site of action for CCK and/or gastrin.