LOCALIZATION OF CHOLECYSTOKININ-A AND CHOLECYSTOKININ-B GASTRIN RECEPTORS IN THE CANINE UPPER GASTROINTESTINAL-TRACT

Background/Aims: 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. Methods: CCK receptors were localized by autoradiographic analysis of I-125-CCK binding to frozen sections of the canine upper gastrointestinal tract. Results: 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. Conclusions: 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.