Discovery of a cholecystokinin-releasing peptide: biochemical characterization and physiological implications.

: Recent studies indicate that the secretion of CCK is mediated by a trypsin sensitive peptide secreted by the proximal small intestine that has been designated "CCK-releasing factor" (CCK-RF). This CCK-RF was found to be identical to the porcine diazepam binding inhibitor by peptide sequencing and mass spectrometry analysis. This peptide is present in abundance in the epithelial cells in the duodenal mucosa. Its release into the lumen is mediated by intestinal submucosal cholinergic neurons. Functionally, this peptide appears to mediate feedback regulation of pancreatic secretion and CCK release in response to peptone and lipid stimulation. It fulfills all the criteria as a physiological regulator of CCK secretion. This represents the first chemical characterization of a luminally secreted enteric peptide functioning as an intraluminal regulator of intestinal hormone release.