Atropine-resistant secretion of a putative luminal CCK-releasing peptide in conscious rats

The changes in levels of the newly discovered luminal CCK-releasing factor (LCRF) in the small intestinal lumen before and after bile-pancreatic juice diversion in conscious rats were examined by a specific RIA. Moreover, we also examined whether LCRF secretion was under cholinergic control. Anti-LC RF antiserum was raised in rabbits, and a sensitive RIA was established. Th e localization of LCRF was examined by immunohistochemistry. The luminal co ntent of LCRF was significantly increased by bile-pancreatic juice diversio n, during which luminal trypsin activity was eliminated. The increase in lu minal LCRF content was not inhibited by intravenous infusion of atropine. T he changes in plasma levels of CCK and pancreatic secretion were similar to those in luminal LCRF contents. LCRF immunostaining was observed in villus tip enterocytes of the small intestine and was most prominent in the duode nal portion. These results support our original hypothesis that LCRF may be released spontaneously into the small intestinal lumen from the villus tip enterocytes and its intraluminal degradation by proteases regulates CCK re lease. Furthermore, LCRF release was not subject to cholinergic regulation.