Stimulatory effect of an endogenous peptide in rat pancreatic juice on pancreatic enzyme secretion in the presence of atropine: evidence for different mode of action of stimulation from exogenous trypsin inhibitors.

A new factor which activated the secretion of pancreatic enzymes was discovered and purified from rat bile-pancreatic juice. A fraction below M.W.10,000 of rat bile-pancreatic juice enhanced trypsinogen secretion by injection into anesthetized rat duodenum. The factor was purified from this fraction using its biological activity as an index by Sephadex G-50, SP Sephadex C-50 and HPLC. This factor was a peptide of which molecular weight was about 6,000 and had trypsin inhibitory activity. From these and some other findings, it was suggested that the peptide was identical with the "Kazal type" inhibitor. In the anesthetized and atropine-treated rat, of which intestinal trypsin was removed by thoroughly washing with saline containing 5 microM soybean trypsin inhibitor (SBTI), pancreatic secretion became basal state, and was not stimulated by injection of SBTI into its duodenum any longer. Under this condition, however, injection of this purified peptide brought about markedly stimulation of pancreatic enzyme secretion. These results suggest that this peptide has a certain function which enhances pancreatic enzyme secretion by the different manner from exogenous trypsin inhibitors such as SBTI.