Trypsin as a regulator of pancreatic secretion in the rat.

The effect of intraduodenally administered trypsin on pancreatic exocrine secretion was investigated in conscious rats surgically prepared with bile--pancreatic fistulae. Introduction of NaHCO3 into the duodenum did not influence pancreatic secretion. Reintroduction of bile--pancreatic juice into the duodenum, however, suppressed pancreatic protein output, mainly because of changes in protein concentration. Infusion of trypsin into the duodenum in the absence of intraluminal pancreatic juice significantly suppressed the secretory volume and pancreatic enzyme output; addition of trypsin inhibitor to the trypsin infusion resulted in an immediate increase of pancreatic secretion. Trypsin inhibitor per se, however, was without effect. Bile--pancreatic juice affected amylase, kipase, and trypsinogen output in a parallel fashion; after addition of trypsin inhibitor to the infusion the inhibitory effects on pancreatic enzyme output was reversed in a parallel manner. The results support the hypothesis that pancreatic exocrine secretion is regulated by a feedback mechanism exerted--at least partly--by intraluminal trypsin.