BOTH FREE AND COMPLEXED TRYPSIN-INHIBITORS STIMULATE PANCREATIC-SECRETION AND CHANGE DUODENAL ENZYME LEVELS

Secretion of pancreatic digestive enzymes was measured in pancreatic c annulated rats after duodenal stimulation with Kunitz or Bowman-Birk p rotease inhibitors or their complexes with trypsin and/or chymotrypsin . Free and complexed inhibitors were bound by the duodenal epithelium, stimulated the discharge of cholecystokinin, and significantly increa sed secretion rates of alpha-amylase, trypsinogen, and chymotrypsinoge n. Inasmuch as secretion rates returned to basal levels with cholecyst okinin-A receptor antagonists, the stimulation was likely to be mediat ed by cholecystokinin. Soya factors also influenced the duodenal conce ntration of pancreatic enzymes under simulated feeding conditions. Thu s the level of oc-amylase increased while the trypsin concentration de creased in rats gavaged with free or complexed inhibitors. The same wa s true for chymotrypsin when the Bowman-Birk inhibitor was used, but t he Kunitz inhibitor and its trypsin complex actually raised the lumina l concentration of chymotrypsin. Accordingly, because soya inhibitors remained effective in stimulating pancreatic secretion after eliminati on of their inhibitory activity by complex formation, it is questionab le whether the signal for cholecystokinin secretion was solely due to lowering of duodenal protease levels.