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Objectives: The pathophysiology of acute pancreatitis is strongly associated with autoactivation of trypsin. The biologic activity of trypsin on cells is attributed to the activation of protease-activated receptor-2 (PAR-2). We hypothesize that trypsin may activate acinar cells or inflammatory cells through PAR-2 signals in acute pancreatitis., Methods: We immunochemically analyzed the expression of PAR-2 in the rat acinar cell line, ARIP, and the rat pancreas, using anti-rat PAR-2 cleavage site (PCS) and anti-rat PAR-2 N-terminal fragment (PNF) antibodies. Plasma levels of PNF were determined. Furthermore, the effects of the anti-rat PCS antibody and nafamostat mesylate, a potent trypsin inhibitor, on PAR-2 activation during acute pancreatitis were also analyzed., Results: ARIP cells expressed PAR-2, which was activated by exogenous trypsin activity. We also showed that PAR-2 is strongly expressed in pancreatic acinar and duct cells and that it is activated in rat cerulein-induced acute pancreatitis. The anti-rat PCS antibody and nafamostat mesylate reduced interleukin-6 and interferon gamma production and alleviated distant organ injury., Conclusions: These results suggest that trypsin and its specific receptor, PAR-2, play an important role in cytokine production and the resultant development of distant organ injury during rat acute pancreatitis.

Pancreaticobiliary diversion (PBD) and biliodigestive shunt (BDS) cause long-standing hypercholecystokininemia followed by pancreatic hyperplasia. These changes have been suggested to be due to the lack of intraluminal trypsin and bile, respectively, in the upper small intestine. The aim of these experiments was to study the effect of restoration of intraluminal trypsin and bile on plasma levels of cholecystokinin (CCK) and the changes found in exocrine and endocrine pancreas after PBD and BDS. Male Sprague-Dawley rats were used. PBD was done in 16 rats, eight of which had trypsin dissolved in 50 mM sodium bicarbonate (SB), and eight had SB only by gastric intubation twice daily. BDS was done in another 16 rats, eight of which had bile dissolved in SB, and eight had SB in a similar manner. Sham-operated rats had SB and served as controls. After 4 weeks, the rats were killed, and the concentrations of circulating CCK, gastrin, glucose, glucagon, and insulin were determined. The pancreas was removed, weighed, and analyzed for contents of water, protein, and DNA. In another study, PBD-operated rats got trypsin in varying dosages or trypsin and taurocholate in combination for 2 weeks before death. The concentrations of plasma CCK and glucagon were elevated after both PBD and BDS. PBD decreased the concentration of gastrin in plasma. PBD caused an increase of pancreatic weight and the contents of protein and DNA. Trypsin substitution to PBD-operated rats did not affect plasma CCK or glucagon levels, but the PBD-induced increases in weight and DNA content were counteracted by trypsin. Higher dosages of trypsin did not further influence the effects seen after PBD. Pancreatic weight and DNA content were increased after BDS. Bile administration completely abolished the increase in plasma CCK and glucagon, as well as the gain in pancreatic weight, and reduced the increase in pancreatic DNA. Substitution with bile to BDS-operated rats abolished the increase in the plasma levels of CCK and glucagon, as well as the trophic effects on the pancreas. Trypsin substitution to PBD-operated rats partly reversed the trophic effects on the pancreas but not the hormonal changes in plasma. Thus the trophic effects on the pancreas exerted by BDS seem to be dependent on the lack of bile in the upper small intestine, whereas the effects of PBD only partly are a consequence of the absence of intraluminal trypsin.

The basal exocrine secretion of the pancreas is maintained at a constant level in conscious rats. We examined the changes in basal secretion with respect to the effect of various time periods of pancreatic duct occlusion (PDL). Male Wistar rats were prepared with cannulae that separately drained bile and pancreatic juice as well as with a duodenal cannula. Rats were placed in restraint cages, and experiments were conducted without anesthesia 4 days after the operation. Cholecystokinin (CCK) release was artificially prevented by the continuous infusion of bile with trypsin into the duodenal lumen throughout the experimental period to avoid the modification of pancreatic response by CCK. After 2-h basal collection, a pancreatic secretion was interrupted for 0.5-4 h, and then the collection of pancreatic juice was initiated again for an additional 2-4.5 h. The pancreatic secretion after the reopening of the 0.5-to 3-h PDL was comparable to basal secretion levels. However, protein secretion was significantly inhibited after the removal of 4-h PDL. Both vagotomy and capsaicin treatment abolished this inhibition, and the protein secretion after 1-h PDL in vagotomized rats increased 1.5-fold high compared with the basal value. These observations indicate that protein secretion was ceased during PDL via vagal nerve, and this may be a self-protective mechanism.

The influences of (a) intraluminal bile deficiency due to common bile duct obstruction and (b) intraduodenal administration of pooled own bile and bovine trypsin on the plasma cholecystokinin (CCK) response to oral fat (Lipomul) ingestion were investigated in seven patients with periampullary tumors and 10 healthy volunteers. Basal and fat-stimulated plasma CCK levels in the patients were significantly higher than in the normal controls. Intraduodenal administration of pooled own bile at a rate of 100 ml/h significantly suppressed both basal and fat-stimulated CCK secretion. Simultaneous administration of pooled own bile (100 ml/hr) and bovine trypsin (600 mg/hr) caused further significant suppression of fat-stimulated CCK secretion compared with that under bile infusion alone. These results indicate that both intraluminal bile and trypsin exert a negative feedback effect on the release of CCK in humans.