EFFECT OF TAUROCHOLATE ON CCK RELEASE AND PANCREATIC-SECRETION PRODUCED BY 2 CCK-RELEASING PEPTIDES IN CONSCIOUS RATS

The role of luminal bile salts (taurocholate) in regulation of rat pancreatic secretion was examined by studies on the effects of luminal stimulants on the pancreas during infusion of various concentrations of taurocholate into the duodenum of conscious rats. Rats with external bile and pancreatic fistulae were used. For 24 h before the experiment, pancreatic juice was excluded from the intestine but bile was continuously returned to the duodenum. From the beginning of the experiment, 8-200 mM of taurocholate was infused at a rate of 1 ml/h instead of returning the bile. Pancreatic juice was collected for a 2-h period and then 2-mu-g of pancreatic secretory trypsin inhibitor-61 (PSTI-61) (= monitor peptide) or partially purified putative CCK-releasing peptide from rat intestine (intestinal CCK-RP) was injected into the duodenum (1 ml/min). Continuous infusion of taurocholate maintained a constant rate of pancreatic secretion, except at a concentration of 8 mM, which resulted in a slight increase in pancreatic secretion. Both PSTI-61 and intestinal CCK-RP significantly increased pancreatic secretions during infusion of 20 or 40 mM taurocholate, but had no significant effect during infusion of 80 or 200 mM taurocholate. Therefore, higher concentrations of taurocholate in the intestine prevented the stimulatory effects of luminal stimulants, probably by preventing the latter from reaching CCK cells.