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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 pg 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 mllrnin). 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.

The effects of endogenous cholecystokinin (CCK) on insulin and pancreatic exocrine secretion were examined in conscious rats. Rats with bile and pancreatic fistulae, one duodenal cannula, and two jugular vein cannulae were divided into four groups, with and without glucose infusion (0.2 g/(ml.h)), and with bile and pancreatic juice (BPJ) diversion and return. Without glucose infusion, BPJ diversion did not have any significant effect on the plasma level of insulin or glucose; but with glucose infusion, it caused a significant increase in plasma insulin concentration 1 h after the diversion. The plasma glucose concentrations in the groups with BPJ diversion and return were not significantly different, and the response of pancreatic exocrine secretion to BPJ diversion was suppressed slightly, but not significantly, by glucose infusion. The plasma CCK concentration was increased significantly by BPJ diversion, but not affected by glucose infusion. These results indicate that, as observed in in vitro experiments with exogenous CCK, in conscious rats, endogenous CCK stimulates both exocrine and endocrine secretion of the pancreas, and that hyperglycemia is necessary for these effects to become apparent.