The effect of atropine (100 micrograms/kg/h, i.v.) on plasma cholecystokinin and pancreatic secretion during diversion of bile and pancreatic juice from the intestine was studied in 8 conscious rats equipped with jugular vein, pancreatic, biliary, and duodenal cannulas, and with pyloric ligation and gastric drainage. Diversion of bile and pancreatic juice to the exterior for 4 h significantly increased pancreatic protein and fluid secretion. Atropine delayed the pancreatic response to diversion, but during 4 h of diversion, neither total nor incremental pancreatic protein or fluid secretion was inhibited by atropine. Plasma cholecystokinin levels were elevated after diverting bile and pancreatic juice and were not significantly reduced by atropine (23.0 +/- 6.6 pM vs. 16.0 +/- 3.9 pM at 1.5 h and 17.3 +/- 5.4 pM vs. 13.1 +/- 2.9 pM at 4 h after bile and pancreatic juice diversion; atropine-treated vs. controls, respectively). These results indicate that cholinergic nerves play no important role in feedback regulation of cholecystokinin release and that the previously reported suppressive effect of atropine on the pancreatic response to diversion of bile and pancreatic juice from the intestine was secondary to inhibition of gastric secretion.