SECRETIN POTENTIATES GUINEA-PIG PANCREATIC RESPONSE TO CHOLECYSTOKININ BY A CHOLINERGIC MECHANISM

The effects of secretin and cholecystokinin on exocrine pancreas secre tion in the guinea pig were investigated. The putative potentiating ef fect of these two hormones was studied in various settings to elucidat e the effect of cholinergic stimuli in such interaction. In anesthetiz ed guinea pig, intravenous infusion of cholecystokinin (0.75 pmol . kg (-1). min(-1)) or secretin (0.5 pmol . kg(-1). min(-1)) resulted in a marked and rapid increase of pancreatic juice flow and protein output. When cholecystokinin was combined with secretin, there was a signific ant increase in pancreatic secretion, compared with cholecystokinin al one. This increase in pancreatic juice secretion and protein output wa s significantly suppressed by the prior administration of 100 mu g/kg atropine. Similar results were obtained when trypsinogen release from pancreatic segments was measured in response to cholecystokinin (32 nM - 32 pM) and (or) secretin (1 mu M - 32 nM). When we assayed the horm onal interaction on amylase release from dispersed pancreatic acini, w e found that secretin (32 nM) failed to influence the secretory respon se to cholecystokinin (1 pM - 10 nM). Thus we conclude that a combinat ion of cholecystokinin and secretin resulted in a marked potentiation of the secretory responses in the exocrine guinea pig pancreas by a me chanism that involves cholinergic interactions present at the tissue l evel but not at the dispersed secretory cell level.