Analysis of the mechanism of action of calcium-induced exocrine pancreatic secretory changes in the dog

In conscious dogs, provided with gastric and duodenal fistulas (Thomas cannula), the effect of an acute i.v. calcium infusion (10 mg./kg./hr.) on the plateau levels of secretin-induced (GIH, 1 CU./kg./hr.) pancreatic juice parameters were analyzed without or with previous cholingergic blockade by a continuous atropine perfusion (1.5 mg./hr.). In the former condition, i.v. calcium raised all pancreatic juice parameters, mainly protein concentration (148%) and output (173%). During atropine blockade, i.v. calcium changed neither flow rate nor bicarbonate output of secretin-induced pancreatic secretion. On the other hand, i.v. calcium exerted a reduced but still evident effect on protein concentration (85%) and output (40%). Intravenous calcium enhances secretin-induced pancreatic secretion plateau values through two mechanisms, mainly by raising the cholinergic tone of the whole "pancreon" and, partially, through a direct stimulus-secretion coupling effect on the acinar cells. Acute hypercalcemia induces the formation of protein plugs in the pancreatic secretion. They are excreted in the course of many days in both basal and secretin-stimulated pancreatic juice.