Effects of calcitonin on dopamine-, secretin- and pancreozymin-induced pancreatic secretion were investigated in the isolated blood-perfused canine pancreas. 2. The volume of pancreatic secretion induced by pancreozymin given intra-arterially (i.a.) was decreased by an i.a. infusion of 1 u/min of calcitonin, but that induced by dopamine or secretin given i.a. was not affected by calcitonin treatment. 3. Amylase concentration in pancreatic juice either in spontaneous secretion in the resting state or in that of stimulated secretion by pancreozymin was decreased approximately 30% by calcitonin treatment, but amylase concentration in pancreatic juice induced by dopamine or secretin was not affected by calcitonin treatment. 4. Calcitonin had no effect on bicarbonate concentration in pancreatic juice stimulated by these secretagogues. 5. Calcium concentration in pancreatic juice in the resting state was reduced about 36% by calcitonin treatment. Calcitonin caused a decrease in a calcium concentration in the pancreozymin-induced secretion, but did not cause any change in the dopamine- or secretin-induced one. 6. These results suggest that calcitonin may affect the secretory mechanism of the acinar cells but not that of the ductular cells, and that the acinar cells are active even in the resting state.
