Characteristics of secretin-stimulated pancreatic secretion in dogs.

The effect of the periodic interdigestive activity of the gut on secretin-stimulated pancreatic secretion was studied in eight conscious dogs each with a Thomas duodenal fistula, a gastric fistula and a Heidenhain pouch. Pancreatic water and bicarbonate responses to a small dose of secretin were greatly augmented in phase with the spontaneous periodic activity of the gut. This augmentation was closely related to pancreatic protein secretion. As the dose of secretin was increased the interval between peaks was prolonged, the peaks became less sharp, the nadirs were raised, and finally the periodic activity was no longer seen. Bilateral cervical vagal blockade with local anaesthetics reduced the secretin-stimulated bicarbonate secretion by 50% but the augmentation at the peak was not abolished. Atropine abolished the periodic augmentation completely and reduced the bicarbonate response by 80%. The peak response of volume and bicarbonate to secretin obeyed Michaelis-Menten kinetics. The nadir secretin dose response, however, was a sigmoid curve with a Hill coefficient larger than one. The action of atropine or hexamethonium was to shift the peak response kinetics to the nadir kinetics. It is concluded that the pancreatic response to secretin is greatly modulated by the spontaneous periodic activity of nerves.