The action of the C-terminal octapeptide of cholecystokinin and related peptides on pancreatic exocrine secretion.

The effect of the C-terminal octapeptide of cholecystokinin-pancreozymin (CCK-PZ), caerulein, and the C-terminal tetrapeptide of gastrin on pancreatic secretion of fluid, electrolyte, amylase, and protein was studied in anaesthetized dogs prepared with pancreatic fistulae. Against background stimulation of fluid secretion with submaximal doses of secretin, all the polypeptides produced a qualitatively similar pancreatic response, causing a highly significant increase in amylase, protein, calcium, and zinc concentrations. Magnesium concentration was significantly increased only when the concentration preceding the administration of the peptide was below 100 mu-equiv/l. Octa-CCK-PZ was 13-35 times and 20-56 times more potent than tetragastrin on weight and molar bases, respectively, as a stimulant of amylase secretion. The threshold doses were largest for amylase, lower for calcium, and lowest for zinc. A significant linear correlation was observed between amylase and calcium concentration, zinc and protein concentration, and magnesium and calcium concentration. The peptides produced some increase in secretin-induced volume flow, whereas bicarbonate, chloride, sodium, and potassium concentrations remained unchanged. The direct relation between bicarbonate concentration and flow rate was limited to rates below 1.5 ml/5 minutes. At higher rates bicarbonate and chloride concentration reached a high and low plateau, respectively, although the first five-min sample of pancreatic juice after secretin stimulation exhibited a relatively low bicarbonate and high chloride concentration compared with its voluminous flow. Chloride concentration varied inversely with bicarbonate concentration, the sum of the two anions being constant.