Potentiating effect of secretin on cholecystokinin-stimulated pancreatic secretion in dogs

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Abstract
A possible potentiating effect of cholecystokinin octapeptide (CCK-OP) on the action of secretin on exocrine pancreatic secretion was studied in 5 dogs with gastric fistulas and modified Herrera pancreatic fistulas. Secretin in a dose, 2.45 pmol (0.03 clinical units) .cntdot. kg-1 .cntdot. h-1, that mimics the plasma secretin level in the postprandial state increased pancreatic bicarbonate secretion, but the increase was not statistically significant. CCK-OP in graded doses, 26.2, 52.5, 109 and 219 pmol (0.03, 0.06, 0.125 and 0.25 .mu.g) .cntdot. kg-1 .cntdot. h-1, given i.v. produced a significant increase in both bicarbonate and protein secretion and the increase was dose related. The plasma concentrations of immunoreactive CCK during i.v. infusion of CCK-OP in doses of 26.2 and 52.5 pmol .cntdot. kg-1 .cntdot. h-1 were found to mimic the postprandial plasma concentrations of immunoreactive CCK in 8 dogs. When CCK-OP in 4 graded doses was added to i.v. infusion of secretin, 2.45 pmol .cntdot. kg-1 .cntdot. h-1, the actual bicarbonate output at each dose level of CCK-OP was greater than the sum of the bicarbonate outputs produced by secretin alone and CCK-OP alone in a corresponding dose. Evidently, the action of secretin in a physiological dose that mimics the plasma level of secretin after a meal is potentiated by CCK-OP in a dose range that produces a plasma CCK-OP level comparable with that in the postprandial state and vice versa. Like secretin, CCK-OP is another necessary agent for pancreatic secretion of bicarbonate during digestion. Although CCK-OP produced a dose-related increase in the protein output, the stimulating effect of CCK-OP on the protein output could not be potentiated by secretin in the dose employed.