Effects of a protein meal, intraduodenal HCl, and oleic acid on portal and peripheral venous secretin and on pancreatic bicarbonate secretion.

We have studied the effect of a protein meal on secretin (IRS) concentration in dogs and humans using a radioimmunoassay of improved sensitivity (8 pg/ml). After a meal, pancreatic bicarbonate secretion (PBS) increased markedly and proximal duodenal pH decreased from 6.2 to 4.3. Portal and peripheral IRS concentrations, however, remained unchanged in eight dogs and five patients with cirrhosis of the liver. Similarly, an alkaline solution of sodium oleate (pH 9.2) stimulated PBS but not IRS. Intraduodenal administration of various amounts of HCl in dogs demonstrated that acid-stimulated PBS was invariably accompanied by rises in peripheral venous IRS concentration. We conclude that the postprandial stimulation of PBS involves mechanisms more complex than acid-stimulated secretin release.