Plasma secretion and pancreatic secretion in response to liver extract meal with varied pH and exogenous secretin in the dog.

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Abstract
In dogs with chronic gastric and pancreatic fistulas, a liver extract meal adjusted to various pH levels ranging from 7.0-2.0 was introduced into the stomach and the increments in plasma secretin levels were correlated with the pH of the liver extract meal and pancreatic bicarbonate outputs. The pH threshold for both bicarbonate secretion and secretin release was .apprx. 4.5. With a stepwise decrease in the pH of the meal below pH 4.5, there were stepwise increments in the plasma secretin concentrations and pancreatic bicarbonate outputs. Exogenous secretin, given in graded doses ranging from 0.03-2.0 clinical U/kg per h, increased the plasma secretin concentrations and bicarbonate secretion in a dose-dependent fashion. The pH threshold for release of endogenous secretin is apparently 4.5. At pH levels below 4.5, pancreatic bicarbonate secretion probably depends upon the duodenal acid load and may be linearly correlated to an increment in plasma secretin concentrations. Endogenous secretin is a major determinant of pancreatic bicarbonate secretion after a meal. Pancreatic protein secretion by intragastric liver extract meal was greatly increased both in experiments with liver extract meal, pH 4.0 or below, and in i.v. infusion of secretin at a dose of 0.12 U/kg per h. It is questioned, however, whether this effect of secretion is physiological.