Plasma secretin concentration and pancreatic exocrine secretion after intravenous secretin or intraduodenal HC1 in anaesthetized pigs.

The concentration of immunoreactive secretin in arterial blood and the exocrine pancreatic secretion were measured during intraportal infusion of secretin in doses of 0.03, 0.06, 0.1 and 3.0 clinical units kg-1 h-1, and during intraduodenal instillation of 50 ml 0.1 mol 1(-1) HC1. The lowest dose of exogenous secretin to significantly increase secretin concentration in blood was 0.03 clinical units kg-1 h-1, which was a subthreshold dose of exocrin pancreatic secretion. A linear relation was found between the dose secretin and the secretin concentrations measured. On the basis of secretin concentrations, release of secretin during instillation of HC1 was estimated to be 0.22 clinical units kg-1 h-1. Maximum pancreatic bicarbonate secretion was obtained with a dose of 1.0 clinical units kg-1 h-1, and the minimal effective dose was between 0.06 and 0.1 clinical units kg-1 h-1. On the basis of the flow rate of pancreatic juice and the pancreatic bicarbonate output, secretin during instillation of HC1 was estimated to be 0.3 clinical unit kg-1 h-1. It is concluded that the radioimmunoassay used has the sensitivity and accuracy necessary for measurements of secretin concentrations in plasma during physiological conditions.