Radioimmunoassay of secretin in plasma.

A sensitive and specific radioimmunoassay for secretin has been developed. 125I synthetic porcine secretin was used as label. Antibodies were raised against synthetic pocrine secretin. Pure natural porcine secretin was used as standard and free and bound hormone was separated by plasma-coated charcoal. Nonspecific interference with the assay system by plasma factors was abolished by extraction of plasma samples. The detection limit was 1.3 pmol/l. Within and between assay reproducibility (five triplicate determinations in each of eight assays) was 0.7 and 0.9 pmol/l respectivel (1 SD) at a concentration of 4.7 pmol/1. Fasting level in seventy normal persons ranged from less than 1.3 to 5.3 pmol/1. High concentrations were found in two patients with Zollinger-Ellison syndrome. In six normal persons intraduodenal acidification was immediately followed by an increase in secretin concentrations in peripheral venous blood to 7.7-23.6 pmol/1 (range), with a median of 15.5 pmol/1. In six anaesthetized pigs a fifty-fold increase in portal plasma secretin concentration after duodenal acidification was followed by a thirty-fold increased in the flow rate of pancreatic juice.