Radioimmunoassay for Secretin Using Nα-Tyrosylsecretin and [Tyr1]-Secretin

Sensitive radioimmunoassay for secretin was developed by using synthetic preparation of porcine secretin and its related analogs. The secretin-specific antisera with titers ranging 1: 20, 000-1: 150, 000 were generated in rabbits against highly purified synthetic secretin. The labeled antigen was prepared by radioiodinating by the chloramine-T method synthetic secretin analog, Nα-tyrosylsecretin or [Tyr1]-secretin, both of which were proved to have almost identical immunoreactivities with that of secretin itself. The immunoassay was performed by the double-antibody method using synthetic secretin as standard. The lowest detectable amount of secretin in the present assays was 5-10pg/tube. Human duodenum extract with hot water contained secretin or secretin-like material that shows a parallel displacement curve to the standard in the immunoassay system used. Serum levels of secretin immunoreactivity in man rose up to 250pg/ml by intraduodenal infusion of HC1 and to 800-1, 000pg/ml by i. v. injection of 1 cu/kg of Boots natural secretin.