Radioimmunoassay for secretin using N.ALPHA.-tyrosylsecretin and (Tyr1)-secretin.

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Abstract
A sensitive radioimmunoassay for secretin was developed by using synthetic preparation of porcine secretin and 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, N.alpha.-tyrosylsecretin or [Tyr1]-secretin, both of which had almost identical immunoreactivities with that of secretin. 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 5-10 pg/tube. Human duodenum extract with hot H2O 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 250 pg/ml by intraduodenal infusion of HCl and to 800-1000 pg/ml by i.v. injection of 1 cu/kg of Boots natural secretin.