Radioimmunoassay of Secretin in Human Plasma

Abstract

A radioimmunoassay is presented which employs ¹²⁵I-Iabelled synthetic secretin, antibody against synthetic secretin, and standards prepared from pure natural porcine secretin. Secretin to be measured was extracted into methanol from heparinized plasma containing aprotinin, which together with cysteine hydrochloride was used as stabilizer throughout the assay. With polyethylene glycol separation, a within assay precision of 10% at 17 pmol/l was found. The between assay precision was 15% at 17 pmol/l and the limit of detection 2.5 pmol/l plasma. Accuracy was 70-85%. The immunoreactive secretin levels in human plasma increased from 4.5 ± 0.5 pmol/l (mean ± S.E.M.) to 19.5 ± 7.5 pmol/l (mean ± S.E.M.) after duodenal acidification (n=5). Pancreatic flow rate increased from 0.5 ± 0.1 ml/min (mean ± S.E.M.) to 4.8 ± 0.5 ml/min (mean ± S.E.M.), and bicarbonate output from 9.6 ± 1.8 μmol/min (mean ± S.E.M.) to 268 ± 51 μmol/min (mean ± S.E.M.) after duodenal acidification.