Radioimmunoassay of Gastric Inhibitory Polypeptide

Abstract

A radioimmunoassay for the measurement of gastric inhibitory polypeptide (GIP) in unextracted plasma in man was developed using a rabbit antiserum raised against porcine GIP. Porcine GIP was employed also as standard and to produce a 125I-labeled tracer. The assay was able to distinguish 110 pg/ml GIP from zero in plasma samples. Negligible cross-reactivity was demonstrated with cholecystokinin, insulin, pancreatic polypeptide, glucagon, secretin and vasoactive intestinal polypeptide. The mean overnight fasting plasma GIP level in 28 normal subjects was 203 pg/ml (range: undetectable-420 pg/ml). Plasma GIP levels rose, within 45 min of eating a mixed meal, to a mean level of 1573 pg/ml.