Preparation of 125I-labeled gastric inhibitory polypeptide, using water-insoluble 1,2,4,6-tetrachloro-3 alpha,6 alpha-diphenylglycoluril (Iodo-gen) as the oxidizing agent.
The preparation and evaluation of a 125I-labeled gastric inhibitory polypeptide (GIP) by means of a modified Iodo-gen method are described. The portal vein fasting plasma GIP concentration was determined in 6 groups of rats with 10 rats in each group. In three of the groups, three separately prepared Iodo-gen tracers were used in the radioimmunoassay, and in the three other groups three separately prepared chloramine-T tracers were used. The mean fasting portal vein plasma GIP concentrations in the three groups were 45.0 +/- 5.0, 41.9 +/- 3.9, and 39.6 +/- 2.7 pmol/l, respectively, with the Iodo-gen tracers and 80.3 +/- 4.6, 78.4 +/- 5.4, and 85.7 +/- 3.7 pmol/l with the chloramine-T tracers. The values obtained in each of the groups with the Iodo-gen tracers were significantly lower than those obtained in each of the groups with the chloramine-T tracers. This may be due to a better preserved immunoreactivity of the Iodo-gen tracer than of the chloramine-T tracer. The explanation of this may be the water insolubility of Iodo-gen, which may prevent oxidation of easily oxidized residues of the peptide during the radioiodination procedure.
D000818:Animals; D002700:Chloramines; D005215:Fasting; D005749:Gastric Inhibitory Polypeptide / Q000097:blood*; D005768:Gastrointestinal Hormones / Q000097:blood*; D007457:Iodine Radioisotopes; D008297:Male; D010084:Oxidation-Reduction; D011863:Radioimmunoassay; D051381:Rats; D014508:Urea / Q000031:analogs & derivatives*
D002700:Chloramines; D005768:Gastrointestinal Hormones; D007457:Iodine Radioisotopes; C012385:1,3,4,6-tetrachloro-3 alpha,6 alpha-diphenylglycoluril; D005749:Gastric Inhibitory Polypeptide; D014508:Urea