HIGHLY SPECIFIC I-125-RADIOIMMUNOASSAY FOR CHOLIC-ACID CONJUGATES

Several modifications of the immunization procedure permitted development of a highly specific radioimmunoassay (RIA) for cholic acid conjugates. Antiserum was produced in guinea pigs using cholic acid-thyroglobulin complex as immunogen. 125 I-Cholylglycylhistamine was prepared as radioactive ligand according to a modification of the method of Spenney et al. (Spenney J.G., Johnson B.J., Hirschowitz B.I., Mihas A.A. and Gibson R. (1977) Gastroenterology 72, 305-311). The association constant of the antisera to taurocholic acid was 1.8 × 107 l/mol, the working range of the assay between 9.5-890 pmol. Cross-reactivities of the antiserum to bile acids other than cholic acid species were less than 3%, which is lower than for any published bile acid RIA. Concentrations of cholic acid conjugates in sera obtained from 17 healthy fasting volunteers ranged from 0.4-1.9 μmol/l. © 1979.