A radioimmunoassay of plasma 18-hydroxy-11-deoxycorticosterone

A radioimmunoassay for the measurement of plasma 18-hydroxy-11-deoxycorticosterone (18-OH-DOC) has been developed. The antiserum for 18-OH-DOC was produced in rabbits immunized with 18-OH-DOC-3-(0-carboxymethyl) oxime-bovine serum albumin. This antiserum was used at a final dilution of 1:40,000 and the main cross reactants were aldosterone at 29.4%, 18-hydroxy-corticosterone at 4.9% and 11-deoxycorticosterone at 3.6%. Silica gel column chromatography (7 X 30 mm, toluene saturated with propylene glycol: dichloromethane, 95:5) and Sephadex LH-20 column chromatography (7 X 60 mm, benzene: methanol, 85:15) were employed for the separation of these cross reactants. The sensitivity was 10pg and the method blank was consistently negligible. The intra- and inter-assay precision was 11.3% and 14.8%, respectively.