Immunoassay of 7-hydroxysteroids: 2. Radioimmunoassay of 7α-hydroxy-dehydroepiandrosterone

Abstract

High sensitivity radioimmunoassay of 3β,7α-dihydroxy-5-androsten-17-one (7α-OH-DHEA) has been developed and evaluated. The method is based on polyclonal rabbit antisera raised against 19- O-(carboxymethyl)oxime bovine serum albumin conjugate and bridge- and position homologous [ 125I]iodotyrosine methyl ester as a tracer. Sensitivity of the assay amounted to 3.12 fmol (0.95 pg)/tube, precision as a mean intra- and interassay coefficient of variation was 7.1 and 10.6%, respectively, and the average recovery of the analyte added to steroid-free serum was 110%. Out of the steroids occurring in human serum which may interfere with the assay, the only important cross-reactants were dehydroepiandrosterone and 3β,7β-dihydroxy-5-androsten-17-one (7β-OH-DHEA) with cross-reactivities of 1.95 and 1.16%, respectively. The levels of free (unconjugated) 7α-OH-DHEA have been determined in 29 sera from healthy volunteers (23 females and 6 males), and from 48 patients (43 females and 5 males) in which dehydroepiandrosterone and its sulfate (DHEA/S) had been measured for various endocrinopathies. The levels in healthy subjects ranged from 0.21 to 6.57 (mean 2.33±1.50) nM, while those of the patients from 0 to 5.99 (mean 1.46±1.52) nM. The levels of 7α-OH-DHEA in patients significantly correlated with those of DHEA and its sulfate.