A combined radioimmunoassay for the measurement of unconjugated and sulfoconjugated pregnenolone, 17 hydroxypregnenolone, dehydroepiandrosterone, and estrone applied to fetal and maternal ovine plasma

This report describes a radioimmunoassay (RIA) method for the combined measurement of four steroid sulfoconjugates and their four unconjugated counterparts in maternal and fetal ovine plasma: pregnenolone (Δ 5P), 17-hydroxypregnenolone (17Δ 5P), dehydroepiandrosterone (DHEA), and estrone (E 1). In the procedure a preliminary ether extraction is utilized to isolate the unconjugated steroids followed by salting out, ethyl acetate extraction, and mineral acid solvolysis of the remaining sulfated steroids. The hydrolyzed sulfoconjugates are then separated chromatographically and measured in a manner identical to their unconjugated counterparts. The combined measurement of these eight steroids in single samples of fetal and maternal ovine plasma has not been reported previously, and plasma concentrations of these steroids were heretofore unknown. Since no previous data was available for comparison, rigorous specificity evaluation of this RIA system was required prior to its use for physiologic studies and the reporting of concentrations in this species.