Stable isotope studies on steroid metabolism and kinetics: sulfates of 3 alpha-hydroxy-5 alpha-pregnane derivatives in human pregnancy

The metabolism and production rates of 3 alpha-hydroxy-5 alpha-pregnan-20-one sulfate and the 3-sulfate and 3,20-disulfate of 5 alpha-pregnane-3 alpha,20 alpha-diol in pregnant women were studied. The steroid sulfates were labeled with deuterium in the 3 beta,11,11- or 3 beta,11,11,20 beta-positions and were injected intravenously. The deuterium content of steroids in the monosulfate and disulfate fraction of plasma collected at different times after the injection was determined by capillary column gas chromatography/mass spectrometry. The injected steroid sulfates underwent oxidoreduction at C-20 and 16 alpha-hydroxylation. In addition, the 3-sulfate of 5 alpha-pregnane-3 alpha,20 alpha-diol became hydroxylated at C-21. The pregnanediol and pregnanetriol monosulfates were also converted to disulfates. No evidence was obtained for a metabolic sequence involving hydrolysis, oxidoreduction, and resulfation at the C-3 position. Production rates and rates of metabolic transformations were determined using different one- and two-pool models. The production rate of the pregnanolone/pregnanediol monosulfate couple was 0.08 to 0.5 mmol/24 h, the variability probably depending both on individual factors and stage of pregnancy. The half-life time for oxidation and reduction at C-20 was 0.1 to 0.4 hours, reduction being the faster process. The half-life time for the turnover of the steroid skeleton was 1.3 to 3.3 hours. The injected steroid monosulfates were 16 alpha-hydroxylated at a rate of 1 to 8 mumol/24 h. A significant fraction of these 16 alpha-hydroxylated steroid sulfates, 0.5 to 25 mumol/24 h, was formed from other, probably unconjugated, precursors. The 16 alpha-hydroxylated steroid monosulfates underwent rapid oxidoreduction at C-20. The 3-sulfate of 5 alpha-pregnane-3 alpha,20 alpha-diol was hydroxylated at C-21. The production rate of 5 alpha-pregnane-3 alpha,20 alpha,21-triol 3-sulfate was 8 to 36 mumol/24 h in four women and 180 mumol/24 h in one woman, and this steroid was not formed from other precursors to a significant extent. 5 alpha-Pregnane-3 alpha,20 alpha-diol disulfate was a metabolic end product accounting for a major part of the elimination of the steroids injected. Its half-life time was 1.4 to 2.8 hours. The results show that the formation of sulfated steroids with a 3 alpha-hydroxy-5 alpha configuration may account for 50% of the metabolism of progesterone in late pregnancy.