Coupling between Steroid Oxidoreductions in vivo. Deuterium Transfer from [17α²‐²H]Estradiol to C₁₉ Steroids

Abstract

Female rats were given [17α‐2H]estradiol, either free intraperitoneally or as the 3‐sulphate in intravenous infusion. Metabolites of reducible steroids were isolated from the steroid disulphate fraction obtained from bile, and the deuterium content was analyzed by gas chromatography – mass spectrometry. Deuterium was transferred to the D‐ring of the 17β‐hydroxysteroid formed from intraperitoneally administered 3α‐hydroxy‐5α‐androstan‐17‐one or 3β‐hydroxy‐5α‐androstan‐l7‐one or 5α‐ androstane‐3,17‐dione. The 5α‐androstane‐3β,17β‐diol contained more deuterium (37 – 52% of the estradiol 2H excess) when formed from 3α‐hydroxy‐5α‐androstan‐17‐one than when it was formed from 3β‐hydroxy‐5α‐androstan‐17‐one or 5α‐androstane‐3,17‐dione (7–11% and 12–19%, respectively, of the estradiol 2H excess). Deuterium was also incorporated in the D‐ring of 5α‐androstane‐3β, 17β‐diol formed from 17β‐hydroxy‐4‐androsten‐3‐one, indicating oxidoreduction of the oxygen function at C‐17. No deuterium was found in this metabolite when the 17‐sulphate was administered. Deuterium from [17α‐2H]estradiol 3‐sulphate was incorporated in the steroid diols formed from the intravenously administered 3‐sulphates of 3α‐hydroxy‐ and 3β‐hydroxy‐5α‐androstan‐17‐one. The deuterium content in these steroids diols was 11–45% of the estradiol 2H excess. The results are consistent with an interaction between estradiol metabolism and oxidoreduction of C19 steroids mediated by a common 17β‐hydroxysteroid: NAD(P) oxidoreductase. The transfer of deuterium might thus be due to a slow dissociation of the enzyme‐reduced coenzyme complex. compared to the dissociation and association of the substrates. The difference in degree of transfer to the 17α‐position of 3α‐hydroxy and 3β‐hydroxy steroids is probably explained by the presence of at least two 17β‐hydroxysteroid: NAD(P) oxidoreductases, differing in specificity and kinetic parameters.