STUDIES ON THE AROMATISATION OF NEUTRAL STEROIDS IN PREGNANT WOMEN.

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Abstract
16[alpha]-Hydroxy-dehydro-epiandrosterone-7a-3H (16[alpha]HO-DHA), 16[alpha]-hydroxyandrostenedione-4-14c (16[alpha]HO-A) and 16[alpha]-hydroxy-testosterone-4-14C (16[alpha]HO-T) were synthesized. Human placentas were perfused in situ at midpreg-nancy with these steroids and the radioactive material recovered from the placentas and perfusates was analyzed. In order to compare the aromatisation of 16[alpha]-hydroxylated and 16-desoxy precursors, in a second series of perfusions 16[alpha]HO-DHA was combined with differently labelled dehydroepiandrosterone (DHA) and 16[alpha]HO-T with testosterone (T). Following the perfusion of 17aHO-DHA, both 16[alpha]HO-A and oestriol (OE3) were isolated from the placentas and perfusates. No labelled androst-5-ene-3[beta],16[alpha],17[beta]-triol ( 5-TRIOL) or 16[alpha]HO-T was detected in these sources. When 16[alpha]HO-A or 16[alpha]HO-T was perfused, OE3 was isolated from the placenta and perfusates. However, there was no interconversion between 16[alpha]HO-A and 16[alpha]HO-T. No oestro-genic ring D ketols were found in the placentas and perfusates in any of the experiments. The extent of aromatisation (judged from the amount of oestrogen isolated from the placenta and perfusate) was approximately the same following the perfusion of 16[alpha]HO-DHA, 16[alpha]HO-A, DHA and T, but was much lower when 16[alpha]HO-T was perfused. The low degree of aromatisation of 16[alpha]HO-T was associated with the presence of large amounts of unchanged 16[alpha]HO-T in the placentas as well as in the perfusates. The transfer of 16[alpha]HO-T to the maternal compartment was also much lower than that of the other precursors studied. It is concluded that a) the placental transfer and aromatization of 16[alpha]HO-T is much lower than those of other oestrogen precursors. This condition might lead to the accumulation of this compound in the placenta. b) The placental metabolism of A 5-TRIOL and 16[alpha]HO-DHA follow separate pathways with no interconversion until the stage of aromatisation, or possibly 19-hydroxylation.