Biosynthesis of oestrogens and their inter-conversion in human placentae from normal and toxaemic pregnancies

In vitro biosynthesis of oestrogens in microsomal and 10,000 g supernatant fractions of placentae, ten each, from normal and toxaemic pregnancies has been investigated. Dehydroepiandrosterone sulphate (DHAS), dehydroepiandrosterone (DHA) and androstenedione were used as substrates and their conversion to oestrone and oestradiol studied. In all the placental preparations the relative efficiency of the conversion of these androgens to oestrogens, though differing greatly between subcellular fractions as well as between normal and toxaemic placentae, was invariably in the order of DHAS greater than DHA greater than androstenedione. The conversion of these androgen precursors to oestrone and oestradiol was reduced in toxaemia compared with the normal placenta. Moreover, formation of oestradiol was much more reduced than that of oestrone. The free oestradiol level in the serum was also found to be lower in toxaemic pregnancies as compared with the normal range. The inter-conversions of oestrogens further showed a significantly reduced conversion of oestrone to oestradiol in toxaemic placentae compared with normal placentae. The results may explain the lowered blood oestradiol levels observed in toxaemia of pregnancy and thus provide an explanation of the usefulness of the estimation of the oestradiol level as an index of feto-placental function.