Metabolism of retrotestosterone and testosterone by midterm human placentas perfused in situ

Abstract Two human placentas in mid-pregnancy were perfused in situ with a combination of 3 H-labelled retrotestosterone and 14 C-labelled testosterone. 14 C-labelled oestrone, 17β-oestradiol, androstenedione and testosterone and 3 H-labelled retrostestosterone and retroandrostenedione were isolated in a radio-chemically homogeneous form from the placentas and perfusates. Neither the oestrone and 17β-oestradiol isolated from the placentas and perfusates, nor the urinary oestrone, 17β-oestradiol and oestriol fractions contained any 3 H-labelled material. Almost 70% of the 3 H-labelled material recovered from the placentas and perfusates was isolated as retrotestosterone and retroandrostenedione. Only 14% of the 14 C-labelled material recovered from the same sources was present as testosterone and androstenedione. Furthermore, whereas only 3·5% of the 14 C-labelled material recovered from the placentas and perfusates was testosterone, more than 32% of the 3 H-labelled material was isolated as retrotesterone. It is concluded that steroids with a 9β,10α configuration cannot be aromatised and that the placental metabolism of retrotestosterone is much more limited than that of testosterone.