Gestational development of human placental 17 beta-hydroxysteroid oxidoreductase types 1 and 2

Human placenta is a rich source of 17 beta-hydroxysteroid oxidoreductase (17-HOR) type 1, a cytosolic enzyme highly specific for 17 beta-oestradiol, and type 2, a microsomal form reactive with both oestradiol and testosterone. Although a number of studies have established that 17-HOR activity is present in placenta as early as weeks 4-5 of gestation, more specific data on the pattern of development of these two enzyme forms are lacking. In this study, samples of villous tissue from weeks 7-20 of gestation were fractionated into cytosol and microsomes and 17-HOR activity assayed under conditions which differentiate between the two enzyme types. Type 1 activity with oestradiol of cytosol and microsomal type 2 activity with oestradiol and testosterone increased from week 7 to week 20. Activities at 17-20 weeks approximated those at 38-40 weeks. The high, cytosolic oestradiol/T activity ratio (160 +/- 20), characteristic of 17-HOR type 1, was constant between weeks 7 and 20, as was the low microsomal ratio (3.4 +/- 0.4) characteristic of the type 2 activity. There was a relationship between cytosolic type 1 activity and microsomal type 2 activity between weeks 7 and 20 (r = 0.59, P = 0.0055). These results indicate both activities increase coincident with the luteal-placental shift and that their temporal patterns of development are related between weeks 7 and 20 of gestation.