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

Human placenta is a rich source of 17-hydroxysteroid oxidoreductase(17-HOR) type 1, a cytosolic enzyme highly specific for 17-oestradiol,and type 2, a microsomal form reactive with both oestradioland testosterone. Although a number of studies have establishedthat 17-HOR activity is present in placenta as early as weeks4–5 of gestation, more specific data on the pattern ofdevelopment of these two enzyme forms are lacking. In this study,samples of villous tissue from weeks 7–20 of gestationwere fractionated into cytosol and microsomes and 17-HOR activityassayed under conditions which differentiate between the twoenzyme types. Type 1 activity with oestradiol of cytosol andmicrosomal type 2 activity with oestradiol and testosteroneincreased from week 7 to week 20. Activities at 17–20weeks approximated those at 38dash;40 weeks. The high, cytosolicoestradiol/T activity ratio (160 ± 20), characteristicof 17-HOR type 1, was constant between weeks 7 and 20, as wasthe low microsomal ratio (3.4 ± 0.4) characteristic ofthe type 2 activity. There was a relationship between cytosolictype 1 activity and microsomal type 2 activity between weeks7 and 20 (r equals; 0.59, P equals; 0.0055). These results indicateboth activities increase coincident with the luteal-placentalshift and that their temporal patterns of development are relatedbetween weeks 7 and 20 of gestation.