| dc.description |
Human placenta is a rich source of 17β-hydroxysteroid oxidoreductase (17-HOR) type 1, a cytosolic enzyme highly specific for 17β-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 38dash;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 equals; 0.59, P equals; 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. |
