COMPARISON OF 17-BETA-HYDROXYSTEROID OXIDOREDUCTASE TYPE-1 AND TYPE-2ACTIVITY CYTOSOL AND MICROSOMES FROM HUMAN TERM PLACENTA, OVARIAN STROMA AND GRANULOSA-LUTEAL CELLS

A large body of evidence suggests multiple forms of 17 beta-hydroxyste roid oxidoreductase (17-HOR) regulate estrogen and androgen levels wit hin gonadal and peripheral tissues. Two kinetically-differing 17-HOR a ctivities have been detected in placental homogenates. 17-HOR type 1, found mainly in the cytosol, is highly reactive with estradiol-17 beta (E2) and estrone (E1) but not testosterone (T) (high E2/T activity ra tio). Microsomal 17-HOR type 2 is reactive with both E2 and T (low E2/ T activity ratio). In this study, 17-HOR activity of cytosol and micro somes from term placenta, ovarian stroma and granulosa-luteal cells wa s assayed under conditions which specifically differentiate between th e two forms of the enzyme. Placenta had the highest activity with eith er E2 or T in both cytosol and microsomes and stroma the lowest. The h ighest specific activity with E2 and E1 was cytosolic in all samples. The highest specific activity with T was microsomal in placenta and ov arian stroma. E2/E1 activity ratios were comparable for cytosol and mi crosomes while E2/T activity ratios were comparable for placenta and s troma, but markedly elevated in granulosa-luteal (G-L) cell cytosol an d microsomes. The results indicate trophoblast and ovarian stroma have more 17-HOR type 2 relative to type 1. G-L cells, in contrast, are re latively enriched in 17-HOR type 1 and thus have a greater capacity fo r net conversion of E1 to E2 under physiologic conditions. These diffe rences may contribute to increasing serum and follicular fluid E2/E1 r atios during development of the dominant follicle.