A comparison of 17 beta-hydroxysteroid oxidoreductase type 1 and type 2 activity of cytosol and microsomes from human term placenta, ovarian stroma and granulosa-luteal cells.
A large body of evidence suggests multiple forms of 17 beta-hydroxysteroid oxidoreductase (17-HOR) regulate estrogen and androgen levels within gonadal and peripheral tissues. Two kinetically-differing 17-HOR activities 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 ratio). 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 microsomes from term placenta, ovarian stroma and granulosa-luteal cells was assayed under conditions which specifically differentiate between the two forms of the enzyme. Placenta had the highest activity with either E2 or T in both cytosol and microsomes and stroma the lowest. The highest specific activity with E2 and E1 was cytosolic in all samples. The highest specific activity with T was microsomal in placenta and ovarian stroma. E2/E1 activity ratios were comparable for cytosol and microsomes while E2/T activity ratios were comparable for placenta and stroma, but markedly elevated in granulosa-luteal (G-L) cell cytosol and microsomes. The results indicate trophoblast and ovarian stroma have more 17-HOR type 2 relative to type 1. G-L cells, in contrast, are relatively enriched in 17-HOR type 1 and thus have a greater capacity for net conversion of E1 to E2 under physiologic conditions. These differences may contribute to increasing serum and follicular fluid E2/E1 ratios during development of the dominant follicle.
Blomquist
C H
CH
Department of Obstetrics and Gynecology, Ramsey Clinic, St. Paul, MN.
Bealka
D G
DG
Hensleigh
H C
HC
Tagatz
G E
GE
D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D004958:Estradiol / Q000378:metabolism; D004970:Estrone / Q000378:metabolism; D005260:Female; D006107:Granulosa Cells / Q000201:enzymology* / Q000648:ultrastructure; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008184:Luteal Cells / Q000201:enzymology* / Q000648:ultrastructure; D008861:Microsomes / Q000201:enzymology; D010053:Ovary / Q000201:enzymology* / Q000648:ultrastructure; D010920:Placenta / Q000201:enzymology* / Q000648:ultrastructure; D011247:Pregnancy; D013379:Substrate Specificity; D013739:Testosterone / Q000378:metabolism
D004970:Estrone; D013739:Testosterone; D004958:Estradiol; D015067:17-Hydroxysteroid Dehydrogenases