title: The effect of epitestosterone on estrogen biosynthesis in vitro.
abstract: OBJECTIVE
  The concentrations of epitestosterone in human serum correlates negatively with that of estradiol. The possible explanation of this relation was addressed, and the influence of epitestosterone on kinetics of estradiol formation in vitro was evaluated.
  
  
  METHODS
  The concentration of epitestosterone was measured in serum of 54 men participating in a screening program for prostate disease. Epitestosterone inhibition of aromatase and 17beta-hydroxysteroid dehydrogenase activities was tested in vitro in the system consisting of human placental microsomes, NADPH or NAD and NADP respectively, and epitestosterone in increasing concentrations. Testosterone, androstenedione, estrone and 17beta-estradiol were utilized as substrates.
  
  
  RESULTS
  A significant negative correlation between epitestosterone and estradiol levels in human male serum was found. No inhibition of aromatase activity was observed; however, inhibition of 17beta-hydroxysteroid dehydrogenase was found preferentially in the direction leading to oxidation of the C-17 hydroxy group. The inhibitory effect of epitestosterone was more pronounced with androgens as substrates.
  
  
  CONCLUSIONS
  Epitestosterone could influence the formation of estradiol in vitro rather by inhibition of 17beta-hydroxysteroid dehydrogenase than by blocking aromatase activity.
authors.affiliation: Institute of Endocrinology, Prague, Czech Republic. mbiciko@endo.cz
authors.forename: M
authors.initials: M
authors.lastname: Bicíková
authors.forename: J
authors.initials: J
authors.lastname: Klak
authors.forename: M
authors.initials: M
authors.lastname: Hill
authors.forename: L
authors.initials: L
authors.lastname: Stárka
mesh_terms: D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism; D000368:Aged; D001141:Aromatase / Q000378:metabolism; D047072:Aromatase Inhibitors; D004845:Epitestosterone / Q000494:pharmacology*; D004958:Estradiol / Q000096:biosynthesis*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D016011:Normal Distribution; D010920:Placenta / Q000187:drug effects / Q000201:enzymology*; D013739:Testosterone / Q000378:metabolism
chemical_list: D047072:Aromatase Inhibitors; D013739:Testosterone; D004845:Epitestosterone; D004958:Estradiol; D015067:17-Hydroxysteroid Dehydrogenases; D001141:Aromatase