[Increased estradiol-estrone quotient in rat liver by hydroxysteroids: an effect of the specific hydrogen transfer...

After addition of estrone to rat liver slices, a quotient of estradiol/estrone of ca. 0.1 is reached within 1 - 2 min. By additional application of 17 beta-hydroxysteroids this quotient is changed in the direction of estradiol, although the applied concentrations of both steroids are far below the concentration of the cytoplasmic redox couple NADH/NAD. Of all the steroids tested, testosterone had the strongest influence on the quotient, especially in the liver of female rats. This influence is smaller in the livers of male rats and infantile animals. The changing of the E2/E1 quotient by testosterone can be inhibited by the antiandrogen cyproteron acetate. Steroids with hydroxy groups at C-3 or C-20 or high concentrations of non-steroids, which can be oxidized by NAD, change the E2/E1 quotient only minimally. The experiments demonstrate that in liver, the redox couple estradiol/estrone is not in equilibrium with the main redox couple of the cytoplasmic NADH/NAD. Only on account of this fact it is possible that relatively low concentrations of testosterone change the E2/E1 quotient via the C-17 leads to C-17 hydrogen transfer between steroids. Biological consequences are discussed.