Relationships between liver testosterone receptor isoforms and aromatase activity in female green frog, Rana esculenta

Testosterone receptors (AR) are present in the liver of the female green fr og, Rana esculenta, which resolve into two fractions (A and B) by ion-excha nge chromatography. Fraction A is primarily located in the nuclei, fraction B predominates in the cytosols, and both fractions show a high affinity an d specificity fur testosterone. Liver AR fraction levels vary dramatically during the frog sexual cycle. Fraction A levels are high only when the live r is engaged in vitellogenin production and the plasma testosterone levels are high: they are maximal when aromatase activity is most intense. Fractio n B levels are high when the liver is not producing vitellogenin and the pl asma testosterone levels are minimal. In addition, in vivo experiments carr ied out on ovariectomized females treated with testosterone show that testo sterone induces both fraction A and liver aromatase activity. This inductio n may be a step in the process that allows the liver to obtain estrogen fro m plasma testosterone which induces vitellogenin synthesis. (C) 2000 Elsevi er Science Inc. All rights reserved.