Male Wistar-Furth rats bearing the transplantable LTW(m)
Leydig cell tumor have elevated serum
estradiol (E2) concentrations. We measured the ability of these
tumors to aromatize
testosterone (T) to E2 by two methods. First,
tumor minces were incubated with [7-3H]T, and the resultant [3H]E2 and [3H]
estrone were purified and measured. In addition,
tumor cell cultures were incubated with [1 beta-3H]T, and the resultant [3H]H2O was determined as a measure of aromatization.
Tumor minces aromatized more actively than normal rat testicular tissue (3.30 +/- 0.15% of the T added was converted to E2 by the
tumor vs. 0.30 +/- 0.25% by normal testis). Most of the aromatizing actitivity was localized to the microsomes. Using cell cultures the maximum velocity was 6.1 pmol/h X 5 X 10(5) cells, and the Km was 98 nM. In neither minces nor cell cultures were we able to show stimulation of aromatization with hCG, (Bu)2cAMP, or
phorbol esters, although we could show stimulation by these agents in normal testicular cells. We were unable to inhibit the
aromatase activity with human
beta-endorphin or stimulate it with
naloxone. However, we were able to inhibit the
aromatase activity with
4-hydroxy-4-androstene-3,17-dione. We conclude that the LTW(m) rat
Leydig cell tumor has an active autonomous
aromatase system that is not responsive to compounds affecting the
adenylate cyclase-cAMP system. It can be inhibited by
4-hydroxy-4-androstene-3,17-dione, a competitive-suicide inhibitor of the
aromatase enzyme(s).