PROGESTERONE SYNTHESIS BY HUMAN LUTEAL CELLS - MODULATION BY ESTRADIOL

To assess the role of estradiol (E(2)) upon progesterone (P-4) synthesis, a well defined human midluteal cell system was used. A dose-dependent inhibition of P-4 synthesis with and without hCG was induced by E(2) In addition, E(2) had a dose related cumulative effect on pregnenolone as compared with control experiments (2-fold, P < 0.05) as well as in hCG-stimulated conditions (3-fold, P < 0.005). On the other hand, the concentrations of 20 alpha-hydroxyprogesterone obtained in all experimental conditions were similar to control values, indicating that the catabolism of P-4 was not modified. 3 beta-Hydroxysteroid dehydrogenase activity was significantly diminished (P < 0.05) in the presence of E(2) Finally, the kinetic studies on P-4 synthesis from pregnenolone showed a competitive type of inhibition with a K-1 of 2.22 X 10(-6) mol/L. These data indicate an inhibition of 3 beta-hydroxysteroid dehydrogenase on human corpus luteum by E(2)