Effect of an Aromatase Inhibitor (4-Acetoxy-4-androstene-3,17-dione) on the Stimulatory Action of Luteinizing Hormone on Estradiol-17β Synthesis by Rat Preovulatory Follicles in vitro1

The effect of 4-acetoxy-4-androstene-3,17-dione (4-acetoxy-A), an inhibitor of aromatase activity, on the steriodogenic response of preovulatory rat follicles to luteinizing hormone (LH) in vitro was examined. In addition to markedly inhibiting the cumulative secretion of estradiol-17β, 4-acetoxy-A significantly increased the accumulation of testosterone, whether or not LH was present during culture; addition of exogenous estradiol to culture media containing LH and 4-acetoxy-A partially inhibited testosterone accumulation. Furthermore, 4-acetoxy-A enhanced progesterone accumulation, particularly when the follicles were stimulated by LH. These latter effects did not appear to be explainable solely on the basis of substrate accumulation due to inhibition of aromatization by 4-acetoxy-A. Though 4-acetoxy-A may have direct effects on steroidogenesis, these data support the hypothesis that intrafollicular estrogen levels play a physiological role in modulating steroidogenic responses of the follicle to LH.