The effect of spironolactone on aromatase activity

Spironolactone, an aldosterone antagonist, causes decreased plasma testosterone (T) levels and gynecomastia in men and is clinically useful in the treatment of hirsutism in women. Many mechanisms of action for spironolactone have been proposed. It has been suggested that one cause for low plasma T levels may result from an increased metabolic clearance rate of T due to increased extraglandular aromatization to 17β-estradiol. The purpose of this investigation was to determine the effect of spironolactone on the rate of activity of aromatase in human fetal liver (hFL) cells. The activity of aromatase was assayed by determining the rate of incorporation of [1-³H]androstenedione into [³H]water in hFL cells exposed to spironolactone (10^-10 to 10^-4 M) for 24 or 72 hours. The aromatase activity in control hFL cells remained constant during the study. Dibutyryl cyclic adenosine monophosphate significantly stimulated aromatase activity from 63 to 257 pmol x mg^-1 protein x 2 hours^-1 after 24 hours and 72 hours exposure, respectively. In contrast, when hFL cells were exposed to spironolactone (10^-10 to 10^-5 M) for up to 72 hours, the activity of aromatase did not differ significantly from that in control hFL cells. It is concluded that spironolactone in therapeutic concentrations does not stimulate aromatase activity in hFL cells maintained in vitro.