Effects of androgens on aromatase activity and 11C-vorozole binding in granulosa cells in vitro

Locally produced androgens and estrogens are important in the hormonal regulation of follicular development. The present study aimed to further elucidate the mechanism through which androgens exert their ambivalent effects on aromatization.

Non-cultured human granulosa-luteal cells (GC) were treated with different concentrations of androstenedione (A4), testosterone (T), 5alpha-androstane-3,17-dione (5alpha-A) and dihydrotestosterone (DHT). The effects on aromatase activity were evaluated in a tritiated water assay (incubation time 2 h) and the availability of aromatase active sites was measured in a radiotracer-binding assay using the non-steroidal competitive aromatase inhibitor [11C]-vorozole (incubation time 15 min).

A4, T and 5alpha-A caused dose-dependent inhibition of both aromatase activity and [11C]-vorozole binding; IC50-values for both inhibition processes were calculated for these three steroids, revealing A4 as the most potent inhibitor and T and 5alpha-A as moderate inhibitors. At low concentrations (0.01 and 0.1 micro M), DHT stimulated aromatase activity but did not affect [11C]-vorozole binding. At the higher concentrations tested (1 and 10 micro M) DHT suppressed both processes thus weakly binding the aromatase active site.

Because the incubation time in the tritiated water assay was short, the stimulation by DHT at low concentrations might therefore most likely include mechanisms other than new synthesis of aromatase protein such as allosteric action of DHT upon aromatase or liganded androgen receptor-aromatase interaction.