Effects of hCG and Cyclic AMP on Aromatization in Purified Leydig Cells of Immature and Mature Rats1

Abstract

Aromatization of testosterone to estradiol was assessed in purified Leydig cells of rats 15, 25, and 60-70 days old. Leydig cells obtained after purification by Metrizamide gradient centrifugation were incubated for 4 h with a saturating concentration of [³H]testosterone (0.6 µM). [³H]-Estradiol was isolated and final identity established by recrystallization. Aromatization of [³H]-testosterone to [³H]estradiol was demonstrated in Leydig cells of all ages. Basal aromatase activity per 10⁶ Leydig cells was highest in Leydig cells of 25-day-old rats, intermediate in Leydig cells of 15-day-old-rats, and lowest in Leydig cells of 60-70-day-old rats. At saturating concentrations of [³H]testosterone, human chorionic gonadotropin or dibutyryl cyclic AMP acutely stimulated aromatization in Leydig cells of 25 and 60-70-day-old rats, but not of 15-day-old rats. A potent competitive inhibitor of aromatase, 7α-(4'-amino)phenylthioandrost-4-ene-3,17-dione, markedly inhibited estradiol production from testosterone in Leydig cells from all ages studied. These results demonstrate that Leydig cells of immature rats have the capacity for aromatization and that this step in steroidogenesis can be acutely stimulated by hCG and cAMP in Leydig cells of 25 and 60-70-day-old rats. The similarity in degree of stimulation of aromatization by dibutyryl cyclic AMP and hCG suggests that acute stimulation of aromatization by hCG is mediated by cyclic AMP.