Acute Stimulation of Aromatization in Leydig Cells by Human Chorionic Gonadotropin in vitro

Aromatization of testosterone in Leydig cells purified from mature rat testes was assessed. Leydig cells incubated for 4 hr with increasing concentrations of [3H]testosterone exhibited maximal aromatization at 0.6 μ M testosterone. At saturating concentrations of testosterone, human chorionic gonadotropin (hCG) acutely stimulated aromatization. This stimulation was first observed at 1 hr, an 8-fold increase being found during a 4-hr incubation. The maximal amount of estradiol produced at saturating concentrations of testosterone and hCG was 1.8 ng per 106cells. These results demonstrate that purified Leydig cells have a high capacity for aromatization and that hCG can acutely stimulate aromatization independently of stimulating testosterone synthesis in vitro.