LH-induced inhibition of follicular androgen formation requires intact steroidogenesis

LH exerts a biphasic effect on rat pre-ovulatory follicular steroidogenesis: an initial (1-4h) overall stimulation followed by a later (4-6 h) occurring inhibition of androgen synthesis. Because exogenous steroids may inhibit androgen formation, we investigated whether the steroids produced initially in response to LH are involved in the late inhibition of androgen synthesis. Isolated pre-ovulatory rat follicles were incubated for 6 h with and without ovine LH and 1 of 3 inhibitors of steroidogenesis (aminoglutethimide, cyanoketone, Su 10603). Accumulation of androstenedione and testosterone in a subsequent 2-h incubation in the presence of exogenous 17-hydroxyprogesterone was measured. LH treatment alone caused inhibition of apparent 17,20-lyase activity. The inhibitors had no effect on basal 17,20-lyase activity but were able to prevent the LH-induced inhibition of this enzyme activity. The results suggest that the physiological decline in pre-ovulatory androgen formation may in part be mediated by local action of follicular steroids.