The effect of testosterone on human chorionic gonadotropin-stimulated ovarian steroidogenesis in vivo in the baboon (Papio cynocephalus).

We have studied the effect of exogenously induced hyperandrogenism on the ovarian response to human chorionic gonadotropin (hCG) in the baboon. Normally cycling baboons were treated with increasing daily doses of hCG for 5 consecutive days from day 10 of the luteal phase (n = 5). Hyperandrogenic baboons received the same hCG regimen 1 hour after a Silastic capsule containing crystalline testosterone (T) had been implanted under the skin (n = 3). Control animals received an empty Silastic capsule (n = 8). All baboons were bled on alternate days from days 6 to 20 of the luteal phase, and daily during hCG treatment. T capsules induced immediate hyperandrogenism, with T levels several times greater than normal luteal phase levels. The use of hCG resulted in an increase in plasma progesterone within 24 hours and levels gradually declined thereafter. Estradiol increased rapidly and remained elevated during hCG treatment. In the presence of elevated T levels, hCG had a significantly reduced effect on the magnitude and duration of plasma progesterone increase. The effect of hCG on plasma estradiol levels was virtually eliminated in hyperandrogenic baboons. This study seems to demonstrate a direct inhibitory effect of T on ovarian steroidogenesis in vivo and may explain the ovarian changes that occur in hyperandrogenic women.