Ovarian Progestins, Androgens and Estrogen Throughout the 4-Day Estrous Cycle in the Rat

Groups of female rats were sacrificed throughout the 4-day estrous cycle and the ovaries assayed for pregnenolone, progesterone, 17-OH-progesterone, 17-OH-pregnenolone, androst-5-ene-3β,17β-diol, androstenedione, testosterone, dihydrotestosterone, androstane-3α, 17β-diol, androstane-3β,17β-diol, and estradiol. Ovarian progesterone levels were relatively high throughout the estrous cycle while ovarian 17-OH-progesterone, androstenedione, testosterone, and estradiol levels increased progressively to about 20-fold throughout the cycle and reached maximal levels on the afternoon of proestrus. In contrast, dihydrotestosterone, androstane-3α,17β-diol and androstane-3β,17β-diol concentrations increased only two- to threefold throughout the 4-day cycle. These results, together with previous in vitro observations, are consistent with the hypothesis that the ovary secretes high levels of androgen precursors which are further aromatized to estradiol.