Although under rather intensive investigation for several years, the interactions of pituitary gonadotropins and ovarian steroids for ovarian functions are not well understood. That the synthesis of pregnenolone from cholesterol is the rate-limiting step in steroid production, ad that this is stimulated by tropic hormones, is uncontested. However, enzyme activities for synthetic pathways from pregnenolone to biologically active steroids are also under gonadotropic control. As a simple working hypothesis we assume that the control of production of steroids beyond pregnenolone involves basically three pivotal enzyme systems: 3Beta-hydroxysteroid dehydrogenase + delt25-3-ketosteroid isomerase: 17ALpha-hydroxylase-C17-20lyase; and 20ALpha-hydroxysteroid dehydrogenase. Our objective is to understand the interrelationships between the latter two enzyme systems for the synthesis of ovarian androgens and estrogens. We will determine the quantitative and temporal changes in activities of these enzyme systems under a variety of physiologic conditions and will correlate these changes with those of ovarian steroid production. Tritiated water produced by the conversion of 17Alpha3H-pregnenolone, or progesterone, to 17Alpha-hydroxyprogestins will be used as an index of hydroxylase activity. The amount of a two-carbon fragement cleaved from 17-OH-14C-21-progesterone will indicate lyase activity while the rate of conversion of progesterone to 20Alpha-dihydroprogesterone will be used to measure 20Alpha-hydroxysteroid dehydrogenase. The effects of follicle stimulating hormone, luteinizing hormone and prolactin, alone and in combinations, as well as various steroid environments, upon the activities of these enzyme systems will be determined. Ovarian function in normal cyclic, persistent estrus androgenized, pseudopregnant, pregnant and lactating rats will be measured using radioimmunoassays. In addition, functions in specific kinds of cells, such as granulosa, lutein and theca-interstitial cells, from animals receiving various treatments will be determined. The results will be used to interpret normal ovarian steroidogenic patterns as well as those resulting from neoplastic changes in the ovary.