Estrogen and Progesterone Production by Developing Porcine Folliclesin Vitro: Evidence for Estrogen Formation by Theca*

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Abstract
Compartmental changes in ovarian follicular estrogen and progesterone production during maturation were studied in vitro using a mechanical technique to separate the granulosa and theca of individual porcine follicles. Follicles were divided by size into 3- to 5-, 7- to 8-, and 9- to 12-mm groups, representing early to midfollicular, late follicular, and immediately preovulatory stages, respectively. The isolated compartments were placed in cell or organ culture, separately or together, in Ham's F-12 medium with 10% fetal calf serum for 1–2 days in 5% CO2 in air. Estrogen (E) and progesteron (P) were measured by RIA. E production by the granulosa compartment without added aromatizable substrate was detectable but remained low during development, while P production increased dramatically in the preovulatory 9- to 12-mm group. The addition of 10-5 M testosterone markedly increased E production by isolated granulosa cells from 4- to 8-mm follicles (10- to 70-fold), but failed to increase thecal E production by the same follicles. Coculture of the separated compartments resulted in lower P production relative to the granulosa compartment in three of four experiments in the 9- to 12-mm group, suggesting a possible thecagranulosa interaction upon P production at this stage. E production by theca-granulosa coculture, while similar to that of theca in the 3- to 5-mm group, was significantly greater than that by theca from 7- to 8- and 9- to 12-mm follicles, suggesting increased granulosa cell aromatization and/or increased production of thecally derived androgens at latter stages of follicular maturation. E production by isolated theca was substantial and accounted for a significant proportion of the total E produced in vitro whether compared to theca/granulosa coculture or to the granulosa compartment incubated in the presence of saturating amounts of testosterone. The finding of a granulosa cell aromatase system capable of converting large amounts of androgen to E was not incompatible with significant thecal E production. While previous studies in other species have tended to support either granulosa cell aromatization of thecally derived androgens or direct thecal E secretion as the predominant source of follicular E, the results of this study indicate that both compartments contribute significantly to E syntheis in the porcine follicle.