Formation of Estradiol by Granulosa and Theca Cells of the Equine Ovarian Follicle

The granulosa and theca cells of the pre-ovulatory equine ovarian follicle were physically separated by careful dissection and the metabolic activities of the isolated cell types were studied. Testosterone 4-l4C was converted in vitro to estrone and estradiol in higher yield by the granulosa cells than by the theca cells. The formation of 19-nortestosterone in much smaller yield was also detected without any indication that this 19- nor compound acted as a free intermediate in the synthesis of the estrogens. Although this study establishes the ability of both the granulosa and theca to aromatize steroids, assignment of meaningful roles to the several cell types of the ovary must await further studies of their enzymatic capacities singly and in combination at each step along the biosynthetic chain for steroid formation. (Endocrinology76: 108, 1965)