Specific nuclear uptake of intracellularly-produced estrogen by rat granulosa cells

Granulosa cells of the ovarian follicle are unique in that they both synthesize steroid hormones and respond to exogenously-administered steroids. Isolated granulosa cells from ovaries of gonadotropin-primed rats were incubated in the presence of [3H]testosterone, which the cells convert to [3H]estradiol. Nuclear extracts of these cells were analyzed by high-performance liquid chromatography in a system of 40% acetonitrile. When cells were incubated in the presence of [3H]testosterone alone, a significant portion of the radioactivity present in nuclei co-eluted with authentic estradiol. The nuclear binding was considered to be specific, since 50-75% of total binding was suppressed when the incubation medium contained excess unlabeled estrogen. Moreover, when an antibody to estradiol was included in the medium, specific nuclear uptake of [3H]estradiol was not abolished, but rather was increased. Granulosa cells may, therefore, directly utilize endogenously-produced estradiol, a mechanism which may play a role in the regulation of ovarian cells.