Site of estrogen action in rabbit ovarian tissue

In superovulated or naturally mated pseudopregnant rabbits, an abrupt premature decline of progesterone production by the corpus luteum occurs after removal of polydimethylsiloxane capsules filled with 17 beta-estradiol. Reinsertion of the estradiol-filled capsules stimulates a striking restoration of progesterone production. We have given [3H]estradiol by arterial infusion to anesthetized rabbits to determine by cellular autoradiography whether the exogenous estradiol localizes to luteal tissues responsible for progesterone production. Autoradiography with both freeze-dried and touch-thaw mounted preparations demonstrated that tritium activity localized to the nuclei of luteal cells and that such uptake could be blocked by radioinert diethylstilbestrol. We extracted the tritium activity sequestered in vivo by the corpora lutea and cocrystallized the extract with 14C-labeled and radiostable 17 beta-estradiol to confirm its presence (greater than 90%) as [3H]estradiol. In addition, we were able to demonstrate that radiostable diethylstilbestrol blocked ovarian uptake of 16 alpha-125I-17 beta-estradiol in vivo. In concert, these observations provide compelling evidence that the exogenous estradiol responsible for restoring progesterone production may act through an estrogen-specific mechanism directly in the luteal cells.