Further characterization of estrogen receptors in the human oviduct

Estrogen binding in human oviducts was studied in vitro by the dextran-coated charcoal assay and sucrose density ultracentrifugation. Estrogen binds with high affinity and limited capacity to cytosol of the human oviduct. The concentration of competitive inhibitors to produce 50% reduction in estrogen binding was 8 x 10(-8) M for the antiestrogen CI-628, 8 x 10(-7) M for the progestogen norethynodrel, and 3 x 10(-6) M for the testosterone derivative danazol at the ligand concentration of 1 nM estradiol. Nuclear estrogen binding was not inhibited by a 100-fold excess of progesterone or by a 10-fold excess of norethynodrel. Estrogen-binding protein with a sedimentation coefficient of 4S was seen in oviductal cytosol of all three anatomic segments. The nuclear 4S peak of estrogen binding was demonstrated in the ampullary tubal segment.