Nuclear and cytoplasmic estrogen receptors in ovine endometrium during the estrous cycle.

Abstract

Binding of estradiol to a specific endometrial cytoplasmic receptor and translocation of the estrogen-receptor complex to the nucleus was studied in ewes on days 0 (estrus), 3, 6 and 10 of the estrous cycle. In addition, total endometrial cytoplasmic and nuclear receptors were determined by use of the estradiol exchange assay. The equilibrium dissociation constant for the estradiol-receptor complex and the maximum concentration of binding sites were determined to be 8.30 nM and 13,700 molecules per cell, respectively. As determined by exchange assay, total estradiol bound to the cytoplasmic receptor was greater (P < 0.01) on days 0 and 3 (6.84 and 9.56 fmol/μg DNA, respectively) than on days 6 and 10 (1.59 and 2.80 fmol/μug DNA, respectively). Total nuclear-bound estradiol averaged 1.21 ± 0.18 (SE) fmol/μg DNA on days 0, 3 and 6; however, it declined to 0.64 fmol/μg DNA on day 10. For each stage of the cycle studied, incubation of endometrium with 2 × 10-8M [3H]estradiol resulted in translocation of 77 / ...