Non-stoichiometric nuclear-cytoplasmic redistribution of estrogen receptor in adult rat uterus, following estradiol injection

Abstract

In immature and ovariectomized rats acutely injected with estradiol (E 2), accumulation of estradiol receptor complexes (E 2R) from the uterine cytosol to the nucleus has been shown to be quantitative by numerous investigators. In the present study, translocation of E 2R from the cytosol to the nuclear fraction in adult and ovariectomized estrogen prestimulated rats was analyzed. Twenty μg of E 2, dissolved in saline containing 10% ethanol and 1 g% bovine serum albumin (B.S.A.) were injected intraperitoneally to the animals and 2 h later E 2R in the cytosol and crude nuclear fractions were assayed by exchange techniques. Unlike a 91% recovery of the depleted cytosol E 2R in the nuclear fraction of ovariectomized rats, only 39.2 and 27.5% were recovered in the adult and ovariectomized estrogen prestimulated rat uterus respectively. Moreover, depending on the temperature and duration of nuclear suspension incubation, from 18 upto 80% of the recovered nuclear E 2R were solubilized in the incubation medium and nuclear post-incubation washes and could be measured by hydroxylapatite treatment (HAP). Saturation assays showed a plateau from 12nM E 2 3H onwards up to 80 nM. The K d values computed for the receptors in the nucleus and HAP in all the three groups were of the order of 2 × 10 −9M. In conclusion, after E 2 administration to adult or ovariectomized estrogen prestimulated rats, a stoichiometric recovery of the depleted cytosol E 2R in the nuclear fraction was not observed, even when leakage of nuclear receptor into the medium in course of exchange was taken into account. Chronic estrogenization appeared to modify the dynamics of uterine receptor.