Nuclear oestrogen receptors in rat liver. Development of assay conditions, characterization and the translocation of oestrogens in vivo.

A method for the determination of specific oestrogen-receptor binding sites in rat liver nuclei is described. Nuclear receptors showed a high affinity for oestradiol (Kd approximately 3 x 10(-9)M), a low capacity, and a distinct specificity for substances with known oestrogenic and anti-oestrogenic activity. No sex differences were seen in the concentrations of nuclear receptors from either vehicle- or ethynyloestradiol-pretreated rats. Only a limited number of binding sites could be extracted with 0.4 M-KCl. The remaining sites, which were solubilized by sonication and treatment with deoxyribonuclease I, sedimented at 3-4 S. Of four oestrogens tested (oestradiol, ethynyloestradiol, diethylstilboestrol, tri-p-anisylchloroethylene), ethynyloestradiol was the most effective translocation agent in vivo, nuclear uptake occurring at doses below 1 microgram/rat; changes in salt extractability of nuclear receptors occurred at doses lower than those required to achieve absolute increases in nuclear receptor concentrations.