Autoradiographic localization of [3H]hydroxytamoxifen to uterine oestrogen- and antioestrogen-binding sites.

Immature rats were injected subcutaneously with 0.36 micrograms of [3H]hydroxytamoxifen ([3H]TAM(OH)) or 0.24 microgram of [3H]oestradiol in oil, and 4 h later uteri were processed for thaw-mount autoradiography. The specificity of [3H]TAM(OH) localization was determined by injecting a 200-fold excess of unlabelled TAM(OH) or a 20-, 200- or 2000-fold excess of oestradiol 1 h before injection of [3H]TAM(OH). After injection of [3H]TAM(OH) or [3H]oestradiol, autoradiograms showed concentration of radioactivity in nuclei of stromal, epithelial and myometrial cells, but this labelling varied among the cell types depending upon which compound was injected. After [3H]TAM(OH) injection, the decreasing order of labelling intensity was stroma, myometrium, epithelium; after [3H]oestradiol injection the decreasing order was stroma, epithelium, myometrium. Injection of TAM(OH) before [3H]TAM(OH) eliminated nuclear labelling in all the uterine cell types. Injection of oestradiol before [3H]TAM(OH) decreased nuclear labelling and resulted in the concentration of label in the cytoplasm of luminal epithelium which was not present when [3H]TAM(OH) was injected alone. Cytoplasmic labelling increased initially as the oestradiol competition dose increased, but the increase in labelling did not continue with increasing concentrations of oestradiol. The results indicate that antioestrogen and oestrogen localize to nuclei of the same uterine cell types, but that cellular uptake differs among the tissue compartments. The results also suggest that a high concentration of antioestrogen-binding sites exist in the cytoplasm of the uterine luminal epithelium.