In Vitro and in Vivo Studies on the Functional Significance of Androgen Receptors in Rat Prostate

Receptors for [1,2-3H]testosterone and [1,2-3H]5α-dihydrotestosterone have been demonstrated in cytoplasmic and nuclear fractions of rat prostate with chromatographic techniques employing cellulose phosphate. Three types of steroid protein complex corresponding to Peaks 1, 2, and 2a were eluted with an ionic gradient consisting of 0 to 0.8 m NaCl in Tris-ethylenediaminetetraacetate buffer, pH 7.0. All three receptor peaks were present in vitro but only Peaks 2 and 2a were recovered in vivo. Under in vitro and in vivo conditions Peak 2 was confined to the cytosol fraction and Peak 2a to the nuclei fraction while the anomalous in vitro Peak 1 was found in cytosol and nuclei. A study of the in vitro binding of [1,2-3H]5α-dihydrotestosterone to nuclei yielded an association constant of 3.5 x 107 m-1 measured by gel filtration on Sephadex G-25. Castration caused a decrease in binding of [1,2-3H]5α-dihydrotestosterone to nuclei and an increase in the binding to cytosol. No corresponding changes occurred in the binding of [1,2-3H]testosterone to these fractions. When the in vivo transfer of androgen from cytoplasm to nuclei was studied with pulse-chase methods, it was found that cytosol Peak 2 and nuclear Peak 2a proteins were labeled in sequence and that the amounts of radioactive androgen lost from one peak and gained by the second were almost equal. Moreover, the composition of the peaks with respect to testosterone and 5α-dihydrotestosterone was virtually identical. Together this evidence indicates that the Peak 2 and Peak 2a proteins are important in promoting the intracellular transport of androgens in vivo.