Studies on the binding of androgens to the cytosol proteins and nuclei of the rat seminal vesicle.

Mince of the seminal vesicles of rats castrated 5--6 days before the experiment was incubated at 37 degree C with 3H-testosterone. Ater 60 min incubation with 10 nM testosterone 73% of the label bound to cytosol proteins and 83% of the label attached to nuclei was in 5alpha-dihydrotestosterone while unbound steroids contained only 29% dihydrotestosterone. The amount of dihydrotestosterone bound to cytosol proteins and nuclei was 0.4 pmol/g tissue and 1 pmol/g tissue, respectively. On the basis of the nuclear binding of this steroid about 1900 binding sites per nucleus were calculated. Both cytosolic and nuclear binding sites were half saturated at about 1 nM testosterone concentration. Most of the binding to cytosol proteins occurred during the first 10 min, while the maximum binding to nuclei was attained after 40 min of incubation. Nuclei were found to bind considerable amounts of testosterone. Binding of testosterone to nuclei reached its maximum between 10--20 min of incubation and declined then to a comparatively low level during the ensuing 40--50 min. Various experimental results suggest that testosterone and dihydrotestosterone are accumulated in the nuclei by independent mechanisms.