Binding sites for glucocorticoids in cytosols from the ventral prostate and seminal vesicle of rats.
Binding sites for 3H-dexamethasone (Dex) were demonstrated in cytosols from the ventral prostate and seminal vesicle of rats only if dithiothreitol (DTT) was present in the incubation mixture. The binding observed in the presence of DTT was high affinity (Kd=1-5 nM) and low capacity (Bmax=approx. 0.1 p mole/mg protein) and exhibited a binding specificity for glucocorticoids. The addition of molybdate (Mo) to the incubation mixture enforced the effect of DTT on the binding but the extent of the effect of Mo in cytosols of the ventral prostate differed from that in the seminal vesicle. The binding sites in the cytosols of these tissues were depleted after administration of Dex to animals. The depletion observed was not due to occupation of the binding sites by injected Dex and this was confirmed by the exchange assay. Addition of the cytosol from the seminal vesicle inhibited the 3H-Dex binding in the liver cytosol but the cytosol from the ventral prostate did not show an inhibitory effect. The binding sites in neither of these male accessory sex organs were modified markedly after the animals were castrated. Although the 3H-Dex binding sites observed in the cytoplasm of male accessory sex organs fit the definition proposed for the steroid hormone receptors, it is not clear whether these tissues are under the influence of glucocorticoid or not; the rate of incorporation of 3H-leucine and 3H-orotic acid into the acid-insoluble fraction from the ventral prostate is not influenced by the administration of Dex to animals.