Two epididymal androgen binding components were separated by polyacrylamide gel electrophoresis and examined in relation to nuclear uptake and binding of androgen after injection of l,2,6,7,3H-testosterone (3H-T) in vivo. The slower moving binding component (CR) was similar to the cytoplasmic receptor in the ventral prostate and was shown to remain in the epididymis after castration or hypophysectomy. The faster moving component, identified as the intraluminal androgen binding protein (ABP), disappeared from the epididymis within 8 days after castration or 10 days after hypophysectomy. The accumulation of androgen in nuclei remained active after the disappearance of ABP, indicating that binding to ABP is not involved in this process. Binding to CR, on the other hand, appeared to be essential for nuclear accumulation. Cyproterone acetate inhibited androgen binding to CR and decreased the nuclear accumulation of androgen without affecting binding to ABP. When rats were castrated for various time intervals (0 to 15 days) prior to in vivo labeling with 3H-T, accumulation of labeled androgen remained high even 15 days after castration in both supernatant and nuclear fractions. Testosterone treatment of the castrate for 8 days did not significantly increase either androgen binding to CR or nuclear receptors per urtit weight of epididymis as compared with the untreated 8-day castrate. Furthermore, androgen binding to CR and nuclear receptors persisted 24 days after hypophysectomy. These results suggested that nuclear accumulation of androgen in the epididymis is dependent on binding to CR. Neither CR nor nuclear acceptor proteins was selectively controlled by pituitary hormones or androgens. Although ABP was not directly involved in the translocation of DHT into epididymal nuclei, it appeared to increase the amount of androgen available for binding to intracellular receptors.
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