Estradiol-17 β inhibition of androgen uptake, metabolism and binding in epididymis of adult male rats in vivo: A comparison with cyproterone acetate

The effects of estradiol-17β on androgen uptake, metabolism and binding were studied in rat epidymis in vivo in comparison with cyproterone acetate. Steroids (250 ug/100 g body weight) were injected 5 min prior to ³H-testosterone in castrate rats. Estradiol-17β inhibited ³H-testosterone uptake into epididymal cytosol by 58% as compared to 38% by cyproterone acetate. ³H-Testosterone uptake into epididymal nuclei was inhibited 95% by estradiol-17β and 83% by cyproterone acetate. Total bound radioactivity in cytosol fractions was reduced to a greater extent by estradiol-17β than cyproterone acetate when either ³H-testosterone or ³H-dihydrotestosterone was injected. Binding of ³H-dihydrotestosterone to nuclear receptors was completely abolished by estradiol-17β; whereas approximately 20% binding remained in the nuclear extract after cyproterone acetate treatment. Metabolism of ³H-testosterone in vivo was also altered by estradiol-17β, resulting in diminished conversion to ³H-dihydrotestosterone. Cyproterone acetate, on the other hand, did not affect ³H-testosterone metabolism. Estradiol-17β and cyproterone acetate inhibited in vitro binding of ³H-dihydrotestosterone to the intracellular cytoplasmic receptor, but not the intraluminal androgen binding protein (ABP). These data suggest that estradiol-17 β may have a more potent antiandrogenic effect on the epididymis than cyproterone acetate due to inhibition of 5 α reduction of testosterone as well as binding to the androgen receptor.