Progestagen nuclear binding sites in the male genital tract of the mouse, studied by autoradiography

Autoradiograms were prepared after injection of 125I progestagen (sp. act. 2200 Ci/mmol) to prepubertal and young adult mice. Nuclear concentration of radioactivity was found in smooth muscle cells at the beginning and the end of the deferent duct and in fibroblasts around the fusion of the deferent duct with the urethra. Nuclear labeling was enhanced in adult animals pretreated with oestradiol-valerate. In prepubertal mice nuclear labeling was more abundant than in adult mice and found in all smooth muscle cells of the deferent duct. No nuclear labeling was observed in other accessory sex organs. Nuclear labeling was prevented by injection of excess of unlabeled R5020. The presence of progestin receptors in smooth muscle cells of the deferent duct suggests a regulatory effect of progestin on contractions in analogy to progestin effects on oviductal and uteral smooth muscle cells. The presence of nuclear progestin receptors in the periurethral region may indicate an involvement of progestins in the etiology and regulation of benign prostate hyperplasia.