Androgens Control Androgen-Binding Sites in Rat Epididymis*

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Abstract
Previous results suggested that the number of androgen-binding sites in rat epididymis was controlled by androgens. Using an exchange technique for receptor determination, cytoplasmic receptor number decreased to about half the control value after 4 days of castration and reached its lowest level (30% of the control value) after 12 days of castration. The Kd for [3H]methyltrienolone for cytoplasmic receptor varied from 2.8 .times. 10-9 M in controls to 0.6 .times. 10-9 M (P < 0.001) after 6 or more days of castration. Nuclear binding sites were reduced to 17% of the control value from the 2nd day of castration on, but no change in the affinity for methyltrienolone was noted. The administration of testosterone propionate (400 .mu.g/day) to rats castrated for 20 days significantly increased the number of nuclear and cytoplasmic binding sites from the 2nd and 3rd days of treatment, respectively. Labeled thymidine incorporation into DNA rose significantly after a 4-day latency period. The proportion of total binding sites capable of translocation into the nucleus was elevated during the early phase (2-4 days) of androgen treatment. These results also suggest the heterogeneity of the cytoplasmic binding site population. Control epididymides were composed of 61.5% receptor-containing epithelial cells, and this proportion was significantly reduced to 53.2% after 20 days of castration. Androgen administration elevated this percentage after an 8-day latency period. Proteolytic activity in cytosol was increased over control values after castration (for 20 days) and until the 4th day after the onset of androgen treatment. However, this activity does not seem to be an important factor in the decrease in binding sites caused by orchidectomy.

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