Epididymal Δ4-5α-reductase and 3ahydroxysteroid dehydrogenase activities have been measured in intact and in experimental animals. It has been found that the level of 3α-hydroxysteroid dehydrogenase activity in the caput-corpus epididymis does not differ from that of the cauda epididymis. This enzyme’s activity in the caputcorpus and cauda epididymis was decreased to 15% of control by castration but could be maintained at control levels in both castrated animals receiving doses of testosterone that maintained the weights of ventral prostate and seminal vesicles and in animals whose efferent ducts were transected. Higher doses of testosterone did not further increase the level of epididymal 3α-hydroxysteroid dehydrogenase activity. Δ4-5α-Reductase activity was five times higher in the caput-corpus than in the cauda epididymis of intact animals. The activity of this enzyme was lowered to undetectable levels by castration in both epididymal segments. Administration of testosterone at doses sufficient to maintain sex accessory organ weights restored Δ5-5α-reductase activity to only 10% in the caput-corpus and 25% in the cauda epididymis. Similar results were obtained by efferent duct transection and by administration of testosterone at a dose designed to approximate androgen concentration in rete testis fluid; i.e., one order of magnitude higher than that of plasma. These results are discussed in terms of possible mechanisms controlling epididymal Δ4-5α-reductase and 3α-hydroxysteroid dehydrogenase.
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