Steroid δ4-5α-Reductase and 3α-Hydroxysteroid Dehydrogenase in the Rat Epididymis1

Abstract

Epididymal .DELTA.4-5.alpha.-reductase and 3.alpha.-hydroxysteroid dehydrogenase activities were measured in intact and in experimental animals. The level of 3.alpha.-hydroxysteroid dehydrogenase activity in the caput-corpus epididymis does not differ from that of the cauda epididymis. This enzyme''s activity in the caput-corpus 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 3.alpha.-hydroxysteroid dehydrogenase activity. .DELTA.4-5.alpha.-Reductase activity was 5 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 .DELTA.5-5.alpha.-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 .DELTA.4-5.alpha.-reductase and 3.alpha.-hydroxysteroid dehydrogense.