Androgen Metabolism by Rat Epididymis. 8. Age Dependent Changes in Androgen Metabolizing Enzymes in Rat Accessory Sex Organs

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Abstract
The effect of age on in vivo 3H testosterone (3H-T) metabolism and on epididymal 5.alpha.-reductase and 3.alpha./.beta.-hydroxysteroid dehydrogenase activity was studied in male Wistar rats. Following i.m. injection of 3H-T to 3 and 25 mo. old functionally hepatectomized rats, the accumulation of 5.alpha.-androstan-17.beta.-ol-3-one (DHT) by both the caput and cauda epididymidis, prostate, and seminal vesicles was significantly higher in the young animals than in the old. The total conversion of 3H-T by both epididymal segments was unaltered with advancing age; a significant decrease was observed in both prostate and seminal vesicles. The ratio between 17.beta.-hydroxy and 17-keto metabolites in the prostate and epididymis of both hepatectomized and intact animals decreased significantly with age. The ratio values for the seminal vesicles showed no significant age variation. The formation of total 5.alpha.-reduced metabolites by epididymal homogenates showed a linear decrease with advancing age. The activity of 5.alpha.-reductase fell from 16.1 to 10.3 ng/mg protein per 30 min. 3.alpha./.beta.-Hydroxysteroid dehydrogenase activity was unaffected by age. The reduced levels of active testosterone metabolites reported with old age are a result of a decrease in 5.alpha.-reductase activity, the ultimate cause of which is most probably an age associated defect in the hypothalamic-pituitary-testicular feedback system.