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Abstract
The effect of age on in vivo tritiated testosterone (3H-T) metabolism and on epididymal 5α-reductase and 3α/β-hydroxysteroid dehydrogenase activity has been studied in male Wistar rats. Following i.m. injection of 3H-T to 3 and 25 month old functionally hepatectomized rats, the accumulation of 5α-androstan-17β-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 whereas a significant decrease was observed in both prostate and seminal vesicles. The ratio between 17β-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 5α-reduced metabolites by epididymal homogenates showed a linear decrease with advancing age. The activity of 5α-reductase fell from 16.1 to 10.3 ng/mg protein/30 min. 3α/β-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 5α-reductase activity, the ultimate cause of which is most probably an age associated defect in the hypothalamic-pituitary-testicular feedback system.