Androgen metabolism and concentration in the seminiferous tubules at different stages of development.

Testosterone 5α and 3α reducing activities have been studied in whole testis, isolated seminiferous tubules and interstitial tissue of rats from birth to maturity. It was found that 5α-androstan-3α-17-β-diol was the main metabolite of testosterone in seminiferous tubules and that its formation was maximal at the time of the first meiotic division, in the 20 to 26-day-old rat. These in vitro studies were confirmed by in vivo determinations of the concentrations of testosterone dihydrotestosterone and 5α-androstan3α, 17β-diol in the tubules through sexual development. Testosterone increased from 39 ng/100 ml proteins at 14 days to 94 at 20 days, and then dropped to 13 at 26 days. There was a gradual increase thereafter to reach again a value of 94 at sexual maturation. The concentration of 5α-androstan-3α 17β-diol also increased from 21 to 89 in 20-day-old rats, but it remained high in 26-day-old animals only to drop thereafter and remain low at sexual maturation. The concentration of dihydrotestosterone did not show a definite peak in young rats but increased markedly between 60 and 90 days of life. It is postulated that testosterone and 5α-androstan-3α,17β-diol might be the active androgens at the time of meiosis. Metabolism of [³H]-testosterone-³H was also studied in the human testis. Formation of reduced products in seminiferous tubules was also correlated with development of spermatogenesis and found to be higher at the time of the first meiotic division, in adolescent boys.