METABOLISM OF TESTOSTERONE AND 5α-REDUCED ANDROGENS BY THE RABBIT PROSTATE AND EPIDIDYMIS: STUDIES IN VITRO AND IN VIVO

Abstract

SUMMARY The metabolism of radioactively labelled testosterone, 5α-dihydrotestosterone, 5α-androstane-3α,17β-diol and 5α-androstane-3β,17β-diol by the rabbit epididymis and prostate has been investigated in vitro and in vivo. In vitro, the rate of conversion of testosterone to 5α-reduced androgens was low in both glands. Varying the nature of the tissue preparation, age of animal or incubation medium did not improve the situation substantially. However, the rabbit prostate and epididymis metabolized 5α-reduced androgens readily. The prostate was particularly efficient at interconverting 5α-androstane-3α,17β-diol and 5α-dihydrotestosterone, whereas the capacity of the epididymis to carry out this step was much lower. Small amounts of 5α-androstane-3,17-dione and androsterone were also identified. Both glands interconverted 5α-dihydrotestosterone and 5α-androstane-3β,17β-diol to a comparable degree. Following the intravenous injection of 3H-labelled testosterone, significant levels of 3H-labelled 5α-dihydrotestosterone were found in the prostate and epididymis within 30 min. Furthermore, 5α-androstane-3α,17β-diol was detected in both glands. In blood plasma, the ratio of radioactively labelled testosterone: 5α-dihydrotestosterone was 2: 1, i.e. similar to that for endogenous steroids. The intravenous injection of 3H-labelled 5α-androstane-3α-17β-diol gave rise to much higher amounts of 5α-dihydrotestosterone in the prostate than in the epididymis, whereas the reverse was found for the levels of unmetabolized diol. The results indicate that the prostate and epididymis of the adult rabbit differ in their capacity to metabolize 5α-reduced androgens and that both glands depend to a large extent on the relatively high levels of 5α-dihydrotestosterone and 5α-androstanediols present in the peripheral circulation, rather than the metabolism of testosterone in situ.