In-vivo uptake and metabolism of testosterone by the skin and other tissues of the rat

Abstract

The uptake and metabolism of radioactively labelled testosterone was investigated in vivo at various time intervals in the skin, plasma and other tissues of adult rats castrated 24 h earlier. After the addition of marker steroids the components of the tissue extracts were separated by partition and development in several chromatographic systems; steroid identification was confirmed by derivative formation and recrystallization to constant 3H:14C ratio. The skin resembled the classical androgen target organs in the uptake and retention of both total and unconjugated radioactivity, but the actual composition of the radioactivity present in the skin was markedly different from that in the accessory glands. Little testosterone was recovered from the ventral prostates and 5α-dihydrotestosterone (5α-DHT), often considered the active intracellular androgenic steroid, constantly occupied the largest proportion of the extracted radioactivity. In the skin samples, however, testosterone was always the major unconjugated steroid detected and 4-androstene-3,17-dione, 5α-DHT, 5α-androstane-3α,17β-diol, androsterone and 5α-androstane-3β,17β-diol were only identified in much smaller quantities, even after 5 h. Although the majority of the plasma radioactivity was conjugated or very polar by 20 min, all the steroids found in the skin were present, albeit in different proportions; testosterone was always predominant and 5α-androstane-3β,17β-diol was also detected in larger amounts than the very low levels of the other steroids. The results suggest that 5α-DHT is not as important in the skin as it is in the prostate of the rat and that other androgenic steroids, most notably testosterone itself, may be involved in the mechanism of androgen action in the skin.