Uptake and metabolism of androgen by the human epididymis in vitro

Uptake and metabolism of [3H]testosterone, mainly to 5 alpha-dihydrotestosterone (5 alpha-DHT and 5 alpha-androstanediol were higher in the caput than in the cauda epididymidis in vitro. The metabolites represented 57, 49 and 47% of the total radioactivity in the caput, corpus and cauda epididymidis, respectively; subcellular distributions of the metabolites in each segment showed 67% of total radioactivity in cytosol and 18% in the nuclei. In both fractions, the amount of 5 alpha-DHT was greater than that of androstanediol while the reverse was true for the mitochondria and microsomes. The distribution of 5 alpha-reductase activity in subcellular fractions was similar to that of the microsomal marker enzyme NADPH: cytochrome C reductase, whilst 3 alpha-hydroxysteroid dehydrogenase was found mainly in the cytosol. Maximal 5 alpha-reductase activity was at pH 5.3, apparent Km values in the microsomal and nuclear fractions were 1.65 +/- 0.7 and 1.75 +/- 0.36 x 10(-6) M respectively, and the Vmax in these preparations was 5.28 +/- 1.19 and 3.1 +/- 0.52 pmol/mg protein/min, respectively. The activity of 5 alpha-reductase was inhibited by Zn2+, Cu2+, Ba2+ and Cd2+ and by epitestosterone, progesterone and 4-androstene-3-one 17 beta-carboxylic acid.