Central and peripheral metabolism of 5α-dihydrotestosterone in the male Japanese quail: biochemical characterization and relationship with reproductive behavior

An in vitro radioenzymatic assay and purification procedure by thin-layer chromatography were used to study the metabolism of dihydrotestosterone (DHT) into 3α- and 3β-androstanediols by the brain and cloacal gland of Japanese quail. Kinetic studies showed that these 2 metabolites are produced in a linear fashion with respect to time of incubation for up to 15 min but that they continue to accumulate for up to 4 h. The maximum velocity of these reactions is high (nmol/mg protein/15 min), but the affinities of the enzymes for DHT are low (in the μM range). The enzymatic activities are not evenly distributed in the brain: they are high in the tuberal hypothalamus and lobus parolfactorius but low in the preoptic area and anterior hypothalamus. Enzyme activities are not markedly affected by treatment of the birds with either testosterone or DHT. The activity of these enzymes is lower in the preoptic area and tuberal hypothalamus of DHT-treated birds which display female-directed sexual behavior than in the same brain areas of birds which are sexually inactive. We discuss the relationships between this reductive metabolism of DHT and the activational effects of the steroid on sexual behavior.