Localization of 17 beta-hydroxysteroid dehydrogenase and characterization of testosterone in the brain of the male frog

Several enzymes involved in the formation of steroids of the pregnene and pregnane series have been identified in the brain, but the biosynthesis of testosterone has never been reported in the central nervous system. In the present study, we have investigated the distribution and bioactivity of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) (EC 1.1.1.62; a key enzyme that is required for the formation of testosterone and estradiol) in the brain of the male frog Rana ridibunda. By using an antiserum against human type I placental 17 beta-HSD, immunoreactivity was localized in a discrete group of ependymal glial cells bordering the telencephalic ventricles. HPLC analysis of telencephalon and hypothalamus extracts combined with testosterone radioimmunoassay revealed the existence of two peaks coeluting with testosterone and 5 alpha-dihydrotestosterone. After HPLC purification, testosterone was identified by gas chromatography/mass spectrometry, Incubation of telencephalon slices with [H-3]pregnenolone resulted in the formation of metabolites which coeluted with progesterone, 17 alpha-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, testosterone, and 5 alpha-dihydrotestosterone. The newly synthesized steroid comigrating with testosterone was selectively immunodetected by using testosterone antibodies. These data indicate that 17 beta-HSD is expressed in a subpopulation of gliocytes in the frog telencephalon and that telencephalic cells are capable of synthesizing various androgens, including dehydroepiandrosterone, androstenedione, testosterone, and 5 alpha-dihydrotestosterone.