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 biosynt hesis of testosterone has never been reported in the central nervous s ystem. 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 testoste rone and estradiol) in the brain of the male frog Rana ridibunda. By u sing an antiserum against human type I placental 17 beta-HSD, immunore activity was localized in a discrete group of ependymal glial cells bo rdering the telencephalic ventricles. HPLC analysis of telencephalon a nd hypothalamus extracts combined with testosterone radioimmunoassay r evealed the existence of two peaks coeluting with testosterone and 5 a lpha-dihydrotestosterone. After HPLC purification, testosterone was id entified by gas chromatography/mass spectrometry, Incubation of telenc ephalon slices with [H-3]pregnenolone resulted in the formation of met abolites which coeluted with progesterone, 17 alpha-hydroxyprogesteron e, dehydroepiandrosterone, androstenedione, testosterone, and 5 alpha- dihydrotestosterone. The newly synthesized steroid comigrating with te stosterone was selectively immunodetected by using testosterone antibo dies. These data indicate that 17 beta-HSD is expressed in a subpopula tion of gliocytes in the frog telencephalon and that telencephalic cel ls are capable of synthesizing various androgens, including dehydroepi androsterone, androstenedione, testosterone, and 5 alpha-dihydrotestos terone.