Localization of 17beta-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 17beta-hydroxysteroid dehydrogenase (17beta-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 17beta-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 5alpha-dihydrotestosterone. After HPLC purification, testosterone was identified by gas chromatography/mass spectrometry. Incubation of telencephalon slices with [3H]pregnenolone resulted in the formation of metabolites which coeluted with progesterone, 17alpha-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, testosterone, and 5alpha-dihydrotestosterone. The newly synthesized steroid comigrating with testosterone was selectively immunodetected by using testosterone antibodies. These data indicate that 17beta-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 5alpha-dihydrotestosterone. IMAGES:

已在大脑中鉴定出多种参与孕烯族与孕烷族类固醇生成的酶，但中枢神经系统中睾酮的生物合成尚未见报道。本研究以雄性池蛙（Rana ridibunda）的脑组织为对象，探究了17β-羟类固醇脱氢酶（17beta-hydroxysteroid dehydrogenase, 17beta-HSD，EC 1.1.1.62，一种催化睾酮与雌二醇生成的关键酶）的分布与生物活性。通过使用针对人I型胎盘17β-羟类固醇脱氢酶的抗血清，发现免疫反应性定位于端脑脑室周边的离散室管膜胶质细胞群中。对端脑与下丘脑提取物进行高效液相色谱（High Performance Liquid Chromatography, HPLC）分析并结合睾酮放射免疫测定，结果显示存在两个与睾酮和5α-二氢睾酮共洗脱的峰。经高效液相色谱纯化后，通过气相色谱/质谱联用法（gas chromatography/mass spectrometry）鉴定出睾酮。将端脑脑片与氚标记孕烯醇酮（[3H]pregnenolone）共孵育，可生成与孕酮（progesterone）、17α-羟孕酮（17alpha-hydroxyprogesterone）、脱氢表雄酮（dehydroepiandrosterone）、雄烯二酮（androstenedione）、睾酮及5α-二氢睾酮共洗脱的代谢产物。利用睾酮抗体可特异性免疫检测到与睾酮共迁移的新合成类固醇。上述结果表明，池蛙端脑胶质细胞亚群表达17β-羟类固醇脱氢酶，且端脑细胞能够合成包括脱氢表雄酮、雄烯二酮、睾酮及5α-二氢睾酮在内的多种雄激素。IMAGES: