Expression and activity of 3 beta-hydroxysteroid dehydrogenase Delta(5)-Delta(4)-isomerase in different regions of the avian brain

Recently, we have demonstrated, using biochemical and immunochemical method s, that the quail brain possesses the cholesterol side-chain cleavage enzym e (cytochrome P450scc) and produces pregnenolone and its sulfate ester. To clarify progesterone biosynthesis in the avian brain, therefore, we examine d the expression of messenger RNA (mRNA) encoding for the enzyme 3 beta-hyd roxysteroid dehydrogenase/Delta(5)-Delta(4)-isomerase (3 beta-HSD) and its enzymatic activity using the quail. RT-PCR analysis together with Southern hybridization indicated the expression of 3 beta-HSD mRNA in the brain of s exually mature birds but with no clear-cut sex difference. Employing bioche mical techniques combined with HPLC analysis, the conversion of pregnenolon e to progesterone was found in brain slices of mature males. Progesterone b iosynthesis was increased in a time dependent manner and completely abolish ed by trilostane, a specific inhibitor of 3 beta-HSD. The enzymatic activit y of 3 beta-HSD was greatest in the cerebrum and lowest in the mesencephalo n. A specific RIA indicated that progesterone concentrations in the differe nt brain regions closely followed the level of 3 beta-HSD activity. High le vels of progesterone concentration were observed in the diencephalon and ce rebrum with lowest values in the mesencephalon. Progesterone levels in the brain regions were significantly higher than those in the plasma. These res ults suggest that the avian brain possesses not only cytochrome P450scc but also 3 beta-HSD and produces progesterone. It is also indicated that proge sterone biosynthesis in the avian brain may be region-dependent. (C) 1999 E lsevier Science B.V. All rights reserved.