We have demonstrated that the quail brain possesses the cholesterol side-chain cleavage enzyme (cytochrome P450scc) and 3β-hydroxysteroid dehydrogenase/Δ5-Δ4-isomerase (3β-HSD) and produces pregnenolone, pregnenolone sulfate and progesterone from cholesterol. We have also demonstrated the expression of cytochrome P450 17α-hydroxylase/c17,20-lyase (P45017α,lyase) and the conversion of progesterone to 17α-hydroxyprogesterone in the same avian species. Therefore, the present study was conducted to investigate androgen biosynthesis from progesterone in the avian brain. Employing biochemical techniques combined with HPLC and TLC analyses, the conversion of progesterone to androstenedione, an androgen precursor, was found in quail brain. The present biochemical analysis further revealed the conversion of androstenedione to testosterone, indicating the presence of 17β-hydroxysteroid dehydrogenase (17β-HSD) in the quail brain. The formation of testosterone from progesterone was also detected in the brain. Testosterone formation was more intense in the diencephalon, whereas the concentration of endogenous testosterone in the diencephalon was lower than those in other brain regions in castrated quails. However, the concentration of endogenous estradiol, a metabolite of testosterone by cytochrome P450arom, was highest in the diencephalon of castrated quails. These results suggest that testosterone biosynthesis occurs in the quail brain, in particular the diencephalon. Testosterone may subsequently be converted to estradiol.
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