Developmental changes in progesterone biosynthesis and metabolism in the quail brain

We have recently 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. To elucidate the developmental changes in progesterone biosynthesis and its metabolism in the quail brain, we examined the expression and activity of 3β-HSD and progesterone metabolite(s) during embryonic and post-hatched ages. Both the progesterone concentration and 3β-HSD mRNA expression in the brain were almost constant during embryonic and post-hatched ages. The conversion of pregnenolone to progesterone (net 3β-HSD enzymatic activity) was also constant during development and at maturity. However, without radioinert progesterone, the production of progesterone was drastically reduced in the embryonic brain, indicating active progesterone metabolism at the embryonic stage. Biochemical analysis together with HPLC and TLC revealed that only the embryonic brain actively produced 5β-dihydroprogesterone from progesterone. Thus, progesterone production may be constant during embryonic and post-hatched development and in adulthood, whereas 5β-dihydroprogesterone may be produced actively only in embryonic life due to 5β-reductase.