The expression of cholesterol side-chain cleavage cytochrome P450 (P450scc), 17α-hydroxylase cytochrome P450 (P45017α), and 17α -hydroxysteroid dehydrogenase (3βHSD) was studied in bovine placenta and fetal adrenal glands throughout gestation. The levels of expression of these enzymes were much lower in the placenta than in the adrenals by Western and Northern analyses. The levels of P450scc, however, remained relatively constant in bovine placenta and fetal adrenal glands at all gestational stages studied. In contrast, P45017α expression was higher in both the placenta and the fetal adrenal glands during the early stages of pregnancy, but declined markedly in both tissues through the period of midgestation. The expression of P45017α increased markedly in the fetal adrenal glands in late gestation. The levels of 3βHSD were extremely low in placental tissues, but were higher in the fetal adrenals, where they were found to be slightly elevated in early and late gestation compared to those in midgestational stages. Immuno-cytochemical examination of the levels of P45017α and 3βHSD in the fetal adrenal glands correlated with the results of Western and Northern analyses. In addition, the morphology and distribution of these two enzymes in the developing bovine fetal adrenal glands indicated that while the early activated gland is functional relative to the ability to secrete steroids, structural and functional organization more typical of mature adrenal glands is not achieved until the time of activation of the fetal adrenals in late gestation.
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