Hypophyseal corticosteroids stimulate somatotrope differentiation in the embryonic chicken pituitary gland |
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Authors: | Jun Zheng Hiroyasu Takagi Chihiro Tsutsui Akihito Adachi Takafumi Sakai |
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Institution: | (1) Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-Ohkubo, Saitama Saitama, 338-8570, Japan |
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Abstract: | Although it is known that glucocorticoids induce differentiation of growth hormone (GH)-producing cells in rodents and birds,
the effect of mineralocorticoids on GH mRNA expression and the origin of corticosteroids affecting somatotrope differentiation
have not been elucidated. In this study, we therefore carried out experiments to determine the effect of mineralocorticoids
on GH mRNA expression in the chicken anterior pituitary gland in vitro and to determine whether corticosteroids are synthesized
in the chicken embryonic pituitary gland. In a pituitary culture experiment with E11 embryos, both corticosterone and aldosterone
stimulated GH mRNA expression and increased the number of GH cells in both lobes of the pituitary gland in a dose-dependent
manner. These effects of the corticosteroids were significantly reversed by pretreatment with mifepristone, a glucocorticoid
receptor (GR) antagonist, or spironolactone, a mineralocorticoid receptor (MR) antagonist. Interestingly, an in vitro serum-free
culture experiment with an E11 pituitary gland showed that the GH mRNA level spontaneously increased during cultivation for
2 days without any extra stimulation, and this increase in GH mRNA level was completely suppressed by metyrapone, a corticosterone-producing
enzyme P450C11 inhibitor. Moreover, progesterone, the corticosterone precursor, also stimulated GH mRNA expression in the
cultured chicken pituitary gland, and this effect was blocked by pretreatment with metyrapone. We also detected mRNA expression
of enzymes of cytochrome P450 cholesterol side chain cleavage (P450scc) and 3β-hydroxysteroid dehydrogenase1 (3β-HSD1) in
the developmental chicken pituitary gland from E14 and E18, respectively. These results suggest that mineralocorticoids as
well as glucocorticoids can stimulate GH mRNA expression and that corticosteroids generated in the embryonic pituitary gland
by intrinsic steroidogenic enzymes stimulate somatotrope differentiation. |
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Keywords: | Chicken Somatotrope Differentiation Glucocorticoid Mineralocorticoid Receptor Antagonist Inhibitor Steroidogenic enzyme |
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