Hypophyseal corticosteroids stimulate somatotrope differentiation in the embryonic chicken pituitary gland

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 3beta-hydroxysteroid dehydrogenase1 (3beta-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.

In ovo injection of betaine promotes adrenal steroidogenesis in pre-hatched chicken fetuses

“…Plasma CORT is vital to embryonic development, and relatively higher level of CORT is required to start up the chick's hatching process ( Mashaly, 1991 ). A previous study pointed out that serum CORT concentration is low in chicken embryos before E9, which remains low until it rises around E14-E16 ( Zheng et al, 2008 ). In this study, betaine injected at E11 in ovo increased plasma CORT concentrations in female fetuses at E19.…”

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“…The eVect of mineralocorticoids and the origin of glucocorticoids that exert this eVect in embryonic development have not been clariWed yet. Zheng et al (2008) established organ culture methods for the chicken embryonic pituitary gland to investigate eVects of corticosterone and aldosterone on growth hormone (GH) mRNA expression. Application of diVerent concentrations of corticosterone and aldosterone lead to a signiWcantly increased number and staining intensity of GH-immunoreactive cells in diVerent parts of the pituitary.…”