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Dexamethasone Increases Growth Hormone (GH)‐Releasing Hormone (GRH) Receptor mRNA Levels in Cultured Rat Anterior Pituitary Cells
Author(s) -
Tamaki M.,
Sato M.,
Matsubara S.,
Wada Y.,
Takahara J.
Publication year - 1996
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1046/j.1365-2826.1996.04779.x
Subject(s) - medicine , endocrinology , glucocorticoid receptor , anterior pituitary , receptor , dexamethasone , glucocorticoid , biology , steroid hormone , messenger rna , growth hormone–releasing hormone , prolactin , gene expression , antiglucocorticoid , somatotropic cell , pituitary gland , hormone , growth hormone , gene , biochemistry
To examine the effects of glucocorticoid (GC) on growth hormone (GH)‐releasing hormone (GRH) receptor gene expression, a highly‐sensitive and quantitative reverse‐transcribed polymerase chain reaction (RT‐PCR) method was used in this study. Rat anterior pituitary cells were isolated and cultured for 4 days. The cultured cells were treated with dexamethasone for 2, 6, and 24 h. GRH receptor mRNA levels were determined by competitive RT‐PCR using a recombinant RNA as the competitor. Dexamethasone significantly increased GRH receptor mRNA levels at 5 nM after 6‐ and 24 h‐incubations, and the maximal effect was found at 25 nM. The GC receptor‐specific antagonist, RU 38486 completely eliminated the dexamethasone‐induced enhancement of GRH receptor mRNA levels. Dexamethasone did not alter the mRNA levels of β ‐actin and prolactin at 5 nM for 24 h, whereas GH mRNA levels were significantly increased by the same treatment. The GH response to GRH was significantly enhanced by the 24‐h incubation with 5 nM dexamethasone. These findings suggest that GC stimulates GRH receptor gene expression through the ligand‐activated GC receptors in the rat somatotrophs. The direct effects of GC on the GRH receptor gene could explain the enhancement of GRH‐induced GH secretion.