title: Glucocorticoids regulate pituitary growth hormone secretagogue receptor gene expression.
abstract: Glucocorticoids regulate growth hormone (GH) secretion by modulating both hypothalamic and pituitary function. At the level of the pituitary, glucocorticoids increase GH and GH-releasing hormone receptor (GHRH-R) gene expression. To test if glucocorticoids might also regulate the pituitary expression of the recently identified GH secretagogue (GHS) receptor, GHS-R; adult male rats were adrenalectomized or sham operated, and treated with the synthetic glucocorticoid (dexamethasone, 200 microg/day) or vehicle for 8 days. Pituitary GHS-R mRNA levels were assessed by reverse transcriptase polymerase chain reaction (RT-PCR). Adrenalectomy decreased pituitary GHS-R mRNA to 45% of vehicle-treated, sham-operated rats (P < 0.05). Administration of dexamethasone increased GHS-R mRNA levels in sham-operated as well as in adrenalectomized rats (199 +/- 24% (P < 0.05) and 369 +/- 48% (P < 0.01) of vehicle-treated controls). Addition of dexamethasone to primary rat pituitary cell cultures increased GHS-R mRNA levels in a dose- and time-dependent manner while the transcriptional inhibitor, actinomycin D, completely blocked the stimulatory action of dexamethasone. Taken together, these results suggest glucocorticoids directly increase pituitary GHS-R mRNA levels by stimulating GHS-R gene transcription.
authors.affiliation: Department of Medicine, Nippon Medical School, Tokyo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Tamura
authors.forename: J
authors.initials: J
authors.lastname: Kamegai
authors.forename: H
authors.initials: H
authors.lastname: Sugihara
authors.forename: R D
authors.initials: RD
authors.lastname: Kineman
authors.forename: L A
authors.initials: LA
authors.lastname: Frohman
authors.forename: I
authors.initials: I
authors.lastname: Wakabayashi
mesh_terms: D000315:Adrenalectomy; D000818:Animals; D003609:Dactinomycin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology*; D008297:Male; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018013:Receptors, Neuropeptide / Q000235:genetics*; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000235:genetics*; D013997:Time Factors
chemical_list: D005938:Glucocorticoids; D019384:Nucleic Acid Synthesis Inhibitors; D012333:RNA, Messenger; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D003609:Dactinomycin; D003907:Dexamethasone; C048250:somatotropin releasing hormone receptor