Glucocorticoids regulate pituitary growth hormone secretagogue receptor gene expression

Glucocorticoids regulate growth hormone (GH) secretion by modulating both h ypothalamic and pituitary function. At the level of the pituitary, glucocor ticoids increase GH and GH-releasing hormone receptor (GHRH-R) gene express ion. To test if glucocorticoids might also regulate the pituitary expressio n of the recently identified GH secretagogue (GHS) receptor, GHS-R; adult m ale rats were adrenalectomized or sham operated, and treated with the synth etic glucocorticoid (dexamethasone, 200 mu g/day) or vehicle for 8 days. Pi tuitary GHS-R mRNA levels were assessed by reverse transcriptase polymerase chain reaction (RT-PCR). Adrenalectomy decreased pituitary GHS-R mRNA to 4 5% of vehicle-treated, sham-operated rats (P < 0.05). Administration of dex amethasone increased GHS-R mRNA levels in sham-operated as well as in adren alectomized rats (199 +/- 24% (P < 0.05) and 369 +/- 48% (P < 0.01) of vehi cle-treated controls). Addition of dexamethasone to primary rat pituitary c ell cultures increased GHS-R mRNA levels in a dose- and time-dependent mann er while the transcriptional inhibitor, actinomycin D, completely blocked t he stimulatory action of dexamethasone. Taken together, these results sugge st glucocorticoids directly increase pituitary GHS-R mRNA levels by stimula ting GHS-R gene transcription.