Regulation of the ghrelin gene: Growth hormone-releasing hormone upregulates ghrelin mRNA in the pituitary

Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor (GHS-R), was originally purified from the rat stomach. Ghrelin specifically releases GH following intravenous administration, and its GH-releasing act ivity in vivo is dependent on growth hormone-releasing hormone (GHRH). We p reviously reported that the expression of the GHS-R gene in the pituitary i s developmentally regulated and GHRH infusion increases pituitary levels of GHS-R mRNA, Ghrelin mRNA and peptide have recently been detected in rat an d human pituitaries. However, the regulation of the ghrelin gene in the pit uitary is unknown. In this study, pituitary levels of ghrelin mRNA were mea sured with the reverse transcriptase-polymerase chain reaction in male rats at embryonic day (e)18 and postnatal days 1, 10, 30, and 75. The highest c oncentrations of ghrelin mRNA in the pituitary were observed at e18 and the n they declined with age. The infusion of GHRH (10 mug/h, 4 h) in freely-mo ving adult male rats resulted in a 1.9-fold increase in ghrelin mRNA levels relative to control rats (P < 0.05). These data indicated that the express ion of the ghrelin gene in the pituitary is developmentally regulated and t he pituitary ghrelin/GHS-R signaling system could modulate the regulation o f GH secretion by GHRH.