J. Kamegai et al., Regulation of the ghrelin gene: Growth hormone-releasing hormone upregulates ghrelin mRNA in the pituitary, ENDOCRINOL, 142(9), 2001, pp. 4154-4157
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.