Chronic Changes in Peripheral Growth Hormone Levels Do Not Affect Ghrelin Stomach mRNA Expression and Serum Ghrelin Levels in Three Transgenic Mouse Models

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Abstract
Ghrelin is an endogenous ligand for the growth hormone secretagogue (GHS) receptor. Ghrelin is involved in feeding behaviour and is a potent stimulator of GH release. Chronically increased GH concentrations are known to negatively regulate the pituitary GHS receptor. This study tested whether chronic changes in peripheral GH levels/action affect ghrelin mRNA expression and circulating concentrations of ghrelin. Stomach ghrelin mRNA expression and serum concentrations of ghrelin were measured in three groups of transgenic mice and the respective control animals: group 1, GH-receptor gene disrupted mice (GHR/KO); group 2, mice expressing bovine GH (bGH); and group 3, mice expressing GH-antagonist (GHA). Ghrelin mRNA expression in the stomach, pituitary and hypothalamus of young adult male rats were measured using reverse-transcription-polymerase chain reaction. Ghrelin mRNA expression levels were approximately 3000-fold higher in rat stomach than in rat pituitary. Ghrelin mRNA expression in rat hypothalamus was below the detection limits of our assay. Stomach ghrelin mRNA expression, as well as serum concentrations of ghrelin, did not change significantly in any of the three mouse groups compared to the respective control group. These data support previous observations that the stomach is the main source of circulating ghrelin, and also indicate that stomach ghrelin mRNA expression and serum concentrations of ghrelin are not affected by chronic changes in peripheral GH/insulin-like growth factor-I levels/action.