Ghrelin Expression in Fetal, Infant, and Adult Human Lung

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Abstract
Ghrelin is a recently identified hormone with potent growth hormone (GH)-releasing activity. It is produced by rat and human gastric endocrine cells and by the pituitary, hypothalamus, placenta, and by gastroenteropancreatic tumors. No evidence of ghrelin production by foregut-derived organs other than stomach has been provided to date. The aim of the present study was to investigate ghrelin expression by human fetal (20 cases), infant (13 cases), and adult (seven cases) lungs by immunohistochemistry, in situ hybridization, and RT-PCR. Expression of the GH secretagogue receptor, the endogenous receptor for ghrelin, was also investigated by RT-PCR. Ghrelin protein was found in the endocrine cells of the fetal lung in decreasing amounts from embryonic to late fetal periods. Its expression was maintained in newborns and children under 2 years but was virtually absent in older individuals. Scattered positive cells were also found in the trachea and the esophagus. Ghrelin mRNA was detected in adult lung by the more sensitive RT-PCR technique. GHS receptor mRNA was detected in nine cases of infant and adult lungs, possibly indicating the existence of local autocrine circuits. We conclude that the fetal lung is an additional source of circulating ghrelin, whose functions at the respiratory tract level remain to be clarified.