Ghrelin is a recently discovered gastric peptide that increases appetite, glucose oxidation, and lipogenesis and stimulates the secretion of GH. In contrast to ghrelin, GH promotes lipolysis, glucose production, and insulin secretion. Both ghrelin and GH are suppressed by intake of nutrients, especially glucose. The role of GH in the regulation of ghrelin has not yet been established.

We investigated the effect of GH on circulating levels of ghrelin in relation to its effects on glucose, insulin, body composition, and the adipocyte-derived peptides leptin and adiponectin. Thirty-six patients with adult-onset GH deficiency received recombinant human GH for 9 months in a placebo-controlled study. Body composition and fasting serum analytes were assessed at baseline and at the end of the study. The GH treatment was accompanied by increased serum levels of IGF-I, reduced body weight (−2%) and body fat (−27%), and increased serum concentrations of glucose (+10%) and insulin (+48%). Ghrelin levels decreased in 30 of 36 subjects by a mean of −29%, and leptin decreased by a mean of −24%. Adiponectin increased in the women only. The decreases in ghrelin and leptin correlated with changes in fat mass, fat-free mass, and IGF-I. The reductions in ghrelin were predicted independently of the changes in IGF-I and fat mass.

It is likely that the reductions in ghrelin and leptin reflect the metabolic effects of GH on lipid mobilization and glucose production. Possibly, a suppression of ghrelin promotes loss of body fat in GH-deficient patients receiving treatment. The observed correlation between the changes in ghrelin and IGF-I may suggest that the GH/IGF-I axis has a negative feedback on ghrelin secretion.