Plasma levels of acylated ghrelin during an oral glucose tolerance test in obese children

Objective: Ghrelin is an acylated peptide with octanoyl modification, which is essential for its GH-releasing ability. Coexpression of GH secretagogue receptor (GHS-R) and ghrelin in the pancreas suggests that this peptide is involved in glucose metabolism. The other form of the molecule, the non-acylated ghrelin, has been reported to be devoid of any pituitaric endocrine activities. Previous reports demonstrated that plasma total ghrelin levels decrease after oral glucose administration in obese children, but no data are available about the plasma levels of acylated ghrelin. Therefore, in the present study the plasma levels of acylated ghrelin were measured in obese and control children during oral glucose tolerance test (OGTT). Materials and methods: Acylated ghrelin response to OGTT was evaluated in 11 obese and 9 age-matched control children. All subjects received 0.75 g/kg (maximum 75 g) glucose solution orally after an overnight fast. Acylated ghrelin, insulin, glucose, and GH were determined at 0, 30, 60 and 120 min, and leptin at 0 min of the OGTT. Results: Plasma basal levels of acylated ghrelin were significantly lower in the obese children than in the controls (66.3 +/- 6.7 vs 97.2 +/- 14.4 pg/ml, p < 0.05). The plasma acylated ghrelin concentration decreased significantly at 30 and 60 min in the control group (53.3 +/- 9.9 and 57.4 +/- 7.0 pg/ml, p < 0.05), but not in the obese group (64.7 +/- 9.6 and 49.3 +/- 4.6 pg/ml) as compared to the basal value. In the obese group the acylated ghrelin level was significantly higher at 120 min, than at 0 min (91.6 +/- 9.8 vs 66.3 +/- 6.7 pg/ml, p < 0.05). Conclusions: There was no rapid fall in plasma levels of acylated ghrelin in obese children after OGTT at 30 min, but there was an increase at 120 min, suggesting that the dynamic of the response to OGTT is slower and there is an upregulation of active ghrelin in the second half of OGTT in obese children.