The presence of both the GH secretagogue (GHS) receptor and ghrelin in the pancreas indicates an involvement of this hormone in glucose metabolism. Ghrelin secretion is increased by fasting and energy restriction, decreased by food intake, glucose load, insulin and somatostatin in normal adults; however, food intake is not able to inhibit circulating ghrelin levels in children, suggesting that the profile of ghrelin secretion in children is different from that in adults. Moreover, how ghrelin secretion is regulated in childhood as a function of fat mass is still unclear.
We studied the effect of oral glucose load (75 g solution orally) on circulating total ghrelin levels in 14 obese children (group A, four boys and 10 girls, aged 9.3 +/- 2.3 years) and 10 lean children (group B, five boys and five girls, aged 9.7 +/- 3.8 years).
In all the sessions, blood samples were collected every 30 min from 0 up to +120 min. GH, insulin and glucose levels were assayed at each time point.
Glucose peaks following an oral glucose tolerance test (OGTT) in groups A and B were similar; however, both basal and OGTT-stimulated insulin levels in group A were higher than in group B (P < 0.05). Basal total ghrelin levels in group A (281.3 +/- 29.5 pg/ml) were lower (P < 0.0005) than in group B (563.4 +/- 81.5 pg/ml). In both groups A and B, the OGTT inhibited total ghrelin levels (P < 0.005). In terms of absolute values, total ghrelin levels in group A were lower (P < 0.0005) than those in group B at each time point after glucose load. The percentage nadir in total ghrelin levels recorded in group A (-25% at 90 min) was similar to that recorded in group B (-31% at 120 min). Total ghrelin levels were negatively associated with BMI (r = 0.5, P < 0.005) but not with glucose or insulin levels.
Ghrelin secretion is reduced in obese children. It is, however, equally sensitive in both obese and lean children to the inhibitory effect of oral glucose load.