Food intake suppresses plasma levels of the gastric peptide ghrelin in humans. We hypothesize that the food intake- suppression of ghrelin could be secondary to the plasma glucose and insulin changes after a meal. The aim of this study was to compare the effect of the administration of a combined pulse of glucose and insulin to the effect of one meal on plasma ghrelin in human subjects. A secondary aim was to study the effect of an oral glucose load on ghrelin levels.
Methods: Experiment 1 (n = 10) studied plasma glucose, insulin, leptin and ghrelin for 6 hours after a 790 kcal liquid meal. In Experiment 2 (n = 7), a subcutaneous pulse of insulin (Humalog 0.03U/kg) and an I.V. infusion of glucose were administered in order to mimic the plasma changes of glucose and insulin after a meal, and plasma ghrelin levels were monitored for 9 h. The OGTT data was used to study the effect of oral glucose on ghrelin.
Results: A mixed liquid meal decreased basal serum ghrelin by 26% at 40 minutes (p = 0.009). A 75 gr oral glucose load suppresses ghrelin by 28% at 30 minutes. Contrary to the meal effect, the parenteral administration of insulin and glucose did not suppress serum ghrelin.
Conclusion: Unlike food intake, the administration of insulin and glucose does not suppress ghrelin levels. These data suggest that the suppressive effect of food intake or oral glucose on serum ghrelin is unlikely mediated by the changes of plasma insulin and glucose observed after the ingestion.