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KC McCowen, JA Maykel, BR Bistrian, and PR Ling

Ghrelin is a peptide secreted mainly by gastric parietal cells that may play a role in appetite regulation. Circulating ghrelin is abruptly lowered by food intake, but factors involved in ghrelin regulation remain unclear. The aim of this study was to determine whether intravenous glucose infusion lowers ghrelin, and to determine whether glucose, insulin or some measure of insulin action best predicts the effect of feeding on ghrelin. Rats were infused over 3 h with either A. saline (controls); B. dextrose to steady state blood glucose approximately 16.7 mM, or C. insulin 7.5 mU/kg x min, plus dextrose as needed to clamp to euglycemic basal concentrations. During 3 h of infusion, group B had significantly greater (P<0.01) glucose, 17.4+/-0.3 mM, than groups A (6.6+/-0.3) or C (6.1+/- 0.2). Groups B and C had hyperinsulinemia at the end of the 3 h infusion (894+/-246, 804+/-156 pM) compared with saline-infused (222+/-24 pM, P<0.01). Ghrelin concentrations were reduced (P<0.01) in both hyperinsulinemic groups (B=85+/-2; C=103+/-0.6 pM) versus controls (163+/-9). Ghrelin was strongly correlated with insulin (r=-0.68), glucose infusion rate (r=-0.75) and free fatty acids (r=0.67), when all 3 groups were combined, although only the 2 latter variables were independent predictors of ghrelin. In conclusion, neither a rise in blood glucose nor presence of nutrient in the stomach is required for the effect of feeding on ghrelin. The data suggest that whole body insulin responsiveness plays either a direct or indirect role in meal-related ghrelin inhibition.