Objective: Concentrations of the orexigenic peptide ghrelin is affected by a number of hormones, which also affect circulating levels of free fatty acids (FFAs). The present study was therefore designed to determine the direct effect of FFAs on circulating ghrelin.
Design: Eight lean, healthy men were examined for 8 h on four occasions using variable infusion rates (0, 3, 6 and 12 microl/kg per min) of intralipid to create different plasma FFA concentrations. Constant levels of insulin and GH were obtained by administration of acipimox (250 mg) and somatostatin (300 microg/h). At the end of each study day a hyperinsulinaemic-euglycaemic clamp was performed.
Results: Four distinct levels of FFAs were obtained at the end of the lipid infusion period (FFA(LIPID): 0.03 +/- 0.00 vs: 0.49 +/- 0.04, 0.92 +/- 0.08 and 2.09 +/- 0.38 mmol/l; ANOVA P < 0.0001) and during hyperinsulinaemia (FFA(LIPID+INSULIN): 0.02 +/- 0.00 vs: 0.34 +/- 0.03, 0.68 +/- 0.09 and 1.78 +/- 0.32 mmol/l; ANOVA P < 0.0001). Whereas, somatostatin infusion alone reduced ghrelin concentration by approximately 67%, concomitant administration of increasing amounts of intralipid reduced circulating ghrelin by a further 14, 19 and 19% respectively (change in ghrelin: 0.52 +/- 0.05 vs: 0.62 +/- 0.06, 0.72 +/- 0.09 and 0.71 +/- 0.05 microg/l; ANOVA P = 0.04). No further reduction in ghrelin concentration was observed during hyperinsulinaemia.
Conclusion: FFA exposure between 0 and 1 mmol/l significantly suppresses ghrelin levels independent of ambient GH and insulin levels.