Differential effects of sham feeding and meal ingestion on ghrelin and pancreatic polypeptide levels: evidence for vagal efferent stimulation mediating ghrelin release

Ghrelin has been suggested to function as an appetite-stimulating signal from the gastrointestinal tract to the brain acting through a vagal afferent pathway. Ghrelin levels rise before meals and fall after meal ingestion. The purpose of this study was to investigate factors which regulate ghrelin release into the circulation by determining changes in systemic ghrelin concentrations after sham feeding and meal ingestion. Methods: Fifteen normal subjects underwent sham feeding of a bacon and cheese toasted sandwich. Serial blood samples were obtained before and every 5 min for another 30 min during sham feeding and for 30 min after actual meal ingestion. Radioimmunoassay was used to measure plasma ghrelin and pancreatic polypeptide concentrations. Results: During sham feeding, plasma ghrelin concentration increased from 1730 +/- 237 to 1917 +/- 269 pg/mL (P < 0.05) and plasma pancreatic polypeptide increased from 417 +/- 50 to 841 +/- 97 pg/mL (P < 0.01). Subsequent meal ingestion was characterized by an increase in pancreatic polypeptide from 782 +/- 88 to 1710 +/- 119 pg/mL (P < 0.01), but no significant change in ghrelin levels. Conclusions: Plasma ghrelin and pancreatic polypeptide concentrations increase with sham feeding. This suggests a vagal efferent pathway mediating ghrelin release. In contrast to pancreatic polypeptide which rises with actual meal ingestion, ghrelin levels did not change.