GLOSSARY

Ghrelin is a 28-amino-acid peptide hormone secreted mainly by X/A-like cells in the gastric fundus; it is the only known peripheral hormone that increases hunger and food intake, which is why it is called the “hunger hormone”.

Characteristics

• Activation: requires acylation (adding octanoic acid) by the enzyme GOAT.
• Secretion pattern: rises before meals (about two-fold) and falls rapidly after eating; influenced by habit and usual mealtimes (a conditioned response).
• Receptor: GHS-R1a in the hypothalamus (arcuate nucleus, activating NPY/AgRP neurons).

Effects

• Stimulating appetite and food intake.
• Stimulating growth hormone release (its name derives from Growth Hormone Release).
• Increasing fat storage and reducing energy expenditure.
• Increasing gastric motility and acid secretion.
• A role in food reward (the dopaminergic system).

Influencing Factors