Ghrelin

Ghrelin is a 28-amino acid peptide hormone predominantly synthesised by enteroendocrine cells of the gastric fundus, earning it the designation as the 'hunger hormone'. It acts as the endogenous ligand for the growth hormone secretagogue receptor type 1a (GHS-R1a), stimulating both appetite and growth hormone (GH) release from the anterior pituitary gland. Ghrelin undergoes a unique post-translational modification called octanoylation at its third serine residue, which is essential for its ability to bind GHS-R1a and cross the blood-brain barrier. Beyond appetite regulation and GH secretion, ghrelin plays roles in glucose metabolism, gastrointestinal motility, cardiovascular protection, and immune modulation. Synthetic peptides like Ipamorelin mimic ghrelin's GH-releasing action while being more selective for the GHS receptor, avoiding ghrelin's broader appetite-stimulating and cortisol-elevating effects.