The etymology of the word is an acronym: GHR (“growth hormone-releasing peptide”) + -lin (“a common hormone suffix”), with an incidental pun on both Proto-Indo-European *gʰreh₁- (“to grow”) and English growling.
It is often referred to as “the hunger hormone”. Also known as lenomorelin (INN), it is a peptide hormone produced by ghrelinergic cells in the gastrointestinal tract which functions as a neuropeptide in the central nervous system.
Besides regulating appetite, ghrelin also plays a significant role in regulating the distribution and rate of use of energy.
When the stomach is empty, ghrelin is secreted. When the stomach is stretched, secretion stops.a It acts on hypothalamic brain cells both to increase hunger, and to increase gastric acid secretion and gastrointestinal motility to prepare the body for food intake.
The receptor for ghrelin, the ghrelin/growth hormone secretagogue receptor (GHS-R), is found on the same cells in the brain as the receptor for leptin, the satiety hormone that has opposite effects from ghrelin.
Ghrelin also plays an important role in regulating reward perception in dopamine neurons that link the ventral tegmental area to the nucleus accumbens (a site that plays a role in processing sexual desire, reward, and reinforcement, and in developing addictions) through its colocalized receptors and interaction with dopamine and acetylcholine.
Ghrelin is encoded by the GHRL gene and is presumably produced from the cleavage of the prepropeptide ghrelin/obestatin. Full-length preproghrelin is homologous to promotilin and both are members of the motilin family.
Continuous infusion of ghrelin increased body mass and food intake, but did not increase muscle mass nor improve muscle function, in a long-term critical illness recovery model. Further studies with pulsatile ghrelin delivery or additional anabolic stimuli may further clarify the utility of ghrelin in survivors of critical illness 1).