Ghrelin growth hormone secretagogue receptor, with the "GHS-R1b" splice being inactive) is involved in mediating a wide variety of biological effects of ghrelin, including: stimulation of growth hormone release, increase in hunger, modulation of glucose and lipid metabolism, regulation of gastrointestinal motility and secretion, protection of neuronal and cardiovascular cells, and regulation of immune function. They are present in high density in the hypothalamus and pituitary, on the vagus nerve (on both afferent cell bodies and afferent nerve endings) and throughout the gastrointestinal tract. Ghrelin promotes intestinal cell proliferation and inhibits apoptosis during inflammatory states and oxidative stress. It also suppresses
Ghrelin promotilin and both are members of the motilin family. Unlike the case of many other endogenous peptides, ghrelin is able to cross the blood-brain-barrier, giving exogenously-administered ghrelin unique clinical potential. Ghrelin was discovered after the ghrelin receptor (called growth hormone secretagogue type 1A receptor or GHS-R) was discovered in 1996 and was reported in 1999. The hormone name is based on its role as a "growth hormone-releasing peptide", with reference to the Proto-Indo-European root "gʰre-", meaning "to grow". The "GHRL" gene produces mRNA which has four exons. Five products arise: the first is the 117-amino acid "preproghrelin". (It is homologous