Definition
The growth hormone secretagogue receptor type 1a, activated by ghrelin and by synthetic GHRPs such as Ipamorelin.
The growth hormone secretagogue receptor type 1a (GHS-R1a) is a G protein-coupled receptor expressed in the pituitary, hypothalamus and other tissues. It signals mainly through phospholipase C and intracellular calcium. Unusually, synthetic ligands came first: Bowers and colleagues developed GH-releasing peptides in the 1980s, the receptor was cloned in 1996, and its natural ligand, ghrelin, an acylated 28-residue stomach peptide, was identified in 1999. Receptor activation stimulates growth hormone release and, in animal studies, food intake. Peptide agonists studied include GHRP-2, GHRP-6, hexarelin and ipamorelin, which differ in their effects on cortisol and prolactin.