Ipamorelin

Ipamorelin is a synthetic pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, with a molecular weight near 712 g/mol. It emerged from a chemistry programme built around compounds lacking the central Ala-Trp dipeptide of growth hormone-releasing peptide-1, and it acts at the ghrelin receptor (GHS-R1a) rather than at the receptor for growth hormone-releasing hormone. The ghrelin receptor itself is a G protein-coupled receptor cloned from pituitary and hypothalamic tissue, and its endogenous ligand, the octanoylated 28-residue peptide ghrelin, was later isolated from stomach tissue.

Ipamorelin in the research literature

In primary rat pituitary cell culture, ipamorelin released growth hormone with potency and efficacy similar to GHRP-6, and profiling with GHRP and GHRH antagonists indicated that it acts through a GHRP-type receptor rather than the GHRH receptor. The same report described growth hormone release in anaesthetised rats and in swine, and noted that, unlike GHRP-6 and GHRP-2, ipamorelin did not raise plasma ACTH or cortisol above levels seen with GHRH stimulation, and that none of the secretagogues examined altered FSH, LH, prolactin or TSH.

A separate rodent study reported an increase in longitudinal bone growth rate measured by tetracycline labelling in the proximal tibia of adult female rats, without changes in total IGF-I, IGF binding proteins or serum markers of bone formation and resorption.