GHRP-6

GHRP-6 is a synthetic hexapeptide, His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, of molecular weight near 873 g/mol and CAS 87616-84-0. First described in 1984, it was among the earliest small peptides shown to act on the pituitary in a way that did not resemble any then-known releasing factor. Its target was later identified as the G protein-coupled growth hormone secretagogue receptor of pituitary and hypothalamus, whose endogenous ligand, ghrelin, is an octanoylated 28-residue peptide isolated from stomach.

GHRP-6 in the research literature

Early characterisation reported concentration-related growth hormone release in pituitary incubates and activity across rats, monkeys, lambs and calves, without concomitant release of LH, FSH, TSH or prolactin. In rat primary pituitary cell monolayer culture, GHRP-6 and GRF-44 showed additive responses and differing culture requirements and cross-desensitisation patterns, which the authors interpreted as action through distinct somatotroph receptors. Specific, saturable and reversible binding sites were subsequently demonstrated on porcine anterior pituitary and hypothalamic membranes, with binding inhibited by D-Lys3-GHRP.

Beyond the pituitary, GHRP-6 has been examined in non-endocrine model systems: in rat hypothalamus and cerebellum it reduced monosodium glutamate-associated activation of caspases 9 and 7 and fragmentation of poly(ADP-ribose) polymerase, and in cultured rat intestinal epithelial IEC-6 cells it increased the rate of cell migration roughly threefold without altering thymidine incorporation.