GHRP-2 vs Kisspeptin

GHRP-2

GHRP-2, also known by the non-proprietary name pralmorelin, is a synthetic hexapeptide that activates the ghrelin receptor, GHS-R1a. Three of its six residues are D-amino acids, including the non-natural D-2-naphthylalanine, a design feature shared with other synthetic growth hormone-releasing peptides. These compounds were developed by screening for growth hormone release before their receptor had been identified; ghrelin, the receptor's natural ligand, was discovered afterwards. GHRP-2 has been examined in receptor and pituitary cell assays, in animal studies, and in short human endocrine studies that measured hormone secretion. Longer-term human data are sparse, and it is not selective for growth hormone, since rises in other pituitary and adrenal hormones have also been recorded.

Kisspeptin

Kisspeptin-10 is a ten-residue peptide amide, the shortest active member of the kisspeptin family encoded by the KISS1 gene. The gene's 145-residue precursor is processed into kisspeptins of 54, 14, 13 and 10 amino acids, which all share the same C-terminal ten residues ending in Arg-Phe-NH2. Research interest in its reproductive role grew after human genetic studies linked loss of kisspeptin receptor function to a failure to enter puberty. It has since been examined in cell and animal models of hypothalamic reproductive control, and in short human physiological studies that measured gonadotropin release. Longer-term human data are limited.

How GHRP-2 acts

GHRP-2 has been reported to act as an agonist at GHS-R1a, a G protein-coupled receptor present on somatotroph cells of the anterior pituitary and on neurons in the hypothalamus. In somatotrophs the receptor couples mainly to Gq and phospholipase C, and the rise in intracellular calcium that follows triggers growth hormone secretion. This route is separate from that of growth hormone-releasing hormone (GHRH), which acts through its own receptor and cyclic AMP. Part of the response is thought to be hypothalamic, through effects on GHRH neurons and on somatostatin signalling. In human studies, modest increases in ACTH, cortisol and prolactin have been reported alongside growth hormone.

How Kisspeptin acts

Kisspeptin-10 has been reported to bind KISS1R, also called GPR54, a G protein-coupled receptor that signals mainly through Gq/11, phospholipase C and intracellular calcium. KISS1R is expressed on gonadotropin-releasing hormone (GnRH) neurons, and kisspeptin signalling is regarded as a principal upstream input controlling their activity. In animal and human physiological studies, exposure has been followed by GnRH release and, downstream, secretion of LH and to a lesser degree FSH from the anterior pituitary. Continuous exposure has been reported in some models to desensitise the receptor, a phenomenon that is itself a topic of study.

The records side by side

• Type: GHRP-2, Growth hormone secretagogue (GHRP); Kisspeptin, Decapeptide (KISS1-derived)
• Length: GHRP-2, 6 amino acids; Kisspeptin, 10 amino acids
• Molecular weight: GHRP-2, 818.0 g/mol; Kisspeptin, 1302.4 g/mol
• Molecular formula: GHRP-2, C45H55N9O6; Kisspeptin, C63H83N17O14

Reading a comparison

A comparison places two records side by side; it does not merge them. Each description above is drawn from that compound's own record, and the two were not necessarily characterised by the same methods, at the same time, or to the same level of detail. Before comparing any attribute, it is worth establishing that both records describe the substance you think they describe — names are not identifiers, and two entries sharing a name can differ in salt form, stereochemistry or the convention used to state a mass. Where a figure carries no method beside it, the comparison is between two reported numbers rather than between two measurements.