Category

GHRPs & Secretagogues

Growth hormone secretagogues that act at GHS-R1a, the ghrelin receptor: four synthetic peptides and one non-peptide. They are filed apart from the GHRH analogues because they reach the somatotroph through a different receptor, and most comparative work in this department pairs one molecule from each shelf rather than treating the two as alternatives.

The four peptides separate by backbone length and by how clean the release is. GHRP-6 is the first-generation hexapeptide — His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, 873.01 g/mol — and the one carrying the appetite, gastric-motility and cytoprotection literature. GHRP-2, also called pralmorelin, swaps the first two residues for D-Ala and D-2-Nal at 817.97 g/mol and is the usual potency reference when secretagogues are ranked against one another. Hexarelin is GHRP-6 with a 2-methyl group added to the tryptophan, 887.04 g/mol, and has CD36 affinity alongside GHS-R1a, which is why it appears in cardiac signalling and receptor-desensitisation work that the others do not. Ipamorelin is the outlier: a pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2 at 711.85 g/mol, and the most selective of the group — the one chosen where a design needs GH release without the cortisol and prolactin movement that accompanies the hexapeptides.

MK-677 (ibutamoren) is not a peptide at all. It is a 528.66 g/mol spiropiperidine that binds the same receptor and survives the gut, so it is stocked as 12.5 mg and 25 mg capsules, thirty per bottle, and needs no reconstitution. The four peptides are lyophilized powder in 2 mg to 10 mg vials, and the strengths are not uniform: ipamorelin and hexarelin start at 2 mg, GHRP-2 and GHRP-6 at 5 mg. A molar-matched comparison across the group therefore needs the reconstitution volume set per vial rather than the same volume in each.