Hexarelin

Hexarelin (His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH₂, also known as examorelin) is a synthetic hexapeptide and the most potent member of the GHRP class of growth hormone secretagogues. Its structure represents the peak of the Bowers medicinal-chemistry optimization program: the D-2-methyltryptophan residue at position 2 creates an extended hydrophobic contact surface with the GHS-R1a receptor-binding pocket, yielding binding affinity and potency that exceed both GHRP-2 and GHRP-6 — and, critically, enabling GH release even under conditions where somatostatin tone is pathologically elevated and other GHRPs fail.

At the pituitary level, hexarelin's primary mechanism mirrors that of other GHRPs: GHS-R1a agonism → Gαq/11 → PLC → IP3 → calcium mobilization → GH vesicle exocytosis, combined with somatostatin antagonism. However, hexarelin's exceptionally high receptor affinity allows it to overcome somatostatin-mediated inhibition more effectively than other GHRPs — a property demonstrated most clearly in critical-illness models where endogenous somatostatin is markedly elevated and other GH secretagogues lose efficacy.

What makes hexarelin mechanistically unique is its direct cardiac activity mediated through the CD36 receptor — a scavenger receptor on cardiomyocytes, endothelial cells, and fibroblasts that is distinct from GHS-R1a. Hexarelin binding to CD36 activates cardioprotective signaling cascades (PI3K/Akt, eNOS) that reduce ischemia-reperfusion injury, inhibit cardiomyocyte apoptosis, and suppress cardiac fibrosis — effects documented at doses that do not elevate systemic GH/IGF-1. This GH-independent cardioprotection has been confirmed in hypophysectomized animals (no pituitary GH production) and is a genuine second pharmacology of hexarelin rather than a downstream consequence of GH elevation. No other GHRP shares this CD36 activity at comparable potency.

Hexarelin was developed in the mid-1990s by Europeptides (France) under the developmental codes EP-23905 and examorelin, building on the GHRP optimization program that began with Bowers' enkephalin-derived peptides. Early clinical development focused on growth hormone deficiency and catabolic states, where its superior potency offered potential advantages over GHRP-2 and GHRP-6.

Human cardiac studies conducted in the 2000s demonstrated that hexarelin infusion improved cardiac output and reduced peripheral vascular resistance in patients with heart failure — effects that occurred within minutes and were temporally dissociated from GH elevation, consistent with direct CD36-mediated cardiac activity rather than GH-dependent remodeling. However, like other GHRPs, hexarelin was not commercialized as a therapeutic — the pharmaceutical industry's focus shifted toward orally active non-peptide GHSs (MK-677) and recombinant GH. Hexarelin remains a uniquely valuable research tool for studying the intersection of GH secretagogue pharmacology and direct cardiac protection, with a mechanism profile that cannot be replicated by any other available research peptide.

Store lyophilized hexarelin at -20°C in a light-protected, desiccated container. The peptide's D-amino acid residues (D-2-methyl-Trp, D-Phe) provide robust resistance to enzymatic degradation; stability exceeds 24 months under optimal storage conditions. The 2-methyltryptophan residue introduces slightly increased hydrophobicity — ensure the vial is tightly sealed to prevent moisture ingress.

After reconstitution with bacteriostatic water, hexarelin should be refrigerated at 2–8°C and used within 21 days. The solution is clear and colorless. Due to the phenomenon of receptor desensitization with continuous daily use — a property more pronounced with hexarelin than other GHRPs — many research protocols employ intermittent dosing schedules (e.g., 5 days on, 2 days off, or every-other-day administration) to preserve GH responsiveness. Do not freeze reconstituted solutions.