Hexarelin - Potent Growth Hormone Releasing Peptide (GHRP)

Hexarelin for Research: Complete Scientific Overview

Hexarelin (also known as Examorelin) is a synthetic hexapeptide with the amino acid sequence His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2. As a highly potent member of the growth hormone releasing peptide (GHRP) family, Hexarelin exhibits exceptional affinity for the growth hormone secretagogue receptor (GHSR-1a), a G-protein coupled receptor primarily expressed in the pituitary gland and hypothalamus. The unique structural features of Hexarelin—particularly the incorporation of a 2-methyl-tryptophan residue—contribute to its exceptional potency and distinct pharmacological profile compared to other GHRPs. Discovered in the 1990s through structure-activity relationship studies aimed at optimizing GHRP activity, Hexarelin has become an important reference compound for studying GHSR-1a pharmacology and the full spectrum of growth hormone secretagogue effects.

Mechanism of Action

Hexarelin exerts its biological effects through specific activation of the GHSR-1a receptor via multiple signaling pathways:

• GHSR-1a Activation (Primary Mechanism): Hexarelin is a high-affinity agonist at the growth hormone secretagogue receptor (GHSR-1a), with binding affinity (Ki ~0.1 nM) comparable to the endogenous ligand ghrelin. The receptor is a G-protein coupled receptor that signals primarily through the Gq/11 pathway, leading to phospholipase C activation, inositol trisphosphate (IP3) production, intracellular calcium mobilization, and subsequent GH release from somatotroph cells.
• Potent GH Stimulation: Hexarelin triggers robust, dose-dependent release of endogenous growth hormone, with potency exceeding that of GHRP-2 and GHRP-6 in many research models. The EC50 for GH release is approximately 0.3-0.5 nM in vitro, making Hexarelin one of the most potent GHRPs available for research.
• Cortisol and Prolactin Effects (Key Distinguishing Feature): Unlike the highly selective GHRP Ipamorelin, Hexarelin stimulates cortisol, prolactin, and ACTH release in addition to GH. This broader hormonal profile is mediated through GHSR-1a activation in the hypothalamus and pituitary, affecting corticotroph and lactotroph function. This property makes Hexarelin valuable for studying the full spectrum of GHSR-mediated effects.
• Ghrelin-like Activity: Hexarelin shares structural similarities with ghrelin and activates GHSR-1a through comparable mechanisms, though with unique binding kinetics. Hexarelin serves as a useful tool for differentiating ghrelin's effects at GHSR-1a from those mediated through other receptors (such as GHSR-1b or non-classical binding sites).
• Pulsatile GH Release: When administered in appropriate research protocols, Hexarelin induces pulsatile GH secretion that mimics natural physiological patterns. The pulsatile nature is important for maintaining the biological activity of GH at target tissues.
• Cardioprotective Effects: Beyond GH release, Hexarelin has been shown to exert direct cardioprotective effects in preclinical models, including improved cardiac function, reduced ischemia-reperfusion injury, and enhanced myocardial recovery. These effects appear to be mediated through GHSR-1a activation on cardiac tissue and are independent of GH release.
• Appetite Stimulation: Like ghrelin, Hexarelin can stimulate appetite and food intake through GHSR-1a activation in the hypothalamus. This effect is mediated through activation of neuropeptide Y (NPY) and agouti-related peptide (AgRP) neurons in the arcuate nucleus.

Comparative Analysis: Hexarelin vs. Other GHRPs

• Hexarelin: Highest potency GHRP among commonly studied GHRPs; broad hormonal effects including GH, cortisol, prolactin, and ACTH stimulation; shortest half-life (~2 hours); unique 2-methyl-tryptophan modification; demonstrated cardioprotective effects.
• GHRP-2 (Pralmorelin): High potency; moderate cortisol and prolactin effects; half-life ~2-3 hours; well-characterized GH stimulation; fewer studies on non-GH effects.
• GHRP-6: Moderate potency; significant appetite stimulation (strongest among GHRPs); moderate cortisol and prolactin effects; half-life ~2-3 hours; widely used in early GHRP research.
• Ipamorelin: Lower potency; highly selective for GH (minimal cortisol, prolactin, or appetite effects); half-life ~2 hours; preferred for studies requiring selective GH activation.
• MK-677 (Ibutamoren): Oral bioavailability; long half-life (~24 hours); non-peptide GHSR agonist; produces sustained GH elevation; not a peptide but often compared in GHRP research.

Research Applications

• Comparative GHRP Pharmacology: Structure-activity relationship studies comparing Hexarelin's potency, efficacy, and receptor binding kinetics with other GHRPs (GHRP-2, GHRP-6, Ipamorelin).
• GHSR-1a Receptor Binding and Signaling: Characterizing GHSR-1a binding affinities, G-protein coupling (Gq/11, Gs, Gi), β-arrestin recruitment, and downstream signaling pathways.
• Pulsatile Growth Hormone Secretion: Investigating the dynamics of GH pulsatility, including amplitude, frequency, and the relationship between GH pulses and target tissue responses.
• Pituitary Somatotroph Function: Studying somatotroph cell biology, including GH synthesis, storage, and release mechanisms in response to GHSR activation.
• Neuroendocrine Regulation: Investigating the interactions between GHRH, somatostatin, ghrelin, and GHRPs in the complex neuroendocrine control of GH secretion.
• Cardioprotective Research: Studying the direct effects of GHSR activation on cardiac tissue, including myocardial protection against ischemia-reperfusion injury, improved contractility, and reduced apoptosis.
• Hypothalamic Function: Investigating the role of GHSR signaling in hypothalamic regulation of appetite, energy balance, and neuroendocrine function.
• Comparative Studies with Ghrelin: Using Hexarelin as a tool to differentiate ghrelin's effects at GHSR-1a versus other potential binding sites.
• Corticotroph and Lactotroph Studies: Investigating the effects of GHSR activation on cortisol, prolactin, and ACTH secretion, including the mechanisms and physiological significance.
• Pulsatility vs. Continuous GH Studies: Using Hexarelin to study the importance of pulsatile GH secretion patterns versus continuous GH exposure on metabolic outcomes.
• Metabolic Research: Investigating the effects of Hexarelin on body composition, lipid metabolism, glucose homeostasis, and protein synthesis.
• Age-Related GH Decline Research: Studying the age-associated decline in GHSR sensitivity and GH secretion, and the potential of GHRPs to restore physiological GH levels.

Structural Characteristics

Hexarelin is a synthetic hexapeptide with several unique structural features:

• 2-Methyl-Tryptophan Modification: The presence of D-2-methyl-tryptophan at position 2 is a key structural feature that distinguishes Hexarelin from other GHRPs and contributes to its enhanced potency and receptor binding affinity.
• D-Amino Acids: Incorporation of D-amino acids (D-2-methyl-Trp and D-Phe) confers resistance to proteolytic degradation, enhancing stability.
• C-Terminal Amidation: The C-terminal lysine is amidated, which improves stability and biological activity.
• Sequence: His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2

Chemical Information

CAS Number: 140703-51-1
Research Codes: Examorelin, Hexarelin acetate, HEX, EP-23905
Molecular Formula: C47H58N12O6
Molecular Weight: 887.0 g/mol
Sequence: His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2
Key Modification: D-2-methyl-tryptophan at position 2
Number of Amino Acids: 6 (hexapeptide)
Receptor Target: GHSR-1a (Growth Hormone Secretagogue Receptor)
Binding Affinity (Ki): ~0.1 nM at GHSR-1a
Half-Life: Approximately 2 hours in vivo
Purity: >99% (HPLC)
Form: Lyophilized powder
Storage: -20°C (lyophilized), 4°C (reconstituted)
Stability: Stable at -20°C for 24 months; reconstituted solution stable at 4°C for 30 days

Reconstitution and Handling Protocols

For optimal stability and research validity, Hexarelin should be reconstituted with sterile bacteriostatic water or sterile saline (0.9% NaCl). Due to the presence of D-amino acids, Hexarelin has enhanced stability compared to all-L peptides, but standard handling precautions should still be observed. Allow the lyophilized powder to dissolve completely without vigorous shaking to maintain peptide integrity. Gently swirl the vial until the solution is clear and free of particulates. Once reconstituted, the solution should be stored at 4°C and used within 30 days. Avoid repeated freeze-thaw cycles to preserve peptide structure and biological activity. For long-term storage, keep the lyophilized powder at -20°C away from light and moisture. Do not vortex or vigorously shake the reconstituted solution, as this may cause aggregation and reduce GHSR-1a binding activity.

Quality Assurance

PeptideVanta's Hexarelin undergoes rigorous quality control including HPLC purity analysis (>99%), ESI-mass spectrometry for molecular weight confirmation (expected 887.0 Da), chiral amino acid analysis to confirm D-amino acid incorporation, endotoxin testing (<1.0 EU/mg), sterility testing, and residual solvent analysis. Each batch is accompanied by a Certificate of Analysis (COA) with complete testing results. The peptide is synthesized using solid-phase peptide synthesis (SPPS) with Fmoc chemistry, incorporating appropriately protected D-amino acids, followed by HPLC purification and lyophilization under sterile conditions.