Hexarelin – Research Compound Profile

Hexarelin – Research Compound Profile

Category: Hormonal Research | Molecular Type: Synthetic Hexapeptide (His-D-2-MeTrp-Ala-Trp-D-Phe-Lys-NH₂) | Research Status: Phase I/II Clinical Data Available

This page compiles published research data for qualified researchers. Hexarelin is sold exclusively as a research compound, is not approved for human use, and this page does not constitute medical advice.

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Molecular Overview

Hexarelin is a synthetic hexapeptide growth hormone secretagogue originally developed by Europeptides (now Mediolanum Farmaceutici). It belongs to the growth hormone-releasing peptide (GHRP) family and has been characterized in the literature as one of the most potent synthetic GH secretagogues in its class, producing GH release reported to substantially exceed that of equimolar growth hormone-releasing hormone (GHRH) in comparative human studies [1][2].

The peptide has a molecular sequence of His-D-2-MeTrp-Ala-Trp-D-Phe-Lys-NH₂, incorporating two D-amino acid residues (D-2-methyltryptophan and D-phenylalanine) that confer enhanced resistance to proteolytic degradation. This structural feature contributes to the compound’s remarkable metabolic stability — pharmacokinetic tracer studies in rats found that the substantial majority of biliary and urinary radioactivity was recovered as unchanged hexarelin following administration, confirming minimal enzymatic breakdown [15].

Structural rationale: The 2-methyl substitution on the D-tryptophan side chain at position 2 is unique to hexarelin among the GHRP family and is believed to contribute to its comparatively higher GHS-R1a binding affinity relative to GHRP-6, from which it is structurally derived. The D-Phe at position 5 blocks chymotrypsin-like proteolysis, and the C-terminal lysinamide removes the carboxypeptidase substrate present in an unmodified linear hexapeptide. Together these substitutions account for the compound’s markedly extended systemic half-life compared with unmodified GHRH fragments.

Beyond its established role as a GH secretagogue acting through the GHS-R1a receptor, hexarelin has attracted significant research interest for its independent cardioprotective activity mediated through the CD36 scavenger receptor in cardiac tissue — a mechanism entirely distinct from the GH/IGF-1 axis [3][4]. This dual-receptor pharmacology distinguishes hexarelin from other members of the GHRP family and has generated a substantial body of cardiovascular research literature.

Mechanism of Action

Hexarelin functions as a potent agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the same receptor that binds the endogenous hormone ghrelin [3][13]. When hexarelin binds GHS-R1a in the hypothalamus and anterior pituitary, it triggers an intracellular signaling cascade involving phospholipase C activation, inositol trisphosphate (IP3)-mediated calcium mobilization from the endoplasmic reticulum, and subsequent calcium influx through voltage-gated L-type channels. This dual calcium surge drives the exocytosis of stored GH granules from somatotroph cells, producing a rapid, transient GH pulse following administration in research settings [1][2].

In addition to GHS-R1a, hexarelin binds to CD36 (cluster of differentiation 36), an 84-kDa class B scavenger receptor expressed on cardiomyocytes and microvascular endothelial cells [4]. This interaction was demonstrated through photoaffinity labeling experiments showing that hexarelin’s cardiac effects — including protection against ischemia-reperfusion injury and reduction of cardiac fibrosis — persist even in GH-deficient animal models where somatotropic axis stimulation is not possible [3][14]. In perfused hearts from CD36-null mice, hexarelin’s coronary vasoconstrictive response was completely absent, confirming that the cardiovascular actions are mediated specifically through CD36 rather than through GH elevation [4].

Pharmacokinetics

Published pharmacokinetic studies have characterized hexarelin as demonstrating first-order kinetics across the exposure range studied, with no evidence of accumulation [15]. Key pharmacokinetic parameters reported in the literature include:

• Bioavailability: Reported at approximately 64% in rat models [15]; substantial biological bioavailability reported in human pharmacokinetic analyses via the subcutaneous route [2]
• Plasma half-life: Approximately 55–76 minutes depending on species and route of administration [1][15]
• Elimination: Primarily via biliary excretion, with smaller urinary and fecal contributions [15]
• Metabolic stability: Tracer studies recovered the substantial majority of biliary and urinary radioactivity as unchanged peptide, indicating remarkable resistance to proteolytic degradation [15]

Published Research Parameters

The following table indexes the study models, durations, and reported observations of selected peer-reviewed publications. Dose, frequency, and administration-route details are deliberately omitted. This is a bibliographic index only — not a protocol and not a recommendation for any use.

Stability & Storage Characteristics

Published data and manufacturer specifications report the following stability parameters for hexarelin:

• Lyophilized form: Stable at −20 °C (−4 °F) for 2+ years. Acceptable stability at 2–8 °C for 6–12 months. Room temperature stability documented for 30–60 days, though degradation rates increase at higher temperatures [10].
• Reconstituted solution: Studies indicate reconstituted hexarelin solutions maintain stability when stored at 2–8 °C (35.6–46.4 °F), protected from direct light, for up to 4 weeks [10]. Freeze-thaw cycles of reconstituted solutions are not recommended.
• Metabolic stability: The peptide demonstrates remarkable proteolytic resistance owing to its D-amino acid substitutions. Tracer pharmacokinetic studies recovered the substantial majority of biliary and urinary radioactivity as unchanged hexarelin, confirming minimal enzymatic degradation [15].
• Light sensitivity: Reconstituted solutions should be protected from direct light to minimize photodegradation. The indole rings of the tryptophan-derived residues (Trp and 2-MeTrp) are the primary sites of oxidative modification under prolonged light exposure.
• Deamidation: The C-terminal amide is subject to slow hydrolytic deamidation in aqueous solution over extended storage, generating a species distinguishable from the parent peptide by a 1-Da mass shift on LC-MS.

Analytical Characterization

Research-grade hexarelin is characterized using an orthogonal analytical panel. Reverse-phase HPLC (RP-HPLC) provides the primary purity assessment and resolves oxidative and hydrolytic degradation products from the intact hexapeptide. Electrospray ionization mass spectrometry (ESI-MS) confirms the intact monoisotopic mass and distinguishes the parent amide from deamidated or oxidized impurities. A peptide-content assay (amino acid analysis or quantitative NMR) determines the fraction of lyophilized vial mass attributable to peptide as opposed to residual counter-ion (commonly acetate), water, and buffer salts. Chiral analysis can additionally confirm that the D-2-MeTrp and D-Phe centers have not undergone racemization during synthesis. Researchers should retain the quality assurance documentation (CoA) for each lot used.

Key Published Research Findings

• Growth hormone secretion (dose-response): In a 1994 European Journal of Endocrinology study using healthy human volunteers, Ghigo et al. demonstrated that hexarelin produced dose-dependent GH release, with the area under the curve substantially exceeding that produced by equimolar GHRH administered to the same subjects [1].

• Multi-route bioavailability: In a 1994 Journal of Clinical Endocrinology & Metabolism study, Ghigo et al. characterized hexarelin’s GH-releasing activity following intravenous, subcutaneous, intranasal, and oral administration in human subjects, documenting substantial biological bioavailability via the subcutaneous route [2].

• 24-hour GH secretion augmentation: In a 1997 Journal of Clinical Endocrinology & Metabolism study in elderly human subjects, Rahim et al. observed that repeated daily subcutaneous hexarelin administration augmented 24-hour integrated GH secretion by selectively amplifying GH pulse mass [5].

• GH-independent cardioprotection: In a 1999 Endocrinology study using a rat coronary artery ligation model, Locatelli et al. demonstrated that chronic hexarelin pretreatment preserved myocardial function and reduced infarct size with a meaningful improvement in stroke volume relative to control, independent of GH status [14].

• CD36-mediated cardiovascular action: In a 2002 Circulation Research study, Bodart et al. demonstrated via photoaffinity labeling and CD36-null mouse models that hexarelin’s cardiovascular effects are specifically mediated through the CD36 scavenger receptor rather than through GH elevation. In perfused hearts from CD36-null mice, hexarelin’s coronary vasoconstrictive response was completely abolished [4].

• Anti-fibrotic cardiac effects: In a 2012 American Journal of Physiology: Heart study using spontaneously hypertensive rats, Xu et al. reported that chronic hexarelin administration significantly reduced interstitial and perivascular myocardial collagen deposition, attenuating cardiac fibrosis independently of blood pressure changes [17].

• Myocardial function preservation: In a 2018 American Journal of Physiology: Heart study, Waddingham et al. demonstrated that hexarelin treatment preserved myocardial function and reduced cardiac fibrosis in a rat model [16].

• Metabolic improvements in insulin resistance: In a 2017 Endocrinology study using insulin-resistant MKR mice, Rodrigue-Way et al. reported that repeated hexarelin administration significantly improved glucose and insulin tolerance and decreased plasma and liver triglyceride levels [18].

• Neuroprotective effects: In a 2023 International Journal of Molecular Sciences study, Conte et al. demonstrated that hexarelin and the analog JMV2894 exhibited protective effects against SOD1-G93A-induced neurotoxicity in human neuroblastoma cell models, suggesting potential relevance in neurodegenerative disease research [19].

• Renal protective effects: In a 2023 Biomedicine & Pharmacotherapy study using an ischemic acute kidney injury model, Li et al. demonstrated that hexarelin attenuated apoptosis and preserved renal function through modulation of the MAPK signaling pathway [20].

Safety Profile in Published Literature

Hormonal Effects

Clinical dose-response studies have documented that hexarelin induces dose-dependent cortisol and ACTH release alongside GH secretion. In a 1996 study by Arvat et al., cortisol increases at the higher exposure levels tested were clinically meaningful, though typically transient [8]. Dose-related prolactin elevation has also been consistently reported in clinical studies [11]. These hormonal effects distinguish hexarelin from more selective GHRPs such as ipamorelin and are reviewed in Sigalos and Pastuszak (2018) [11].

Receptor Desensitization (Tachyphylaxis)

The most significant pharmacological limitation documented in the literature is tachyphylaxis with repeated administration. Rahim et al. (1996) demonstrated progressive attenuation of the GH response over several weeks of continuous daily administration [6]. This desensitization has been reported to be more pronounced with hexarelin compared to GHRP-2 or GHRP-6. Published research literature has noted that intermittent, cycled administration schedules were associated with better preservation of receptor sensitivity than continuous daily use [6][7].

Body Composition Effects on Response

Maccario et al. (1999) published findings in Clinical Endocrinology demonstrating that increasing total fat mass was associated with a blunted GH response to hexarelin, with leaner subjects consistently showing higher peak GH levels [12].

Sleep Architecture Effects

Frieboes et al. (2004) reported in Psychoneuroendocrinology that hexarelin decreased slow-wave sleep duration while stimulating nocturnal GH, ACTH, cortisol, and prolactin secretion in healthy volunteers [9].

Reported Adverse Effects in Clinical Studies

Published clinical investigations have documented mild fluid retention, paresthesia (tingling/numbness in extremities), and transient joint stiffness consistent with elevated GH/IGF-1 signaling. As a ghrelin receptor agonist, appetite stimulation has also been noted, though reported to be generally less pronounced than with GHRP-6 [11].

Toxicology and Regulatory Considerations

Hexarelin has not been approved by the FDA for human therapeutic use. It is classified as a research compound. Researchers should be aware that the FDA has issued general guidance regarding the compounding and sale of peptides for non-approved uses. All research involving hexarelin must comply with applicable federal and institutional regulations.

Regulatory Status

• FDA Approval: Hexarelin is not FDA-approved for any human therapeutic indication.
• Clinical Trial Status: Phase I and Phase II clinical data exist characterizing pharmacokinetics, dose-response relationships, and acute safety profiles in healthy volunteers [1][2][8].
• Current Classification: Sold exclusively as a research compound for in vitro and preclinical investigation.
• Researcher Responsibility: All research must comply with applicable laws, regulations, and institutional review board guidelines.

References

1. European Journal of Endocrinology (1994) — Ghigo E, Arvat E, et al. “Growth hormone-releasing activity of hexarelin in humans: A dose-response study.” View Source

2. Journal of Clinical Endocrinology & Metabolism (1994) — Ghigo E, Arvat E, Muccioli G, et al. “Growth hormone-releasing activity of hexarelin, a new synthetic hexapeptide, after intravenous, subcutaneous, intranasal and oral administration in man.” View Source

3. Journal of Geriatric Cardiology (2014) — Mao Y, Tokudome T, Kishimoto I. “The cardiovascular action of hexarelin.” View Source

4. Circulation Research (2002) — Bodart V, Febbraio M, Demers A, et al. “CD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart.” View Source

5. Journal of Clinical Endocrinology & Metabolism (1997) — Rahim A, O’Neill PA, Shalet SM. “Impact of two or three daily subcutaneous injections of hexarelin on 24-hour GH secretion.” View Source

6. Clinical Endocrinology (1996) — Rahim A, O’Neill PA, Shalet SM. “The effect of repeated administration of hexarelin, a growth hormone releasing peptide, on GH secretion.” View Source

7. International Journal of Molecular Sciences (2017) — Howick K, Griffin BT, Cryan JF, Schellekens H. “From belly to brain: Targeting the ghrelin receptor in appetite and food intake regulation.” View Source

8. Journal of Clinical Endocrinology & Metabolism (1996) — Arvat E, et al. “Hexarelin-induced growth hormone, cortisol, and prolactin release: a dose-response study.” View Source

9. Psychoneuroendocrinology (2004) — Frieboes RM, Antonijevic IA, et al. “Hexarelin decreases slow-wave sleep and stimulates the secretion of GH, ACTH, cortisol and prolactin during sleep in healthy volunteers.” View Source

10. BenchChem Technical Support Center — “Hexarelin peptide: Application notes and protocols for research.” View Source

11. Sex Medicine Reviews (2018) — Sigalos JT, Pastuszak AW. “The safety and efficacy of growth hormone secretagogues.” View Source

12. Clinical Endocrinology (1999) — Maccario M, et al. “The effect of body composition on hexarelin-induced growth hormone release in humans.” View Source

13. Endocrine Reviews (1997) — Smith RG, Van der Ploeg LHT, et al. “Peptidomimetic regulation of growth hormone secretion.” View Source

14. Endocrinology (1999) — Locatelli V, Rossoni G, et al. “Growth hormone-independent cardioprotective effects of hexarelin in the rat.” View Source

15. Drug Metabolism & Disposition (2000) — Bhargava V, et al. “Kinetics and disposition of hexarelin, a peptidic growth hormone secretagogue, in rats.” View Source

16. American Journal of Physiology: Heart (2018) — Waddingham MT, et al. “Hexarelin treatment preserves myocardial function and reduces cardiac fibrosis.” View Source

17. American Journal of Physiology: Heart (2012) — Xu XB, et al. “Chronic administration of hexarelin attenuates cardiac fibrosis in the spontaneously hypertensive rat.” View Source

18. Endocrinology (2017) — Rodrigue-Way A, et al. “Hexarelin, a growth hormone secretagogue, improves lipid metabolic abnormalities in nonobese insulin-resistant mice.” View Source

19. International Journal of Molecular Sciences (2023) — Conte E, et al. “Protective effects of hexarelin and JMV2894 in a human neuroblastoma cell model.” View Source

20. Biomedicine & Pharmacotherapy (2023) — Li J, et al. “Hexarelin alleviates apoptosis on ischemic acute kidney injury via MAPK signaling pathway.” View Source

⚠️ Disclaimer: This page is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment recommendations. Hexarelin is sold exclusively as a research compound and has not been approved by the FDA for human consumption. It is not intended for human use or self-administration. All information is derived from published peer-reviewed literature. Research must comply with all applicable laws, regulations, and institutional guidelines.

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