Hexarelin

Hexarelin (Examorelin) is a synthetic hexapeptide with the sequence His-D-2-Me-Trp-Ala-Trp-D-Phe-Lys-NH2 and a molecular weight of approximately 887 Da. It belongs to the growth hormone releasing peptide (GHRP) family and is one of the most potent synthetic GH secretagogues characterized to date. The inclusion of D-amino acids (D-2-methyltryptophan at position 2 and D-phenylalanine at position 5) confers resistance to enzymatic degradation, while the C-terminal amidation enhances receptor binding affinity. Hexarelin was first synthesized and characterized by researchers at Tulane University and has been the subject of over 200 published studies.

Hexarelin stimulates GH release through two distinct mechanisms. Its primary action is as an agonist at the growth hormone secretagogue receptor type 1a (GHSR-1a) on anterior pituitary somatotrophs, triggering GH release via the phospholipase C/IP3/calcium signaling cascade. This produces rapid, strong GH pulses that peak approximately 15-20 minutes after subcutaneous administration, with GH levels reaching 5-7x baseline. Its secondary mechanism involves direct action on the hypothalamus, where it suppresses somatostatin release and stimulates GHRH secretion, amplifying the pituitary signal. Unlike the more selective Ipamorelin, Hexarelin also stimulates ACTH and cortisol release (acutely) and prolactin release, reflecting broader receptor engagement.

The cardioprotective properties of Hexarelin are its most distinctive research feature and operate independently of GH release. Hexarelin binds directly to a specific receptor on cardiac tissue (identified as CD36, a scavenger receptor class B type I) that is distinct from GHSR-1a. Locatelli et al. (Annals of Medicine, 1999) demonstrated that Hexarelin binds to receptors on cardiomyocytes and exerts direct cardioprotective effects in ischemia-reperfusion models, reducing infarct size by approximately 35%. In a Phase 2 clinical trial in post-myocardial infarction patients (Bisi et al., J Clin Endocrinol Metab, 1999, N=30), Hexarelin administration improved left ventricular ejection fraction and cardiac output parameters. Additionally, Hexarelin activates PPAR-gamma in macrophages (Avallone et al., J Biol Chem, 2006), reducing foam cell formation and inhibiting atherosclerotic plaque development. This dual GH-releasing and cardioprotective profile is unique among all GH secretagogues.

Pharmacokinetically, Hexarelin is administered subcutaneously or intravenously, with peak GH release occurring at 15-20 minutes post-injection. The peptide itself has a short plasma half-life of approximately 30-40 minutes, but the GH pulse it triggers lasts 2-3 hours. Hexarelin is metabolized by plasma peptidases and cleared renally. An important pharmacological consideration is desensitization: unlike Ipamorelin, which shows minimal desensitization, Hexarelin produces progressive attenuation of GH release with continuous daily dosing, typically becoming apparent after 4-8 weeks. This is attributed to GHSR-1a receptor downregulation. Pulsatile dosing schedules (5 days on, 2 days off, or 4 weeks on, 2 weeks off) are commonly used in clinical protocols to mitigate this effect.

Hexarelin lyophilized powder should be stored at -20C and is stable for 24+ months. Reconstitute with bacteriostatic water or sterile water, adding solvent slowly down the vial wall. The reconstituted solution should be clear and stored at 2-8C, used within 21 days. Hexarelin is relatively stable in solution compared to larger peptides due to the protective D-amino acid substitutions. The reconstituted pH should be approximately 5.5-7.0 for optimal stability.

Published research protocols for Hexarelin typically use doses of 1-2 mcg/kg intravenously or subcutaneously, with 1 mcg/kg being the most common dose in clinical studies. Higher doses (up to 2 mcg/kg) produce proportionally greater GH release but also greater cortisol and prolactin elevations. Most protocols administer Hexarelin 1-3 times daily, with the most common schedule being twice daily (morning and pre-sleep). Research cycles typically run 4-8 weeks with 2-4 week off-periods to restore receptor sensitivity. Some cardioprotective research protocols use longer continuous dosing periods since the cardiac effects operate through CD36 rather than GHSR-1a and may not desensitize.

The safety profile of Hexarelin is generally favorable with important caveats. The acute cortisol and prolactin elevations are transient and typically normalize within 2-3 hours post-dose, but chronic use should include monitoring of both hormones. In clinical trials, the most commonly reported side effects are transient flushing, increased appetite, and mild water retention. The post-MI clinical trial (N=30) reported no serious adverse events attributable to Hexarelin over the study period. Desensitization is a practical limitation rather than a safety concern. There is no evidence of pituitary suppression after Hexarelin discontinuation, and GH responsiveness returns to baseline within 1-2 weeks of cessation.