Hexarelin

Hexarelin is a synthetic hexapeptide growth hormone secretagogue that acts primarily through the growth hormone secretagogue receptor (GHS-R1a), also known as the ghrelin receptor, on somatotroph cells in the anterior pituitary gland. Upon binding, it triggers a robust, dose-dependent release of growth hormone (GH) into the bloodstream. Research suggests that hexarelin produces one of the strongest GH responses among synthetic secretagogues, with peak GH levels significantly exceeding those achieved by GHRP-6 or GHRP-2 at comparable doses.

Beyond the pituitary axis, hexarelin has demonstrated direct cardioprotective effects that appear to be independent of GH release. Studies indicate that it binds to a distinct cardiac receptor — now identified as CD36, a scavenger receptor involved in fatty acid transport and atherosclerotic plaque formation. Through this pathway, hexarelin has been shown to protect cardiomyocytes from ischaemia-reperfusion injury, reduce infarct size, and improve cardiac function in animal models of heart disease.

Hexarelin also stimulates the release of ACTH, cortisol, and prolactin to a greater degree than more selective secretagogues like ipamorelin. While this broader hormonal activation limits its selectivity, it has made hexarelin a valuable research tool for studying the interplay between the somatotropic, adrenal, and lactotropic axes. Its resistance to enzymatic degradation, conferred by the D-amino acid substitutions at positions 2 and 5, gives it a functional half-life suitable for experimental protocols.

Hexarelin was first synthesised in the early 1990s by a team led by Romano Deghenghi at Europeptides, as part of a systematic effort to develop potent growth hormone-releasing peptides. It was derived by modifying the structure of GHRP-6, incorporating a 2-methyl-tryptophan substitution and D-phenylalanine to enhance receptor binding affinity and metabolic stability. Early clinical studies published between 1994 and 1997 confirmed its potent GH-releasing activity in both healthy volunteers and GH-deficient patients, establishing it as the most potent hexapeptide secretagogue of its class.

Subsequent research through the 2000s shifted attention to hexarelin's cardiovascular properties. Landmark studies demonstrated its ability to reduce cardiac fibrosis, prevent ventricular remodelling after myocardial infarction, and protect against doxorubicin-induced cardiotoxicity. The discovery that these cardioprotective effects were mediated through CD36 rather than GHS-R1a opened an entirely new avenue of research. However, clinical development was complicated by the observation that hexarelin's GH-releasing efficacy diminishes with repeated administration due to receptor desensitisation, a finding that has directed research toward intermittent dosing strategies and combination protocols.