Hexarelin

Chemically, hexarelin is GHRP-6 with one tryptophan swapped for 2-methyl-tryptophan. That small change raises binding to the ghrelin receptor GHS-R1a and to the surface protein CD36, and it gives the hexapeptide two axes of activity that research examines separately.

The evidence:

• In twelve healthy volunteers, intravenous hexarelin released roughly twice as much GH as GHRH. Bioavailability was 77% subcutaneously, 4.8% through the nose and 0.3% by mouth (1994).
• After 16 weeks of two doses a day the GH response was partly blunted; four weeks off restored it. IGF-1 and body composition had not moved (1998).
• In rats without a pituitary, hexarelin prevented the loss of cardiac function after ischemia and reperfusion, hence without GH and probably through receptors of its own in heart tissue (1999).
• In 2002 CD36 was identified as the binding protein in the heart: in perfused hearts coronary perfusion pressure rose dose-dependently, but not in animals lacking CD36.

Hexarelin therefore sits in two places: in GH secretion research, where it counts among the most potent compounds of the class and produces larger GH rises than other GHRPs in preclinical models, and in cardiovascular models that examine myocardial repair, reduced apoptosis of heart cells and remodeling after injury. Its half-life of about 60 minutes is comparatively long for a GHRP, and the dual axis of GH plus CD36 is why the peptide now shows up mainly in heart-focused study designs.

Described are:

• Reactions at the injection site: redness, pressure, brief irritation.
• Fluid retention and tingling or numbness in the hands as a consequence of raised GH levels, dose-dependent and reversible.
• As a non-selective GHRP, hexarelin moderately raises cortisol and prolactin and increases hunger.
• Habituation: with continuous dosing the GH response fades comparatively quickly; in the 16-week study this reversed after a break.
• No robust human data exist over long periods; the picture rests on short studies and anecdotal reports.

This summary is no substitute for medical advice.

• Growth hormone-releasing activity of hexarelin, a new synthetic hexapeptide, after intravenous, subcutaneous, intranasal, and oral administration in man - comparison of administration routes in twelve volunteers.
• Growth hormone status during long-term hexarelin therapy - 16 weeks of twice-daily dosing and the recovery afterwards.
• CD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart - identification of CD36 as the cardiac binding protein.