GHRP-6 is short for growth hormone releasing peptide-6. It is a synthetic analogue of ghrelin that contains just six amino acids. It is also a potent growth hormone releasing factor. GHRP-6 is often referred to as a ghrelin receptor analogue because it binds to the ghrelin receptor. The amino acid sequence for GHRP-6 is Histidine-D-Trypotophan-Alanine-Tryptophan-D-Phenylalanine-Lysine.
It is worth nothing that D-Tryptophan and D-Phenylalanine are not amino acids that naturally occur in biological molecules. GHRP-6 is part of a series of compounds developed by Polygen (Germany) and Tulane University (United States) in an effort to created easily administered analogues of growth hormone releasing hormone1 .
Effects of GHRP-6
There are two primary effects of GHRP-6. The first is the release of growth hormone (GH) through interaction with the ghrelin receptor. Release of GH results in the release of insulin-like growth factor-1 (IGF-1) from the liver as well as the release of a multitude of other hormones and peptides. The net effect of GH release is the stimulation of growth in a number of organs including skeletal muscles and bone. Growth is the result of both hyperplasia (cell division and an increase in the number of cells in the tissue) as well as hypertrophy (increase in the size of cells). GH release also increases fat metabolism, decreases blood sugar (glucose) levels, increased cardiomyocyte (heart muscle cell) function, increased renal function2 , and improved memory.
The second effect of GHRP-6 is appetite stimulation. Ghrelin is a well-known appetite stimulant and the ghrelin receptor has long been a therapeutic target by scientists wishing to control appetite. Ghrelin is often referred to as the “hunger hormone.”
GHRP-6 has shown promise in rat models as an effective treatment against amyloid beta3 . Amyloid beta is one of the primary components of amyloid plaques, which appear in the brains of patients with Alzheimer’s disease. GHRP-6 has also been shown to affect levels of acetylcholinesterase (AChE), a molecule that plays an active role in cognition and memory.
A Note on GHRP-6 Biochemistry
GHRP-6 is not a growth hormone releasing hormone receptor (GHRHR) agonist. That is to say, GHRP-6 does NOT bind to the GHRHR, but rather produces all of its effects through the ghrelin receptor. Binding of the ghrelin receptor, by ghrelin or any other agonist, can and does lead to GH release4 . The importance of this distinction is that GHRP-6 has effects that differ from molecules like growth hormone releasing hormone and its analogues (GRF (1-29), CJC-1295, etc.).
- Pralmorelin: GHRP 2, GPA 748, growth hormone-releasing peptide 2, KP-102 D, KP-102 LN, KP-102D, KP-102LN. Drugs RD5, 236-239 (2004).
- Rodriguez Salgueiro, S. et al. Role of epidermal growth factor and growth hormone-releasing peptide-6 in acceleration of renal tissue repair after kanamycin overdosing in rats. Iran. J. Kidney Dis.8, 382-388 (2014).
- Madhavadas, S., Kutty, B. M. & Subramanian, S. Amyloid beta lowering and cognition enhancing effects of ghrelin receptor analog [D-Lys (3)] GHRP-6 in rat model of obesity. Indian J. Biochem. Biophys.51, 257-262 (2014).
- Magdaleno-Méndez, A. et al. Ghrelin increases growth hormone production and functional expression of NaV1.1 and Na V1.2 channels in pituitary somatotropes. Endocrine48, 929-936 (2015).