GHRP-6

Produktbeschreibung

What is GHRP-6?

GHRP-6 (Growth Hormone-Releasing Peptide-6) is a synthetic hexapeptide with the sequence His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂, which is a representative of the first generation of growth hormone secretagons (GHS). The compound was developed in the 1980s by Cyril Bowersi's team as an analogue of met-enkephalin, in which substitution with D-amino acids gave the molecule the ability to stimulate the secretion of growth hormone (GH) instead of its opioid effect.

Structurally, GHRP-6 contains two D-amino acids (D-Trp at position 2 and D-Phe at position 5), which are crucial for the biological activity and metabolic stability of the peptide. The molecular weight is approximately 873 Da and the molecular formula is C₄₆H₅₆N₁₂O₆. The presence of histidine at the N-terminus and amidated lysine at the C-terminus is characteristic of this class of compounds.

GHRP-6 works through the growth hormone secretagon receptor (GHS-R1a), the same receptor that binds endogenous ghrelin. However, unlike later, more selective GHRPs, GHRP-6 has a broader action profile, including stronger appetite stimulation and greater effects on cortisol and prolactin levels.

As the first widely studied peptide of this class, GHRP-6 played a key role in understanding the mechanisms of regulation of growth hormone secretion and contributed to the discovery of ghrelin as an endogenous ligand of the GHS-R1a receptor in 1999. Despite the emergence of newer and more selective alternatives, GHRP-6 remains an important research tool.

Mechanism of action

Phosphatidylinositol pathway activation - GHRP-6 binds to the GHS-R1a receptor on pituitary somatotropes, initiating a signaling cascade based on phosphatidylinositol metabolism. Activation of phospholipase C leads to the generation of trisphosphatidylinositol (IP3) and diacylglycerol (DAG), mobilization of intracellular calcium and activation of protein kinase C (PKC). This mechanism is independent of cAMP and different from the pathway activated by GHRH.

Dependence on endogenous GHRH - Studies have shown that the GH response to GHRP-6 is approximately 95% dependent on the presence of endogenous GHRH. Administration of a GHRH antagonist virtually abolishes the GH response to GHRP-6. This suggests that GHRP-6 acts as an amplifier of the GHRH signal rather than as an independent stimulator of GH synthesis.

Appetite stimulation by NPY neurons - GHRP-6 potently stimulates neuropeptide Y (NPY) neurons in the arcuate nucleus of the hypothalamus by activating GHS-R1a receptors. This leads to increased NPY mRNA expression and increased food intake. This pathway involves activation of Akt kinase and phosphorylation of transcription factors that regulate the expression of orexigenic genes.

Myogenic properties - A 2023 study showed that a GHRP-6 biotin conjugate (GHRP-6-biotin) increases the levels of myogenic proteins (MyoD, myogenin, MYH) in C2C12 cell cultures. This effect is mediated by activation of the AKT pathway and suggests a direct anabolic effect independent of GH.

Cytoprotective effect - GHRP-6 has protective properties against various cell types, in part through binding to the CD36 receptor. This mechanism includes inhibition of apoptosis, reduction of oxidative stress and modulation of the inflammatory response.

Directions of scientific research

Research on GHRP-6 includes its effects on growth hormone secretion, metabolism, muscle function, and potential applications in cachexia and sarcopenia.

Stimulation of growth hormone secretion

Classic studies by Bowersi and colleagues showed that GHRP-6 is a strong stimulator of GH secretion in both animals and humans. In healthy volunteers, intravenous administration of GHRP-6 resulted in a multiple increase in plasma GH concentration. The effect was synergistic with GHRH - the combined administration of both peptides produced a response that far exceeded the sum of the effects of the individual compounds.

Appetite regulation and energy metabolism

Studies in animal models have shown that GHRP-6 significantly increases food intake by activating NPY neurons in the hypothalamus. In the study by Tian et al. (2022) GHRP-6 was shown to cause Akt phosphorylation in AgRP/NPY neurons, leading to increases in body weight, adipose tissue, and NPY expression. This effect is mediated by the GHS-R receptor and can be blocked by antagonists of this receptor.

Myogenic and anabolic properties

A 2023 study (Cordova-Galaviz et al.) found that a GHRP-6-biotin conjugate increased myogenic protein levels in C2C12 myotubes, suggesting potential applications in sarcopenia and muscle atrophy. Activation of the AKT pathway by GHRP-6 may support muscle protein synthesis independently of increased GH levels.

Cardiac cachexia and cardiometabolic functions

In models of cardiac cachexia, GHRP-6 demonstrated the ability to improve body composition and metabolic function. The peptide may counteract the catabolic effects of chronic heart failure on skeletal muscle. Studies also suggest a direct cardioprotective effect through the CD36 receptor.

Dystrophic myopathy

Preliminary research suggests potential benefits of GHRP-6 in dystrophic myopathies. The peptide may support muscle regeneration by stimulating satellite cells and modulating the inflammatory response in damaged muscle fibers.

Scientific context

GHRP-6 holds a special place in the history of research on growth hormone regulation as the first broadly characterized peptide of this class. Its discovery in the 1980s opened a new era in endocrinology and ultimately led to the identification of ghrelin as the endogenous ligand of the GHS-R1a receptor.

Compared to other growth hormone releasing peptides:

• GHRP-2 - stronger GH stimulator, less impact on appetite
• Hexarelin - the strongest of the GHRPs, but a greater effect on cortisol
• Ipamorelin - the most selective, minimal effect on other hormones
• GHRP-1 — less powerful, less frequently used

GHRP-6 has a strong effect on appetite, which may be beneficial in cases of cachexia, but is a disadvantage in the context of cosmetic or sports applications. It is also one of the cheapest peptides in this class, which contributes to its popularity in non-clinical settings.

GHRP-6 is on the WADA Prohibited Substances List as a peptide mimetic of growth hormone. The detection of the peptide in anti-doping tests is well documented, with the possibility of detection in urine for several hours after administration.

Research safety profile

General Tolerance - In clinical studies, GHRP-6 demonstrated an acceptable safety profile with short-term use. The peptide was generally well tolerated at doses used in research and diagnostic protocols.