Growth Hormone Releasing Peptides
Synthetic hexapeptides that stimulate growth hormone release through the ghrelin receptor, distinct from GHRH pathway.
Chemical Identity
| Property | Value |
|---|---|
| Examples | GHRP-6, GHRP-2 (Pralmorelin), Hexarelin |
| Peptide Class | Synthetic Hexapeptides |
| Receptor | Ghrelin receptor (GHS-R1a) |
| Route | SC, IV, intranasal |
Structure
Growth hormone releasing peptides (GHRPs) are synthetic hexapeptides that stimulate GH release through a mechanism distinct from GHRH. GHRP-6 (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) was the first member, followed by GHRP-2 and hexarelin with improved potency and oral activity.
Mechanism of Action
GHRPs bind the growth hormone secretagogue receptor (GHS-R1a, the ghrelin receptor) on pituitary somatotrophs and hypothalamic neurons. This activates phospholipase C/IP3/calcium signaling, synergizing with GHRH to amplify GH release. They also stimulate appetite through hypothalamic pathways.
Clinical Applications
- GH deficiency: Diagnostic stimulation testing
- Body composition: Investigational for muscle wasting
- Appetite stimulation: Ghrelin receptor activation
- Cardiac protection: Hexarelin cardioprotective effects
- Sports doping: Prohibited by WADA
Pharmacology
- GHRP-6: First generation, moderate potency
- GHRP-2 (Pralmorelin): 2-3x more potent than GHRP-6
- Hexarelin: Most potent, some tachyphylaxis
- Synergy: 10x amplification with GHRH co-administration
Safety and Side Effects
Hunger (most common), flushing, cortisol and prolactin elevation (mild), water retention, and joint pain. Long-term safety data limited. Prohibited in athletic competition.
References
- Bowers, C.Y., et al. (1995). GH-releasing peptides. Endocrine Reviews, 16, 63-82.
- Ghigo, E., et al. (1999). GHRPs: mechanism of action. Growth Hormone & IGF Research, 9, 12-17.
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