Maple GHRP-2 (pralmorelin) is a synthetic hexapeptide growth hormone secretagogue that activates both the ghrelin receptor (GHS-R1a) and the CD36 scavenger receptor, producing a bifurcated pharmacological profile spanning growth hormone axis stimulation and GH-independent cytoprotective activity across hepatic, cardiovascular, and musculoskeletal tissues. First synthesized by Cyril Bowers and colleagues in the early 1990s, GHRP-2 remains one of the most potent GH-releasing peptides characterized to date, with a research literature spanning over three decades of receptor pharmacology, signal transduction mapping, and preclinical organ protection studies.
Chemical Identity and Structural Features
GHRP-2 carries the INN designation pralmorelin and the development codes KP-102 and GPA-748. Its amino acid sequence is D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH2, yielding a molecular formula of C45H55N9O6 and a molecular weight of 817.97 g/mol (CAS 158861-67-7). The incorporation of two D-amino acids (D-Ala at position 1 and D-Phe at position 5) confers resistance to enzymatic degradation by aminopeptidases, extending the peptide’s functional half-life relative to endogenous ghrelin. The C-terminal amidation further stabilizes the molecule against carboxypeptidase cleavage, a design feature common to synthetic secretagogues intended for sustained receptor engagement in research settings.
Structurally, GHRP-2 belongs to the second generation of growth hormone releasing peptides, optimized from the earlier GHRP-6 scaffold through systematic substitution at positions 1 and 5. The D-2-naphthylalanine (D-2-Nal) at position 2 is the critical pharmacophore for GHS-R1a binding affinity, producing stronger receptor activation than the D-Trp residue found in GHRP-6.
Primary Mechanism: GHS-R1a Receptor Pharmacology
GHRP-2 functions as a full agonist at the growth hormone secretagogue receptor type 1a (GHS-R1a), a G-protein coupled receptor expressed on somatotroph cells in the anterior pituitary gland and in the hypothalamic arcuate nucleus. Upon binding, GHRP-2 activates Gq/11 signaling cascades, triggering phospholipase C (PLC) hydrolysis of phosphatidylinositol 4,5-bisphosphate into inositol trisphosphate (IP3) and diacylglycerol (DAG). The IP3-mediated mobilization of calcium from intracellular stores triggers exocytosis of GH-containing secretory granules, producing acute, pulsatile GH release.
In bovine pituitary cell cultures, Cheng and colleagues (1997) demonstrated that GHRP-2 stimulates GH secretion through Ca2+ influx via voltage-gated calcium channels and activates both protein kinase C (PKC) and cyclic AMP (cAMP) signaling pathways, suggesting partial crosstalk with the GHRH receptor signaling apparatus (published in the Journal of Endocrinology). This dual-pathway activation distinguishes GHRP-2 from pure GHRH analogs and explains the synergistic GH amplification observed when GHRP-2 is co-administered with GHRH in research models.
Key Research Findings
- GH release potency: Arvat et al. (1997), studying healthy young adults, found that GHRP-2 at 1 mcg/kg intravenous produced GH responses exceeding the maximal effective dose of GHRH, with dose-dependent increases up to approximately 2 mcg/kg before reaching a plateau. GHRP-2 simultaneously stimulated ACTH and cortisol to a degree comparable to human corticotropin-releasing hormone (published in the European Journal of Endocrinology).
- Pediatric GH-deficient model: Mericq, Bowers et al. (1998) treated six prepubertal GH-deficient children with escalating subcutaneous doses of GHRP-2 (0.3, 1.0, and 3.0 mcg/kg/day) over eight months, observing dose-dependent increases in overnight episodic GH secretion and higher growth velocity during treatment compared to pre- and post-treatment periods, with no reported adverse effects.
- Food intake regulation: Laferrere et al. (2005) conducted a randomized, double-blind, placebo-controlled study in healthy men using subcutaneous GHRP-2 infusion at 1 mcg/kg/h. Total caloric intake increased by 35.9 +/- 10.9% with GHRP-2 versus placebo (9409 +/- 1229 kJ vs. 7118 +/- 1078 kJ, p=0.004), with every subject responding to the infusion (published in the Journal of Clinical Endocrinology & Metabolism).
- Anti-inflammatory activity in arthritis: Granado et al. (2005) administered GHRP-2 at 100 mcg/kg/day for 8 days to male Wistar rats with adjuvant-induced arthritis. GHRP-2 decreased the arthritis score, increased serum leptin concentrations, and ameliorated external symptoms of disease (published in the American Journal of Physiology-Endocrinology and Metabolism, 288(3), E486-E492).
- Hepatoprotection in endotoxemia: Granado et al. (2008) demonstrated that GHRP-2 administration in LPS-treated rats attenuated increases in transaminases, nitrites/nitrates, and TNF-alpha while preventing the LPS-induced decline in IGF-I, with evidence of direct protective effects on hepatic nonparenchymal cells independent of systemic GH elevation (published in the American Journal of Physiology-Endocrinology and Metabolism).
- Muscle-sparing effects: Granado et al. (2005) separately reported that GHRP-2 prevented the arthritis-induced upregulation of E3 ubiquitin-ligating enzymes MuRF1 and MAFbx in skeletal muscle, two key mediators of muscle protein degradation in catabolic states (published in the American Journal of Physiology-Endocrinology and Metabolism).
Secondary Mechanism: CD36 Scavenger Receptor Signaling
Beyond GHS-R1a, GHRP-2 binds the CD36 scavenger receptor (also known as fatty acid translocase), a class B scavenger receptor expressed on macrophages, dendritic cells, endothelial cells, cardiomyocytes, and hepatocytes. This interaction is pharmacologically distinct from ghrelin receptor activation and accounts for the cytoprotective properties observed in GHRP research that persist even in GHS-R1a knockout or GH-deficient models.
A 2017 review by Berlanga et al. in Clinical Medicine Insights: Cardiology (PMC5392015) mapped the CD36-mediated downstream signaling cascade of growth hormone releasing peptides. The pathway includes activation of PI-3K/AKT1, promoting cell survival and reducing apoptosis; upregulation of PPARgamma, which drives downstream anti-fibrotic gene expression; suppression of TGF-beta, connective tissue growth factor (CTGF), and platelet-derived growth factor (PDGF), three central mediators of fibrotic remodeling; blunting of NF-kappaB nuclear translocation, reducing pro-inflammatory cytokine transcription; and induction of HIF-1alpha under ischemic conditions, enhancing cellular hypoxia tolerance.
This dual-receptor architecture gives GHRP-2 a pharmacological footprint that extends well beyond GH axis biology, placing it at the intersection of endocrine, immune, and tissue repair signaling in preclinical research.
Cardiovascular Cytoprotection Research
The CD36-mediated cytoprotective effects of GHRPs have been most extensively characterized in cardiovascular models. In myocardial ischemia/reperfusion research, GHRP-2 and related secretagogues interrupted the injury cascade by reducing cardiac fibrosis, decreasing perivascular collagen deposition, and downregulating fibrosis-associated gene expression. The anti-fibrotic mechanism operates through the PPARgamma/TGF-beta axis: CD36 engagement activates PPARgamma, which transcriptionally suppresses TGF-beta and CTGF, the two primary drivers of collagen overproduction in damaged cardiac tissue.
Importantly, these cardiovascular protective effects appear to be independent of GH release. The CD36 receptor is not part of the classical somatotroph axis, and cytoprotective responses have been documented in experimental designs where GH elevations were either absent or pharmacologically blocked. This mechanistic separation has significant implications for research design, as it means studies investigating GHRP-2’s organ-protective properties must account for both receptor systems to avoid misattributing observed effects to a single pathway.
Hepatic Protection and Anti-Inflammatory Signaling
The hepatoprotective potential of GHRP-2 was directly investigated by Granado and colleagues in a 2008 study published in the American Journal of Physiology-Endocrinology and Metabolism. Using a lipopolysaccharide (LPS)-induced endotoxemia model in rats, the researchers demonstrated that GHRP-2 administration attenuated the LPS-induced increases in serum transaminases (markers of hepatocellular damage), reduced circulating nitrites/nitrates (indicators of nitric oxide overproduction), and suppressed TNF-alpha elevations. Critically, GHRP-2 also prevented the LPS-induced decline in IGF-I, a hepatically-produced growth factor whose suppression during sepsis contributes to catabolic wasting.
The investigators provided evidence that GHRP-2 acts directly on hepatic nonparenchymal cells (primarily Kupffer cells and hepatic stellate cells) rather than exclusively through systemic GH elevation. This finding aligns with the known expression of both GHS-R1a and CD36 on hepatic macrophages and supports a model in which GHRP-2 simultaneously modulates the inflammatory response at the tissue level while maintaining anabolic signaling through the GH/IGF-I axis.
Musculoskeletal Research: Anti-Catabolic Mechanisms
Chronic inflammatory conditions produce skeletal muscle wasting through upregulation of the ubiquitin-proteasome pathway, which systematically degrades myofibrillar proteins. Granado and colleagues (2005) investigated whether GHRP-2 could counteract this process in adjuvant-induced arthritis in rats. Daily administration of GHRP-2 at 100 mcg/kg for 8 days prevented the arthritis-induced increase in the E3 ubiquitin-ligating enzymes MuRF1 (muscle RING-finger protein-1) and MAFbx (muscle atrophy F-box, also known as atrogin-1) in gastrocnemius muscle.
These two enzymes are the rate-limiting step in muscle protein ubiquitination and subsequent proteasomal degradation. Their suppression by GHRP-2 suggests that the peptide interrupts the catabolic cascade upstream of actual protein breakdown, potentially through both GH-mediated anabolic signaling and direct anti-inflammatory effects that reduce the cytokine-driven upregulation of atrogene expression. This dual mechanism positions GHRP-2 as a research tool for studying the interplay between inflammation, endocrine signaling, and muscle protein homeostasis.
Comparative Pharmacology: GHRP-2 vs. Other Secretagogues
Within the GHRP family, GHRP-2 occupies a specific pharmacological niche. Compared to GHRP-6, it produces comparable or slightly greater GH pulse amplitude with reduced appetite stimulation, likely due to differences in binding kinetics at the ghrelin receptor. The Laferrere (2005) data showed a 35.9% increase in food intake with GHRP-2, which is meaningful but generally considered moderate relative to the more pronounced orexigenic effects reported with GHRP-6 in comparable study designs.
Compared to ipamorelin, GHRP-2 produces greater GH release per unit dose but also stimulates ACTH, cortisol, and prolactin to a measurable degree. Ipamorelin is notable for its selectivity, producing GH release with minimal effects on other pituitary hormones, making it the cleaner secretagogue from a hormonal specificity standpoint. GHRP-2’s broader hormonal profile is not necessarily a disadvantage in research contexts where the interaction between GH, cortisol, and inflammatory mediators is itself the subject of investigation.
Relative to CJC-1295 (a GHRH analog), GHRP-2 operates through a fundamentally different receptor system. CJC-1295 stimulates GH release via the GHRH receptor on somatotrophs through Gs/cAMP/PKA signaling, while GHRP-2 uses Gq/PLC/IP3/calcium mobilization. This mechanistic separation explains why combinations of GHRH analogs and GHRPs produce synergistic rather than additive GH responses in preclinical research, as the two pathways converge on GH granule exocytosis through non-overlapping intracellular cascades.
Orexigenic Signaling and Metabolic Research Applications
The appetite-stimulating properties of GHRP-2 have made it a valuable research tool for studying the ghrelin system’s role in energy homeostasis. The Laferrere (2005) double-blind, placebo-controlled study is particularly notable because every single subject (n=10) responded to the GHRP-2 infusion with increased caloric intake, with individual responses ranging from 12% to 95% above placebo. The kJ eaten per kilogram of body weight rose from 101 +/- 10 kJ/kg (placebo) to 136 +/- 13 kJ/kg (GHRP-2, p=0.008), accompanied by significantly higher subjective hunger ratings on visual analog scales.
A follow-up study by the same group (Laferrere et al., 2006, published in Obesity) extended this work to obese subjects, finding that the orexigenic response to GHRP-2 was preserved in obesity despite elevated baseline leptin levels and presumed ghrelin resistance. This finding has implications for understanding the pharmacology of ghrelin receptor agonism in metabolically altered states and remains relevant to ongoing research into hypothalamic appetite regulation.
Research Considerations and Analytical Verification
GHRP-2’s multi-receptor pharmacology introduces complexity into experimental design. Researchers investigating GH-axis effects must account for the potential confounding influence of CD36-mediated cytoprotection, and vice versa. The use of selective GHS-R1a antagonists (such as [D-Lys3]-GHRP-6) or CD36 blocking antibodies can help dissect pathway-specific contributions in preclinical models.
For research-grade GHRP-2, analytical verification by HPLC and mass spectrometry is essential to confirm both identity and purity. The hexapeptide structure is susceptible to racemization at the D-amino acid positions during synthesis, and incomplete deprotection or truncation products can reduce effective concentration. At Maple Research Labs, all peptides are verified through independent third-party COA testing by Janoshik Analytical, providing researchers with batch-specific purity data, mass spectrometry identity confirmation, and endotoxin testing results before any material enters an experimental protocol.
Proper storage of lyophilized GHRP-2 at -20C protects against degradation, and reconstituted solutions should be aliquoted to minimize freeze-thaw cycles. Researchers working with this compound can find detailed handling protocols in our GHRP-2 product page and broader guidance in our compound comparison resources.
For research purposes only. Not for human consumption. Not for diagnostic or therapeutic use.
For peer-reviewed research on this topic, visit PubMed.
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