GHRP-2 (Pralmorelin) – Research Compound Profile

GHRP-2 (Pralmorelin) – Research Compound Profile

Category: Hormonal Research | Molecular Type: Synthetic Hexapeptide (D-Ala-D-β-Nal-Ala-Trp-D-Phe-Lys-NH₂) | Research Status: Approved in Japan as a GH Diagnostic Agent; Investigational Elsewhere

This page compiles published research data for qualified researchers. GHRP-2 (Pralmorelin) is not approved for human therapeutic use outside of its limited diagnostic application in Japan. It is sold exclusively as a research compound, is not intended for human consumption or self-administration, and this page does not constitute medical advice.

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Molecular Overview

GHRP-2 (pralmorelin, KP-102) is a synthetic hexapeptide growth hormone secretagogue with the amino acid sequence D-Ala-D-β-Nal-Ala-Trp-D-Phe-Lys-NH₂. It was originally developed in Cyril Bowers’ laboratory in the 1980s as part of a systematic effort to create synthetic compounds capable of stimulating growth hormone (GH) release from the anterior pituitary [18]. The peptide’s unnatural amino acid residues (D-Ala, D-β-Nal, D-Phe) confer resistance to enzymatic degradation, yielding a subcutaneous half-life of approximately 31 minutes (0.52 hours), which is longer than the related peptide GHRP-6 (~18 minutes) [4][6].

Among the growth hormone releasing peptides, GHRP-2 is widely regarded in the literature as one of the most potent members of its class for stimulating GH secretion [1][2]. It is the only GHRP to have achieved any form of regulatory approval, having been authorized in Japan as a diagnostic provocative test for growth hormone deficiency [3][4]. Pharmacokinetic studies have characterized its oral bioavailability at 0.3–1.0%, consistent with typical peptide limitations in gastrointestinal absorption [4]. Unlike the closely related GHRP-6, GHRP-2 has been documented in comparative studies to produce a milder orexigenic (appetite-stimulating) response [5][6].

Structural rationale: The three D-amino acid substitutions each serve a distinct steric purpose. D-Ala at position 1 removes a chiral centre otherwise vulnerable to aminopeptidase attack; D-β-Nal (D-2-naphthylalanine) at position 2 introduces a bulky bicyclic aromatic side chain that fills a hydrophobic subpocket of GHS-R1a inaccessible to natural L-amino acids, contributing disproportionately to binding affinity; and D-Phe at position 5 blocks the chymotrypsin-like cleavage that rapidly degrades related linear tryptophan/phenylalanine-containing peptides. The C-terminal amidation (–NH₂ in place of a free carboxylic acid) removes the substrate recognized by carboxypeptidases, a modification shared across the entire GHRP family and one of the principal reasons these hexapeptides survive systemic circulation far longer than unmodified peptide fragments of similar length.

Mechanism of Action

GHRP-2 acts as a potent agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the endogenous receptor for ghrelin [1][2]. Upon binding, GHRP-2 activates GHS-R1a receptors located on two primary sites: somatotroph cells of the anterior pituitary and neurons in the arcuate nucleus of the hypothalamus [1][2].

Pituitary-level signaling: At the anterior pituitary, GHS-R1a activation triggers a Gq/11-coupled phospholipase C signaling cascade that mobilizes intracellular calcium stores, directly stimulating GH exocytosis from somatotroph storage granules [2][19]. Howard et al. (1996) identified and cloned the GHS-R, establishing it as the molecular target through which GHRPs exert their secretagogue effects [19].

Hypothalamic-level signaling: At the hypothalamic level, GHRP-2 simultaneously amplifies GH-releasing hormone (GHRH) neuronal output and suppresses somatostatin tone, creating a permissive neuroendocrine environment for amplified pulsatile GH release [1][18]. This dual-site mechanism underlies the well-documented synergy between GHRP-2 and GHRH — Bowers (1998) and Smith (2005) noted that when administered together in research settings, combined GH output far exceeds the sum of either agent alone [1][2][18]. Gondo et al. (2001) further confirmed that GHRP-2 activates GH release through a pathway independent of the GHRH receptor, demonstrating preserved GH secretion in subjects with inactivating GHRH receptor mutations [9].

Negative feedback preservation: A key physiological distinction between GHRP-2 and exogenous recombinant GH documented in the literature is that GHRP-2 preserves endogenous somatostatin and IGF-1 negative feedback mechanisms [1][6]. Sigalos and Pastuszak (2018) emphasized that this feedback preservation is associated with a reduced risk of the supraphysiological GH excursions described with exogenous GH administration [6].

Orexigenic signaling: Beyond GH release, GHRP-2 activates ghrelin-mediated orexigenic pathways in the arcuate nucleus involving NPY/AgRP neurons. Laferrère et al. (2005) documented this appetite-stimulating effect, though comparative work by Arvat et al. (1997) indicates it is less pronounced with GHRP-2 than with GHRP-6 or native ghrelin [5][20].

Published Research Parameters

The following table indexes the study models, durations, and reported observations of selected peer-reviewed publications. Dose, frequency, and administration-route details are deliberately omitted. This is a bibliographic index only — not a protocol and not a recommendation for any use.

Stability & Storage Characteristics

Published data and manufacturer specifications indicate the following stability characteristics for GHRP-2:

• Lyophilized form: Lyophilized GHRP-2 demonstrates long-term stability when stored at −20 °C (−4 °F). The compound remains stable at room temperature for short periods (e.g., during shipping), though freezer storage is recommended for long-term preservation of peptide integrity [16].
• Reconstituted solution: When dissolved in bacteriostatic water, GHRP-2 solutions stored at 2–8 °C (35.6–46.4 °F) maintain stability for approximately 4 weeks according to manufacturer data [16].
• Freeze-thaw sensitivity: Repeated freeze-thaw cycles degrade peptide integrity. For extended storage of reconstituted solutions, single-use aliquots frozen at −20 °C and thawed only once before use are referenced in product literature [16].
• Light sensitivity: GHRP-2 solutions should be protected from direct light exposure. Secondary containment (e.g., amber vials or foil wrapping) is referenced in product handling guidelines [16].
• Temperature limits: Reconstituted GHRP-2 should not be exposed to temperatures above 25 °C (77 °F) for prolonged periods, as thermal degradation may compromise peptide structure [16].
• Deamidation and oxidation risk: As with other Trp-containing hexapeptides, the indole ring of the tryptophan residue is susceptible to oxidative modification under prolonged light or elevated-temperature exposure, and the C-terminal amide is a slow site of hydrolytic deamidation in aqueous solution over extended storage. Both pathways generate mass-shifted species detectable by LC-MS and are the principal drivers of purity loss during shelf-life studies [16].

Analytical Characterization

Research-grade GHRP-2 is characterized using an orthogonal analytical panel consistent with standard peptide reagent quality control. Reverse-phase HPLC (RP-HPLC) provides the primary purity determination and resolves related hydrolytic and oxidative degradation products from the parent hexapeptide. Electrospray ionization mass spectrometry (ESI-MS) confirms the intact monoisotopic mass and distinguishes the amidated parent from any deamidated (+1 Da mass shift relative to the free acid) impurity. A dedicated peptide-content assay (typically amino acid analysis or quantitative NMR) is used to determine the fraction of vial mass attributable to peptide versus residual counter-ion (commonly acetate or trifluoroacetate), water, and salts, since the gross lyophilized mass systematically overstates true peptide content. Chiral HPLC or enzymatic digestion assays can additionally verify that the D-amino acid centers have not undergone racemization or substitution during synthesis. Researchers should retain the quality assurance documentation (CoA) for each lot used.

Key Published Research Findings

The following findings are derived from peer-reviewed publications and are presented as research observations, not as established therapeutic outcomes.

• GH Secretion Potency: In a 1997 Peptides study, Arvat et al. administered GHRP-2 intravenously to adult subjects and observed dose-dependent increases in circulating GH levels, with concurrent transient elevations in prolactin, ACTH, and cortisol [5]. In a 2004 Journal of Clinical Endocrinology & Metabolism study, Bowers et al. reported that continuous subcutaneous infusion produced peak circulating GH levels far exceeding baseline values in older adults [11]. Laferrère et al. (2005) documented a substantial elevation in GH area-under-curve versus placebo during subcutaneous infusion in lean healthy men [20].

• Growth Velocity in Pediatric Models: In a 1998 Journal of Clinical Endocrinology & Metabolism study, Mericq et al. administered graded subcutaneous doses of GHRP-2 to GH-deficient children over 8 months and observed a statistically significant increase in growth velocity relative to baseline, with no toxicity reported [7]. In a separate 1997 Journal of Endocrinology study, Pihoker et al. administered intranasal GHRP-2 to children with short stature over 18–24 months and documented a sustained increase in growth velocity [14].

• Sustained IGF-1 Axis Activation: Bowers et al. (2004) documented that 30-day continuous subcutaneous infusion in older men and women produced sustained elevations in IGF-1, IGFBP-3, and IGFBP-5 concentrations throughout the study period, with pulsatile GH secretion remaining robust and no evidence of desensitization [11]. In a 2002 Clinical Endocrinology study, Van den Berghe et al. reported that GHRP-2 infusion over 5 days in critically ill men with prolonged ICU stays normalized previously suppressed IGF-1, IGFBP-3, and ALS concentrations [21].

• Appetite and Body Weight Effects: Laferrère et al. (2005) demonstrated in a controlled study that GHRP-2 infusion increased ad libitum food intake in lean healthy men, an effect comparable to native ghrelin [20]. In a 2015 Journal of Cachexia, Sarcopenia and Muscle case report, Haruta et al. documented that extended intranasal GHRP-2 administration in a severely emaciated anorexia nervosa patient was associated with body weight increase, improved muscle strength, and reduced fatigue [22]. Mericq et al. (2003) observed transient appetite rating increases in GH-deficient children receiving oral GHRP-2, though this did not translate to sustained BMI changes over the observation period [23].

• GH-Releasing Hormone-Independent Pathway: Gondo et al. (2001) demonstrated that GHRP-2 stimulated GH secretion in subjects with inactivating mutations of the GHRH receptor, confirming that GHRP-2 activates GH release through a mechanism that does not require functional GHRH signaling [9].

• Tachyphylaxis Observations: Nijland et al. (1998) conducted a five-day study of twice-daily subcutaneous GHRP-2 in healthy young men and documented measurable GH response attenuation by day five. However, the response stabilized and did not disappear entirely, suggesting partial receptor desensitization rather than complete tachyphylaxis [10].

• Synergistic Effects with GHRH: Multiple studies have documented that GHRP-2 and GHRH produce synergistic GH output when administered together in research settings, with the combined response far exceeding the additive sum of either agent alone. Bowers (1998) and Smith (2005) reviewed this synergy in detail, attributing it to the dual pituitary and hypothalamic mechanism of action [1][2][18].

Safety Profile in Published Literature

Published studies have documented the following safety observations:

• Cortisol and ACTH effects: Arvat et al. (1997, 2001) reported that GHRP-2 produces modest, dose-dependent ACTH and cortisol elevations that peak within the first hour post-administration and normalize within approximately two hours [5][12]. The cortisol response was described as comparable to mild CRH stimulation and was not considered clinically significant at the doses studied [12].

• Prolactin effects: Arvat et al. (1997, 2001) documented transient, dose-dependent prolactin increases accompanying GHRP-2 administration — comparable to those observed with hexarelin but substantially lower than TRH-stimulated values [5][12]. These increases dissipated rapidly and were not associated with clinical hyperprolactinemia at the doses studied.

• Appetite stimulation: While less pronounced than with GHRP-6, GHRP-2 was observed to transiently increase hunger sensations post-administration in several studies [5][20]. Mericq et al. (2003) noted transient appetite rating increases in GH-deficient children, without sustained BMI changes over the observation period [23].

• Long-term tolerance: Mericq et al. (1998) reported no toxicity over 8 months of graded-dose subcutaneous GHRP-2 in GH-deficient children [7]. Haruta et al. (2015) observed no adverse effects over 14 months of intranasal GHRP-2 in a case study [22]. Bowers et al. (2004) reported no serious adverse effects during 30-day continuous infusion in older adults [11].

• Potential insulin sensitivity effects: Sigalos and Pastuszak (2018) noted that, as a class effect of GH secretagogues, chronic GH elevation may modestly reduce insulin sensitivity, though this has been documented more extensively with the non-peptide GHS agonist ibutamoren (MK-677) than with GHRP-2 specifically [6].

Regulatory Status

• Japan: GHRP-2 (pralmorelin, marketed as GHRP Kaken 100) is approved as a diagnostic provocative agent for growth hormone deficiency evaluation [3][4].
• United States / EU: GHRP-2 has not received FDA or EMA approval for any therapeutic indication. It remains an investigational compound. Phase I pharmacokinetic studies have been conducted in pediatric populations [13].
• Clinical trials: Multiple published clinical studies have evaluated GHRP-2 in various populations including GH-deficient children [7][8][14], healthy adults [10][20], older adults [11][12], critically ill patients [21], and a cachexia/anorexia nervosa case [22].
• Research use: GHRP-2 is sold for research purposes only. It is not approved for human therapeutic use, self-administration, or consumption.

References

1. Cell Mol Life Sci (1998) — Bowers CY. “Growth hormone-releasing peptide (GHRP).” Comprehensive review of GHRP discovery, receptor mechanisms, and dual pituitary-hypothalamic action sites. View Source

2. Endocr Rev (2005) — Smith RG. “Development of growth hormone secretagogues.” Historical overview of GHS development from synthetic peptides to non-peptide mimetics, including GHS-R signaling mechanisms. View Source

3. Endocr J (2014) — “Increased Secretion of Endogenous GH after Treatment with GHRP-2.” Reports on pralmorelin’s approval in Japan as a diagnostic agent and its clinical utility. View Source

4. Horm Metab Res (2016) — Vodnik M, Strukelj B, Lunder M. “Ghrelin Receptor Ligands Reaching Clinical Trials.” Systematic review of GHS-R ligands including GHRP-2 pharmacokinetics (half-life 0.52 hr, oral bioavailability 0.3–1.0%). View Source

5. Peptides (1997) — Arvat E et al. “Effects of GHRP-2 and hexarelin, two synthetic GH-releasing peptides, on GH, prolactin, ACTH and cortisol levels in man.” Dose-dependent comparison with GHRH, TRH, and CRH effects. View Source

6. Sex Med Rev (2018) — Sigalos JT, Pastuszak AW. “The Safety and Efficacy of Growth Hormone Secretagogues.” Comprehensive review of GHS safety profiles including GHRP-2 (half-life, bioavailability, side effects, and clinical evidence). View Source

7. J Clin Endocrinol Metab (1998) — Mericq V et al. “Effects of eight months treatment with graded doses of a growth hormone-releasing peptide in GH-deficient children.” Reported statistically significant growth velocity increase. View Source

8. Metabolism (1995) — Tuilpakov AN et al. “Growth hormone-releasing effects of synthetic peptide GHRP-2 and GHRH in children with GH insufficiency.” Dose-response characterization of GHRP-2 in pediatric populations. View Source

9. J Clin Endocrinol Metab (2001) — Gondo RG et al. “GHRP-2 stimulates GH secretion in GH-deficient patients with mutated GH-releasing hormone receptor.” Confirms GHRP-2 activates GH release via a GHRH-independent pathway. View Source

10. Eur J Endocrinol (1998) — Nijland EA et al. “A five-day treatment with daily subcutaneous injections of GHRP-2 causes response attenuation and does not stimulate IGF-I secretion in healthy young men.” Key study on acute tachyphylaxis with repeated GHRP-2 dosing. View Source

11. J Clin Endocrinol Metab (2004) — Bowers CY et al. “Sustained elevation of pulsatile GH secretion and IGF-I, IGFBP-3, and IGFBP-5 concentrations during 30-day continuous subcutaneous infusion of GHRP-2 in older men and women.” View Source

12. Endocrine (2001) — Arvat E et al. “GH/IGF-1 response to acute and chronic GHRP-2, GHRH 1-44, and their combination in older adults.” Dose-response and hormonal axis effects of GHRP-2. View Source

13. J Clin Endocrinol Metab (1998) — Pihoker C et al. “Pharmacokinetics and pharmacodynamics of growth hormone-releasing peptide-2: a phase I study in children.” SC pharmacokinetic profiling. View Source

14. J Endocrinol (1997) — Pihoker C et al. “Treatment effects of intranasal growth hormone releasing peptide-2 in children with short stature.” Documented sustained increase in growth velocity over an 18–24 month observation period. View Source

15. J Clin Endocrinol Metab (1993) — Jaffe CA et al. “Effects of a prolonged growth hormone-releasing peptide infusion on pulsatile GH secretion in normal men.” Demonstrates GH pulse dynamics and the impact of metabolic state on responsiveness. View Source

16. Genaxxon Bioscience — Product Information: Growth Hormone-Releasing Peptide-2 (GHRP-2) technical specifications, storage, and stability guidelines. View Source

18. Endocrinology (1984) — Bowers CY et al. “On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone.” Original landmark publication on GHRP discovery. View Source

19. Science (1996) — Howard AD et al. “A receptor in pituitary and hypothalamus that functions in growth hormone release.” Identification and cloning of the GHS-R, establishing the molecular target for GHRPs. View Source

20. J Clin Endocrinol Metab (2005) — Laferrère B et al. “Growth hormone releasing peptide-2 (GHRP-2), like ghrelin, increases food intake in healthy men.” Reported markedly elevated GH area-under-curve and increased food intake versus placebo. View Source

21. Clin Endocrinol (2002) — Van den Berghe G et al. “The combined administration of GHRP-2, TRH and GnRH to men with prolonged critical illness.” GHRP-2 infusion normalized IGF-1, IGFBP-3, and ALS in critically ill subjects within 5 days. View Source

22. J Cachexia Sarcopenia Muscle (2015) — Haruta I et al. “One-year intranasal application of GHRP-2 improves body weight and hypoglycemia in a severely emaciated anorexia nervosa patient.” 14-month intranasal case study reporting body weight increase and no adverse effects. View Source

23. J Pediatr Endocrinol Metab (2003) — Mericq V et al. “Changes in appetite and body weight in response to long-term oral administration of the ghrelin agonist GHRP-2 in growth hormone deficient children.” Transient appetite effects without sustained BMI change. View Source

⚠️ Disclaimer: This page is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment recommendations. GHRP-2 (Pralmorelin) is sold exclusively as a research compound and has not been approved by the FDA for human consumption or therapeutic use. Its sole regulatory approval is as a diagnostic agent in Japan. It is not intended for human use, self-administration, or consumption. All information is derived from published peer-reviewed literature. Research must comply with all applicable laws, regulations, and institutional guidelines.

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