GHRP-2

Background

Growth hormone–releasing peptide‑2 (GHRP‑2, pralmorelin; development codes KP‑102, GPA‑748) is a synthetic hexapeptide growth hormone secretagogue (GHS) originally developed in the 1980s–1990s as part of the second generation of non–GHRH‑mimetic GH‑releasing peptides.[12][5] It is structurally distinct from endogenous growth hormone–releasing hormone (GHRH) and instead mimics the activity of ghrelin, acting as an agonist at the growth hormone secretagogue receptor type 1a (GHSR1a).[12][11]

GHRP‑2 emerged from medicinal chemistry optimization of early GHRPs such as GHRP‑6, with the aim of increasing potency, receptor selectivity, and oral or intranasal bioavailability.[12][5] Preclinical pharmacology was characterized extensively under the code KP‑102, including receptor binding, GH‑releasing activity, and general pharmacology studies in rodents and dogs.[5][6] Pralmorelin later advanced into clinical development, particularly in Japan, where it has been approved as a diagnostic agent for adult and pediatric GH secretory function.[11]

Unlike many other GHRPs, pralmorelin obtained formal clinical approval (in Japan) as a GH stimulation test agent, making it the only GHRP with established regulated medical use, although it has also been detected on the black market as a performance‑enhancing substance.[2]

Mechanism of action

Receptor targets

The primary pharmacological target of GHRP‑2 is GHSR1a, the ghrelin receptor, a G‑protein–coupled receptor predominantly expressed in the pituitary somatotrophs and hypothalamus.[11][12] GHRP‑2 functions as a potent agonist at this receptor, leading to:

• Stimulation of growth hormone (GH) release from pituitary somatotrophs
• Secondary increases in circulating insulin‑like growth factor‑1 (IGF‑1) via hepatic GH action[13]

In addition to GHSR1a, GHRP‑2 can interact with CD36, a scavenger receptor involved in lipid handling and oxidative stress in vascular tissues.[13] This interaction has been implicated in GH‑independent vascular effects in preclinical models.[13]

Endocrine and metabolic effects

Binding of GHRP‑2 to hypothalamic and pituitary GHSR1a activates Gq/11 and other G‑protein pathways, increasing intracellular calcium, promoting GH exocytosis, and modulating hypothalamic neuropeptide release.[12][5] Compared with GHRP‑6 and earlier secretagogues, KP‑102 (GHRP‑2) is characterized as more potent and with relatively selective GH‑releasing activity in animal studies.[5]

In rats, GHRP‑2 also exhibits ACTH‑releasing activity mediated primarily by hypothalamic corticotropin‑releasing factor (CRF) release, indicating an influence on the hypothalamic–pituitary–adrenal (HPA) axis.[7] In portal vein infusion models, pralmorelin (acting via GHSR1a) inhibits glucose‑stimulated GLP‑1 secretion, linking ghrelin receptor activation to gut–pancreatic axis modulation.[15]

As a ghrelin mimetic, GHRP‑2 also increases appetite and food intake, consistent with clinical observations of hyperphagia and weight gain in a long‑term intranasal case report.[11]

Non‑endocrine actions

Preclinical studies indicate that GHRP‑2 exerts anti‑oxidative and anti‑inflammatory effects independent of GH in vascular and inflammatory models. In ApoE‑/‑ mice, chronic GHRP‑2 administration increased IGF‑1 modestly but significantly suppressed vascular superoxide production and pro‑inflammatory gene expression without reducing atherosclerotic lesion area, effects partly attributed to CD36‑related signaling.[13] In arthritic rat models, GHRP‑2 reduced inflammatory parameters, consistent with broader tissue‑protective properties of ghrelin agonists.[4]

Evidence summary

Preclinical pharmacology

Foundational pharmacology of KP‑102 (GHRP‑2) was described in a series of studies:

• Pharmacological Characteristics of KP‑102 (GHRP‑2): In rats and dogs, subcutaneous GHRP‑2 produced robust, dose‑dependent GH release with higher potency than GHRP‑6 and synergistic effects with GHRH.[5] The study reported consistent GH secretory responses across repeated dosing, suggesting limited tachyphylaxis in the tested timeframe.[5]
• General Pharmacology of KP‑102: Broad safety pharmacology in rodents and dogs indicated no major adverse cardiovascular, respiratory, or CNS effects at pharmacologically active doses, although transient changes in blood pressure and heart rate were observed at higher exposures.[6]
• ACTH‑releasing activity: In rats, KP‑102 increased plasma ACTH; pharmacological blockade experiments suggested that CRF release was the primary mediator, demonstrating HPA axis activation beyond GH release.[7]

Structural and conformational work defined minimal bioactive structures for GHRPs. A widely cited analysis demonstrated that highly potent cyclic analogs of GHRP‑2 helped establish a convergent model for the active conformation of GH secretagogues, supporting rational design of small‑molecule GHSs.[12]

In vascular disease models, chronic GHRP‑2 treatment (24 μg/kg twice daily for 12 weeks) in ApoE‑/‑ mice increased IGF‑1 by 1.2–1.6‑fold and lowered interferon‑γ levels by 66%, while decreasing aortic superoxide production and inflammatory gene expression without altering lesion size.[13]

Human clinical data

Human data are dominated by diagnostic use and small studies rather than large therapeutic trials.

• GH stimulation and diagnostic use: In Japanese development programs (summarized in regulatory and clinical literature), pralmorelin administered orally or intravenously produced rapid, dose‑dependent increases in serum GH suitable for dynamic testing of pituitary GH reserve, with peak GH typically within 30–60 minutes after dosing.[11] Detailed numeric sample sizes and dose–response data are reported in Japanese clinical pharmacology studies (not all are freely accessible), but pralmorelin achieved regulatory approval for GH stimulation testing based on reproducible GH peaks and acceptable safety.[11]

• Anorexia nervosa case report: A one‑year case study described intranasal GHRP‑2 in a severely emaciated woman with anorexia nervosa and hypoglycemia.[11] Nasal pralmorelin was titrated over time (total daily dose not specified in the abstract) and administered for 12 months. Reported outcomes included improved body weight, reduction of hypoglycemic episodes, and increased appetite; GH and ghrelin‑like actions were implicated.[11] This remains anecdotal, with no controlled data.

• GLP‑1 secretion model: In a human‑relevant mechanistic rat study, intraportal pralmorelin infusion suppressed glucose‑stimulated GLP‑1 release, comparable to ghrelin’s effect, and this was reversed by a GHSR antagonist.[15] Although preclinical, the work underscores potential implications for glucose and incretin physiology.

There are no large randomized phase 3 therapeutic trials of pralmorelin for chronic indications reported in the accessible literature; most clinical use is as a single‑ or short‑dose diagnostic agent, primarily in Japan.[11]

Clinical and research uses

Approved or established uses

• Diagnostic GH stimulation test (Japan): Pralmorelin is approved in Japan as an oral or intravenous diagnostic agent to assess GH secretory capacity in adults and children with suspected GH deficiency or related disorders.[11] Clinical protocols typically involve single‑dose administration followed by serial GH measurements.

No approvals are documented in the United States or European Union for either diagnostic or therapeutic indications.[14]

Investigational and off‑label contexts

• Potential therapeutic use in anorexia and cachexia: The aforementioned intranasal case suggests possible benefit on appetite and weight in severe anorexia nervosa, but evidence is limited to a single uncontrolled case report.[11]
• Cardiovascular and vascular protection: Preclinical work in atherosclerosis models suggests antioxidant and anti‑inflammatory vascular effects via GH‑dependent and GH‑independent pathways, but no human cardiovascular trials have been reported.[13]
• Inflammation and arthritis: GHRP‑2 demonstrated anti‑inflammatory effects in arthritic rats, reducing joint inflammation and systemic inflammatory markers, but remains non‑translated clinically.[4]
• Sports and performance enhancement: Analytical and anti‑doping literature documents the detection of pralmorelin and analogs in seized vials and athlete samples, reflecting illicit use as a performance‑enhancing agent; this has led to its inclusion on the World Anti‑Doping Agency (WADA) prohibited list.[2][3]

Dosing context

The following information reflects research and diagnostic protocols and does not constitute dosing recommendations.

• Diagnostic GH stimulation (Japan): Oral pralmorelin is reported in clinical and regulatory literature to be administered as a single dose, with GH sampling over 60–120 minutes; typical adult diagnostic doses in Japanese practice are in the range of several hundred micrograms orally, but exact values vary by protocol and are not consistently detailed in open‑access sources.[11]
• Preclinical animal studies: In ApoE‑/‑ mice, GHRP‑2 was administered subcutaneously at 24 μg/kg twice daily for 12 weeks.[13] In rodent pharmacology, a range of intravenous and subcutaneous doses has been used to construct GH dose–response curves, generally in the low microgram per kilogram range.[5][6]
• Case report in anorexia nervosa: Intranasal GHRP‑2 was escalated during a year of therapy in a single patient, but the abstract does not provide specific dosing, highlighting the limited transparency for translational dosing guidance.[11]

Because of regional regulatory restrictions, off‑label or non‑regulated use often relies on nonstandard formulations and dosing regimens that are not supported by controlled clinical data.

Safety profile

Adverse effects

Across preclinical and diagnostic human use, GHRP‑2 exhibits a relatively benign acute safety profile, with the caveat of limited long‑term data.

• Acute tolerability: General pharmacology studies in rodents and dogs reported no significant organ toxicity at pharmacologically active doses, though transient cardiovascular changes (blood pressure, heart rate) were noted at higher doses.[6]
• Endocrine effects: By design, pralmorelin induces GH and modest IGF‑1 elevations.[5][13] These may theoretically exacerbate conditions sensitive to GH/IGF‑1 (e.g., active malignancy, proliferative retinopathy), though such risks have not been systematically evaluated.
• Appetite and weight gain: Ghrelin‑mimetic effects can increase appetite; in the anorexia nervosa case, intranasal GHRP‑2 was associated with weight gain, considered beneficial in that context but potentially adverse in obesity or metabolic syndrome.[11]
• HPA axis activation: ACTH and cortisol elevation via CRF‑dependent mechanisms has been demonstrated in rats, implying potential stress‑axis activation in humans at some doses.[7]
• Metabolic and incretin effects: In rats, intraportal pralmorelin suppressed GLP‑1 release during glucose challenge, suggesting a possible adverse effect on incretin‑mediated insulin response, although direct human data are lacking.[15]

Post‑marketing safety data from Japanese diagnostic use are not comprehensively available in English. Serious adverse reactions appear uncommon in the context of single‑dose GH stimulation testing, but systematic long‑term safety evaluation is absent.

Contraindication considerations (theoretical/indirect)

Formal contraindication lists are jurisdiction‑specific; however, based on mechanism and limited data, caution or avoidance is generally considered in:

• Patients with known or suspected active malignancy sensitive to GH/IGF‑1 signaling (theoretical risk)
• Conditions where exogenous GH stimulation is unsafe, such as uncontrolled intracranial hypertension
• Severe cardiovascular instability, given potential transient hemodynamic effects observed preclinically at high doses[6]
• Significant metabolic dysregulation (e.g., poorly controlled diabetes), in light of possible interactions with glucose and GLP‑1 physiology inferred from preclinical studies[15]

Definitive human data on these risks are lacking, and clinical decision‑making where the drug is approved typically follows local regulatory guidance.

Regulatory status

• Japan: Pralmorelin is approved as a diagnostic GH secretagogue for GH stimulation testing in children and adults with suspected GH deficiency or hypopituitarism.[11] It is marketed under proprietary names in oral and intravenous formulations for this purpose.
• United States: There is no FDA‑approved pralmorelin product for diagnostic or therapeutic use. GHRP‑2 is not listed among approved peptide therapeutics in recent FDA‑related peptide overviews, and it does not appear in U.S.‑approved GH stimulation test agents, which primarily include macimorelin and traditional pharmacological stimuli.[14]
• European Union: No EMA‑approved pralmorelin product is documented in recent reviews of peptide therapeutics and regulatory databases; its clinical use in the EU is not established.[14]
• Anti‑doping status: GHRP‑2 and related GHRPs are classified as prohibited substances by WADA. Analytical methods for detecting pralmorelin and its metabolites in urine using LC–MS/MS have been published and are employed in doping control laboratories.[2][3]

Consequently, outside Japan’s diagnostic context, GHRP‑2 is generally regarded as an investigational or non‑approved peptide, with use largely confined to research settings or unregulated markets.