GHRP-2

Overview

GHRP-2 (Growth Hormone-Releasing Peptide-2), also called pralmorelin, is a synthetic hexapeptide that stimulates growth hormone release. It acts as an agonist at the growth hormone secretagogue receptor (GHS-R1a), the same receptor targeted by the endogenous hormone ghrelin.

The peptide was developed at Tulane University by Cyril Bowers, who founded the GHRP research tradition. It belongs to a series of small peptides that potently stimulate growth hormone release.

One feature sets GHRP-2 apart within this database: it has completed a formal clinical pathway. In Japan, pralmorelin is registered as a diagnostic agent for the assessment of hypothalamic-pituitary function. That registration is a fact about a regulator, not an application that Peptalis proposes. Among the growth hormone secretagogues in this database, such regulatory status is rare.

GHRP-2 is also orally active. For a peptide that modulates the growth hormone axis, that is unusual: most comparable compounds require injection. Oral activity has been documented in both animal and human studies.

Mechanism of action

GHRP-2 is an agonist at GHS-R1a with a dual point of action: directly on pituitary somatotrophs and indirectly via modulation of hypothalamic GHRH and somatostatin neurons. The net effect is a strong, pulsatile growth hormone release that is synergistic with GHRH.

GHS-R1a at the pituitary

• Binds with high affinity to GHS-R1a, the primary growth hormone secretagogue receptor.
• Activation drives pulsatile growth hormone release from the somatotrophs of the pituitary, the cells that produce and store growth hormone.
• The pathway does not run through the GHRH receptor. In a cell model with and without the human GHRH receptor, GHRP-2 retained its activity. That finding establishes a separate mechanism.

Modulation in the hypothalamus

• In animal models, GHRP-2 increases expression of GHRH in the posterior arcuate nucleus, a hypothalamic nucleus.
• At the same time it lowers expression of somatostatin, the hormone that inhibits growth hormone release.
• The net effect is a dual push in the same direction: more stimulatory GHRH, less inhibitory somatostatin.

Synergy with GHRH

• Combined administration of GHRP-2 and GHRH evokes a substantially larger growth hormone pulse than either alone.
• The synergy has been observed in both children and adults.
• It persists with oral administration, again an unusual feature for a peptide in this class.

Research findings

• Healthy children showed a measurable growth hormone response after oral administration.
• Synergy between GHRP-2 and GHRH has been confirmed in human studies.
• A diagnostic test based on GHRP-2 is used clinically to assess hypothalamic-pituitary function; a recent study in 36 patients also examined the ACTH response to avoid missing adrenal insufficiency.
• A separate study in 5 patients evaluated the test in a rare type of pituitary adenoma.
• In mice with a non-functional GHRH receptor, a limited but significant growth hormone response remained, evidence that GHRP-2 operates in part independently of the GHRH route.
• Modulation of GHRH and somatostatin in the hypothalamus has been observed across multiple animal models.
• Oral efficacy has been confirmed across multiple animal models.

Human studies

• Healthy children showed a measurable growth hormone response after oral administration.
• Synergy between GHRP-2 and GHRH has been confirmed in human studies.
• The diagnostic test is used clinically to assess hypothalamic-pituitary function; a study in 36 patients also examined the ACTH response.
• A separate study in 5 patients evaluated the test in a rare pituitary adenoma.

Animal models

• In mice with a non-functional GHRH receptor, a limited but significant growth hormone response remained, evidence for partial independence from the GHRH route.
• Modulation of hypothalamic GHRH and somatostatin has been observed across multiple animal models.
• Oral efficacy has been confirmed across multiple animal models.

Research context

GHRP-2 carries a sturdier clinical profile than most growth hormone secretagogues in this database. The diagnostic registration in Japan grants it a regulatory status that compounds such as Ipamorelin and the CJC-1295 variants lack.

Therapeutic development followed a different course. Phase II trials in growth hormone deficiency and short stature were launched, by Kaken in Japan and Wyeth in the United States, but were discontinued without published outcome data. The compound therefore entered the clinic through the diagnostic door while the therapeutic door closed without a published result. Why that happened, a commercial decision or a missing effect, cannot be inferred from the public literature. That question is still open.

Within the growth hormone secretagogues, GHRP-2 belongs to the best-studied alongside Hexarelin and Ipamorelin. Together they offer complementary pharmacological profiles for research into growth hormone signalling.

Open questions

GHRP-2 has a strong diagnostic and mechanistic profile. Therapeutic development has stalled, but the scientific basis for research use is solid.

• Therapeutic development for growth hormone deficiency was discontinued without published outcome data. Whether the phase II results can still be released is an open question for clinical research groups.
• The long-term risk profile under repeated administration has not been systematically characterised. This calls for controlled studies with structured monitoring.
• The long-term interplay with the endogenous ghrelin system is not fully characterised. Mechanistic laboratories working on GHS-R1a signalling will find a natural anchor here.
• Direct head-to-head data with more selective secretagogues such as Ipamorelin remain limited. A standardised comparison would help advance the field.

Research outlook

Diagnostic applications beyond the growth hormone axis are being further investigated, including in rare pituitary adenomas.

Combination protocols with GHRH remain scientifically relevant given the documented synergy.

Oral activity makes GHRP-2 an interesting model for research on oral peptide delivery, a broader question in pharmacology.

GHS-R1a as a target draws broader interest for research on metabolism and cachexia, the loss of muscle and body mass in chronic disease.

Scientific interest

GHS-R1a pharmacology and the action of growth hormone secretagogues

The dual point of action on pituitary and hypothalamus

Synergy with GHRH in growth hormone release

Oral activity as a model for peptide pharmacology

Specifications

References

1. Growth hormone-releasing peptides: clinical and basic aspects. · Argente J, García-Segura LM, Pozo J, Chowen JA. · Hormone Research · 1996
2. Growth hormone-releasing peptide-2 (GHRP-2) does not act via the human growth hormone-releasing factor receptor in GC cells. · Chen C, Farnworth P, Petersenn S, et al. · Endocrine · 1998
3. Pralmorelin: GHRP 2, GPA 748, growth hormone-releasing peptide 2, KP-102 D, KP-102 LN. · Drugs in R&D editorial. · Drugs in R&D · 2004
4. Growth hormone response to growth hormone-releasing peptide-2 in growth hormone-deficient little mice. · Peroni CN, Hayashida CY, Nascimento N, et al. · Clinics (São Paulo) · 2012
5. Growth hormone secretagogues: history, mechanism of action, and clinical development. · Ishida J, Saitoh M, Ebner N, et al. · ESC Heart Failure · 2014
6. Evaluation of growth hormone-releasing peptide-2 for diagnosis of thyrotropin-producing pituitary adenomas. · Kageyama K, Sakihara S, Kameda W, et al. · Endocrine Journal · 2018
7. Clinical Usefulness of the Growth Hormone-Releasing Peptide-2 Test for Hypothalamic-Pituitary Disorder. · Suzuki S, Ruike Y, Ishiwata K, et al. · Journal of the Endocrine Society · 2022

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