GHRP-2

GHRP-2, known in the literature as pralmorelin and under the development code KP-102, is a synthetic hexapeptide with the sequence D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH2. Half its residues are non-canonical: two carry the D configuration, and position two is 3-(2-naphthyl)alanine, a bulky aromatic residue absent from ribosomally made proteins. The C-terminus is amidated. Those substitutions came out of structure-activity work aimed at potency and resistance to peptidase cleavage. The free-base molecular formula is C45H55N9O6 with an average mass of 818.0 g/mol, indexed as PubChem CID 6918245, and CAS 158861-67-7 refers to that same free base.

Reference sources place GHRP-2 in the growth hormone secretagogue class, meaning a molecule characterised through the receptor now designated GHS-R1a. It has no sequence relationship to growth hormone-releasing hormone and is not a fragment or analogue of it. Material reaching a laboratory is normally a lyophilized (freeze-dried) acetate salt rather than the free base tabulated above. GHRP-2 holds no approved indication in the United States and appears here strictly as a research-use-only reference compound. In receptor pharmacology work it is routinely mixed up with the earlier hexapeptide GHRP-6 and with hexarelin.

GHRP-2 came out of the peptide series Cyril Bowers and colleagues built after the original growth hormone-releasing hexapeptide. GHRP-1 and GHRP-2 were its second-generation members, and Kaken Pharmaceutical took the molecule forward as KP-102. Bowers set out the series in 1993 (PubMed 8374685).

Preclinical characterisation followed. Kamegai and colleagues showed that systemic KP-102 induced c-fos messenger RNA in the rat arcuate nucleus, locating a hypothalamic site of action (PubMed 8804723). Chen and colleagues tested GHRP-2 in pituitary cells transfected with the human GRF receptor and reported no signalling through that receptor, which separated it from the growth hormone-releasing hormone family (PubMed 9798733).

The record is best read for what it is: a substantial receptor-pharmacology literature, most of it assembled in the 1990s, with no completed development programme behind it. Nothing in that work supports an efficacy conclusion.

Published work describes GHRP-2 as an agonist at GHS-R1a, the G protein-coupled receptor whose endogenous ligand is ghrelin. Reported consequences in pituitary preparations include phospholipase C activation, inositol phosphate turnover and calcium entry through voltage-dependent channels. Roh and colleagues found calcium channel blockade abolished the bovine cell response and implicated protein kinase C and cyclic AMP (PubMed 9331879). Those are cell-culture observations.

Two distinctions guide control selection. Receptor family comes first: GHRP-2 and GHRP-6 bind the ghrelin receptor, while CJC-1295, Sermorelin, Tesamorelin and Mod GRF 1-29 are growth hormone-releasing hormone analogues at a separate, cyclic AMP-coupled receptor. The two hexapeptides then differ from each other: GHRP-6 is documented in rodent studies as producing a pronounced effect on food intake, whereas GHRP-2 is described as more selective. That contrast belongs to those animal models.

A methodology caveat applies. Reported signalling shifts with species and preparation: rat and bovine pituitary systems gave different second-messenger readouts in the studies cited. Potency assignments travel with the assay, not the molecule.

Sealed lyophilized GHRP-2 is held frozen, conventionally at -20°C, protected from light and kept out of repeated freeze-thaw cycling. No duration is given here: the stability window belongs on the batch Certificate of Analysis.

Chemistry sets the priorities. Tryptophan and the naphthylalanine residue absorb ultraviolet light and are oxidation-sensitive, so light exclusion matters. Dried peptide of this class is hygroscopic, meaning it draws in atmospheric moisture, so a sealed container is equilibrated to room temperature first.

Reconstitution is the term for returning a lyophilized compound to solution. It defines the term, not a procedure. GHRP-2 carries a free lysine amine and an amidated terminus and sits in the aqueous-soluble class, though its aromatic D-residues make it less polar than shorter secretagogue peptides.

Weighing is done in low humidity with short open-container exposure. Recording the lot number beside experimental data keeps identity traceable to one Certificate of Analysis, which matters where several secretagogue hexapeptides share a freezer box.

Identity and purity are established by reversed-phase HPLC with mass spectrometry. An observed mass consistent with 818.0 g/mol is the first checkpoint, and it separates GHRP-2 from GHRP-6 and hexarelin, whose masses differ. Verified purity is documented per lot on the Certificate of Analysis.

Salt form matters for gravimetric accuracy. Supplied GHRP-2 is generally an acetate salt, catalogued in places as a diacetate, so vial contents weigh more than the free-base value above, and residual water shifts it further. Net peptide content on the Certificate of Analysis is the figure to reconcile against vial strength.

GHRP-2 is best read alongside other secretagogues and the class it is confused with.

• GHRP-6.
  The parent hexapeptide of the series, same receptor, different animal-model selectivity.
• Hexarelin.
  A synthetic hexapeptide used as a comparator in ghrelin receptor characterisation.
• Ipamorelin.
  A pentapeptide ligand at GHS-R1a, reported as selective in preclinical assays.
• MK-677.
  A non-peptide research compound at the same receptor, a structural contrast.
• IGF-1 LR3.
  A downstream growth factor analogue rather than a secretagogue.

Bowers CY. (1993). GH releasing peptides, structure and kinetics. J Pediatr Endocrinol.
PubMed 8374685

Kamegai J, Hasegawa O, et al. (1996). The growth hormone-releasing peptide KP-102 induces c-fos expression in the arcuate nucleus. Brain Res Mol Brain Res.
PubMed 8804723

Roh SG, He ML, et al. (1997). Mechanisms of action of growth hormone-releasing peptide-2 in bovine pituitary cells. J Anim Sci.
PubMed 9331879

Chen C, Farnworth P, et al. (1998). Growth hormone-releasing peptide-2 does not act via the human growth hormone-releasing factor receptor in GC cells. Endocrine.
PubMed 9798733

GHRP-2 is carried as a single listing: lyophilized powder in a sealed vial at 10mg from one supplier brand. No capsule or liquid spray format is stocked for this compound. The per-vial strength is a product specification, and the lot is batch tested with a published Certificate of Analysis documenting identity and verified purity for that batch.

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These products are sold for Research Use Only and are not intended for human consumption.