Ipamorelin is a five-residue synthetic peptide that activates the growth hormone secretagogue receptor, the same receptor the hormone ghrelin acts on. It is one of the smallest compounds in the secretagogue family and one of the most selective, and that selectivity is the reason it appears in so many pituitary research designs. Here is what the molecule is and what the original work established.
Structure
Ipamorelin is a pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2. Its registry identifiers are CAS 170851-70-4, molecular formula C38H49N9O5, and molecular weight 711.85. Three features of that short sequence carry most of the weight.
- Aib at position one. Alpha-aminoisobutyric acid is a non-natural residue that constrains the backbone and resists enzymatic cleavage at the N-terminus.
- Two D-amino acids. D-2-naphthylalanine and D-phenylalanine are mirror-image residues that proteases handle poorly, which extends the peptide's survival in biological media.
- A C-terminal amide. The NH2 cap removes the free carboxyl group, another common stability modification.
None of those choices are decorative. A five-residue all-L peptide with free termini would be degraded too quickly to be useful as a reagent.
Where it came from
Ipamorelin was described by Raun and colleagues in 1998 in the European Journal of Endocrinology, under the heading of the first selective growth hormone secretagogue. The work characterised the compound in pituitary cell preparations and in anaesthetised rats and pigs. The receptor it acts on had been identified two years earlier by Howard and colleagues, and the endogenous ligand for that receptor, ghrelin, was not reported until 1999. So ipamorelin arrived before the natural hormone it mimics was known, which is a common pattern in this family.
What selective actually means here
The earlier secretagogue GHRP-6 released growth hormone in animal models but also raised adrenocorticotropic hormone, cortisol and prolactin. Those extra signals are a problem for a research reagent, because any downstream readout becomes hard to attribute. The 1998 work reported that ipamorelin released growth hormone in the pig and rat models without the accompanying rise in adrenocorticotropic hormone, cortisol or prolactin seen with GHRP-6 at comparable activity. That is the selectivity claim, and it is the single most cited property of the compound.
| Property | Ipamorelin | GHRP-6 |
|---|---|---|
| Residues | 5 | 6 |
| Receptor | Growth hormone secretagogue receptor | Growth hormone secretagogue receptor |
| Growth hormone release in the original animal work | Yes | Yes |
| Adrenocorticotropic hormone and cortisol rise | Not observed at comparable activity | Observed |
| Prolactin rise | Not observed at comparable activity | Observed |
Why it is paired with a GHRH analog
The pituitary somatotroph sits under two separate inputs. Growth hormone releasing hormone acts through the GHRH receptor, and ghrelin acts through the secretagogue receptor. The two pathways converge on the same cell by different routes, which is why co-stimulation in pituitary cell models produces a larger response than either input alone. That is the reason so many designs pair a secretagogue with a GHRH analog rather than running one on its own.
We supply both halves of that pairing. Sermorelin is the GHRH(1-29) fragment, the shortest sequence that retains full GHRH receptor activity. The co-lyophilized CJC-1295 without DAC with ipamorelin vial carries a modified GHRH(1-29) analog alongside the secretagogue in a single vial, with both masses printed on the label. The broader logic of the family is covered in growth hormone secretagogues explained.
What it is used to model
Published research work with this compound concentrates on pituitary pharmacology: receptor binding and signaling assays in cells expressing the secretagogue receptor, growth hormone release from cultured or perfused pituitary cells, and comparative selectivity studies against other secretagogues in rodent models. Gastrointestinal motility models also appear in the literature, since the same receptor is expressed outside the pituitary. All of this is preclinical work in cell and animal systems.
Sizes and handling
We carry 5 mg and 10 mg vials. Ipamorelin is a short, hydrophilic peptide with no fatty acid modification, so it dissolves quickly and cleanly. A 5 mg vial with 2 mL of diluent gives 2.5 mg/mL, and a 10 mg vial with 2 mL gives 5 mg/mL. Because the working masses in cell assays are small, many labs deliberately choose a larger diluent volume and a lower concentration, since measurement error on a small draw is proportionally larger than on a big one. The arithmetic is worked through in reconstituting lyophilized peptides.
Two other handling notes. The C-terminal amide and the D-residues make the peptide robust as a powder but not immune to degradation in solution, so refrigerate after reconstitution and record the date. And because the molecule is small, mass spectrometry gives an unusually clean identity confirmation. Ask for the lot-matched certificate before you order, and read it against the guidance in how to read a peptide COA.
Frequently asked questions
Is ipamorelin the same thing as ghrelin?
No. Ghrelin is a 28-residue acylated hormone produced in the stomach. Ipamorelin is a synthetic pentapeptide that activates the same receptor with a very different structure. Sequence similarity is not the mechanism here; receptor occupancy is.
Why do vials often contain a GHRH analog as well?
Because the two act through separate receptors on the same pituitary cell. Co-lyophilizing them puts both inputs in one vial, which removes a pipetting step and keeps the ratio between the two fixed across an experiment.
Does the D-amino acid content affect analysis?
Not for routine HPLC and mass spectrometry. The mass is unchanged by stereochemistry, so mass spec confirms composition rather than chirality. Retention time on a reverse-phase column is affected slightly, which is why the method should be stated on the certificate.
References
- Raun K, et al. 1998. Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology.
- Bowers CY, et al. 1984. On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. Endocrinology.
- Howard AD, et al. 1996. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science.
- Kojima M, et al. 1999. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature.
Research use only. This article describes laboratory and preclinical research. Items in our research peptide collection are not for human or animal use, are not drugs, and are not intended to diagnose, treat, cure or prevent any disease. Nothing here is medical advice.
