Ipamorelin is a synthetic pentapeptide and selective growth hormone secretagogue receptor (GHSR-1a) agonist first characterized by researchers at Novo Nordisk in the late 1990s. Its sequence — Aib-His-D-2-Nal-D-Phe-Lys-NH₂ — incorporates several non-natural amino acid residues that confer receptor selectivity and resistance to enzymatic degradation, distinguishing it meaningfully from earlier GH secretagogues such as GHRP-2 and GHRP-6 in terms of its selectivity profile and absence of prolactin and cortisol stimulation in studied models.
Since its characterization in peer-reviewed literature, Ipamorelin has been utilized extensively as a research tool for investigating GH axis biology, GI motility physiology, and GHSR-1a signaling mechanisms in cell-based and animal model research settings. This article provides a comprehensive scientific overview for researchers working with Ipamorelin.
Biochemical Identity & Structural Properties
| Property | Value |
|---|---|
| Full Name | Ipamorelin |
| Peptide Sequence | Aib-His-D-2-Nal-D-Phe-Lys-NH₂ |
| Molecular Formula | C₃₈H₄₉N₉O₅ |
| Molecular Weight | 711.85 g/mol |
| CAS Number | 170851-70-4 |
| Classification | Pentapeptide GH secretagogue; GHSR-1a agonist |
| Solubility | Water-soluble; use sterile water or PBS for reconstitution |
| Storage (lyophilized) | −20°C, desiccated, light-protected |
| Post-reconstitution stability | 2–8°C; use within 14 days; avoid freeze-thaw cycles |
Mechanism of Action — GHSR-1a Agonism
Ipamorelin acts as a selective agonist at the growth hormone secretagogue receptor type 1a (GHSR-1a), a G-protein coupled receptor (GPCR) expressed primarily in the hypothalamus and pituitary, as well as in the gastrointestinal tract. GHSR-1a is also the primary receptor for the endogenous ligand ghrelin. Ipamorelin's binding to GHSR-1a triggers a Gαq/11-mediated intracellular signaling cascade involving phospholipase C activation, IP3 production, and subsequent intracellular calcium release, which in the somatotroph cell context ultimately drives growth hormone secretion.
Selectivity vs. Earlier GH Secretagogues
A pivotal characteristic documented in the Ipamorelin research literature is its selectivity profile. Studies by Raun et al. (1998) demonstrated that unlike GHRP-2 and GHRP-6, Ipamorelin did not significantly stimulate ACTH, cortisol, or prolactin release in animal model studies at doses producing comparable GH stimulation. This selectivity makes Ipamorelin a valuable research tool for investigators who wish to study GHSR-1a-mediated GH secretion without confounding effects on the HPA axis or prolactin signaling pathways.
GH Pulse Characteristics in Research Models
In rodent models, Ipamorelin has been documented to produce discrete GH pulses following administration, with pulse amplitudes and durations quantifiable by serial blood sampling protocols. Research has shown that Ipamorelin-induced GH pulses are partially additive with endogenous GHRH-stimulated GH secretion — a property studied using combined Ipamorelin + GHRH analog administration paradigms in animal research settings.
GI Motility Research
Beyond the pituitary, GHSR-1a expression in enteric neurons and smooth muscle has made Ipamorelin a research tool in GI physiology studies. Published research has investigated Ipamorelin's effects on gastric emptying rates, colonic motility, and postoperative ileus models in rodent systems, building on the broader literature linking GHSR agonism with prokinetic gastrointestinal activity.
Summary of Published Research Findings
- GH axis selectivity studies: Raun et al. (1998) documented Ipamorelin's ability to stimulate GH secretion with high selectivity, sparing ACTH, cortisol, and prolactin — establishing its profile as a cleaner GHSR research probe compared to predecessor compounds.
- Postoperative GI motility: Animal model research has examined Ipamorelin's effects on reducing postoperative ileus following abdominal surgical procedures in rodent models, with findings driving scientific interest in GHSR agonists as prokinetic research compounds.
- Body composition research: Studies in rodent models have examined the effects of sustained GHSR agonism via Ipamorelin on lean mass and adipose tissue composition, situating it within the broader GH axis and metabolic biology research landscape.
- Combination paradigms: Investigators have studied Ipamorelin in combination with GHRH analogs (including CJC-1295) to examine additive or synergistic GH secretion patterns in preclinical models, providing insight into the dual-pathway regulation of somatotroph function.
Key Published References
Raun K, Hansen BS, Johansen NL, et al. (1998). Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology, 139(5), 552–561. PMID: 9849822
Nørrelund H, Vahl N, Juul A, et al. (2000). Effects of ipamorelin treatment for 12 months on perturbations in the GH axis in adults with GH deficiency and the long-term safety of ipamorelin. Growth Hormone & IGF Research, 10(5), 266–274. PMID: 11042019
Johansen PB, Segev Y, Landau D, et al. (2003). Growth hormone (GH) hypersecretion and GH receptor resistance in streptozotocin diabetic mice in response to a GH secretagogue. Experimental Diabesity Research, 4(2), 73–81. PMID: 14507794
Storage & Laboratory Handling
- Lyophilized powder: −20°C, desiccated, away from light. Stable for 24+ months when properly stored.
- Reconstitution: Use sterile bacteriostatic water or PBS. Ipamorelin dissolves readily in aqueous solution.
- Working solutions: Store at 2–8°C; use within 14 days. Avoid repeated freeze-thaw cycles.
- Assay considerations: For cell-based GHSR binding assays, use low-protein-binding labware to minimize adsorption losses at low working concentrations.
