Ipamorelin Acetate
Ipamorelin | NNC 26-0161
Mechanism of Action
Ipamorelin is a synthetic pentapeptide growth hormone secretagogue that acts as a selective agonist of the ghrelin/growth hormone secretagogue receptor (GHS-R1a). Unlike earlier GHS compounds such as GHRP-6 and GHRP-2, ipamorelin is notable for its high selectivity — it stimulates growth hormone release without significantly affecting cortisol, prolactin, or ACTH levels at GH-stimulating doses. This selectivity was first characterized by Raun and colleagues at Novo Nordisk in 1998.
Ipamorelin binds GHS-R1a on pituitary somatotroph cells, triggering intracellular calcium influx via phospholipase C and IP3 pathways. This calcium mobilization causes GH-containing granule fusion with the cell membrane and GH exocytosis. The peptide produces dose-dependent GH release with a well-defined dose-response curve and a ceiling effect, meaning higher doses do not produce proportionally greater GH release — a property that contributes to its safety profile.
Research has also explored ipamorelin's effects on gastrointestinal motility. Hansen et al. demonstrated that ipamorelin accelerates gastric emptying and colonic transit time in post-operative ileus models, leading to investigation as a potential prokinetic agent. This GI activity is mediated through ghrelin receptor activation in the enteric nervous system.
Key Research Findings
- Raun et al. (1998) demonstrated ipamorelin is the first GH secretagogue to show complete selectivity for GH release over ACTH, cortisol, and prolactin in swine models.
- Johansen et al. (1999) showed ipamorelin releases GH with efficacy and potency comparable to GHRP-6 in rats but without the broad endocrine side effects.
- Hansen et al. (2009) demonstrated ipamorelin accelerated postoperative recovery of gastrointestinal function in a rat model of post-operative ileus.
- Beck et al. (2004) showed chronic ipamorelin treatment increased bone mineral content and body weight gain in female rats without affecting blood glucose.
References
Dosage in Research
In animal studies, ipamorelin is typically dosed at 0.1-1 mg/kg. The selective GH release window is observed at doses up to 1 mg/kg, above which ACTH stimulation begins. Human phase II trials for post-operative ileus used IV infusions of 0.03 mg/kg/hr.
Storage & Handling
Store lyophilized powder at -20C. Reconstituted solution should be refrigerated at 2-8C and used within 28 days. Relatively stable peptide compared to larger growth factors.
Frequently Asked Questions
What makes ipamorelin different from other GH secretagogues?
Ipamorelin is the first GH secretagogue shown to be truly selective — it stimulates growth hormone release without significantly affecting cortisol, prolactin, or ACTH at effective doses. This distinguishes it from GHRP-2 and GHRP-6, which activate broader endocrine responses.
Why is ipamorelin often combined with CJC-1295?
Ipamorelin (a ghrelin receptor agonist) and CJC-1295 (a GHRH analogue) work through different receptor pathways. Research by Bowers et al. established that co-administration of GHRP and GHRH pathway agonists produces synergistic GH release far exceeding either alone.
What is ipamorelin's effect on gastric motility?
Research has shown ipamorelin accelerates gastric emptying and colonic transit through ghrelin receptor activation in the enteric nervous system. It was investigated in clinical trials as a treatment for post-operative ileus.
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