Attenuation of Visceral and Somatic Nociception by Ghrelin Mimetics. — VialBase Research
Preclinical rat data indicate ipamorelin, acting peripherally through the ghrelin receptor, attenuates visceral and somatic pain independent of inflammation — a mechanistic signal beyond its established GH-secretagogue role, though not yet studied in humans.
- In a rat model of non-inflammatory visceral hypersensitivity (0.6% acetic acid colonic infusion) and somatic mechanical allodynia, both the peripherally restricted ghrelin mimetic ipamorelin (IV) and the globally active mimetic HM01 (oral) significantly attenuated colonic hypersensitivity and paw-withdrawal allodynia versus vehicle.
- Colonic sensitivity was quantified via visceromotor response (abdominal contractions) to graded colorectal distension (0-60 mmHg); somatic allodynia was quantified via von Frey filament paw-withdrawal counts.
- The anti-nociceptive effects of ipamorelin and HM01 were blocked by the ghrelin receptor antagonist H0900, confirming the effects are mediated through the ghrelin receptor.
- Because ipamorelin is peripherally restricted, its anti-nociceptive activity in this model indicates ghrelin-receptor-mediated pain modulation can occur without requiring central (CNS) drug penetration.
- The authors conclude ghrelin mimetics represent a potential novel approach for treating acute visceral and somatic pain in the absence of active inflammation.
Summary
This preclinical study examined whether ghrelin receptor agonism can attenuate visceral and somatic pain in the absence of active inflammation, comparing a peripherally restricted ghrelin mimetic (ipamorelin, administered intravenously) against a globally active mimetic (HM01, administered orally) in rats. Visceral hypersensitivity was induced by dilute (0.6%) acetic acid infusion into the colon without epithelial inflammation, and colonic sensitivity was quantified via the visceromotor response (abdominal contractions) to graded colorectal distension; somatic mechanical allodynia was quantified via paw-withdrawal responses to von Frey filament stimulation. Both ipamorelin and HM01 significantly reduced colonic hypersensitivity and somatic allodynia relative to vehicle controls. Co-administration of the ghrelin receptor antagonist H0900 blocked the anti-nociceptive effects of both compounds, confirming a ghrelin-receptor-dependent mechanism. Because ipamorelin does not readily cross into the central nervous system, its efficacy here suggests the anti-nociceptive effect can arise from peripheral ghrelin receptor activation alone. The authors conclude that ghrelin mimetics may represent a novel therapeutic avenue for acute visceral and somatic pain that is not driven by active inflammation.
Key Findings
- In a rat model of non-inflammatory visceral hypersensitivity (0.6% acetic acid colonic infusion) and somatic mechanical allodynia, both ipamorelin (IV, peripherally restricted) and HM01 (oral, globally active) significantly attenuated colonic hypersensitivity and paw-withdrawal allodynia versus vehicle.
- Colonic sensitivity was assessed via visceromotor response (number of abdominal contractions) to graded colorectal distension (0-60 mmHg); somatic allodynia via calibrated von Frey filament paw-withdrawal counts.
- The ghrelin receptor antagonist H0900 blocked the anti-nociceptive effects of both ipamorelin and HM01, confirming a ghrelin-receptor-dependent mechanism rather than an off-target effect.
- Ipamorelin’s peripheral restriction combined with its efficacy in this model suggests ghrelin-receptor-mediated anti-nociception does not require central nervous system penetration.
- The authors conclude ghrelin mimetics may offer a novel approach for treating acute visceral and somatic pain in the absence of active inflammation.
Relevance to Ipamorelin
Ipamorelin was tested here as the peripherally restricted comparator to the globally active ghrelin mimetic HM01, so this is a two-agent mechanistic study rather than an ipamorelin-only trial. Even so, the finding is directly relevant to ipamorelin: it significantly reduced both visceral (colonic) hypersensitivity and somatic mechanical allodynia in rats, and this effect was abolished by a ghrelin receptor antagonist, tying the anti-nociceptive activity to on-target ghrelin receptor agonism rather than an incidental effect. This adds a pain-modulation angle to ipamorelin’s established growth-hormone-secretagogue pharmacology, though the evidence is preclinical (rodent) only, mechanistic in design, and has not been evaluated in human pain models or clinical trials.
Citation
N Mohammadi E, Louwies T, Pietra C, et al. Attenuation of Visceral and Somatic Nociception by Ghrelin Mimetics. Journal of Experimental Pharmacology. 2020;12:267-274. doi:10.2147/JEP.S249747.
See Also
- Parent compound: Ipamorelin
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