Blocking Substance P Didn't Relieve Allergy Symptoms in Rats — But Changed Airway Tissue

What the researchers found

In an ovalbumin-induced allergic rhinitis rat model, aprepitant (a substance P receptor antagonist) failed to reduce nasal symptoms like scratching and sneezing, while antihistamines and leukotriene receptor antagonists (LTRA) significantly improved those symptoms.

However, aprepitant did produce histopathological changes — it significantly reduced pseudostratification (abnormal cell layering) in the laryngeal mucosa compared to untreated allergic rats. The study also found that the allergic rhinitis model produced measurable allergic changes in the larynx, not just the nose.

Why it matters

Substance P is a neuropeptide that drives inflammation and secretion in the airways, making it a logical drug target for allergic rhinitis. This study shows that blocking substance P with aprepitant changes tissue architecture but doesn't relieve nasal symptoms — suggesting substance P plays a structural rather than symptomatic role in airway allergy, and that current antihistamines and LTRAs remain more effective for symptom relief.

The numbers in context

34 rats · 5 groups · Aprepitant: no effect on nasal symptoms · Significant reduction in laryngeal pseudostratification vs allergy group

How the study worked

Researchers induced allergic rhinitis in 34 female Sprague Dawley rats (8–12 weeks old) using ovalbumin sensitization. The rats were divided into 5 groups and treated with aprepitant, antihistamine, leukotriene receptor antagonist, or controls. Nasal symptoms (scratching, sneezing) were scored by observation, and nasal and laryngeal tissue was examined histopathologically after treatment.

Who was studied

34 female Sprague Dawley rats with ovalbumin-induced allergic rhinitis

What this study cannot tell us

Animal model results may not translate to humans. Small sample size (34 rats across 5 groups means ~7 per group). The study only assessed short-term effects and tissue changes, not long-term clinical outcomes. Aprepitant dosing in rats may not reflect optimal human dosing.

How to read the evidence

This is a small animal study with ~7 rats per group. While it provides mechanistic insights, animal models of allergic rhinitis don't reliably predict human responses, and the sample size limits statistical confidence.

When this study was published

Published in 2023, this study addresses an area of active research — neuropeptide-targeted allergy treatment — though substance P antagonists remain a niche therapeutic approach.

The bigger picture

Substance P and the tachykinin peptide family have long been implicated in neurogenic inflammation — the type of inflammation driven by nerve signaling rather than just immune cells. This study adds nuance: blocking substance P may modify tissue-level inflammation without the obvious symptom relief that patients and clinicians look for, suggesting its role in allergic disease is more complex than simple symptom generation.

Questions still open

• Would combining aprepitant with antihistamines produce better outcomes than either alone by addressing both symptomatic and structural aspects of allergic rhinitis?
• Does substance P play a larger role in chronic tissue remodeling from allergies rather than acute symptom generation?
• Would higher doses or longer treatment with substance P antagonists eventually produce measurable symptom improvement?

Common questions

Read the original research

The Role of Substance P Receptor Antagonists in Allergic Rhinitis: Ovalbumin-Induced Rat Model.

The Laryngoscope, 133(11), 2891-2897

Citation

Becerik, Çağrı; Karaca, Çiğdem T; Özcan, Zühal; Kul, Selim; Toros, Sema Z. (2023). The Role of Substance P Receptor Antagonists in Allergic Rhinitis: Ovalbumin-Induced Rat Model.. The Laryngoscope, 133(11), 2891-2897. https://doi.org/10.1002/lary.30628