Cineole, Thymol and Camphor Nasal Challenges and their Effect on Nasal Symptoms and Cough in an Animal Model

Inhalation of aromatic vapours suppressed coughing induced by citric acid (CA) in naive animals. No data are available about their effects in an animal model with primarily up-regulated cough reflex. New data indicate that aromatic vapours suppress cough via effect on nasal sensory nerves.

The aim of our study was to ascertain the efficacy of nasal application of 1,8-cineole, thymol and camphor on nasal symptoms and CA induced cough in validated model of up-regulated cough reflex. Guinea pigs (n=13) were sensitized by intraperitoneal administration of ovalbumin (OVA) and sensitization was confirmed 21 days later by skin tests. Sensitized animals were repeatedly challenged with nasal OVA to induce rhinitis, and further experiments (cough challenges) were performed during the early phase of allergic inflammation.

Cough was induced by CA in plethysmograph for 10 minutes after nasal pre-treatment with aromatic substances (10^-3M) in rhinitis model. Cough was recognized from record of sudden airflow changes interrupting breathing pattern and cough sound. Final count of coughs was established by blind analysis using SonicVisualiser Software. Dose responses curves, total cough count and cough latency were analyzed.

Repeated intranasal challenge with OVA induces progressively worsening symptoms, and cough induced by CA during acute phase of allergic rhinitis was enhanced. Nasal pre-treatment with 1,8-cineole, thymol and camphor did not prevent onset of nasal symptoms, and the magnitude of symptoms was comparable to those without pretreatment. Camphor had the most potent antitussive effects (number of coughs 25±3 vs. 7±2, p<0.05) followed by thymol (number of coughs 25±3 vs. 14±2, p<0.05). The data for nasal 1,8-cineole challenge did not reach statistical significance. Cough latency followed this trend.

Although the magnitude of nasal symptoms is not influenced, the effect on cough is in case of camphor and thymol significant. Our data showed that nasal application of aromatic substances suppress citric acid induced cough in animals with up-regulated cough reflex.