Objective: Linalool, a monoterpene compound and a principal component of several aromatic herbs, possesses antispasmodic and smooth muscle relaxant properties. This study aimed to examine the relaxant effect of linalool on the tracheal smooth muscle (TSM) of rats and the mechanisms involved.
Materials and Methods: Tracheal rings (3–4 cartilaginous rings per trachea) from Wistar rats (200–250 g) of both sexes were used. After anesthesia using ketamine plus xylazine, followed by cervical dislocation, the trachea was removed. Cumulative concentrations of linalool (0.1, 0.2, 0.4 and 0.8 mg/ml) were added every 5 minutes to non-incubated tissues precontracted with methacholine or KCl for 7 minutes. The same concentrations were added to precontracted tissues pre-incubated (10 min) with propranolol, glibenclamide, diltiazem, papaverine, chlorpheniramine, indomethacin, L-NAME and atropine. Theophylline and saline served as positive and negative controls, respectively (n = 6–7 per group).
Results: Linalool showed concentration-related relaxant responses in non-incubated TSM precontracted by methacholine and KCl (p<0.01 to p<0.001). The relaxant responses of tissues incubated with propranolol, glibenclamide, diltiazem, papaverine, chlorpheniramine and indomethacin were not significantly different from non-incubated tissues. However, in L-NAME- and atropine-incubated tissues, some concentrations showed significantly lower relaxant effects than non-incubated tissues (p<0.05 to p<0.001). The highest concentration of linalool had a relaxant effect comparable to theophylline.
Conclusion: Linalool showed a pronounced relaxant action on TSM, similar to that of theophylline. The involvement of muscarinic receptor blockade and/or enhanced nitric oxide generation is proposed. Its bronchodilatory effect should be investigated in future clinical studies.