Composition and Bronchodilator activity of the fruits of Trachyspermum ammi L. Essential oil

Trachyspermum ammi is used traditionally to manage respiratory problems. The essential oil of the fruits was analyzed using GC-MS and the bronchodilator potential was explored using isolated guinea-pig trachea in an ex-vivo model. The GC-MS analysis revealed that thymol is major compound with 65% yield. T. ammi oil exhibited comparable potency in inhibiting contractions caused by carbachol (CCh, 1 µM) and high K+ (80 mM), with corresponding EC50 = 0.28 mg/mL (0.26-0.31, n=4) and 0.32 mg/mL (0.29-0.35, n=4) in a fashion similar to papaverine known to inhibit both Ca+2 channels and the phosphodiesterase enzyme (PDE). In contrast, Verapamil, a selective Ca+2 channel blocker, suppressed contractions induced by elevated K+ levels with significantly higher potency than those induced by CCh, as indicated by the EC50 = 0.82 µM (0.68–1.02, n=5) and 17.84 µM (15.64–1.86, n=5), respectively. Tissues preincubated with 0.03 and 0.1 mg/mL of the oil were able to attenuate the Ca+2 produced contraction and suppressing the maximum response in a manner comparable to verapamil and papaverine further supporting the Ca+2 channel inhibitory effect. PDE blockage was settled when tracheal tissues preincubated with T. ammi essential oil at 0.1 and 0.3 mg/mL expressed potentiation of isoprenaline relaxant effect against CCh, similar to papaverine. Preincubation with verapamil did not show any potentiation. Therefore, our results demonstrated that T. ammi essential oil have bronchodilator activities mediated by dual inhibition of Ca+2 channels and PDE, although other mechanisms may also be involved.