Relaxant action mechanism of essential oil of Agastache mexicana aereal parts on guinea-pig trachea smooth muscle

In this study was investigated the relaxant action mechanism of essential oil of Agastache mexicana (EOAM) in guinea-pig isolated trachea model. The major components of this oil were estragole (80.28%) and D-limonene (17.55%). EOAM relaxed the carbachol (3µM, EC50 =18.25 ± 1.026 µg/mL) or histamine (3µM, EC50 =13.3 ± 1.026 µg/mL)-induced contractions in tracheal muscle. The relaxant effect of EOAM was not modified by the presence of propranolol (3µM), glibenclamide (10µM) or 2',5'-dideoxyadenosine (10µM), suggesting that relaxant effect of this essential oil is not related to β2-adrenergic receptors, ATP-sensitive potassium channels or adenylate cyclase activation. EOAM was more potent to antagonize histamine, whit pA'2 of -1.507 ±.122 (32.13 ± 1.32 µg/mL) than carbachol, with pA'2 of -2.180 ± 0.357 (151.35 ± 2.27 µg/mL). Also, EOAM antagonized the calcium chloride-induced contractions. These results suggest that relaxant effect of EOAM is due to an antihistaminic and anticholinergic effect in addition to the blockade of calcium influx in the guinea-pig trachea smooth muscle. It is possible that estragole and D-limonene are the responsible compounds of the relaxant effect of the essential oil of Agastache mexicana.