Mechanism of action of relaxant effect of Agastache mexicana ssp mexicana essential oil in guinea-pig trachea smooth muscle

Context: Agastache mexicana ssp. mexicana (Kunth) Lint & Epling (Lamiaceae), popularly known as 'toronjil morado', is used in Mexican traditional medicine for the treatment of several diseases such as hypertension, anxiety and respiratory disorders. Objective: This study investigates the relaxant action mechanism of A. mexicana ssp. mexicana essential oil (AMEO) in guinea-pig isolated trachea model. Materials and method: AMEO was analyzed by GC/MS. The relaxant effect of AMEO (5-50 mu g/mL) was tested in guinea-pig trachea pre-contracted with carbachol (3 x 10(-6) M) or histamine (3 x 10(-5) M) in the presence or absence of glibenclamide (10(-5) M), propranolol (3 x 10(-6) M) or 2',5'-dideoxyadenosine (10(-5) M). The antagonist effect of AMEO (10-300 mu g/mL) against contractions elicited by carbachol (10(-5)-10(-3) M), histamine (10(-15)-10(-3) M) or calcium (10-300 mu g/mL) was evaluated. Results: Essential oil composition was estragole, D-limonene and linalyl anthranilate. AMEO relaxed the carbachol (EC50 = 18.25 +/- 1.03 mu g/mL) and histamine (EC50 = 13.3 +/- 1.02 mu g/mL)-induced contractions. The relaxant effect of AMEO was not modified by the presence of propranolol, glibenclamide or 2',5'-dideoxyadenosine, suggesting that effect of AMEO is not related to beta(2)-adrenergic receptors, ATP-sensitive potassium channels or adenylate cyclase activation. AMEO was more potent to antagonize histamine (pA(2)' = -1.507 +/- 0.122) than carbachol (pA(2)' = -2.180 +/- 0.357). Also, AMEO antagonized the calcium chloride-induced contractions. Conclusion: The results suggest that relaxant effect of AMEO might be due to blockade of calcium influx in guinea-pig trachea smooth muscle. It is possible that estragole and D-limonene could contribute majority in the relaxant effect of AMEO.