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 μg/mL) was tested in guinea-pig trachea pre-contracted with carbachol (3 × 10 - 6 M) or histamine (3 × 10 - 5 M) in the presence or absence of glibenclamide (10 - 5 M), propranolol (3 × 10 - 6 M) or 2',5'-dideoxyadenosine (10 - 5 M). The antagonist effect of AMEO (10-300 μg/mL) against contractions elicited by carbachol (10 - 15-10 - 3 M), histamine (10 - 15-10 - 3 M) or calcium (10-300 μg/mL) was evaluated.
Results: Essential oil composition was estragole, d-limonene and linalyl anthranilate. AMEO relaxed the carbachol (EC50 = 18.25 ± 1.03 μg/mL) and histamine (EC50 = 13.3 ± 1.02 μg/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 β2-adrenergic receptors, ATP-sensitive potassium channels or adenylate cyclase activation. AMEO was more potent to antagonize histamine (pA2' = -1.507 ± 0.122) than carbachol (pA2' = -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.
Keywords: Estragole; airways; asthma; d-limonene; pA2′.