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

Abstract

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′.

Figure 1.

Concentration-relaxant response curve of AMEO in guinea-pig tracheal tissue after (A) carbachol (3 × 10 ^− 6 M) or (B) histamine (3 × 10 ^− 5 M)-induced contractions. Each point represents mean ± S.E.M. of at least six experiments.

Figure 2.

Modified Schild plot for noncompetitive antagonism effect, according to the equation pA₂′ = pB_x′ + Log (X-1), where pB_x′ is the negative logarithm of the concentration (-Log B′) of antagonist (AMEO) and X is the ratio between maximal effect (E_max) of (A) carbachol or (B) histamine in the absence of antagonist (AMEO) and that in the presence of antagonist (AMEO on guinea-pig tracheal tissue. The pA₂′ value is the abscissa to the origin of the graph Log (X-1) vs pB_x′, when X = 2. Each point represents mean ± S.E.M. of at least six experiments.

Figure 3.

Calcium chloride-induced contractions on guinea-pig tracheal tissue in absence (•) or in presence of AMEO (▪ 25 μg/mL; ^ 50 μg/mL; ♦ 100 μg/mL). Each point represents mean ± S.E.M. of at least six experiments.

Figure 4.

Concentration-response curve of AMEO alone (^) and in the presence of (A) propranolol 3 × 10 ^− 6 M (▴), (B) 2′,5′-dideoxyadenosine 3 × 10 ^− 6 M (▪) or (C) glibenclamide 10 ^− 7 M (•). The graphs depict the logarithm of the concentration of AMEO (5–50 μg/mL) plotted against tension expressed as % of contraction elicited by carbachol 3 × 10 ^− 6 M in guinea pig-tracheal tissue. Each point represents the mean ± S.E.M of at least six experiments.