Possible mechanism(s) of the relaxant effect of asafoetida (Ferula assa-foetida) oleo-gum-resin extract on guinea-pig tracheal smooth muscle

Objective: Asafoetida (Ferula assa-foetida) is known as a valuable remedy for whooping cough, pneumonia, bronchitis in children and asthma treatment in folk medicine. In the present study the relaxant effects of the asafoetida on tracheal smooth muscle of guinea pigs and its probable mechanism(s) were examined. Materials and Methods: The relaxant effects of three cumulative concentrations of the aqueous extract (2, 5 and 10 mg/ml), theophylline (0.25, 0.5 and 0.75 mM) and saline were examined on non-incubated tracheal smooth muscle of guinea pig precontracted by 10 μM methacholine (group 1); preincubated tissues by propranolol and chlorpheniramine, contracted by methacholine (group 2) and preincubated tissues by propranolol, contracted by methacholine (group 3), (n=6 for each group). Results: All concentrations of theophylline in group 1 and all concentrations of the extract in the other three groups showed significant relaxant effects compared to that of saline (p<0.001 for all cases). There was not significant difference in the relaxant effect of the extract between three groups. The relaxant effects of two last concentrations of the extract (5 and 10 mg/ml) only in group 2 were significantly lower than that of theophylline (p<0.05 for both case). There was no significant difference between relaxant effects of the extract and theophylline in group 2. There were significant positive correlations between the relaxant effects of the extract with their concentrations in all three groups (p<0.001 for all cases). Conclusion: These results showed a potent relaxant effect for the asafoetida extract on tracheal smooth muscle which is perhaps due to muscarinic receptor blockade.