Possible mechanism(s) for relaxant effects of Foeniculum vulgare on guinea pig tracheal chains.

In a previous study the relaxant (bronchodilatory) effect of Foeniculum vulgare on isolated guinea pig tracheal chains was demonstrated. To study mechanisms responsible for this effect the present study evaluated the inhibitory effect of this plant on contracted tracheal chains of guinea pig. The relaxant effects of aqueous and ethanol extracts and an essential oil from Foeniculum vulgare were compared to negative controls (saline for aqueous extract and essential oil and ethanol for ethanol extract) and a positive control (diltiazem) using isolated tracheal chains of the guinea pig precontracted by 10 microM methacholine (group 1) and 60 mM KCl (group 2, n = 7 for each group). In the group 1, experiments diltiazem, ethanol extract, and essential oil from Foeniculum vulgare showed a significant relaxant effect on methacholine induced contraction of tracheal chains compared to those of negative controls (p < 0.05 to p < 0.001). In addition the effect of the ethanol extract was significantly greater than that of diltiazem (p < 0.001). However, the aqueous extract did not show any relaxant effect in group 1. In the group 2 experiments, only diltiazem showed a significant relaxant effect on KCl induced contraction of tracheal chains (p < 0.001). The relaxant effects of ethanol extracts and essential oil obtained in the group 2 experiments were significantly lower than those in group 1 (p < 0.05 to p < 0.001). These results confirm the bronchodilatory effects of ethanol extract and essential oil from Foeniculum vulgare. However with regard to the effect of KCl on calcium channels, the results indicated that the inhibitory effect of ethanol extracts and essential oil from Foeniculum vulgare on calcium channels is not contributing to their relaxant (bronchodilatory) effects on guinea pig tracheal chains. However the results suggest a potassium channel opening effect for this plant, which may contribute on its relaxant effect on guinea pig tracheal chains.