Relaxant Effect of Foeniculum vulgare on Isolated Guinea Pig Tracheal Chains

Abstract

Foeniculum vulgare is a grassy plant which is believed to have several therapeutic effects including anti-asthmatic uses. We have therefore studied the relaxant (bronchodilatory) effect of this plant on isolated guinea pig tracheal chains and its possible mechanism(s). The bronchodilatory effects of aqueous and ethanol extracts, essential oil, and 1µM theophylline in comparison with controls were examined by their relaxant effects on precontracted isolated tracheal chains of guinea pig in two different conditions including: non-incubated tissues (group 1) and incubated tissues with 1µM propranolol and 1µM chlorpheniramine (group 2). In addition, the anticholinergic effects of essential oil and 10 nM atropine were tested by performing the cumulative log-concentrationresponse curves of methacholine induced contraction of tracheal chains compared with that of saline (for all experimental conditions n = 8). In group 1 and 2 experiments, essential oil and theophylline and, in group 1, ethanol extract showed significant relaxant effects compared to those of saline and ethanol, respectively. Although bronchodilatory effects of essential oil was lower than theophylline in group 1 (p < 0.01), there was no significant difference between the effect of ethanol extract in both groups and the effect of essential oil in group 2 experiments with that of theophylline. The relaxant effect obtained in group 2 for essential oil was significantly greater (p < 0.05) and for ethanol extract nonsignificantly lower than those of group 1 experiments. The results also showed non-parallel rightward shift of methacholine-response curves and nonsignificant difference of EC 50 (the effective concentration of methacholine, causing 50% of maximum response) obtained in the presence of essential oil compared to those of saline. These results indicated bronchodilatory effects of ethanol extract and essential oil from Foeniculum vulgare which is not due to inhibitory properties of the plant on muscarinic and histamine H 1 and/or an stimulatory effect on ß 2 -adrenergic receptors.