Relaxant effect of Pimpinella anisum on isolated guinea pig tracheal chains and its possible mechanism(s)

We have studied the relaxant effect of Pimpinella anisum on isolated guinea pig tracheal chains and its possible mechanism(s). The bronchodilatory effects of aqueous and ethanol extracts and essential oil were examined on precontracted isolated tracheal chains of the guinea pig by 10 muM methacholine in two different conditions including: non-incubated tissues (group 1) and incubated tissues with 1 muM propranolol and 1 muM chlorpheniramine (group 2). In addition, the anticholinergic effects of essential oil and 10 nM atropine were tested by comparing the cumulative log concentration-response curves of methacholine induced contraction of tracheal chains and the effective concentration of methacholine, causing 50% of maximum response (EC50) in the presence of essential oil or atropine. Aqueous and ethanol extracts, essential oil and theophylline (1 mM) showed significant relaxant effects compared to those of controls. Although relaxant effect of essential oil was lower than theophylline, there was no significant difference between the effect of aqueous and ethanol extracts and that of theophylline. There was also no significant difference between the relaxant effects obtained in group 1 and 2 experiments. The results also showed parallel rightward shifts of methacholine-response curves and significant increase in EC50 with the presence of atropine or essential oil. These results indicated bronchodilatory effects of essential oil, aqueous, and ethanol extracts from P. anisum. The results also showed that the relaxant effect of this plant is not due to an inhibitory effect of histamine (H-1) or stimulatory effect of beta (2)-adrenergic receptors, but due to inhibitory effects on muscarinic receptors. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.