Relaxant effect of Crocus sativus (saffron) on guinea‐pig tracheal chains and its possible mechanisms

As indicated in ancient Iranian medical books, Crocus sativus has therapeutic effects on respiratory diseases. The relaxant effect of this plant has been observed also on smooth muscles in previous studies. Therefore, in this study the relaxant effects of aqueous‐ethanolic extracts of C. sativus and one of its main constituents, safranal, were examined on guinea‐pig tracheal chains. The relaxant effects of four cumulative concentrations of aqueous‐ethanolic extract (0.15, 0.3, 0.45, and 0.60 g %) and safranal (0.15, 0.30, 0.45, and 0.60 mL 0.2 mg mL−1 solution) in comparison with saline, as negative control, and four cumulative concentrations of theophylline (0.15, 0.30, 0.45, and 0.60 mM), as positive control, were examined using guinea‐pig precontracted tracheal chains. The tracheal chains had been precontracted by three different methods. Group 1 had been precontracted using 10 μM methacholine. The other two groups had been precontracted using 60 mM KCl at two different conditions: non‐incubated tissues (group 2) and tissues incubated with 1 μM propranolol, 1 μM chlorpheniramine and 1 μM atropine (group 3) (for each group, n = 6). In group 1 all concentrations of theophylline, extract and safranal showed significant relaxant effects compared with saline (P < 0.05 to P < 0.001). In group 2 theophylline, extract and safranal showed concentration‐dependent relaxant effects also compared with saline (P < 0.05 to P < 0.001 for different concentrations except two low concentrations of safranal). However, in group 3 the extracts of C. sativus showed a weak relaxant effect (P < 0.05 only for the highest concentration). The effects of the last concentration of safranal (0.60 mL 0.2 mg mL−1 solution) in group 1, and all its concentrations in group 2 were significantly lower than those of theophylline (P < 0.05 to P < 0.001). In addition, the effects of safranal 0.45 and 0.60 mL 0.2 mg mL−1 solution in groups 1 and 2 were significantly lower than that of C. sativus extract. There were significant correlations between the relaxant effects and concentrations for extract, safranal and theophylline in all experimental groups (P < 0.001 for all cases). These results showed a potent relaxant effect of C. sativus on tracheal chains of guinea‐pigs that was comparable to or even higher than that of theophylline at the concentrations used. The results indicated that safranal was, at least in part, responsible for the relaxant effect of C. sativus.