the relaxant effect of crocin on rat tracheal smooth muscle and its possible mechanisms

Crocin, a component of saffron, showed hypotensive activity which is perhaps due tovascular smooth muscle relaxant effect. the relaxant effects of saffron on tracheal smoothmuscle also could be due to its constituent, crocin. in the present study, the relaxant effectsof crocin and its possible mechanisms on rat tracheal smooth muscle were investigated.the relaxant effects of three cumulative concentrations of crocin (30, 60, and 120 μm) ortheophylline (0.2, 0.4, 0.6 mm) as positive control were examined on pre-contracted trachealsmooth muscle by methacholine or kcl in non-incubated or incubated conditions withdifferent agents including atropine, chlorpheniramine, indomethacin, diltiazem, glibenclamide,and propranolol. in non-incubated tracheal smooth muscle, crocin showed significant relaxanteffects on kcl induced muscle contraction (p < 0.001 for two higher concentrations). however,crocin did not show relaxant effect on methacholine induced tissue contraction. in incubatedtissues with chlorpheniramine, indomethacin, diltiazem and propranolol, there were nosignificant differences in the relaxant effects of crocin between non-incubated and incubatedtissues. however, the relaxant effects of crocin obtained in incubated tissues with atropine andglibenclamide were significant lower than non-incubated tracheal smooth muscle (p < 0.05to p < 0.001). the ec50 value obtained in incubated tissue with propranolol was significantlyincreased. theophylline showed significant relaxant effect on both kcl and methacholineinduced tissue contraction (p < 0.01 to p < 0.001). a relatively potent relaxant effect of crocinon tracheal smooth muscle, lower than that of theophylline was shown. muscarinic receptorblocking, potassium channels opening and ß2-adrenoreceptors stimulation were also suggestedas possible mechanisms of this effect.