Relaxant Effects of Quercetin and Rutin on Human Isolated Bronchus

Increasing epidemiological evidence supports the view, that quercetin has protective roles in a multitude of disease states in human who have a high intake of polyphenols. To investigate the ability of quercetin and its rutinoside, rutin, to modulate the relaxation of human airways smooth muscle and to determine the mechanism (s) of such relaxation, isolated human bronchus rings were suspended in individual organ baths, precontracted with acetylcholine or with histamine and the relaxing effects of quercetin and rutin were determined by measurement of isometric tension. Quercetin induced concentration-dependent relaxant responses on acetylcholine or histamine precontracted human bronchial rings and with almost equal effectiveness. In terms of potency (pD₂) and efficacy (E_max), quercetin is more potent than rutin on relaxant responses of human bronchus. K⁺ and Ca²⁺ concentration-dependent contraction curves were inhibited after incubation with increasing concentrations of quercetin. Quercetin potentiated in a concentration-dependent manner the relaxant effects of isoprenaline or sodium nitroprusside. Rutin had no effect on K⁺-induced contraction and on relaxant activity of isoprenaline or sodium nitroprusside. Our results suggest that the bronchodilator effects of quercetin are modulated by an increase in cyclic nucleotide levels as well as an alteration in availability of Ca²⁺ to the contractile machinery