[Comparison of vasodilatation effect between quercetin and rutin in the isolated rat thoracic aorta]

To determine the possible difference in vasodialtation effect of quercetin and rutin.

The isolated rat thoracic aorta was treated with phenylephrine (PE), and the effects of quercetin and rutin on the preconstricted aorta rings with or without endothelium were determined by organ bath technique. Nitric oxide synthase inhibitor L-N(G)-nitroarginine methyl-ester (L-NAME), guanylyl cyclase inhibitor methylene blue, cyclooxygenase inhibitor indomethacin were used to explore the mechanism.

Quercetin (10-160 micromol/L) caused vasorelaxation of aorta rings preconstricted with PE in endothelium-intact and denuded aorta rings in a dose-dependent manner. Rutin(10-160 micromol/L) caused dose-dependent vasorelaxation in endothelium-intact rings preconstricted with phenylephrine, but not in denuded aorta rings. The maximal response (Rmax) values calculated from vasorelaxation curves of quercetin and rutin were (77.20+/-6.11)% and (44.28+/-7.48)%, respectively. There was no difference between median effective concentration (EC(50)) values of quercetin and rutin. Pretreatment with L-NAME (0.1 mmol/L) abolished the vasorelaxation by rutin,but did not influence the vasodilating effect of quercetin in endothelium-intact rings. Pretreatment with methylene blue (10 mmol/L) canceled the vasorelaxation both by quercetin and rutin. Pretreatment with indomethacin (10 micromol/L) attenuated the vasodilatation of quercetin, but did not affect the vascular effect of rutin.

The vasodilatation effect of quercetin is more potent than rutin. The vasodilatation effect of quercetin might be mediated by guanylyl cyclase and cyclooxygenase-dependent pathway, while the vasodilatation by rutin might be via nitric oxide-guanylyl cyclase pathway.