The flavonoid quercetin is metabolized into isorhamnetin, tamarixetin, and kaempferol, the vascular effects of which are unknown. In the present study, the effects of quercetin and its metabolites were analyzed on isometric tension in isolated rat thoracic and abdominal aorta, in isolated intact and ␤-escinpermeabilized iliac arteries, and on perfusion pressure in the isolated mesenteric resistance vascular bed. In noradrenalineprecontracted vessels, the four flavonoids produced a vasodilator effect, which was inversely correlated with the diameter of the vessel studied; i.e., quercetin, isorhamnetin, tamarixetin, and kaempferol were 5-, 25-, 4-, and 6-fold, respectively, more potent in the resistance mesenteric bed (Ϫlog IC 50 ϭ 5.35 Ϯ 0.15, 5.89 Ϯ 0.11, 5.34 Ϯ 0.10, and 5.66 Ϯ 0.06, respectively) than in the thoracic aorta (Ϫlog IC 50 ϭ 4.68 Ϯ 0.08, 4.61 Ϯ 0.08, 4.73 Ϯ 0.11, and 4.81 Ϯ 0.13, respectively; n ϭ 4 -6). The vasodilator responses of quercetin and isorhamnetin were not significantly modified after removal of the endothelium in the thoracic aorta or in the mesenteric bed. Furthermore, the guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 10 Ϫ6 M), the adenylate cyclase inhibitor SQ22536 [9-(tetrahydro-2-furanyl)-9H-purin-6-amine; 10Ϫ6 M], KCl (40 mM), or ouabain (10 Ϫ3 M) had no effect on isorhamnetin-induced vasodilation in the mesenteric bed. In permeabilized iliac arteries stimulated with Ca 2ϩ (pCa of 5.9), isorhamnetin was also significantly more potent (Ϫlog IC 50 ϭ 5.27 Ϯ 0.15) than quercetin (Ϫlog IC 50 ϭ 4.56 Ϯ 0.15). In conclusion, quercetin and its metabolites showed vasodilator effects with selectivity toward the resistance vessels. These effects are not due to or modulated by endothelial factors and are unrelated to changes in cytosolic Ca 2ϩ .Flavonoids comprise a large group of secondary metabolites widely distributed throughout the plant kingdom, including food plants. The daily flavonoid intake in the human diet (mainly from onions, apples, grapes, wine, tea, berries, herbs, and spices) is highly variable, with estimations ranging from 23 mg (flavonols plus flavones; Hertog et al., 1993b) to more than 500 mg (total flavonoids;

Nitric oxide (NO) has been implicated in a number of diverse physiologic processes, including regulation of vascular tone. Carbon monoxide (CO) is another endogenously generated diatomic gas that may play an important physiologic role in vascular smooth muscle homeostasis. The purpose of this study was to compare the responses to exogenous NO and CO in isolated vessels (pulmonary arteries, pulmonary veins, and mesenteric arteries) from 12-to 24-h-old and 2-wk-old piglets. Vessels precontracted with the thromboxane A 2 mimetic U46619 (10 Ϫ7 M) relaxed in response to CO (2 ϫ 10 Ϫ6 to 2 ϫ 10 Ϫ4 M) and NO (2 ϫ 10 Ϫ9 to 2 ϫ 10 Ϫ7 M); these effects were not affected by endothelium removal but were completely abolished by the soluble guanylate cyclase inhibitor ODQ (10 Ϫ5 M). In pulmonary arteries, the maximal relaxation to NO increased with postnatal age from 33 Ϯ 4% of the precontraction value to 56 Ϯ 5%, in 12-to 24-h-old and 2-week-old piglets, respectively (p Ͻ 0.01), but the response to CO decreased from 25 Ϯ 3% to 12 Ϯ 1%, respectively (p Ͻ 0.01). The maximal response to CO was greater in pulmonary veins than in pulmonary or mesenteric arteries for both age groups (p Ͻ 0.01). Vasorelaxation induced by endogenous NO (stimulated by acetylcholine) was also greater in pulmonary veins when compared with pulmonary arteries and increased with postnatal age in both vessels. In contrast, no age-related differences were observed in the vasorelaxation induced by the cGMP analog 8-bromo cGMP in pulmonary arteries. When the response to NO was analyzed under three different extracellular O 2 concentrations (PO 2 4.51 Ϯ 0.03, 19.32 Ϯ 0.17, and 86 Ϯ 0.62, kPa), no significant differences were found. However, in the presence of superoxide dismutase (100 U/mL). the response to CO remained unchanged, and the response to NO improved in pulmonary arteries from 2-week-old but not from newborn piglets. In conclusion, both NO and CO relaxed neonatal vessels through soluble guanylate cyclase activation. However, when compared with NO, CO exhibited a poor vasorelaxant activity. Pulmonary vasorelaxation induced by NO increased with postnatal age, whereas that induced by CO decreased. Changes in extracellular oxygen concentration did not alter the pulmonary vascular response to NO. However, the presence of superoxide dismutase improved the response to NO, indicating that oxidant activity limits the vasorelaxant response to NO but not to CO. (Pediatr Res 48: 546-553, 2000) Abbreviations NO, nitric oxide CO, carbon monoxide sGC, soluble guanylate cyclase HO, heme oxygenase SOD, superoxide dismutase U46619, 9,11-dideoxy-11␣,9␣-epoxymethano-prostaglandinNO is known to be involved in the regulation of multiple physiologic processes, including the regulation of pulmonary vascular tone (1). On the other hand, another diatomic gas, CO, traditionally considered as a toxic pollutant, poisons by binding to the iron-containing heme group found in Hb and other enzymes (2). Recently, evidence is accumulating that CO can be also a physiologic endogenous ...

Isorhamnetin and quercetin produced endothelium-independent vasodilator effects in rat aorta, rat mesenteric arteries, rat portal vein and porcine coronary arteries. The effects of the two flavonoids were similar in arteries stimulated by noradrenaline, KCl, U46619 or phorbol esters but the two flavonoids were more potent in the coronary arteries than in the aorta. At high concentrations, they also induced a positive inotropic effect in isolated rat atria. Therefore, at least part of the in vivo effects of quercetin may result from its conversion to isorhamnetin which is the main metabolite of quercetin found in plasma. The arterial, venous and coronary vasodilator effects may contribute to the protective effects of flavonoids in ischaemic heart disease observed in epidemiological studies.

The maturation in the vasodilator response to nitric oxide (NO) in isolated intrapulmonary arteries was analyzed in newborns and 15- to 20-day-old piglets. The vasodilator responses to NO gas but not to the NO donor sodium nitroprusside increased with age. The inhibitory effects of the superoxide dismutase inhibitor diethyldithiocarbamate and xanthine oxidase plus hypoxanthine and the potentiation induced by superoxide dismutase and MnCl(2) of NO-induced vasodilatation were similar in the two age groups. Diphenyleneiodonium (NADPH oxidase inhibitor) potentiated the response to NO, and this effect was more pronounced in the older animals. The nonselective cyclooxygenase inhibitors indomethacin and meclofenamate and the preferential cyclooxygenase-1 inhibitor aspirin augmented NO-induced relaxation specifically in newborns, whereas the selective cycloxygenase-2 inhibitor NS-398 had no effect. The expressions of alpha-actin, cycloxygenase-1, and cycloxygenase-2 proteins were similar, whereas Cu,Zn-superoxide dismutase decreased with age. Therefore, the present data suggest that the maturational increase in the vasodilatation of NO in the pulmonary arteries during the first days of extrauterine life involves a cycloxygenase-dependent inhibition of neonatal NO activity.

1 We have compared the mechanisms involved in sodium nitroprusside (SNP)-induced relaxation and [Ca 2+ ] i reduction in isolated piglet pulmonary (PA) and mesenteric (MA) arteries. 2 SNP (10 M7361075 M) evoked a concentration-dependent relaxation of PA and MA (pD 2 =6.66+0.06 and 6.74+0.14, respectively) stimulated by noradrenaline, which was markedly reduced by the guanylate cyclase inhibitor ODQ. In fura 2-incubated PA and MA, SNP produced a parallel reduction in contractile force and in [Ca 2+ ] i , expressed as the ratio of emitted¯uorescence at 340 and 380 nm (F340/F380).