Reactive oxygen species mediate arachidonic acid-induced dilation in porcine coronary microvessels

Reactive oxygen species (ROS) have been proposed to mediate vasodilation in the microcirculation. We investigated the role of ROS in arachidonic acid (AA)-induced coronary microvascular dilation. Porcine epicardial coronary arterioles (110+/-4 mum diameter) were mounted onto pipettes in oxygenated Krebs buffer. Vessels were incubated with vehicle or 1 mM Tiron (a nonselective ROS scavenger), 250 U/ml polyethylene-glycolated (PEG)-superoxide dismutase ( SOD; an O-2(-) scavenger), 250 U/ml PEG-catalase (a H2O2 scavenger), or the cyclooxygenase (COX) inhibitors indomethacin (10 muM) or diclofenac (10 muM) for 30 min. After endothelin constriction (30-60% of resting diameter), cumulative concentrations of AA (10(-10)-10(-5) M) were added and internal diameters measured by video microscopy. AA (10(-7) M) produced 37+/-6% dilation, which was eliminated by the administration of indomethacin (4+/-7%, P<0.05) or diclofenac (-8 +/- 8%, P<0.05), as well as by Tiron (-4+/-5%, P<0.05), PEG-SOD (-10 +/- 6%, P<0.05), or PEG-catalase (1+/-4%, P<0.05). Incubation of small coronary arteries with [H-3] AA resulted in the formation of prostaglandins, which was blocked by indomethacin. In separate studies in microvessels, AA induced concentration-dependent increases in fluorescence of the oxidant-sensitive probe dichlorodihydrofluorescein diacetate, which was inhibited by pretreatment with indomethacin or by SOD + catalase. We conclude that in porcine coronary microvessels, COX-derived ROS contribute to AA-induced vasodilation.