Evidence for superoxide radical-dependent coronary vasospasm after angioplasty in intact dogs.

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Abstract
BACKGROUND Active oxygen species can influence vascular tone and platelet activation through a variety of mechanisms. This study assessed the role of the superoxide anion, the hydroxyl radical, and hydrogen peroxide in vasoconstriction and mural thrombosis after coronary artery angioplasty in intact dogs. METHODS AND RESULTS Injury was induced by inflation of a balloon catheter 50 +/- 6% above baseline arterial diameter; dogs were followed for 2 hours before death. Epicardial coronary diameters at arteriography and extent of thrombus deposition at serial histological sections were analyzed in controls (n = 20) and in dogs pretreated with superoxide dismutase (SOD, a superoxide radical scavenger, n = 10); other dogs were pretreated with the hydrogen peroxide scavenger catalase (n = 8), the iron chelator deferoxamine (n = 6), or the hydroxyl radical scavenger 1,3-dimethyl-2-thiourea (n = 9). Angioplasty-induced injury was similar among groups. After angioplasty, control dogs exhibited localized and persistent vessel constriction, which was maximal at the initial 5 minutes (28.9 +/- 6.3% diameter decrease versus baseline). Corresponding arterial diameters of SOD-treated dogs were 24-69% larger (95% confidence interval, p less than 0.001) than controls at 5 minutes and, on average, 32% larger than controls thereafter (p less than 0.01). Vasoconstriction was not prevented by the other treatments. The SOD dose used accounted for inhibition of zymosan-stimulated blood cytochrome c reduction versus baseline (7 +/- 3 versus 30 +/- 6 nmol/min/10(6) cells, respectively, p = 0.003); such inhibition occurred in no other group. Prevalence of mural thrombosis was similar among all groups, but large thrombi (greater than 15% of lumen area) were absent in SOD-treated dogs, contrary to control group (p = 0.028); other groups were similar to control. In the absence of injury, SOD alone induced no change in coronary diameter, coronary blood flow, or platelet aggregation. CONCLUSIONS These data provide evidence implicating the superoxide radical in the genesis of vasoconstriction after coronary angioplasty in vivo. Such effects seem to be independent of its conversion to hydroxyl radicals and availability of hydrogen peroxide or catalytic iron complexes.