Background: The effects of oxygen free radicals on coronary vasoreactivity remain unknown.
Objective: To examine whether oxygen free radicals increase coronary arterial tone and sensitivity to vasoconstrictor stimulation in closed-chest dogs.
Methods: Oxygen radicals were generated by the reaction of xanthine plus xanthine oxidase (XXO) and effects of these substances on the left coronary artery (the percentage diameter change) and on the constrictor effect of ergonovine were examined in vivo in 19 anesthetized, closed-chest dogs by selective coronary angiography. The effects of XXO solution and ergonovine were assessed in a cumulative fashion using 100, 200, and 300 ml XXO and 50, 100, 150, and 200 micrograms ergonovine, in 5 (group I) and 6 dogs (group II), respectively. The effects of XXO on the constrictor responses elicited by 50 micrograms ergonovine were examined in eight dogs (group III). Changes in the vascular endothelium were examined by postmortem electron microscopic examination.
Results: Oxidative injury alone produced slight constriction of the coronary artery, but the change was not significant. However, ergonovine-induced vasoconstriction was enhanced after administration of 100 and 200 ml (cumulative amount) XXO solution (P < 0.05, group II versus group III). The enhancement was no longer observed after administration of 300 ml (cumulative amount) XXO solution. Scanning and transmission electron microscopies revealed the formation of blebs and ulceration in the coronary endothelium after administration of XXO solution.
Conclusion: These results suggest that oxygen radicals can enhance the ergonovine-induced coronary vasoconstriction in a concentration-dependent manner. There seems to be a critical level of oxygen radicals for the production of the effect.