Abstract
Ambient ozone (O3) levels are associated with cardiovascular morbidity and mortality, but the underlying pathophysiological mechanisms driving extrapulmonary toxicity remain unclear. This study examined the coronary vascular bed of rats in terms of constrictive and dilatory responses to known agonists following a single O3 inhalation exposure. In addition, serum from exposed rats was used in ex vivo preparations to examine whether bioactivity and toxic effects of inhaled O3 could be conveyed to extrapulmonary systems via the circulation. We found that 24 h following inhalation of 1 ppm O3, isolated coronary vessels exhibited greater basal tone and constricted to a greater degree to serotonin stimulation. Vasodilation to acetylcholine (ACh) was markedly diminished in coronary arteries from O3-exposed rats, compared with filtered air-exposed controls. Dilation to ACh was restored by combined superoxide dismutase and catalase treatment, and also by NADPH oxidase inhibition. When dilute (10%) serum from exposed rats was perfused into the lumen of coronary arteries from unexposed, naïve rats, the O3-induced reduction in vasodilatory response to ACh was partially recapitulated. Furthermore, following O3 inhalation, serum exhibited a nitric oxide scavenging capacity, which may partially explain blunted ACh-mediated vasodilatory responses. Thus, bioactivity from inhalation exposures may be due to compositional changes of the circulation. These studies shed light on possible mechanisms of action that may explain O3-associated cardiac morbidity and mortality in humans.