Cardiovascular Depression in Rats Exposed to Inhaled Particulate Matter and Ozone: Effects of Diet-Induced Metabolic Syndrome

BACKGROUND: High ambient levels of ozone (O-3) and fine particulate matter (PM2.5) are associated with cardiovascular morbidity and mortality, especially in people with pre-existing cardio-pulmonary diseases. Enhanced susceptibility to the toxicity of air pollutants may include individuals with metabolic syndrome (MetS). OBJECTIVE: We tested the hypothesis that cardiovascular responses to O-3 and PM2.5 will be enhanced in rats with diet-induced MetS. METHODS: Male Sprague-Dawley rats were fed a high-fructose diet (HFrD) to induce MetS and then exposed to O-3, concentrated ambient PM2.5, or the combination of O-3 plus PM2.5 for 9 days. Data related to heart rate (HR), HR variability (HRV), and blood pressure (BP) were collected. RESULTS: Consistent with MetS, HFrD rats were hypertensive and insulin resistant, and had elevated fasting levels of blood glucose and triglycerides. Decreases in HR and BP, which were found in all exposure groups, were greater and more persistent in HFrD rats compared with those fed a normal diet (ND). Coexposure to O-3 plus PM2.5 induced acute drops in HR and BP in all rats, but only ND rats adapted after 2 days. HFrD rats had little exposure-related changes in HRV, whereas ND rats had increased HRV during O-3 exposure, modest decreases with PM2.5, and dramatic decreases during O-3 plus PM2.5 coexposures. CONCLUSIONS: Cardiovascular depression in O-3- and PM2.5-exposed rats was enhanced and prolonged in rats with HFrD-induced MetS. These results in rodents suggest that people with MetS may be prone to similar exaggerated BP and HR responses to inhaled air pollutants.