Effects of ozone and fine particulate matter (PM2.5) on rat cardiac autonomic nervous system and systemic inflammation

Objective To study the effects of ozone and fine particulate matter (PM2.5) on rat cardiac autonomic nervous system and systemic inflammation and the interconnected relationship of these two pathways. Methods 48 Wistar rats were randomly assigned to 8 groups (n = 6). Rats were intratracheal instillation of 0.2, 0.8 and 3.2 mg/rat PM2.5 as low-dose, medium-dose and high-dose PM2.5 alone exposure groups. Ozone combined PM2.5 groups were exposed to 0.8 ppm ozone 4 hours and then instilled 0.2, 0.8 and 3.2 mg/rat PM2.5 separately. Rats only inhaled 0.8 ppm ozone for 4 hours as ozone alone exposure group. Control rats were instilled with saline. Each exposure protocol applied twice a week for three continuous weeks. Systolic blood pressure and electrocardiograph (ECG) morphology of rats were recorded at 24 hours post-exposure of the last exposure. Serum TNF-alpha, IL-6 and CRP were analyzed. Right ventricles were used as pathological examination with HE staining. Results HRV indices in PM2.5 alone and combined exposure groups showed significant difference compared to control. However, heart rate only reduced significantly in ozone combined PM2.5 groups. Blood pressure rose significantly in combined groups and high-dose PM2.5 alone exposure. TNF-alpha and IL-6 increased significantly in PM2.5 alone/and ozone groups. CRP showed obvious dose-dependent relationship in PM2.5 alone and combined groups. Cardiac histopathology results revealed that PM2.5 deposition and myocardial inflammation were also observed in high-dose PM2.5 rats. Conclusion Ozone can enhance the cardiac autonomic nervous system and systemic inflammation induced by PM2.5.