Adverse cardiovascular effects with acute particulate matter and ozone Exposures: Interstrain variation in mice

Objectives: Increased ambient particulate matter (PM) levels are associated with cardiovascular morbidity and mortality, as shown by numerous epidemiology studies. Few studies have investigated the role of copollutants, such as ozone, in this association. Furthermore, the mechanisms by which PM affects cardiac function remain uncertain. We hypothesized that PM and O₃ induce adverse cardiovascular effects in mice and that these effects are strain dependent. Study Design: After implanting radiotelemeters to measure heart rate (HR) and HR variability (HRV) parameters, we exposed C57B1/6J (B6), C3H/ HeJ (HeJ), and C3H/HeOuJ (OuJ) inbred mouse strains to three different daily exposures of filtered air (FA), carbon black particles (CB), or O₃ and CB sequentially [O₃CB; for CB, 536 ± 24 μg/m³; for O₃, 584 ± 35 ppb (mean ± SE)]. Results: We observed significant changes in HR and HRV in all strains due to O₃CB exposure, but not due to sequential FA and CB exposure (FACB). The data suggest that primarily acute HR and HRV effects occur during O₃CB exposure, especially in HeJ and OuJ mice. For example, HeJ and OuJ mice demonstrated dramatic increases in HRV parameters associated with marked bradycardia during O₃CB exposure. In contrast, depressed HR responses occurred in B6 mice without detectable changes in HRV parameters. Conclusions: These findings demonstrate that important interstrain differences exist with respect to PM- and O₃-induced cardiac effects. This interstrain variation suggests that genetic factors may modulate HR regulation in response to and recuperation from acute copollutant exposures.