Cardiovascular and systemic responses to inhaled pollutants in rodents: Effects of ozone and particulate matter

Striking similarities have been observed in a number of extrapulmonary resp onses of rodents to seemingly disparate ambient pollutants. These responses are often characterized by primary decreases in important indices of cardi ac and thermoregulatory function, along with secondary decreases in associa ted parameters. For example, when rats are exposed to typical experimental concentrations of ozone (O-3), they demonstrate robust and consistent decre ases in heart rate (HR) ranging from 50 to 100 beats per minute, whereas co re temperature (T-infinity) often falls 1.5-2.5 degreesC. Other related ind ices, such as metabolism, minute ventilation, blood pressure, and cardiac o utput, appear to exhibit similar deficits. The magnitudes of the observed d ecreases may be modulated by changes in experimental conditions and appear to vary inversely with both ambient temperature and body mass. More recent studies in which both healthy and compromised rats were exposed to either p articulate matter or its specific components yielded similar results. The a gents studied included representative examples of ambient, combustion, and natural source particles, along with individual or combined exposures to th eir primary metallic constituents. In addition to the substantial decreases in HR and T-CO, similar to those seen with the O-3-exposed rats, these ani mals also displayed numerous adverse changes in electrocardiographic wavefo rms and cardiac rhythm, frequently resulting in fatal outcomes. Although th ere is only limited experimental evidence that addresses the underlying mec hanisms of these responses, there is some indication that they may be relat ed to stimulation of pulmonary irritant receptors and that they may be at l east partially mediated via the parasympathetic nervous system.