Recent epidemiological studies have reported a positive association between
levels of ambient particulate matter (PM) and daily morbidity and mortalit
y due to respiratory or cardiovascular causes; however, toxicological evide
nce supporting these findings is limited. The present study compared cardia
c and thermoregulatory responses to intratracheal instillations of residual
oil fly ash (ROFA) in normal and cardiopulmonary-compromised male Sprague-
Dawley rats. Animals (n = 64) were implanted with radiotelemetry transmitte
rs capable of continuously monitoring heart rate, core body temperature, an
d electrocardiographic waveforms. Comparisons of ROFA toxicity were conduct
ed between (1) healthy rats and rats with cardiopulmonary stress or disease
, including (2) rats exposed to an ambient temperature of 10 degrees C, (3)
rats preexposed to ozone to induce pulmonary inflammation, and (4) rats pr
etreated with monocrotaline (MCT) to induce pulmonary hypertension and vasc
ulitis. Animals from each regimen were instilled with 1 of 4 doses of ROFA
(0, 0.25, 1.0, 2.5 mg), and telemetry data were acquired for 96 h following
ROFA instillation. Dose-related hypothermia and bradycardia were observed
in healthy animals following exposure to ROFA; the magnitude and duration o
f these responses were potentiated in ail compromised models. Delayed hypot
hermic and bradycardic responses occurred in healthy animals receiving 2.5
mg ROFA up to 48 h following instillation. These delayed responses were exa
cerbated in the MCT- and 10 degrees C-exposure models, but attenuated in th
e O-3-preexposed group. Additional observed effects of ROFA included induct
ion of cardiac arrhythmias and increased mortality. These results demonstra
te a distinct cardiac component to ROFA toxicity that agrees with epidemiol
ogical findings of PM-related excess cardiovascular mortality. Furthermore,
the dose-related hypothermia and bradycardia observed in rodents from this
study may confound the interpretation of results from similar air pollutio
n toxicology studies.