Ozone toxicity in the rat. I. Effect of changes in ambient temperature on extrapulmonary physiological parameters

These studies examined the effects of exposure to near environmental levels of ozone (O3) on the unanesthetized unrestrained rat as well as the influence of changes in ambient temperature (Ta) on the observed responses. Male Fischer 344 rats were implanted with radiotelemetry transmitters that permitted continuous monitoring of electrocardiogram, heart rate, core body temperature (Tco), and activity. Telemetry animals (n = 4-5/group) were combined with nontelemetry animals to produce nine treatment groups (n = 44-50/group) composed of combinations of one of three O3 exposure regimens (0.0 ppm x 24 h/day, 0.5 ppm x 6 h/day, or 0.5 ppm x 23 h/day) paired with one of three Ta levels (10, 22, or 34 degrees C). The experimental protocol consisted of a Control Period (filtered air; 1 day), Treatment Period (O3; 5 days), and Recovery Period (filtered air; 7 days). At specific intervals during the experiment, subgroups (n = 6) of nontelemetry animals were randomly selected from each treatment group, anesthetized with urethan, and intubated, and their lungs were lavaged with warm saline. In general, results from the bronchoalveolar lavage procedure indicated that toxicity increased in magnitude and duration as the length of time of O3 exposure increased and the Ta decreased. Similarly, whereas minimal extrapulmonary effects were observed at an Ta of 34 degrees C, O3 exposures at Ta levels of 22 and 10 degrees C produced significant decreases in heart rate (160 and 210 beats/min, respectively), Tco (2.0 and 3.5 degrees C, respectively), and body weight (15 and 40 g, respectively). Decreases in these functional parameters reached their maxima over the first 2 exposure days and returned to control levels after the 3rd day of exposure. These data demonstrate the profound impact of Ta on Tco and other extrapulmonary parameters in the conscious unrestrained rat exposed to O3. Furthermore, these results suggest an integral role for both Tco and Ta in determination of the uptake of inhaled pollutants and modulation of the subsequent toxic effects and may have important implications with respect to the assessment of toxic risk.