Acute Effects of Ozone on Heart Rate and Body Temperature in the Unanesthetized, Unrestrained Rat Maintained at Different Ambient Temperatures

Publisher Website
Google Scholar
Abstract
The present studies were conducted to investigate the concentration-response characteristics of acute ozone (O3) exposure on the cardiovascular and thermoregulatory function of the unanesthetized, unrestrained rat, and to examine the modulating effects produced by changes in ambient temperature (T a) on the induced toxic response. For all studies, groups of male Fischer 344 rats (n - 4-6/group) were implanted with radiotelemetry transmitters and allowed to recover overnight. The transmitters permitted continuous monitoring of electrocardiogram (ECG) and body core temperature (T co); heart rate (HR) was derived from the ECG signal. Frequency of breathing (f) was obtained in selected experiments using a barometric plethysmograph. All animals were monitored according to the following protocol: control (filtered air, 0.25 hr); exposure (O3, 2 hr); recovery (filtered air, 3–18 hr). For the concentration-response experiments, O3 concentration was varied from 0.25 to 1.0 ppm and all exposures were conducted at T a - 18–20°C. Significant decreases in HR and T co were demonstrated at O3 concentrations as low as 0.37 ppm. To investigate the influence of T a on the O3-induced response, a second series of experiments was conducted according to the above protocol using a single O3 concentration of 1.0 ppm. Two groups of rats were used for these experiments. The first group of rats was maintained at T a - 18–20°C throughout the experiment and exhibited an average drop of 3.6°C in T co accompanied by a 185 bpm decrease in HR. The second group of rats was maintained at T a - 30–32°C. These rats also showed decreases in T co and HR; however, the decreases observed in the higher T a group animals were attenuated when compared to those of the lower T a group animals and only averaged 0.9°C and 114 bpm, respectively. In addition to demonstrating significant concentration-related changes in cardiovascular and thermoregulatory function in the conscious, unrestrained rat following acute exposure to O3, these studies illustrate the profound impact exerted by T a on this O3-induced response.