Abstract
Sprague-Dawley rats exposed to atmospheres containing low levels of nitrogen dioxide (NO 2) for 24 hr had increased levels of nitrate in their urine on the day of exposure and on the 3 subsequent days. The total increase in urinary nitrate was linearly related to the nitrogen dioxide concentration administered. We recovered in urine 8.4 ± 1.1 μmol nitrate/ppm NO 2 24 -hr exposure (slope ± 95% confidence limits) for 185-g rats. Both the linearity and magnitude of this effect imply that reaction with respiratory tract water is not a major pathway of NO 2 absorption in the lung. Instead, our observations support the hypothesis that the major interaction of NO 2 in the lung is with readily oxidizable tissue components to form nitrite. We estimate that 9.6 μmol of nitrite is formed in the respiratory tract of the rat per ppm NO 2 per 24-hr exposure. We also estimate that humans breathing air containing 0.1 ppm NO 2 have about 3.6 mg of nitrite formed in their respiratory tract per day.
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