Effects of low-concentration NOxSO2 gas mixtures on lung structure and blood-oxygen affinity in rats.

The respiratory effects of low levels of SO2 alone or associated with NO or NO2 were studied in rats exposed for periods of one day to thirteen weeks. Control rats were exposed to ambient air. Both control and treated rats appeared similarly active and grew uniformly. Erythrocytic variables (hemoglobin, hematocrit, red cell counts, 2,3-DPG, glucose, lactate, methemoglobin) and oxyhemoglobin dissociation curves were determined at different times throughout exposure to the gaseous mixture. Blood variables of the exposed rats were not significantly different from those of controls, and hemoglobin affinity was not modified. Bronchiolar and tracheal epithelia were studied by scanning (TEM) to detect a possible loss of cilia. The alveolar walls were investigated by Light Microscopy and TEM after each period of exposure. No striking changes were observed in rat lung structures under Light Microscopy or TEM. Bronchiolar and tracheal epithelia were normally ciliated. No synergistic effects were produced by either SO2 + NO or SO2 + NO2.