Abstract
The acute and subacute effects of exposure of rats to nitrogen dioxide (NO2) at low levels on lung, liver and red blood cells were examined biochemically and cytologically. In addition, influences of nitrate and nitrite, chemical intermediates of inhaled NO2, on red blood cells and hepatic microsomes were examined in vitro to clarify the mechanisms responsible for in vivo effects of NO2. The biological significance of responses to NO2 was discussed with respect to physiological adaptation to low levels of NO2. I. In the lung, a metabolic enhancement developed in several days of NO2 inhalation. This was followed by an increase in alveolar cells such as macrophages and Type II epithelial cells. These results suggest that epithelial cells increase as a response compensating degeneration of lung cells produced by NO2 inhalation. II. In the blood, an initial response to NO2 inhalation was an increase in younger red blood cells. This increment seems to occur as compensation for accelerated aging of red blood cells presumably induced by NO2 inhalation. Some membrane constituents of red blood cells were decreased initially by NO2 inhalation. This decrement was due to an increasing level of blood nitrate produced by NO2 inhalation. III. In the lung and liver, NO2 inhalation periodically decreased the components of microsomal drugmetabolizing systems and mitochondrial respiratory system. These periodic alterations appear to be a reflex of degeneration of membranous components and subsequent stimulation of biosynthesis. It is also suggested that hepatic microsomal components decrease due to a reaction of blood nitrate increased by NO2 inhalation.
