Lung proteolytic activity and serum protease inhibition after NO2 exposure

Proteolytic activity (PA) of lung extracts was measured in control hamsters and in those exposed to 20 ppm NO2 for 24 hours (acute) and 30 days (chronic). Total PA of these lungs as measured by pH 7.4 caseinolysis was slightly increased after the 24-hour, but normal following the 30-day exposure. Lung extract fractions from NO2-exposed animals display an increased PA at pH 3.0 and 9.0, but are near control levels at pH 7.0. Serum protease inhibitor (PI) activity is significantly increased after short NO2 exposure as compared with control conditions. No significant increase is observed in PI after chronic exposure. Increase in 24-hr NO2 lung extract PA is associated with increase in PI, which may neutralize the augmented proteolysis. These studies are consistent with previous observations that indicate prolonged NO2 exposure does not produce significant emphysema in the hamster lung.