Pulmonary arteriovenous differences in serum antiprotease activity during experimental pneumonitis

The trypsin-inhibiting activity in pulmonary arterial blood and in blood of the left atrium was measured in rabbits with bacterial or papain-induced pneumonitis. In both experimental models, the trypsin-inhibiting activity was significantly lower (P less than 0.001 and P less than 0.002) in blood after it had passed through the inflamed lung than in pulmonary arterial blood. Healthy rabbits had no arteriovenous difference of antitryptic activity in the pulmonary circulation. Consumption or alteration of inhibitors by protease in the inflamed tissue is a reasonable explanation for this difference. We interpreted these data as supporting the hypothesis that protease inhibitors in serum exert a protective function against proteolytic enzymes during inflammation. In conditions of low serum protease-inhibiting activity, as in alpha1-antitrypsin deficiency, proteolytic damage to lung tissue could result.