Pulmonary fibrosis after endotoxin-induced permeability edema

To know the pathogenesis of the lung fibrosis after ARDS, we investigated the role of PMN-elastase after endotoxin-induced pulmonary edema in awake sheep with chronic lung lymph fistulas. The permeability of the pulmonary circulation increased 2 hours after endotoxin injection. Four hours after endotoxin injection, WBC migrated to the lung interstitium and the number of WBC in BALF increased. Endotoxin increased PMN-elastase in plasma and lymph whereas the level of alpha-1-protease inhibitor (alpha-1-PI) did not change. The activity of alpha-1-PI measured by trypsin inhibitory capacity was zero in the exudative phase. The level of PMN-elastase in lymph was significantly higher 1 week after endotoxin injection than baseline levels. Histologically, pulmonary fibrosis developed 1 week after endotoxin injection. These results suggest that inflammatory mediators released from PMN play an important part in progress to the fibrotic phase after ARDS.