Modulation of tissue fibrinolysis from hypoxia and hyperoxia

The effects from alterations in inspired oxygen tension on the fibrinolytic activity in vessel walls was studied in rats. Tissue plasminogen activator activity was measured semiquantitatively with the histochemical technique. During severe hypoxic conditions (FIO2 = 0.05) the fibrinolytic activity in the aorta was significantly reduced as compared to control animals. At 24 hours with slightly higher oxygen tension (FIO2 = 0.08) the activity was increased. When breathing pure oxygen (FIO2 = 1.0) the fibrinolytic activity was increased in the aorta after 8 hours. Following chronic hypoxia for 6 weeks (FIO2 = 0.1) the activity in the caval vein was increased. Changes in inspired oxygen tension thus affected the endothelial cells and changed their expression of plasminogen activator activity.