Lung capillary endothelial cells produce and secrete urokinase-type plasminogen activator

Bovine lung capillary endothelial cells (BLuEC) were isolated, and their ability to produce plasminogen activator (PA) in vitro was demonstrated. BLuEC secreted more than 10 times as much as urokinase-type PA (u-PA) as did bovine aortic, hepatic capillary and adrenal capillary endothelial cells, and lung fibroblasts. BLuEC secreted u-PA on both sides of the cell layer, the luminal surface, and the basic surface attached to the basement membrane. u-PA mRNA was detected in BLuEC by Northern blotting, but not in endothelial cells from other tissues and fibroblasts. These results suggest that BLuEC may contribute not only to the patency of lung vessels but also to the maintenance of alveolar functions through the production and secretion of u-PA.