Stimulation of endothelial secretion of tissue-type plasminogen activator by repetitive stretch

Endothelial cells (EC) synthesize many of the fibrinolytic components and anticoagulants present in plasma. EC have been demonstrated to release tissue type plasminogen activator (t-PA) and its rapid inhibitor type 1 plasminogen activator inhibitor (PAI-1). In vivo, EC lining a blood vessel are exposed to the forces of the circulation, predominantly shear stress and pulsatile stretch. We have previously reported that repetitive stretch of EC in culture will stimulate prostacyclin secretion. In this study, the effects of cyclic stretch on the production of t-PA and PAI-1 by cultured EC were examined. EC harvested from human saphenous vein were seeded in culture plates with flexible membrane bottoms and grown to confluence. Vacuum (-20 kPa) was used to deform the membrane bottoms to 24% maximum strain. EC in the experimental group were subjected to 24% maximum strain at 60 cycles/min (0.5 sec elongation alternating with 0.5 sec relaxation), while control EC were grown on the same membranes but kept stationary in the same incubator. After 1, 3, and 5 days, the cell numbers were counted and the media were collected and analyzed for t-PA and PAI-1 by ELISA. The result shows a significant increase in t-PA production with the cyclic stretch on Days 3 and 5. There was no significant difference in PAI-1 levels in stretched versus stationary EC. We concluded that cyclic stretch of EC in vitro can selectively stimulate t-PA production and may account for the relative nonthrombogenicity of the endothelium in vivo.