FIBRINOLYTIC AGENTS INHIBIT PLATELET-ADHESION ONTO COLLAGEN TYPE I-COATED SURFACES AT HIGH BLOOD-FLOW CONDITIONS

The effect of fibrinolytic agents on platelet adhesion onto insolubili zed collagen type I was evaluated. Normal human whole blood samples we re incubated with agents and perfused over collagen-coated surfaces in a parallel-plate flow chamber. Platelet adhesion and aggregation were analyzed by video microscopy and image processing. When blood was per fused at 1500/s, both streptokinase and urokinase, each at 500 U/ml, c aused a significantly less normalized platelet deposition, compared wi th controls. At 480/s, platelet deposition was not different between c ontrols and test samples. Inhibition of platelet deposition at high fl ow rates was partly due to inhibition of platelet adhesion. Both risto cetin- and ADP-induced platelet aggregation were inhibited in test sam ples. The agents caused proteolytic degradation of plasma fibrinogen, but no degradation of platelet glycoproteins Ib and IIb-IIIa (GPIb and GPIIb-IIIa) and of plasma von Willebrand factor in test samples prior to perfusion. Post-perfusion von Willebrand factor degradation was no t found. Plasmin may cause functional changes to plasma proteins and/o r platelet receptors, altering their adhesive properties under flow. A t high shear, fibrinogen degradation products may interfere with GPIIb -IIIa binding to insolubilized von Willebrand factor, leading to decre ased platelet adhesion. Inhibition of platelet adhesion by thrombolyti c agents could help maintain vessel patency after recanalization in st enosed arteries. Blood Coag Fibrinol 9:213-226 (C) 1998 Lippincott-Rav en publishers.