BINDING OF FACTOR-VIII-VONWILLEBRAND FACTOR TO HUMAN ARTERIAL SUBENDOTHELIUM PRECEDES INCREASED PLATELET-ADHESION AND ENHANCES PLATELET SPREADING

Abstract

Time-dependent studies of platelet adhesion and binding of F VIII-VWF [factor-VIII-von Willebrand factor] to human arterial subendothelium were carried out in vitro, using 51Cr-labeled platelets and 125I-labeled F VIII-VWF. Rapid binding of F VIII-VWF was found, resulting in a constant surface concentration after 1-2 min of perfusion. The number of platelets adhering in the 1st minute is similar in the absence and presence of F VIII-VWF, but the platelet coverage is .apprx. twofold higher after perfusions of 2-5 min in the presence of F VIII-VWF. Binding of F VIII-VWF precedes the increase in platelet adhesion. The number of contact platelets (nonspread platelets) is lower in the presence of F VIII-VWF. The ratio of contact platelets to spread platelets decreases in time at a higher rate when F VIII-VWF is present. F VIII-VWF apparently enhances platelet spreading on arterial subendothelium. The spreading apparently is impaired in VWD [Von Willeband''s disease]. The enhancement may be caused directly by F VIII-VWF or indirectly as the result of a better attachment of contact platelets.