title: Interaction of von Willebrand factor with human platelets in the plasma milieu.
abstract: The binding of von Willebrand factor (vWf) to stimulated platelets in the plasma milieu was performed using a radiolabeled monoclonal antibody to vWf. Plasma proteins specifically inhibited the thrombin- and ADP/epinephrine-induced vWf binding to activated platelets but did not inhibit the ristocetin-induced vWf binding. When normal plasma was heat defibrinated, monoclonal-labeled vWf was bound to platelets following thrombin or ADP/epinephrine stimulation. Furthermore, monoclonal-labeled vWf from afibrinogenemic plasma bound normally to platelets. The binding of vWf to stimulated platelets in either heat-defibrinated normal plasma or afibrinogenemic plasma was specifically inhibited by the addition of normal plasma fibrinogen in a concentration-dependent manner. At levels of fibrinogen less than 1 mg/ml, however, vWf binding could be demonstrated. The inhibition by fibrinogen of vWf binding to platelets was competitive and overcome by increased concentrations of vWf. These studies show that thrombin-induced and ADP/epinephrine-induced vWf binding to platelets does not occur in the plasma milieu, although at reduced levels of fibrinogen, vWf binding to stimulated platelets can be demonstrated.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000347:Afibrinogenemia / Q000097:blood; D000911:Antibodies, Monoclonal; D001779:Blood Coagulation Factors / Q000502:physiology*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D001798:Blood Proteins / Q000502:physiology*; D004837:Epinephrine / Q000494:pharmacology; D005340:Fibrinogen / Q000494:pharmacology; D006023:Glycoproteins / Q000276:immunology; D006801:Humans; D010980:Platelet Membrane Glycoproteins; D012310:Ristocetin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D014842:von Willebrand Diseases / Q000097:blood; D014841:von Willebrand Factor / Q000276:immunology / Q000502:physiology*
chemical_list: D000911:Antibodies, Monoclonal; D001779:Blood Coagulation Factors; D001798:Blood Proteins; D006023:Glycoproteins; D010980:Platelet Membrane Glycoproteins; D014841:von Willebrand Factor; D012310:Ristocetin; D000244:Adenosine Diphosphate; D005340:Fibrinogen; D013917:Thrombin; D004837:Epinephrine