Comparison of the coagulant activities of platelets and phospholipids.

The coagulant activities of various phospholipid preparations were compared with those of platelets. Folch phospholipid with maximal platelet factor 3 (PF3) activity produced long recalcified clotting times of relatively undiluted plasma in plastic tubes whereas untreated or ADP-treated platelets with minimal PF3 activity produced short clotting times in the same test system which is sensitive to activators of the contact system of intrinsic coagulation. Bell and Alton phospholipids with maximal PF3 activity produced recalcified clotting times similar to those in the presence of platelets. Bell and Alton phospholipids had tissue factor activity, but Folch phospholipid and platelets did not. Bell and Alton phospholipids and gum acacia (used as a vehicle in one of the preparations) activated factor XII as did platelets, but Folch phospholipid did not. The multiple coagulant activities of Bell and Alton phospholipids (i.e. PF3, tissue factor and contact activating) may account for the absence of coagulant superiority of platelets in the undiluted system in plastic tubes. The coagulant activities of platelets are also complex but different from Bell and Alton phospholipids whereas Folch phospholipid would appear to possess only PF3 activity.