Fibrinogen as a Co-factor in the Reaction of Platelets with Kaolin

Abstract

WE have shown¹ that the clotting time of platelet-rich plasma (PRP) is progressively shortened by incubation at 37° C with a suspension of kaolin, and that this reflects a progressive increase in availability of platelet factor 3 (PF3) as well as activation of the plasma clotting system. Since maximal acceleration of clotting by kaolin was only achieved when platelets and plasma were activated to-together, it seemed likely that a plasma component was required for the reaction of platelets with kaolin. In order to determine whether a plasma coagulation factor was concerned in this reaction, investigations were carried out on the PRP of patients with a series of congenital coagulation defects. Equal volumes (0.1 ml.) of PRP and kaolin (5 mg per ml. of buffered saline, pH 7.3) were incubated at 37° C for 20 min and then recalcified with 0.1 ml. of 0.025 M calcium chloride, 0.1 ml. of a partially purified preparation of the deficient factor (or of buffered saline) being added in each case immediately before or after incubation with the kaolin. In the cases of factor-XII and factor-XI deficiency, activation product (prepared by the method of Nossel²) was used in place of the respective purified factors. Factors V and VIII were prepared by ammonium sulphate precipitation from barium sulphate-adsorbed platelet-poor oxalated normal plasma and factors VII, IX and X by adsorption of normal serum on to barium sulphate and subsequent elution into 5 per cent trisodium citrate. The fibrinogen reagent used (kindly provided by the Blood Products Laboratory of the Lister Institute) was prepared from fresh plasma by the method of Kekwick and Mackay³ and was 66 per cent clottable; it also contained plasminogen and some factor VIII and anti-von Willebrand activity.