Studies of Factors V and VIII:C in an animal model of disseminated intravascular coagulation.

An experimental animal model of disseminated intravascular coagulation (DIC) induced by the co-infusion of coagulant-active phospholipid and activated Factor X (Factor Xa) is described. The infusion of Factor Xa at a dose of 6.6 X 10(-12) mol/kg with phosphatidylcholine/phosphatidylserine (PCPS) lipid vesicles at a dose of 4.0 X 10(-8) mol/kg was associated with significant falls in the levels of fibrinogen and Factors V and VIII, and a bleeding diathesis developed. Assays of Factors V and VIII were performed by a one-stage prothrombin time and activated partial thrombin time system, respectively. In additional experiments, the effect of the same dose combination of Factor Xa/PCPS on Factor V kinetics was studied by preinfusing 125I-labeled Factor V. After Factor Xa/PCPS infusion, Factors VIII and V were reduced at 2 min by 90 and 50% of the preinfusion levels, respectively, and at 1 h by 80 and 75%, respectively. During the same period, there was little change in the total circulating radioactivity. Autoradiography indicated small but detectable levels of circulating proteolytic products of Factor V that comigrated with peptides obtained by the incubation of Factor V with Factor Xa and activated protein C. The majority of radioactivity remained associated with the intact single-chain precursor Factor V. These observations suggested maintenance of the precursor pool after the onset of DIC. This was confirmed by performing two-stage assays of Factors V and VIII, whereby each was completely converted to the active cofactor, i.e., Va and VIII:Ca, by preincubation of the test sample with thrombin before assaying in a one-stage system as before. The Factor V levels assayed by the two-stage procedure did not change appreciably over 1 h. The Factor VIII levels fell but corrected within 1 h at a time when the level measured by a one-stage assay remained depressed. These results indicate that in the dog, infusion of Factor Xa/PCPS induces changes characteristic of DIC, and this is associated with the appearance of Factor V peptides characteristic of the expression of Factor Xa and activated protein C-like activities. The differences noted between the one-stage and two-stage assays suggest that the one-stage assay is measuring the activated fraction of each cofactor and not the total level of the available precursor for each activated species. The results suggest a close correlation between the activated fraction of both cofactors and the hemostatic abnormality that occurs in DIC.