Effect of heparin on chronically induced intravascular coagulation in dogs.

When intermediate-strength thromboplastin was continuously infused into dogs for 10 days or more, platelet counts decreased sharply and factor VIII concentrations decreased by more than 50%. There was little change in plasma fibrinogen, prothrombin, factor V, antithrombin III, plasminogen, prothrombin time, and thrombin time values. When heparin was infused (25-50 U/kg per h) along with the same thromboplastin, there was no change in onset or degree of thrombocytopenia. However, the decrease in factor VIII was abolished and there were significant increases in fibrinogen, prothrombin, and factor V. The absolute concentrations of the various clotting factors seemed to give no indication of their turnover rates. Unexplained is the remarkable heparin tolerance that developed in these dogs.