Heparin-enhanced inhibitors during reversible disseminated intravascular coagulation

Intravenous injection of homologous lung or brain tissue thromboplastin in dogs under general anesthesia induced changes of conventional hemostasis variables consistent with acute DIC (prolongation of prothrombin times, thrombin times, APTT, drop of fibrinogen and a transient reduction of the platelet count). The animals reacted with accelerated respiration and pulse rates. After recovery from anesthesia they resumed their normal activity as before. Fibrinogen reached a minimum within 40 min after the DIC trigger dose had been injected. Dependent on the size of the latter up to 80% of clottable fibrinogen was consumed. No consumption of antithrombin III and heparin cofactor II could be demonstrated by functional assays based on thrombin inhibition by diluted plasma in the presence of heparin or dermatan sulfate. Prothrombin measured amidolytically by an Echis Carinatus venom assay remained practically unchanged. These findings are consistent with free thrombin concentrations in the nanomolar range sufficient to clot fibrinogen rapidly without visibly affecting the up to 1,000 fold higher concentrations of inhibitors and prothrombin. Heparin administered before tissue thromboplastin virtually suppressed the evolution of DIC but its protective effect was overcome by higher trigger doses. Heparin injected after the induction of DIC had no protective effect. The reversible DIC model in dogs may be a promising tool to study activated coagulation in vivo at practically constant inhibitor concentrations. One dog can be used for several acute experiments with homologous tissue thromboplastin, thus the number of animals and their costs may remain within reasonable limits.