STUDIES OF THE INITIAL ANTICOAGULANT RESPONSE IN TISSUE-THROMBOPLASTIN INDUCED INTRAVASCULAR COAGULATION

The very early anticoagulant response was analysed in non-pregnant fem ale New Zealand rabbits infused with rabbit brain tissue thromboplasti n for a period of 10 min (n = 6), 20 min (n = 6), and 30 min (n = 6). The rabbits infused with thromboplastin responded with a significant d rop in mean arterial pressure (P < 0.05), an increase in blood p(a)O(2 ) (P < 0.05) and a decrease in p(a)CO(2) (P < 0.05), while control ani mals remained stable with respect to these variables. The thromboplast in-treated animals had an immediate drop in platelet count (P < 0.05), plasma fibrinogen (P < 0.05) and a prolongation in prothrombin time ( P < 0.05) and activated partial thromboplastin time (P < 0.05). The co ncentrations in a number of proteins involved in the anticoagulant res ponse (antithrombin, plasminogen, antiplasmin) as well as global fibri nolytic activity did not change significantly following 10, 20 and 30 min infusion of thromboplastin, while the concentration of protein C d ecreased continuously during the infusion periods (P < 0.05) to reach the lowest level (similar to 60%) in animals infused with thromboplast in for 30 min. The animals infused with tissue thromboplastin had micr othrombi in 1-6% of the renal glomeruli, but the number of microthromb i did not differ significantly between animals infused for 10, 20 and 30 min. It is concluded that the protein C system may play a key role during the initial phase of intravascular coagulation and immediate ac tivation of protein C may protect against excessive deposition of fibr in.