Continuous thrombin infusion leads to a bleeding phenotype in sheep

BackgroundIn addition to a recognized role in the coagulation cascade and haemostasis, thrombin is known to have multiple functions. We aimed to establish an ovine model to study thrombin effects in vivo.MethodsThrombin (0.0004-0.42 IU/kg/min) was continuously infused in Austrian Mountain Sheep over five hours in the dose escalation study (n = 5 animals; 15 experiments). In the dose verification study animals received 0.42 IU/kg/min of thrombin vs. saline solution in a cross-over design (n = 3 animals; 7 experiments).ResultsThrombin at an infusion rate of 0.42 IU/kg/min decreased fibrinogen levels by 75% (p < 0.001) and increased degradation products of the fibrinogen beta-chain as shown in a proteomic analysis. Thrombin decreased platelet counts by 36% (p = 0.006), prolonged thrombin time by 70% (p = 0.012) and activated partial thromboplastin time by 32%. Interestingly, thrombin infusion significantly increased the activity of coagulation factors V and X (p < 0.05) and decreased the activity of the coagulation factors VIII and XIII (p < 0.05). Accordingly, thrombin displayed predominantly anti-coagulant and anti-platelet effects: 1) thrombin prolonged clotting time/clot formation time 7-fold (p = 0.019) and induced a 65% decrease in maximal clot firmness (p < 0.001); 2) thrombin reduced collagen- induced platelet aggregation by 85% and prolonged collagen/adenosine diphosphate closure time 3-fold; and 3) thrombin caused lung haemorrhage but not thromboembolism.ConclusionProtracted intravenous infusion of thrombin over a period of five hours offers a new experimental model to study thrombin effects in a large animal species.