The results of the fibrinolysis experiments are shown in Figure 1. Saline produced 11% ±2% thrombolysis. Increasing doses of rt-PA produced increasing thrombolytic effects. The observed lysis rates were 24% ±3%, 41% ±3%, 66% ±6%, and 81% ±7% for the 4 increasing doses of rt-PA, respectively. These lysis rates would correspond to a final thrombus size of 267 |xg in saline-treated rabbits and sizes of 228, 177, 102, and 57 in rabbits treated with the 4 increasing doses of rt-PA. These results confirmed those obtained in previous experiments.
The results of the thrombus-growth studies obtained in different rabbits are shown in Figure 2. In saline-treated rabbits, 54 ±8 |xg of new radioactive fibrin accreted on the preformed experimental thrombi. In rabbits treated with the 4 increasing doses of bolus rt-PA, 51 ±6, 48±5, 39±6, and 28±4 |xg of new radioactive fibrin accreted on the thrombi, respectively. By combining the data from the fibrinolysis and thrombus-growth inhibition experiments obtained in 2 sets of animals, it is possible to assess the relative contribution of old and new fibrin in determining the final thrombus volume. In saline-treated rabbits, as much as 20.2% of the residual thrombi was due to fibrin newly accreted on the thrombi. In rabbits that received the 4 increasing bolus doses of rt-PA, the values were 22.3%, 27.1%, 38.2%, and 49.1%, respectively (Fig 3).
Figure 1. Thrombolytic effects of increasing bolus doses of rt-PA.
Figure 2. Effect of increasing bolus doses of rt-PA on the accretion of new fibrin on the preformed thrombi.
Figure 3. Relative proportion of preformed fibrin and fibrin newly accreted on the thrombi in determining final thrombus size after increasing bolus doses of rt-PA.