Sequential injury of the rabbit abdominal aorta induces intramural coagulation and luminal narrowing independent of intimal mass: Extrinsic pathway inhibition eliminates luminal narrowing

Abstract

We hypothesized that activation of the coagulation cascade is involved in arterial remodeling in response to sequential injury. An active site- inhibited recombinant human factor VIIa (FVIIai) was used to inhibit tissue factor, the primary cofactor in the extrinsic pathway of coagulation, in a sequential balloon injury model of the rabbit abdominal aorta. Single balloon injury produced limited intimal thickening at 3 weeks (intimal area, 0.40±0.05 mm2) and no loss in luminal area (12.2±0.9 mm2 before injury and 12.1±0.9 mm2 at 6 weeks after injury). Sequential balloon injury, 3 weeks after the first balloon denudation, produced a progressive loss of lumen, with 22% and 47% loss of luminal area, respectively, at 3 and 6 weeks. Luminal loss could not be accounted for by intimal growth (at 3 weeks after sequential injury, the intimal area was 0.47±0.08 mm2, <4% of the initial luminal area). Sequential injury acutely produced expensive mural and intramural fibrin deposition. Treatment with FVIIai inhibited both the fibrin deposition and the chronic loss of lumen. At 3 weeks after sequential injury, luminal cross-sectional areas were 9.8±0.6 mm2 for control rabbits and 14.3±1.4 mm2 for FVIIai-treated rabbits. Neither neointimal area nor cell proliferation was reduced by FVIIai treatment. The intimal cell proliferation index 3 days after injury was 7.6±1.1% in control rabbits, versus 5.8±1.1% in treated rabbits (P>0.05). These results indicate that tissue factor is an important mediator of coagulation in repeat injury and implicate the extrinsic coagulation cascade in a blood vessel remodeling response that is independent of neointimal growth but leads to extensive loss of lumen.