Aspirin and dipyridamole decrease intimal hyperplasia in experimental vein grafts

Release from platelets of a factor mitogenic for smooth muscle cells is a postulated mechanism for the pathogenesis of vascular intimal hyperplasia. In this study the effect of antiplatelet therapy was evaluated. Aspirin (165 mg twice daily) and dipyridamole (25 mg twice daily) were administered to six rhesus monkeys and six were given placebo only. Bilateral vein bypass grafts were placed in the iliac arteries. In addition, to evaluate the relative contribution of adventitial dissection and intimal injury, on one side the carotid artery and femoral vein were stripped of adventitia and on the other side the intima of these vessels were injured by the single passage of an inflated balloon tipped catheter. Animals were killed after 16 weeks. In grafts relative luminal area was determined by a photographic gravimetric method at three standard locations. Femoral veins and carotid arteries were classified as histologically normal or as exhibiting hyperplasia. All vessels with adventitial stripping were normal. All vessels with intimal injury in the placebo group except one exhibited intimal hyperplasia compared to the drug treated group in which over half were normal. Relative intimal area was significantly less in grafts from drug treated animals at all three locations and luminal area greater in two. These data suggest that vascular intimal hyperplasia can be reduced by treatment with antiplatelet agents.