Platelet activation and aggregation after endothelial injury. Assessment with indium-111-labeled platelets and angiography.

Although platelet activation and aggregation after endothelial injury are well documented, the time course of platelet deposition and the relationship between platelet aggregation and the release of vasoactive products have not been fully clarified in vivo. To study the effect of platelet vasoactive products, a collateral blood supply was induced by ligating the superficial femoral artery in male New Zealand white rabbits. Two weeks later, endothelial injury to the distal abdominal aorta was produced by cytologic brush or mimicked with a metal coil embolus. Platelet aggregation was assessed with indium-111 (111In)-labeled platelets, and scintigraphy demonstrated significant, progressive platelet deposition up to 3 hours after injury and evidence of residual activity 24 hours later. Angiography showed that the time course of peripheral vasoconstriction matched closely that of platelet deposition, indicating release of vasoactive substances from the aggregating platelets. These pathophysiologic changes secondary to endothelial injury may have significant implications for intravascular interventional procedures.