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The study was undertaken to determine the influence of various doses of aspi rin (ASA) therapy on platelet adherence to injured endothelium. Twenty-four mongrel dogs were assigned to one of four treatment groups in a randomized, blinded fashion. Each group received ASA in one of three doses: 1 mg/kg, 5 mg/kg, or 10 mg/kg or no ASA therapy (control group). After five days of ASA therapy, the dogs underwent unilateral carotid endarterectomy (CEA), in a ran domized fashion, with the contralateral carotid artery serving as control within each dog. Indium 111 oxine-labeled autologous platelets were injected into the dogs twenty minutes before the reestablishment of flow through the endarterec tomized carotid artery. Platelet scintigraphy was performed at hours 3, 24, 48 and 72 postoperatively. ASA therapy was continued postoperatively for seventy- two hours. Data were analyzed by comparing the mean platelet uptake ratios (operative to nonoperative sites) between groups. When all ASA groups were combined and compared with control values, ASA therapy significantly decreased (p < 0.05) platelet adherence up to seventy-two hours postoperatively. The same effect was observed with low- (1 mg/kg) and medium- (5 mg/kg) dose ASA, which significantly reduced (p < 0.05) platelet adherence to the endarterectomized site at hours 3, 24, 48, and 72. In contrast, there was no significant reduction in platelet uptake in the high-dose (10 mg/kg) ASA group. These results indi cate that ASA therapy given in a dosage of 1 or 5 mg/kg for at least five days preoperatively is beneficial in decreasing platelet adherence after CEA in dogs. Conversely, at a dose of 10 mg/kg, platelet uptake is not consistently inhibited. This study supports previous findings that lower doses of ASA (1-5 mg/kg) are superior to high-dose ASA (10 mg/kg) in inhibiting platelet adherence to injured endothelium in vivo.

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