[Role of platelets in atherosclerosis and arterial thrombosis].

A thrombus is an abnormal manifestation of normal haemostasis occurring on the internal surface of the blood vessels. Endothelial injury is the first event which ultimately may result in arterial thrombosis. Platelets stick to subendothelial components, are activated and release a number of mediators which aggregate new platelets. Simultaneously, thrombin is generated on the platelet surface and enhances these phenomenons. Due to the high blood flow which avoids local thrombin accumulation, arterial thrombosis is mainly composed of platelets with a poor fibrin content. A mural arterial thrombosis may embolize, be incorporated in the vessel wall, or occlude the lumen of the artery. Platelets are involved in the development of atherosclerosis: severe thrombocytopenia or von Willebrand disease protect efficiently against experimental atherosclerosis; several clinical conditions known to increase cardiovascular diseases are also associated with an increased platelet aggregability; in contrast, polyunsaturated fatty acids decrease platelets aggregability and protect against vascular diseases.