Platelet behavior and aging in the circulation.

This review of the development of knowledge concerning the fate and function of circulating platelets and our recent experiments with a radioisotope label for platelet surface glycoproteins support the hypothesis that platelets are continualy involved in reversible contact interactions for the support of endothelial integrity. These encounters result in the loss of pieces of the platelet surface membrane and could contribute to the structural and functional changes of platelet senescence. The concepts of continuous involvement of platelets in hemostatic encounters and a fixed circulating lifespan are not mutually exclusive phenomena: platelet hemostatic encounters could preferentially involve younger platelets and be mostly reversible while the metabolic machinery which determines platelet survival deteriorates in a manner unrelated to these platelet-surface interactions. Obviously the nature of platelet behavior and aging in the circulation requires much more precise definition.