BRIEF REPORT Protein Synthesis in Aging Blood Platelets

A GINC OF A BLOOD CELL is associated with the progressive loss of its physiologic functions ultimately leading to disintegration of its structure. Only a few attempts have been made to study aging phenomena in blood platelets. It is known that platelets gradually decrease in size as they age in the circulation.1 Differences in response to osmotic stress have been observed in human platelets.2 The latter experiments have demonstrated the presence of two morphologically different populations probably reflecting platelet aging. The suggestion that young platelets may possess a greater degree of adhesive property than old platelets was advanced long ago by \Vright. The content of AlT in the platelets decreases with aging.4 The reduction of nucleotides in the aging platelets has been thought to be associated with a change in platelet adhesiveness which could contribute to the physiologic disappearance of platelets from the circulation5 although, platelet adhesiveness to glass has been demonstrated to be independent of aging.#{176}#{176}#{176} Adhesiveness to collagen, however, has been reported decreased in aged rabbit platelets.11 The present experiments were carried out to study the rate of protein synthesis in relation to platelet aging. Since blood platelets do not contain DNA,7 it is expected that the function of the messenger RNA may he limited in time SO that protein synthesis may progressively decrease in aging platelets. This was, indeed, demonstrated by measuring the rate of protein synthesis in separate cohorts of rat platelets of different ages. Male Sprague-Dawley rats ( 300-350 Gm. ) were divided into groups of 5 animals each. A total of 70 rats were used. Platelet counts were performed in each animal prior to the I.V. injection of 0.2 ml. platelet antiserum and were followed daily in 2 representatives of each group of animals. When the number of circulating platelets approximately reached the initial level, which was usually 96 hours after the administration of the platelet antiserum, the first group of animals was sacrificed. Platelets were isolated from the rat blood collected in EDTA by differential centrifugation. The platelets were washed once in 0.85 per cent sodium chloride and resuspended in it. The contamina-