Platelet size, ATP content, and clot retraction in relation to platelet age

¹ Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee

The in vivo aging of rat blood platelets has been studied by comparing the ability to promote clot retraction, size, and ATP content of young, old, and normal populations of platelets. Young platelets were obtained 2 days after injecting rats with antiplatelet serum. Old platelets were obtained by incubating fresh platelets for 2 days in rats made thrombocytopenic by 900 r of whole-body X irradiation. There was a decrease with age in the size of platelets of about 25% between young and old. There was no statistically significant age-related difference in the content of ATP when expressed as micromoles of ATP/10¹¹ platelets or micromoles of ATP/ml of packed platelets. The clot-retracting ability of old platelets was about 10% less than that of young platelets. Constancy of ATP on the basis of both platelet number and platelet volume is not consistent with a change in platelet size. It seems probable that there was a decrease in micromoles of ATP/platelet, although it was not statistically significant. The reduction in clot retraction may be due to a small decrease in the size of the ATP pool or to an impairment of the platelet's ability to metabolize glucose for the production of the additional ATP necessary for clot retraction.