Density subpopulations of rabbit platelets: size, protein, and sialic acid content, and specific radioactivity changes following labeling with 35S-sulfate in vivo.

The relationships among platelet size. density. protein and sialic acid content. and age have been investigated. More than 90% of the platelets were obtained from anticoagulated rabbit blood and separated into three density subpopulations by centrifugation in isosmolar discontinuous arabinogalactan (STRactan) density gradients. The size of the most dense platelets was greater than that of the least dense platelets. Most dense platelet subpopulations contained significantly larger amounts of protein and sialic acid per platelet than least dense; however, no relationship between nanomoles sialic acid per milligram protein and platelet density was observed. 3 SO was injected intravenously into rabbits as a cohort label of young platelet proteoglycans. The incorporation and loss of radioactivity in the platelet density subpopulations was determined daily for 5 days. By 24 hr. the relative specific