A Comparison of Platelet Size, Platelet Count, and Platelet35S Incorporation as Assays for Thrombopoietin

Abstract

In mice injected with rabbit anti-mouse platelet serum (RAMPS) average platelet size increased as mice were recovering from thrombocytopenia. Also, 35S-measurements on platelets of these mice showed significant increases in cpm/average platelet 2-4 days after RAMPS treatment. Significant increases in 35S-incorporation into the total circulating mass of platelets were found on days 3-4. In normal mice or mice in rebound-thrombocytosis injected with thrombopoietin, platelet size remained unchanged, but the platelet count and 35S-incorporation into platelets were significantly increased. A dose-response experiment in mice pretreated with RAMPS showed a slight increase in platelet count as the dose of TSF [thrombopoiesis stimulating factor] was increased, but platelet sizes were unalterd. The percentage of 35S-incorporation into platelets showed a significant linear dose-response, i.e., as the dose of thrombopoietin was increased, an increase in percentage of 35S-incorporation into platelets was observed. Of the 3 indirect measurements of thrombopoietin, the percentage of 35S-incorporation into mouse platelets was the most sensitive, followed by platelet counting; the least sensitive measurement of thrombopoiesis was change in platelet size.