Measurement of thrombopoiesis in rabbits using 75selenomethionine

Abstract

Incorporation of ⁷⁵selenomethionine (⁷⁵SeM) has been used to study platelet production in rabbits. Radioactivity of platelets was low after the intravenous administration of ⁷⁵SeM and rose to a maximum approximately 3 days after administration. Platelet radioactivity was independent of concurrent plasma levels. The life span of rabbit platelets, as estimated with this technique, was 4-5 days. In vivo reutilization of ⁷⁵SeM previously incorporated into plasma proteins was not detected. In vitro incorporation of ⁷⁵SeM by platelets in platelet-rich plasma was not demonstrated. Acute hemorrhage 24 hr before administration of ⁷⁵SeM increased the incorporation of ⁷⁵SeM into platelets. Transfusion-induced thrombocytosis reduced the incorporation of ⁷⁵SeM to approximately 30% of that observed in control animals. Suppression of bone marrow function with nitrogen mustard resulted in decreased numbers of platelets in the circulation, and a decrease in incorporation of ⁷⁵SeM. Delayed appearance of ⁷⁵SeM was observed in circulating platelets during recovery from marrow suppression. Injection of 75-225 ml of plasma from thrombocytopenic donors into normal rabbits increased incorporation of ⁷⁵SeM into platelets while normal plasma did not have this effect. The rate of appearance of ⁷⁵SeM in circulating platelets appears to provide a sensitive and specific method for the study of production of platelets by megakaryocytes. The data suggest more rapid entry of platelets into the circulation, and a sustained increase in incorporation of ⁷⁵SeM into platelet protein after stimulation of platelet production. The results are consistent with the concept of a humoral agent (thrombopoietin) that acts on megakaryocytes to regulate platelet production.