Isotope bioassay for "thrombopoietin".

An assay system has been developed in mice for the humoral agent "thrombopoietin." This is based on utilization in newly-formed platelets of the radio-amino-acid (75)Se selenomethionine 24 hours after intravenous injection. The possibility that the results could be due to the effects of species antibody, to foreign protein, or to an effect primarily on selenomethionine metabolism, has been explored, but the findings are consistent with the presence of a physiological humoral factor. Thrombopoietin has been shown to be present in the plasma of patients suffering from severe thrombocytopenia of varied aetiology.