Serum Thrombopoietic Activity Following Administration of Vinblastine

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Abstract
A possible role of humoral factors in the pathogenesis of vinblastine-induced thrombocytosis was examined. The thrombopoietic activity in serum of experimental animals was tested for its ability to stimulate the incorporation of 75-Se-selonemethionine into platelets of thrombocythyemic mice. The administration of low doses (0.1-0.5 mg/kg body wt) of vinblastine to rabbits caused a significant increase in serum thrombopoietic activity. Higher doses of vinblastine (1-5 mg/kg body wt) also increased the serum thrombopoietic activity but this increase was preceded by a transient drop in the platelet count of peripheral blood. This thrombocytopenia could be a stimulus for an increase in thrombopoietic activity, through a compensatory feedback mechanism. The vinblastine-induced increase in thrombopoietic activity was abolished by bilateral nephrectomy but not by bilateral ureteral ligation. Kidney tissue may be a major source of the serum thrombopoietic factors.