Evidence that stimulation of megakaryocytopoiesis by low dose vincristine results from an effect on platelets.

Appropriate low dosages of vincristine stimulate megakaryocytopoiesis and produce thrombocytosis. In this study of the thrombocytotic action of vincristine, administration of a single dose of 0.1 mg/kg to rats produced an increase in megakaryocyte concentration, diameter and 24 h [3H]thymidine labelling index. Transfusion of one body equivalent of platelets from normal donors prevented stimulation of megakaryocytopoiesis by vincristine whereas platelets from vincristine-treated donors did not. These results suggest that vincristine stimulates megakaryocytopoiesis by altering the functional role of circulating platelets in the regulation of thrombopoiesis.