Altered platelet kinetics in thrombocytopenic mice with L5178Y leukemia

Thrombocytopenia is a consistent feature of murine leukemia L5178Y. To define the mechanism(s) associated with the decrease in platelets, serial thrombokinetic studies were performed on various days after intravenous inoculation of 10(6) L5178Y ascites cells. At the nadir of thrombocytopenia (day 5), the recovery and circulating half-time of transfused normal 51Cr-platelets was only one half of control values. The loss of circulating radioactivity (70%) at 1 hr was accounted for by splenic (40%) and hepatic (30%) accumulation of labeled platelets. However, the liver contained three times more radioactivity per milligram of tissue than the spleen. There was no increase in hepatic accumulation of 59Fe-labeled red cells under the same conditions. When 51Cr-labeled leukemic platelets (day 3) were infused into normal animals, the circulating half-time was 50% of control. Despite spleen and liver enlargement, the blood volume of the leukemic mice did not increase. The megakaryocyte concentration remained unchanged after inoculation of leukemic cells, but the diameter of megakaryocytes increased significantly from days 5 to 10. These studies show that thrombocytopenia in mice transplanted with L5178Y leukemia occurs as a result of shortened platelet survival and increased organ sequestration. The increase in hepatic platelet accumulation suggests that the mechanism of thrombocytopenia is platelet specific and is not due to passive organ pooling.