Megakaryocytopoiesis in irradiated, splenectomized mice.

The hypomegakaryocytic state that develops after exposure to sublethal doses of ionizing radiation was evaluated in splenectomized and intact mice. The percentage reduction of marrow megakaryocytes was greater than that of platelets at comparable times post-irradiation. After initial recovery a secondary drop in platelet counts occurred earlier in intact than in splenectomized mice. The average size of mature megakaryocytes was found to be increased, due primarily to marked reductions in megakaryocytes of smaller size. These results indicate that the spleen acts more to reduce than to increase the platelet count after exposure to sublethal doses of whole body radiation and that megakaryocyte size may be increased by reduction in numbers of small megakaryocytes without an increase in large megakaryocytes.