Macromegakaryocytosis After Hydroxyurea 1

Abstract

Abstract

A single injection of hydroxyurea (OHU) produced transient megakaryocytopenia in mice. An increase in the average mean size of mature, stage III megakaryocytes coincided with their depopulation. This was due to a selective reduction in numbers of smaller cells. In contrast, the macromegakaryocytosis of immunothrombocytopenia showed substantial increases in numbers of larger cells and reductions in smaller. Further reduction in numbers of smaller cells occurred when OHU was given to mice with immunothrombocytopenia, and the megakaryocytopenia was somewhat more severe than that produced by OHU in normal mice. OHU produced mild thrombocytopenia in normal mice and compromised recovery of the platelet count from immunothrombocytopenia. The most likely explanation for the increase in mean megakaryocyte size in the hypomegakaryocytic state produced by OHU is that the temporary imbalance between a low rate of influx and a normal rate of maturation produced a shift of the age distribution of the cells due to a deficiency of immature cells.