Megakaryocyte Polyploidization in Myeloproliferative Disorders

In 5 cases of polycythaemia vera and 2 cases with other myeloproliferative disorders accompanied by thrombocythaemia (megakaryocytic myelosis), the megakaryocytes were differentiated and studied by use of the combined application of cytophoto-metric determination of the DNA content and autoradiography with tritiated thymidine (3H-TdR) in vitro. A shift to the right of the megakaryocyte series, occurence of high polyploidy cells at 64c and a decrease of the3H-TdR-labeling indices were observed. The data suggest a disturbance of the rhythmical polyploidization of the megakaryocytes, consisting of an elevated proportion of rest cells at the different ploidy stages. The maturation capacity of megakaryocytes may be related more to the resting than to the DNA synthesizing cells.