Macrocytosis Resulting from Early Denucleation of Erythroid Precursors.

By SATIMARU SENO, MASANOBU MIYAHARA, HIKARU ASAKUBA, OSAMU Oc:HI, KENICHI MATSUOKA AND TAKENORI Toyu t M ACROCYTOSIS has long been recognized as a common occurrence during the development or recovery from acute anemia.1 It was ascribed to the appearance of large numbers of reticulocytes in the peripheral blood. Recently, Brecher and Stohlman demonstrated that the macrocytosis after administration of phenyihydrazine to rats, bleeding or administration of erythropoietin is not due to reticulocytosis per se, but to the production of macrocytic reticulocytes in response to the “emergency” demand of massive erythropoietic stimulation.2’3 Since erythroid precursors progressively reduce their size during maturation through repeated cell divisions, the appearance of macrocytic reticulocytes could best be explained by a skipped terminal cell division.4 Experimental evidence showing existence of such a mechanism was provided by Seno,5 whose quantitative estimation of ribonucleic acid ( RNA ) in reticulocytes and nucleated red cell precursors suggested that the large red cells were produced by the denucleation of an earlier stage in erythroid maturation than is normally the case. The present case extends these findings and indicates that the macrocytosis in rabbits made anemic by phenyihydrazine or bleeding is due to denucleation of normoblasts at the polychromatic stage of maturation.