MEGAKARYOCYTOPOIESIS IN THE RAT - RESPONSE TO THROMBOCYTOPENIA INDUCED BY EXCHANGE-TRANSFUSION

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 13  (10) , 1048-1054
Abstract
We have studied the megakaryocytopoietic response in rats to acute thrombocytopenia induced by exchange transfusion of platelet-poor blood. Our analysis included serial determinations of (a) peripheral blood counts, (b) the size and number of megakaryocytes in sections of humeral marrow, (c) the numbers of megakaryocytic (CFU-Meg) and granulocyte-macrophage (CFU-GM) colony-forming cells in marrow and spleen, and (d) the proportion of CFU-Meg and CFU-gM in DNA synthesis. With exchange transfusion, the platelet count fell to 11% of the control value (101,000 .+-. 49,000/mm3; mean .+-. SD) and returned to normal by day 3; rebound thrombocytosis (peak 1,720,000 .+-. 246,000/mm3) was observed on days 4 and 5. The average size of marrow megakaryocytes increased significantly on days 2 and 3 compared with normal (p < 0.01), but the numbers of recognizable megakaryocytes did not change through day 5. The numbers of splenic CFU-Meg and CFU-GM increased significantly (p < 0.05) on days 2-4 and on day 2, respectively, after the exchange; however, the numbers of marrow progenitors, which account for over 95% of total body progenitors, remained unchanged throughout the duration of the study. The proportion of CFU-Meg in DNA synthesis (mean .+-. SD) increased from a baseline value of 17% .+-. 4% to 33% .+-. 11% (p < 0.02) and 35% .+-. 6% (p < 0.001) on days 1 and 2, respectively, and returned to control values thereafter. There were no changes in the cell cycle activity of CFU-GM. Thus, acute selective thrombocytopenia induced by exchange transfusion causes an enlargement of marrow megakaryocytes and an increase in the fraction of CFU-Meg in cell cycle. These changes, occurring in the absence of immunologically mediated events, are the direct result of lowered platelet count.