Effect of hypertransfusion on bone marrow restoration after localized depletion

The reconstitution of marrow in a mechanically depleted medullary cavity was compared in normal and hypertransfused mice. Polycythemia (hematocrit of approximately 70%) prevented the emergence of recognizable erythroid cells but not of erythropoietin-responsive cells as revealed by autoradiographic studies with 55Fe after erythropoietin treatment. The similar regeneration of erythropoietin-responsive cells in normal and hypertransfused mice was shown by comparison of 55Fe labeling in the repopulating relative to the contralateral marrow; in each case, labeling in the repopulating marrow was about 20% of that in the intact contralateral marrow. Polycythemia did not influence the recovery of granulocytic elements in the regenerating marrow even though the myeloblast-metamyelocyte population of the intact contralateral marrow was increased. The findings are intrepreted to support the concept that hematopoietic stem cell commitment to one or another pathway of differentiation is basically a local phenomenon.