Velocity sedimentation profiles of normal and regenerating primitive erythroid burst-forming units: relation to phase of cell cycle and growth in vitro.

The primitive burst-forming unit-erythroid (BFU-e) derived from normal and regenerating murine bone marrow was examined by velocity sedimentation at unit gravity. An increase in the modal sedimentation velocity and the percentage of rapidly sedimenting BFU-e was found in regenerating marrow as compared to normal marrow. Neither hypertransfusion-induced plethora nor administration of erythropoietin (Ep) during regeneration altered the changes from normal in the velocity sedimentation profile observed during regeneration. Separated marrow cells were pooled as rapidly sedimenting and slowly sedimenting and then examined for percentage of BFU-e in DNA synthesis and growth response in vitro to increasing concentrations of a partially purified Ep preparation. The percentage of BFU-e in DNA synthesis as determined by tritiated thymidine killing does not correspond to the BFU-e growth response to Ep in vitro. No difference in growth was noted between BFU-e from rapidly and slowly sedimenting normal marrow cells despite an increased percentage in DNA synthesis of normal BFU-e which sedimented rapidly. No significant difference in the percentage of BFU-e in DNA synthesis was found between the rapidly and slowly sedimenting subpopulations of regenerating BFU-e, but the latter had a reduced growth response to low concentrations of Ep.