Effect of bleeding on hematopoiesis following irradiation and marrow transplantation.

In previous studies, bleeding after irradiation did not affect the rate of regeneration of endogenous spleen colony-forming cells, but induced an early (4-6 days after irradiation) appearance of erythrocytic colonies which differentiated and disappeared by days 7-8. This "abortive" wave was associated with a similarly abortive wave of splenic 59Fe uptake. The present experiments were done to determine whether or not an abortive wave of erythropoiesis could be induced in the transplanted, exogenous stem cell system. Lethally irradiated mice were given normal bone marrow cells and one-half of the group were bled of about one-third their blood volume within 4 hr of irradiation. Groups were killed on days 3-10 after irradiation. Seventeen to twenty hours prior to killing, 59Fe was injected. Hematocrits, spleen weights, colony numbers, and per cent 59Fe uptake were determined. Hematocrits of bled mice averaged about 70% of those of cell-injected controls. Spleen weights, colony counts, and per cent 59Fe uptake per spleen began to increase about 1 day earlier in bled mice (days 4-5 as compared to days 5-6), and rates of increase were the same as those of controls. However, no abortive wave of erythropoiesis was detected. A large cell dose resulted in earlier increases in all parameters than a small dose. Thus, bleeding after injection of cells produced results similar to those obtained by increasing the cell dose. The inability of bleeding to induce an early abortive wave of erythropoiesis in transplanted as compared to endogenous colony-forming systems may reflect differences in the cell cycling characteristics of these systems.