[The 5-fluorouracil sensitivity of the hematopoietic stroma of the bone marrow and spleen].

We studied the effect of a single injection of 5-fluorouracil (5-FU) (150 mg/kg) on the numbers of stromal precursor cells (CFU-F) in the bone marrow and spleen and their capacity for formation of hemopoietic foci after ectopic transplantation under the renal capsule. 5-FU decreased the number of CFU-F in the bone marrow and spleen of mice and rats to 30 - 50% of the control values. The size of transplants, as estimated according to the number of hemopoietic clonogenic (CFU-S) and nucleated cells, diminished within the first two months after transplantation. Within four months after transplantation the size of the bone marrow transplants approached the control level, while that of the spleen transplants markedly exceeded the control level. Differences in the growth rate of regenerating transplants of the hemopoietic organs are discussed with special reference to the organ specific features of populations of the stromal cells.