EFFECTS OF 5-FLUOROURACIL ON MOUSE BONE-MARROW

Summary. 5‐Fluorouracil (150 mg/kg) was injected intravenously into 11‐week‐old male mice. Its effects on marrow structure over the following 9 d were assessed using light microscopic examination of semi‐thin transverse sections of decalcified humeri. The extravascular compartment became markedly depleted of cells and decreased in size, reaching a minimum on day 5 post‐treatment. Proliferating haematopoietic cells disappeared within 2 d. Post‐replicative erythrocytic cells underwent extra‐vascular phagocytosis by resident macrophages, whilst mature granulocytes continued to pass into the circulation. Repopulation was underway by day 6, and re‐expansion of the extravascular compartment by day 7 when megakaryocytes, of larger than normal average size, occupied most of the extravascular compartment. Megakaryocyte dominance gave way over days 8 and 9 as other haematopoietic cells proliferated and the extravascular compartment continued to enlarge. The significance of the results is discussed in relation to marrow micro‐circulation, egress of haematopoietic cells into the circulation, and cell proliferation in the marrow. Endotoxin, administered 4 h after 5‐fluorouracil, accelerated depletion of the marrow and recovery of haematopoiesis by about 1 d. Copyright © 1979, Wiley Blackwell. All rights reserved