This study represented an effort to determine if there were quantitative or morphological changes in marrow stromal cells in busulfan-induced marrow failure and to relate these changes to other disturbances in blood and bone marrow. Mice received four busulfan (BU) injections at two-week intervals and were killed at various time points up to 40 weeks after the first injection. Evaluation techniques included complete blood counts, in vitro assay of short-term adherent cell colonies per femur (STACC per femur) and colony-forming unit- culture (CFU-C) per femur, light microscopy of sternebral marrow and spleen, and electron microscopy (EM) of sternebral marrow taken at 40 weeks. STACC per femur were acutely reduced to 25% of control, but recovered to 76% by 40 weeks. CFU-C per femur dropped to below 10% of control and never recovered. Histologically, we found that hypoplasia of acutely affected marrow was associated with heightened endosteum and cortical bone thickening. In the chronic phase of BU injury, bones became osteoporotic, and the frequency of adipocytes and mast cells rose. BU-affected spleens generally had enhanced erythropoiesis. No stromal cell changes in 40-week marrow were discernible by EM. We concluded that there were morphological changes in BU marrow stroma specifically involving endosteum, bone, adipocytes, and mast cells. Also, there was quantitative depression in stromal cells measured by the STACC assay, but this improved substantially with time, unlike damage to hematopoietic stem cells measured by the CFU-C.

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