Effect of chronic γ-irradiation upon camine hematopoietic (CFU-GM) and non-hematopoietic (CFU-F) progenitor populations

Clonogenic assays for progenitors of the myeloid-macrophage series (CFU-GM) were performed on dogs that had been chronically irradiated and on their littermate or age-matched controls. In conjunction with these assays, in vitro irradiation dose response studies were performed on marrow-derived fibroblasts (CFU-F). Dogs exposed to continuous γ-irradiation demonstrated a significant decrease in the number of immature myeloid progenitors responsive to colony-stimulating factors (PCM, SCM), whereas no change was seen in numbers of macrophage and mature granulocyte colony types. This decrease in myeloid progenitors for CFU-GM was accompanied by a marked inability to respond to indomethacin. Those irradiated dogs with the most radioresistant bonemarrow derived fibroblasts also had the lowest numbers of immature myeloid colonies