| Abstract: | Under the influence of a selective irreversible inhibitor of ornithine decarboxylase (ODC), DL-alpha-difluoromethylornithine (DFMO), early hematopoiesis was enhanced. In the bone marrow, the absolute number of cells that give rise to spleen colonies in lethally irradiated mice (CFU-S), granulocytic colonies in diffusion chambers in mice (CFU-DG), and granulocyte-monocyte colonies in agar in vitro (CFU-C) was increased 2-4 fold. This could be abrogated by administration of putrescine, confirming the association of the stimulatory effect with polyamine biosynthesis most likely via depression of ornithine decarboxylase activity and subsequent synthesis of putrescine. Analysis of cell cycle characteristics by 3H-TdR suicide technique demonstrated that the proportion of CFU-S, CFU-DG, and CFU-C in S-phase was significantly increased. Additionally, the stimulatory effect was reflected by enhanced colony formation in diffusion chambers implanted intraperitoneally in mice receiving DFMO. This could also be eliminated by treatment of the host animal with putrescine, again suggesting that polyamine biosynthesis plays an important role at the early stages of hematopoiesis in vivo. Effect of DFMO on colony formation in vitro (CFU- C) was inhibitory and not reversible with putrescine. It could be partially eliminated by aminoguanidine, which neutralizes diamine oxidase present in fetal calf serum used in the CFU-C assay. These data suggest that the effect of DFMO in vitro was nonspecific. |
