Effect of actinomycin D on hematopoietic stem cells

: The effect of actinomycin D on stem hemopoietic cells in the bone marrow of adult mice has been studied by means of spleen colonies. The antibiotic at a dose of 0.4 mu g/ml (g) inhibited the colony formation when applied in vitro and stimulated this process in vivo. The reaction of stem hemopoietic cells to the antibiotic at a dose 0.04 mu g/ml (g) varied: in most experiments no cytotoxic effect was observed both in vitro and in vivo; moreover, in some cases the colony formation increased 1.5--2 times. Possible causes of the stimulating and inhibiting effect of the antibiotic are discussed.