Study of a CFUs stimulating factor liberated by bone marrow cells after total and partial body irradiation.

Data reported in this paper show that a long range stimulating factor is released by irradiated bone marrow 15 minutes after exposure and that the secretion of the factor precedes CFUs proliferation. The factor seems to be elaborated by liver cells as is demonstrated by dose effect experiments as well as by the fact that protected bone marrow secretes a factor, albeit with different kinetics of secretion from those of irradiated bone marrow. The liberation of the factor seems to be regulated by the size of the stem cell compartment.