[Patterns in the compensatory reaction of the precursor cell system of the bone marrow fibroblasts to ionizing radiation].

Compensatory unspecific processes taking place in irradiated bone marrow stroma are caused by qualitative and quantitative reactions of the stromal cell populations to the damaging effect. The authors studied the regularities of the compensatory quantitative reaction of the stroma--the system of fibroblast colony forming units (CFUf) of guinea-pig bone marrow--to exposure to ionizing radiation. They confirmed the existence of a "reserve" of the bone marrow CFUf system whose cell elements acquire adhesive and mitotic activity in the immediate periods (60-90 minutes) after irradiation. It is shown that the character of the dose-effect curves according to the criterion of the absolute CFUf number 60-90 minutes after irradiation is determined by two processes: the death of stromal precursor cells in proportion to the irradiation dose, and activation of the "reserve" population of the CFUf system proportionally to the level of the action of the ionizing radiation. The quantitative degree of activation of the CFUf "reserve" is characterized. Radiosensitivity was appraised in vivo of two guinea-pig bone marrow CFUf populations forming dense and loose fibroblast colonies in a monolayer culture.