Proliferative Activity of the Stem Cells in the Bone-marrow of Mice after Single and Multiple Irradiations (Total-or Partial-body Exposure)

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Abstract
After a whole-body irradiation of 150 rads, an increase in the proportion of S cells observed during the first day suggests that the bone-marrow is stimulated by an unknown but probably compensatory mechanism. In the first hours after a partial-body irradiation with the same dose, the proliferative activity of the protected bone-marrow increases, and at 24 hours all the stem cells seem to be engaged in a mitotic cycle. In the irradiated areas, the same phenomenon occurs, but later. During a course of subtotal daily irradiation, the number of stem cells in the shielded area decreases and levels off around 10 per cent of its initial value. The number of stem cells in the irradiated zone plateaus at a lower value. The progressive depletion of the protected bone-marrow observed during the beginning of the course of radiotherapy and the plateau observed later, seem to be due to a migration of haematopoietic cells between the protected and the irradiated regions.