Abstract
Summary
Studies were made of the effect of X-irradiation with 1000 R on marrow restoration after localized depletion of the rabbit femur. The femur was X-irradiated immediately before or after depopulation by dextran perfusion or 9 days later. In some experiments, the femur was X-irradiated without subsequent marrow extrusion. Regeneration was evaluated by determining the uptake of tritiated thymidine into DNA and the number of hemic cells in the depopulated and/or irradiated femoral marrow relative to the contralateral marrow. Impairment, i.e., delay of regeneration, was similar whether the femur was irradiated just before or after marrow removal. However, the radiation effect at this time was greater than that when regeneration was in progress. The response of the 9-day regenerating system resembled closely that of normal marrow. Reconstitution of the microenvironment precedes hemic cell repopulation, and it is noteworthy that a connective tissue matrix and vasculature have already been formed by 9 days after marrow removal. The difference in degree of effect with irradiation before and after regeneration has been initiated can be explained in several ways. It does not necessarily indicate a differential radiosensitivity at the cellular level.
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