Partial marrow shielding and total-body irradiation

The effects of shielding one femur on bone marrow morphology and function were studied in rats receiving total-body irradiation. Animals were exposed to 550 r from a Co60 source. Shielding consisted of 100 mm of lead, reducing exposure to one femur to 16 r. Marrow cell counts, radioiron localization in femurs, plasma iron turnover, red cell radioiron utilization, and peripheral cell counts were observed. Phlebotomy in some animals served as a functional stress. There was no observed morphological change in shielded marrow despite marked depopulation of nucleated cells in heavily irradiated marrow. In phlebotomized shielded animals, the rate of hemoglobin synthesis was nearly half that of unirradiated controls although retarded by several days whereas in unshielded animals, hemoglobin synthesis was further delayed and less than a third of control values. Initially the erythropoietic function resides primarily in shielded marrow as evidenced by radioiron localization and marrow cell counts with no evidence of indirect depression. Cellular repopulation appears more rapidly in partially shielded animals and compares favorably with the effectiveness of marrow transfusion.