Quantitative Response of Bone Marrow Colony-Forming Units (CFU-C and PFU-C) in Weanling Beagles Exposed to Acute Whole-Body γ Irradiation

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Abstract
Using a methylcellulose-supported bone marrow culture system, dose-response relationships of suspended granulocyte-monocyte colonies (CFU-C) and adherent fibroblastic colonies (PFU-C) were investigated in 2-3 mo. old beagles exposed to acute whole-body .gamma.-irradiation. Groups of weanling beagles were exposed at a rate of 140 R/h delivered from a 60Co .gamma. source achieving total exposures ranging from 0-586 R. Following irradiation [24 h], bone marrow was collected, plated into methylcellulose, and after 1 wk of incubation both colony types were quantitated. Bone marrow cellularity determinations were made for a variety of bones using an 56Fe-labeling technique. A D37 37% survival dose for the linear part of the slope of 70 R for CFU-C. Although within limits of the experiment a D37 was not established for the fibroblastic populations, a substantial degree of radioresistance for these elements was indicated supporting previous studies on PFU-C, performed on mice, which suggested a D37 of .apprx. 400 R for the progenitors of these fibroblastic elements.