RESIDUAL INJURY IN THE ERYTHROPOIETIC SYSTEM OF SHEEP AFTER Co60 GAMMA RADIATION

Erythropoietic activity, as measured by Fe59 uptake, was determined in nonirradiated sheep and in sheep surviving midlethal exposures to Co60 radiation approximately two years prior to this study. A group of survivors of the midlethal exposure and sheep which received 50 R approximately 6 months previously were challenged with 170 R X-irradiation during this study to determine the effects of this stressing exposure on erythropoietic activity. Nonirradiated sheep and those previously given 50 R were 2 - 2 1/2 years of age and survivors were 3 - 3 1/2 years of age at the time of this study. Fe59 uptake in sheep surviving the midlethal exposure, when compared with Fe59 uptake in nonirradiated sheep over four days following injection of the isotope, was significantly higher both in percent of the injected aliquot reappearing in the peripheral circulation and in the rate at which it reappeared. Although the survivors were 1 - 1 1/2 years older than the nonirradiated group at the time of this study, age differential was not considered to be responsible for the increased uptake observed. The data suggest that increased erythropoietic activity in sheep two years after midlethal exposure may be due to a radiation induced aberration of the stem cell pool resulting in a sustained increase in proliferation of this compartment. (Author)