Erythropoietic recovery and residual injury in rats exposed repeatedly to x-rays

¹ U.S. Naval Radiological Defense Laboratory, San Francisco, California

Rats exposed repeatedly to 300-r x-rays showed a decrease in Fe⁵⁹ incorporation which attained its lowest point 48 hours postirradiation. Thereafter iron uptake increased until normal values were measured. This return to normalcy was delayed further with each newly repeated irradiation. On any day during the recovery period Fe⁵⁹ uptake decreased exponentially with repeated x-irradiations. This decrease is a measure of residual injury to the erythropoietic system. Since, after each repeated irradiation, a reduced amount of Fe⁵⁹ was incorporated at the beginning of the recovery period, while the rate of recovery was similar, it is postulated that the decrease in radio iron uptake is due to an impairment in the functional capacity of the stem cells to proliferate erythrocytes. A working hypothesis for the calculation of erythrocyte stem cell damage is presented. Although the functional capacity of the stem cells to produce erythrocytes was reduced, the daily red cell turnover was normal. Only when this reduction was below a certain limit did a permanent anemia ensue.