Residual Injury Induced in the Erythropoietic System of the Rat by Periodic Exposures to X-Radiation

Rats were irradiated periodically in order to assess any remaining injury of previous exposures after a 3 month interval. One group of female and one of male rats were subjected to 300 r x rays, 250 kvp, while another group of females was exposed to 400 r, 250 kvp. A significant decrease in Fe(sup 59) incorporation was observed with each periodic exposure in all 3 experimental groups. These decreases were logarithmic. A titration experiment based on the additional acute dose necessary to mimic the effects of periodic x ray exposures indicated an approximate 30% residual injury after one repeated irradiation to either 300 or 400 r and 43% after 2 exposures. In contrast to the bone marrow changes, peripheral engthroid decreases were small until thc last period in the two female radiation groups as measured by the hematocrits. This indicates that the quantity of stem cells available for erythrocyte production must greatly exceed the number required in the daily red cell turnover. It must be questioned whether rats with an impaired erythrocyte proliferation system could respond to emergency situations as well as normal animals. Other observations more » included relatively early appearance of mammary tumors in the female rats and weight decreases in all groups immediately aftcr radiation. These changes were however not unique in irradiated rats because they eventually appeared in old controls. (auth) « less