Tolerance of rats to a cold environment during multiple exposures to a low dose of x rays

¹ Division of Biological and Medical Sciences, U.S. Naval Radiological Defense Laboratory, San Francisco, California

A lethal dose of X irradiation can be made sublethal by the fractionation of a dose into a series of smaller doses separated by adequate time intervals. The results reported here demonstrate how an environmental stress, such as cold, may affect this mitigating action of dose fractionation. Rats were maintained at 6 C while receiving a total dose of 600 r in one or eight exposures with various intervals between exposures. A greater interval was required between radiation exposures at 6 C than at 23 C to reduce the lethal response following irradiation. From the results of the food consumption measurements, it appears that cold exposure emphasizes the consequence of the reduced food intake which follows daily doses of 75 r in the rat. The irradiated rat was able to increase the amount of food consumed during cold exposure; however, the increase was not sufficient for adaptation. The lowered consumption which followed eight daily 75-r exposures was sufficient to cause death in pair-fed rats maintained at 6 C, but not at 23 C.