Enhanced Effect of Total-Body X-Irradiation in Mice Under Mild Hypothermia

Eight-week-old albino male mice were anesthetized with intraperttoneal sodium pentobarbitone and suspended by a plastic collar in a thermostatically controlled water bath, the entire body with the exception of the head being immersed. The bath was kept at various temperatures between 29 and 37 deg , and the colonic temperature of each mouse was continuously recorded. The effects of wholebody irradiation with a dose of 550 r were studied, but the head, not being shielded by the water, received 12% more irradiation. The criterion of an irradiation effect was death of the animal within 30 days. The majority of fatalities occurred between the tenth and twentieth day following irradiation. The chief cause of death was found to be marrow failure. The results show an increased mortality among the animals treated under mild hypothermic conditions 131 to 35 deg ). At a temperature of 29 deg a protective effect was noted. Hypothermia, by lowering the metabolic rate and by increasing the amount of oxygen dissolved in the plasma, may lead to an increase in the oxygen environment of tissues and therby perhaps an increase in radiosensitivity.