RADIATION MORTALITY OF RODENTS UNDER HYPOBARIC-HYPOXIC CONDITIONS

The purpose of this study was to establish whether reduced oxygen concentration (hypoxia) and reduced atmospheric pressure (hypobarism) significantly change the radiosensitivity of rodents. Approximately 1,800 male Swiss-Webster mice, committed in groups of 50, and 56 male Sprague-Dawley rats were gamma-irradiated at low dose rates in an altitude chamber. Experimental groups of hypoxic and hypobaric mice received total doses of 900 to 2,100 R cobalt-60 gamma rays. Survival in all experimental groups was negligible; in one instance less than that of corresponding controls. In most experimental groups, however, the hypoxic-hypobaric groups achieved a longer mean survival time than did corresponding controls. At 1,300 R, the control group achieved a mean survival time of 7.3 days. Three groups similarly irradiated but hypoxic and hypobaric at 22,500 ft. recorded mean survival times of 9.7 days, 9.9 days, and 9.7 days, respectively. Additionally, three groups similarly irradiated but hypoxic and hypobaric at 15,000 ft. achieved mean survival times of 10.2 days, 12.7 days, and 12.4 days, respectively. The LD50/30 for normal mice irradiated as controls in the apparatus at ambient pressure and oxygen concentration was calculated to be 850 plus or minus 72 R. By assuming the validity of the hypothesis that hypoxia is radioprotective, simultaneous hypobarism appears to nullify, at least partially, this radioprotective effect. (Author)