Modification of Irradiation Response of Female Rats by Population Density

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Abstract
Four hundred female albino rats weighing 160 - 175 grams were exposed to various levels of whole-body x-radiation and assigned to treatments in which the females were either singly- or multiple-housed in cages which measured 7 x 10 x 7 inches. Singly-housed females given 500 r exhibited no mortality during the subsequent 30-day period while those that were housed in multiples of 2, 4 or 6 to a cage showed a combined mortality of 12.5 per cent. Singly-housed females exposed to 750 r exhibited 56% mortality during the subsequent 30 days, while those multiple-housed females exhibited 100% mortality. Fifty per cent of the group-housed females were dead by the 11th day after irradiation as compared to 22 days for the singly-housed animals. Though all females exposed to 1000 r exhibited 100% mortality within 30 days, 50% of all the group-housed females died significantly sooner than the singly-housed females. Thus population density can significantly alter the lethality of x-radiation not only in terms of survival per se but also in terms of significant shifts in the mortality curve.