Radiosensitivity of Ileum Crypt Cells in Hibernating, Arousing, and Awake Ground Squirrels (Citellus tridecemlineatus)

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Abstract
Radiosensitivity of ileal crypt cells, to cobalt-60 .gamma.-radiation, was studied in ground squirrels (C. tridecemlineatus) during hibernation, arousal and the euthermic state. Survival of ileal crypt cells, assayed by the microcolony technique from stained transverse sections of ileum, was greater in animals irradiated in hibernation or 1 h after initiation of arousal from hibernation. Crypt survival returned to the level of irradiated nonhibernating controls in animals irradiated 3-7 h after initiation of arousal. Over the exposure range of 1500-2400 R, the survival of crypt cells for euthermic controls gave a D0 [cell sensitive dose] = 133 .+-. 12 R and for animals irradiated in hibernation it gave D0 487 .+-. 92 R. In animals irradiated 1 h after initiation of arousal, when core temperature is within the range of euthermic controls, crypt survival was almost as high as in the hibernators. The increased resistance of ileal crypt cells in hibernating animals may be due to hypoxia, although no direct evidence of hypoxia in hibernation was established. The changes in mitotic index of ileal crypt cells during hibernation and arousal indicate an alteration in the distribution of cells in the phases of the cycle. This change in distribution may also have contributed to the increased radioresistance of hibernators.

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