Continuous Irradiation of the Rat at High Dose Rates: A Study of Jejunal Damage, Recovery, and Radioresistance Using Tritiated Thymidine

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Abstract
Exposure of August rats to continuous gamma irradiation at 415 rads/day showed that the jejunal epithelium, after approximately three days, was maintained morphologically in a steady state while the crypt cells developed an increased intensity of labelling with tritiated thymidine. In addition, the jejunal epithelium becomes more radioresistant to an acute dose of irradiation, as measured by the clearing of debris, mitotic frequency and the appearance of the villi. When rats were removed from continuous irradiation, the villi soon returned to normal length, whereas the crypt mitotic counts increased considerably within 1 day. Intravenous isologous marrow, given to continuously irradiated rats, reduced the early likelihood of a hemorrhagic type of death when administered after not more than 5 days total irradiation at the above dose rate.