Proliferative patterns in the mouse jejunal epithelium after fractionated abdominal x-irradiation

Cell proliferation was studied in the intestinal epithelium of mice exposed to fractionated abdominal X-irradiation. Exposures were separated by 12, 24, 48 or 72 hr. Labelled nuclei and mitotic figures per crypt using the crypt squash technique were determined at closely-spaced time intervals (1 to 96 hr) after 1, 2, 3, 5, 7 and 9 exposures. Cell cycle times including estimates of G-1, S, G-2 and M were determined at 12 and 24 hr. These data show that the intestinal epithelium has a remarkable potential to repair damage and recover following severe injury if sufficient time is allowed for the acceleration in proliferative activity. The damage-repair-recovery pattern, i.e., increase in size of proliferative population and acceleration of the generation cycle, is similar for single and fractionated exposures. The number of 300 R exposures which can be tolerated by a highly organized in vivo cell population is dependent upon time interval between fractions; e.g., when interval between fractions is 12 hr eight 300 R exposures kill all animals, but when the interval is increased to 72 hr some animals survive 20 doses, although time of death is highly variable. The compensatory recovery potential is maintained over a large number of exposures.