Effect of Continuous Gamma Irradiation of the Generation Cycle of the Duodenal Crypt Cells of the Mouse and Rat

Abstract

In a previous experiment on the effect of daily protracted Co60 y-irradiation on the generation cycle of the duodenal crypt cells of the mouse (1), the disturbance of the cycle after 1 day of exposure was found to be similar to that produced by a single brief exposure (2). There is a prolongation of G2 + M, and the shape of the curve for percentage of labeled mitotic figures versus time suggests that movement of cells through other phases of the cycle is retarded. On subsequent days, however, the rapidly dividing crypt cells appear to compensate for the radiation damage. Mitotic arrest is no longer observed, and the crypt cells undergo repeated divisions at virtually the normal rate, maintaining an intact epithelium for 3 weeks in spite of continued irradiation to accumulated doses in excess of 3000 R within 15 days (1). Similar results were found at 12 R/day (3). In the following experiments, the generation cycle of the duodenal crypt cells was studied in both rats and mice exposed to 50 rads/day at various intervals after the start of irradiation. At this exposure level, mice can accumulate mean lethal doses of 6000 to 7000 rads, and rats can accumulate doses exceeding 10,000 rads (4, 5). Thus, it is possible with this exposure condition to study the effects of large accumulated doses on the generation cycle and to compare the cycles of two species that differ markedly in their resistance to chronic exposure.