The Effect of Hypoxia on the Sensitivity of the Epithelial Cells of the Jejunum

SummaryDose—effect curves for clones arising 11 days after the irradiation of a segment of the mouse jejunum have been obtained. The D0s for animals breathing oxygen or nitrogen at the time of irradiation obtained from regression lines fitted to a common extrapolation on zero dose are 117 (105–130) rads and 306 (276–344) rads, respectively, giving an OER of 2·6.This OER is not different from the OER obtained from the LD50/5 values (2·7). The LD50/5 doses for animals breathing oxygen or nitrogen during irradiation both fall on the extrapolated jejunal clone dose—effect curve at the same clone/test area level, suggesting that the primary cause of animal killing within 5 days of irradiation is depletion of the stem-cell population of the small intestine.The dose—effect curve for animals breathing air and irradiated at 6 krads/min has a D0 of 268 (218–342) rads, which is not different from that obtained for animals breathing nitrogen. This is due to hypoxia induced by the consumption of oxygen by radiation at this high dose-rate. At a lower dose-rate, 500 rads/min, the dose—effect curve for jejunal clones in animals irradiated while breathing air is the same as that for animals irradiated while breathing oxygen.