Histopathologic changes induced in rats by localized x-irradiation of an exteriorized segment of the small intestine.

The sequence of histopathological changes was described after X-irradiation of the exteriorized segment (3 cm) of the rat ileum with a single dose of 2200 R. A one-year follow-up was provided in rats whose exteriorized intestinal segments were irradiated. Comparisons were made between one group of animals in which the superior mesentric artery and vein were clamped during irradiation and a second group in which these vessels were not clamped. A third group of sham-irradiated controls was used for comparisons. There was a delay in the onset and progression of the radiation damage to the mucosa of the hypoxic animals in the acute post-irradiation phase. In addition, prolongation of survival in the rats with the superior mesenteric vessels clamped was observed. Mucosal regeneration was noted, occurring at 52 days post-exposure. No adenocarcinomas were found up to 354 days after irradiation. An angiofibroma and a highly differentiated osteoid lesion were described.