Histological changes in rat duodenum mucosa after whole-body gamma irradiation.

In order to understand the mechanisms of intestinal injuries due to ionizing radiation, various groups of rats have been whole-body irradiated by gamma-rays at two dose rates (1 Gy/min and 1 Gy/hr), three doses (1, 2 and 4 Gy) and two post-irradiation times (24 and 48 hr). Duodenum samples of the animals were prepared for light microscopy, according to classical methods for histology and TUNEL reaction. A small number of morphological differences were observed within the mucosa between the two dose rates used. The extent and the number of lesions were more important at the slower dose rate (1 Gy/hr) and increased with the total dose. Clear cavities were seen inside the lamina propria which appeared like capillaries free of blood cells. The mitotic index calculated from crypt cells showed a regular decrease with the dose, which was exacerbated at 48 hr post-irradiation. On the other hand, the apoptotic index increased with the dose and the postirradiation time. Our results lead to hypothesize another mechanism of intestinal mucosa renewal allowing to explain mucosa denudations observed after radiotherapy. Thus we propose a new concept in which the duodenal mucosa renewal may occur by whole villi shedding into the duodenal lumen.