The difference of radiosensitivity between small and large intestines toward high dose of radiation

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Objective To measure the difference of radiosensitivity between small and large intestines toward high dose of radiation and investigate the role of stem cells in this difference. Methods C57BL/6 male mice, 6–8 weeks old, were randomly divided as control group and radiation group received 19 Gy whole body γ–ray irridiation. Large and small intestines of the mice were collected 6, 12, 24, 48, 72 and 96 h after radiation. The proliferation and apoptosis of the large and small intestines and their stem cells were then detected by immunochemistry, and the change of stem cell number in the large and small intestines were detected by in-situ hybridization. Results HE staining showed that 19 Gy γ-ray irradiation caused more severe injury in the small intestine, and all the crypt in the small intestine were extinct at 48 h post-radiation. However, the proliferation index of crypt in the large intestine was as high as 0.23 (t=4.67, P<0.05). Compared with the small intestine, the apoptotic index of epithelial cells in the crypt of large intestine was much lower at 12 and 24 h after irradiation (t=–1.92, –2.42, P<0.05). The apoptotic population of stem cells in the small intestine at 12 and 24 h post irradiation were significantly lower than that in the large intestine (t=–1.98, –2.33, P<0.05), and the number of stem cell in the large intestine was significantly higher than that in the small intestine 24, 48 h after radiation (t=1.98, 3.31, P<0.05). Conclusions The radiosensitivity of small intestine toward high dose of irradiation is significantly higher than that of the large intestine, where the difference in radiosensitivity of stem cells between large intestine and small intestine may be involved. Key words: Stem cells; Radiosensitivity; γ-rays; Apoptosis; Proliferation