Hashimoto N, Endoh D, Kuwabara M, Satoh H, Sato F
Department of Radiation Biology, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
J Vet Med Sci. 1994 Jun;56(3):493-8. doi: 10.1292/jvms.56.493.
Murine model for lung tumor induction was studied in C3H/He male mice, a strain with low spontaneous incidence of lung tumors. Dose-response relationships in lung tumor induction were compared following irradiation with single doses and split doses of X-rays to the thorax either at night or in the daytime. The tumor incidence after a single 1.25 Gy dose at night during the period of nocturnal activity almost reached the maximum level after a 5 Gy dose in the daytime. Proliferative activity determined by observing the labeling index with tritiated thymidine in the normal lung was low as a whole, but tended to decrease in the daytime. When the proliferative response was induced by X-irradiation, significantly higher activity was observed at night. These circadian fluctuations were thought to affect radiosensitivity and lung tumor induction in mice. When split doses or fractionated doses of X-rays were applied to the thorax, lung tumor incidence definitely increased. The incidence after two 7.5 Gy doses with a 12 hr-interval was 41%, 3-fold higher than that after a single 15 Gy dose. Moreover, fractionated whole body irradiations (three times at 3 Gy with 3-month-interval) after a single 7.5 Gy thoracic irradiation was most effective in increasing not only the incidence (47%) but also the multiplicity of the lung tumor. More than 30% of tumor-bearing mice had two or more tumors following thoracic and whole body irradiations, while only 10% of tumor-bearers had multiple tumors after single or fractionated thoracic irradiation alone.
在C3H/He雄性小鼠中研究了肺肿瘤诱导的小鼠模型，该品系肺肿瘤的自发发生率较低。比较了在夜间或白天对胸部进行单次X射线照射和分次照射后肺肿瘤诱导中的剂量反应关系。在夜间活动期间单次给予1.25 Gy剂量后，肿瘤发生率几乎达到白天给予5 Gy剂量后的最高水平。通过观察正常肺中用氚标记胸腺嘧啶核苷的标记指数来确定的增殖活性总体较低，但在白天有下降趋势。当通过X射线照射诱导增殖反应时，在夜间观察到明显更高的活性。这些昼夜波动被认为会影响小鼠的放射敏感性和肺肿瘤诱导。当对胸部应用分次剂量或分割剂量的X射线时，肺肿瘤发生率肯定会增加。间隔12小时给予两次7.5 Gy剂量后的发生率为41%，比单次给予15 Gy剂量后的发生率高3倍。此外，在单次7.5 Gy胸部照射后进行分次全身照射（3个月间隔，每次3 Gy，共三次）不仅在增加肺肿瘤发生率（47%）方面最有效，而且在增加肺肿瘤的多发性方面也最有效。在胸部和全身照射后，超过30%的荷瘤小鼠有两个或更多肿瘤，而仅进行单次或分次胸部照射后，只有10%的荷瘤小鼠有多个肿瘤。
