褪黑素对小鼠胸腺细胞电离辐射损伤的防护作用

目的：探讨外源性褪黑素（MLT）对电离辐射所致小鼠胸腺细胞损伤的影响及其机制。 方法：通过腹腔注射方式给予昆明系小鼠外源性MLT，分别建立单次给药和连续给药两种动物模型。对于单次给药动物模型，腹腔注射不同浓度MLT后60 min给予1 Gy X射线全身照射，12 h后采用流式细胞术和荧光分光光度法分别检测胸腺细胞凋亡小体百分率和DNA裂解率的变化；对于连续给药动物模型，连续1周腹腔注射不同浓度MLT后给予1 Gy X射线全身照射，24 h后检测胸腺细胞数量及³H-TdR掺入率的变化。 结果：单次给药动物模型，小鼠受1 Gy X射线全身照射后12 h，胸腺细胞数显著低于假照组（P<0.001），凋亡小体百分率和DNA裂解率显著高于假照组（P<0.001）。照射前预先给予外源性MLT，与0 mg?kg^-1 MLT组（单纯照射组）比较，胸腺细胞数增多，以0.5 mg?kg^-1 MLT组增多最明显（P<0.01）；凋亡小体百分率和DNA裂解率降低，在0.1~2.5 mg?kg^-1 MLT浓度范围内差异均具有显著性（P<0.001）。连续给药动物模型，小鼠受1 Gy X射线全身照射后24 h，胸腺细胞数及³H-TdR掺入率均显著低于假照组（P<0.001）。照射前预先给予外源性MLT，与单纯照射组相比，胸腺细胞数和³H-TdR掺入率均显著增多，前者在0.01~0.10 mg?kg^-1 MLT浓度范围内差异具有显著性（P<0.01），后者在0.1~1.0 mg?kg^-1 MLT浓度范围内差异均有显著性（P<0.05）。 结论：照射前预先给予外源性MLT可减轻电离辐射所致小鼠胸腺细胞损伤，对小鼠免疫功能具有保护作用。

Protective effects of melatonin on damage of thymocytes in mice induced by ionizing radiation

Objective To explore the effects of melatonin (MLT) on the damage of mouse thymocytes in vivo induced by ionizing radiation and its mechanism. Methods The exogenous MLT was given to Kunming mice to establish the animal models of single and successive administration of MLT through intraperitoneal injection before whole-body irradiation with 1 Gy X-rays. For single administration of MLT, the apoptotic body percentage(ABP) and DNA lytic rate(DLR) in the thymocytes were determined with flow cytometry and fluorospectrophotometry, respectively, 12 h after irradiation. For successive administration of MLT, 3H-TdR incorporative rate (HTIR) was determined 24 h after irradiation. Results The number of thymocytes in single adminstration group was significantly lower than that in the sham-irradiation group 12 h after irradiation with 1 Gy X-rays (P<0.001), while ABP and DLR increased significantly (P<0.001). When single administration of exogenous MLT was given before irradiation, the number of thymocytes in the 0.5 mg·kg -1 MLT group was significantly higher, while the ABP and DLR were significantly lower than those in 0 mg·kg -1 MLT group (simple irradiation, P<0.01 or P<0.001). The number of thymocytes and HTIR in adminsitration groups 24 h after irradiation were significantly lower than those in the sham-irradiation group (P<0.001). When successive administration of MLT was given for 1 week before irradiation, the numbers of thymocytes in adminsitration groups with 0.01~0.1 mg·kg -1 MLT were significantly higher than that in 0 mg·kg -1 MLT group (P<0.05), and the HTIR in 0.1~1.0 mg·kg -1 MLT group was also significantly higher (P<0.05). Conclusion The administration of exogenous MLT before irradiation can decrease the damage of mouse thymocytes induced by ionizing radiation, and has the protective effect on immune functions in mice.