Bernabei P A, Balzi M, Saccardi R, Becciolini A, Ferrini P R
U.O. di Ematologia dell'Università, USL 10/D, Firenze, Italy.
Haematologica. 1992 Jan-Feb;77(1):21-4.
It has been shown that the light-darkness cycle affects the proliferative activity of the hemopoietic system, possibly acting on the distribution of the cells in the cell-cycle phases at different hours of the day. This could determine time-dependent modifications in ionizing radiation damage to hemopoietic progenitors.
In this study the influence of the irradiation time on the radiosensitivity of rat CFU-GM was assessed by in vitro clonogenic assay. Rats were exposed to 3 Gy gamma rays at four time points (00:00, 06:00, 12:00, 18:00 hours). Bone marrow CFU-GM cultures were performed at various intervals ranging between 12 hours and 45 days after irradiation and compared with unirradiated controls.
A marked decrease of femoral CFU-GM was observed in the five days following total body irradiation, regardless of the irradiation time point. From this interval on all the irradiated groups showed an increasing proliferation of CFU, which was particularly evident in the group irradiated during the day light period. At the latest intervals (45 days) the post-acute damage to hematopoietic progenitors lacked any evidence of time dependence.
With the experimental model used, time scheduling does not seem to affect markedly either the acute depletion of CFU-GM in the 5 days following total body irradiation or the late consequence to the CFU-GM compartment.
已有研究表明，昼夜循环会影响造血系统的增殖活性，可能是通过作用于一天中不同时间点细胞周期各阶段的细胞分布来实现的。这可能会导致造血祖细胞电离辐射损伤的时间依赖性改变。
在本研究中，通过体外克隆形成试验评估照射时间对大鼠粒系巨噬系集落形成单位（CFU-GM）放射敏感性的影响。大鼠在四个时间点（00:00、06:00、12:00、18:00）接受3 Gy的γ射线照射。照射后12小时至45天的不同时间间隔进行骨髓CFU-GM培养，并与未照射的对照组进行比较。
全身照射后的五天内，无论照射时间点如何，均观察到股骨CFU-GM显著减少。从这个时间间隔开始，所有照射组的CFU增殖均增加，在白天照射组中尤为明显。在最晚的时间间隔（45天），造血祖细胞的急性后损伤没有任何时间依赖性的证据。
在所使用的实验模型中，时间安排似乎对全身照射后5天内CFU-GM的急性消耗或CFU-GM区室的后期后果均无明显影响。
