Shadley J D, Wiencke J K
Department of Radiation Oncology, University of Chicago Medical Center, IL 60637.
Int J Radiat Biol. 1989 Jul;56(1):107-18. doi: 10.1080/09553008914551231.
Human lymphocytes pretreated with low (0.01 Gy) but not high (0.5 Gy) doses of X-rays become somewhat refractory to the induction of chromatid deletions by subsequent exposure to high (1.5 Gy) doses of X-rays (i.e. the yield of chromatid deletions is less than the sum of the yields induced by the pre-exposure and the subsequent challenge doses). This adaptive response can also be induced by pretreating the cells with very low, or even high, concentrations of tritiated thymidine. Because high concentrations of tritiated thymidine result in high doses of radiation that are delivered at very low dose-rates (i.e. less than 0.01 Gy/min), the lack of adaptation following high pre-treatment doses of X-rays could be attributed to their higher dose-rates. To test the effect of X-ray intensity on the induction of the adaptive response, lymphocytes were irradiated with 0.5 Gy of X-rays at 0.005-0.5 Gy/min at 28-30 h of culture, and then irradiated with 1.5 Gy at 48 h. Chromatid deletions were measured 6 h later. The results show that 0.5 Gy of X-rays given at low dose-rates (0.005 or 0.01 Gy/min), but not at high dose-rates (0.1, 0.2, or 0.5 Gy/min), are capable of inducing the adaptive response. Furthermore, experiments in which a male subject's cells exposed to 0.5 Gy given at 0.005 Gy/min were cocultivated with a female subject's cells irradiated with 0.5 Gy at 0.5 Gy/min showed that cells exposed to radiation at low and high intensity progress to metaphase equally and, therefore, that the lack of an adaptive response at high dose-rates cannot be attributed to selection of radioresistant cells. Although the induction of the adaptive response at higher X-ray doses occurs at low radiation intensity, there seems to be a minimum dose required for this effect; e.g., 0.01-Gy pretreatments induced the adaptive response when given at 0.2 Gy/min, but not at 0.005 Gy/min. Thus, the adaptive response is dependent both on the total dose of the pretreatment and on the rate at which the dose is given.
用低剂量（0.01戈瑞）而非高剂量（0.5戈瑞）的X射线预处理人类淋巴细胞后，这些细胞对随后暴露于高剂量（1.5戈瑞）X射线诱导的染色单体缺失变得有些耐受（即染色单体缺失的产额低于预照射和随后激发剂量诱导的产额之和）。用极低甚至高浓度的氚化胸腺嘧啶预处理细胞也能诱导这种适应性反应。由于高浓度的氚化胸腺嘧啶会导致以非常低的剂量率（即小于0.01戈瑞/分钟）传递高剂量的辐射，高预处理剂量X射线后缺乏适应性反应可能归因于其较高的剂量率。为了测试X射线强度对适应性反应诱导的影响，在培养28 - 30小时时，以0.005 - 0.5戈瑞/分钟的剂量率用0.5戈瑞的X射线照射淋巴细胞，然后在48小时时用1.5戈瑞照射。6小时后测量染色单体缺失情况。结果表明，以低剂量率（0.005或0.01戈瑞/分钟）给予的0.5戈瑞X射线能够诱导适应性反应，而高剂量率（0.1、0.2或0.5戈瑞/分钟）则不能。此外，将以0.005戈瑞/分钟给予0.5戈瑞照射的男性受试者细胞与以0.5戈瑞/分钟给予0.5戈瑞照射的女性受试者细胞共培养的实验表明，暴露于低强度和高强度辐射的细胞进入中期的进程相同，因此，高剂量率下缺乏适应性反应不能归因于抗辐射细胞的选择。尽管在较高X射线剂量下适应性反应的诱导发生在低辐射强度时，但似乎存在产生这种效应所需的最小剂量；例如，0.01戈瑞的预处理在以0.2戈瑞/分钟给予时可诱导适应性反应，但在以0.005戈瑞/分钟给予时则不能。因此，适应性反应既取决于预处理的总剂量，也取决于给予剂量的速率。
