Ⅱ　化学物质与电离辐射之间的交叉适应性反应

Ⅱ.Cross-resistance to ionizing radiation and to chemical mutagens.

本文作者利用小鼠生殖细胞对低剂量辐射（５０ｍＧｙ）Ｘ射线和低浓度化学物质（ＭＭＣ，Ｈ＿２Ｏ＿２，ＣＰ）之间的交叉耐受性作了研究。首次证明在整体条件下的生殖细胞中，无明显毒性剂量的ＭＭＣ（０．１和０．５ｍｇ／ｋｇ）和Ｈ＿２Ｏ＿２（０．０２和０．０５ｍｏｌ／Ｌ）均可诱导抗１．５ＧｙＸ射线诱发的生殖细胞染色体损伤；并且５０ｍＧｙ射线也可诱导抗大剂量ＭＭＣ（３．０和５．０ｍｇ／ｋｇ）和Ｈ２Ｏ２（０．５和１．０ｍｏｌ／Ｌ）诱发的生殖细胞染色体损伤。与此相反，低浓度的烷化剂环磷酰胺（０．５和１．０ｍｇ／ｋｇ）不能诱导抗电离辐射诱发生殖细胞染色体损伤的适应性反应；低剂量辐射也不能诱导抗大剂量环磷酰胺（２５和４０ｍｇ／ｋｇ）的适应性反应，这些结果说明：辐射与ＤＮＡ交联剂和ＤＮＡ氧化性损伤因子之间存在着广泛低剂量诱导相互耐受性的适应性反应，而与产生ＤＮＡ烷基化损伤的烷化剂之间不存在着交叉抗性。

In this study, the cross-adaptive response to radiation and to chemical mutagens (mitomycin C, H2O2 ,cyclophosphamide)was observed in vivo in mouse germ cells. The results showed that low concentration of mitomycin C (0.1, 0.5mg/kg) and H2O2, (0.02, 0.05 mol/L) could reduce the frequency of chromosome aberration in mouse germ cells in vivo caused by subsequent irradiation (1.5 Gy X-rays);and 50 mGy X-rays also made the cells have a resistance to chromosome damage by high concentration mitomycin C (3.0, 5.0 mg/kg) and H2O2 (0.5 and 1.5 mol/L) .Contrary to those mentioned above, low concentration of cyclophosphamide (0.5, 1.0 mg/kg)made the germ cells more susceptible to induction of chromosome aberration by ionizing radiation, and at the same time,low dose radiation also made the cells more susceptible to the chromosome damage by high concentration cyclophosphamide (25, 40 mg/kg) .These results indicate that there is a cross-resistance to ionizing radiation and to DNA cross-linking agents (mitomycin C) and DNA oxidizing agents (H2O2) , but there is no cross-resistance to radiation and to alkylating agents (cyclophosphamide ).All these results provide some important materials for elucidating the mechanism of the adaptive response induced by ionizing radiation.