Abstract: BACKGROUND ＆ AIM: To make further understanding in the action of Cd to inhibit the repair of DNA lesions in human cells. MATERIAL AND METHODS: The simplified method of unscheduled DNA synthesis(UDS)test with human whole blood cells(lymphocytes and monocytes were the main cell types involved in the test)was adopted to investigate the effect of CdCl2 on the repair processes of DNA damage induced by N-methyl-N'-nitro-N-nitrosoguanidine(MNNG)and ultraviolet(UV).RESULTS: Treatment of human blood cells with Cd caused a dose-dependent increase in the amounts of 3H-TdR incorporated in DNA through UDS,but the cpm value was significantly elevated only at 10 μmol/L Cd dose as compared with the negative control, which indicated apparent DNA damage induced by Cd .MNNG- induced UDS was weakened to some extent by Cd dose from 0.1 to 10 μmol/L,the remarkable inhibition was observed at Cd concentration of 1 μmol/L, while treatment with Cd of this concentration alone did not induce positive UDS.In contrast to MNNG,UV-induced UDS was strongly enhanced by 1 μmol/L CdCl2.The analysis of variance showed an evident synergistic interaction between this dose of Cd and UV.CONCLUSION: Cd itself can induce DNA damage at relatively high dose, while the lower Cd dose may interfere with DNA repair process and these direct and indirect genotoxic mechanisms may be involved in the carcinogenicity of Cd compounds.

Key words: cadmium chloride, unscheduled DNA synthesis(UDS)