Objective To observe the ratios of Zn/Cd, Cu/Cd in liver metallothionein induced by zinc or copper, under exposure to Cd in rats.
Methods Wistar male rats were divided into 7 groups, 4 animals for each group. Group 0 was left nontreated as blank control. Group A1 and A2 were subcutaneously injected with normal saline, Group B1 and B2 were injected with ZnCl2 in the dose of 25mg Zn/kg Body Mass and Group C1 and C2 with CuSO4 in the dose of 12.5 mg Cu/kg Body Mass. Twenty four hours after Zn or Cu pre-treatment, Group A1, B1 and C1 and Group A2, B2 and C2 were administered cadmium-metallothionein (CdMT) in the dose of 0.1 or 0.4mg Cd/kg Body Mass, respectively. After 24 hours of CdMT injection, liver was taken and homogenized. Cytosol gained after centrifugation(105 000 g)was applied to gel chromatography on Sephadex G-75.
Results Among animals in Group 0, Zn was the dominant metallic element bound to MT in liver, but neither Cd nor Cu could be detected. In the non-pretreated group, there was a dose related increase of MT and Cd concentration, with 20.0 and 10.0 of Zn/Cd ratio for A1 and A2, respectively. The ratios of Zn/Cd in MT were 20.8 in Group B1 and 20.3 in Group B2, and Cu was below the detection limit for both. The ratios of Cu/Cd were 80.0 in Group C1 and 36.5 in Group C2, and however, the level of Zn decreased considerably.
Conclusion The results showed in this in viro experiment that Zn bound to MT was more easily replaced by Cu than Cd bound to MT. The non-MT-bound Zn in liver tissues may be one of the explanations for the difference.
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