Abstract:
[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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