Effect of dietary zinc deficiency on the accumulation of cadmium and metallothionein in selected tissues of the rat

The effect of continuous dietary zinc deficiency on the metabolism of the toxic heavy metal cadmium has not been widely studied. This investigation was designed to assess the effects of subadequate dietary zinc intake on the accumulation of dietary cadmium and on metallothionein (MT) and zinc concentrations in target organs of cadmium toxicity. Adult male Wistar rats (180-200 g) were allowed, ad libitum, diets either adequate (60 ppm) or deficient (7 ppm) in zinc for a total of 9 wk. The zinc-deficient diet resulted in an approximately 40% reduction in plasma zinc (assessed at 3, 6, and 9 wk) in the absence of overt signs of zinc deficiency (i.e., reduced weight gain, alopecia, etc.). Separate groups of rats were also maintained on zinc-defined diets for a total of 9 wk, but cadmium was added to the diet (0, 12.5, 25, 50, 100, and 200 ppm) at the end of wk 3 and maintained at that level throughout the remaining 6 wk of the study, when the rats were killed. The feeding of the zinc-deficient diet markedly enhanced the accumulation of cadmium in the liver, kidney, and testes. Hepatic, renal, and testicular zinc concentrations were not affected by suboptimal zinc intake alone. However, marked reductions in renal and testicular zinc concentrations were caused by zinc deficiency in concert with cadmium exposure. MT levels, when related to tissue cadmium concentrations, were elevated to a significantly lesser extent in the kidneys of zinc-deficient animals. These results indicate that marginal zinc deficiency markedly increases cadmium accumulation in various organs and reduces zinc content and MT induction in some organs.