Background: Cadmium is one of the toxic metals, which can enter the body through several routes due to its numerous applications and lead to some disorders. This study aimed to investigate the protective effect of zinc on cadmium-induced damages in the serum parameters related to the thyroid and parathyroid glands.

Materials and Methods: In this study, 40 male rats weighting 201±30g were divided into the four separated groups (consisting of 5 rats): the cadmium treatment, zinc treatment, combination of zinc and cadmium and control groups. The normal saline containing 1 mg cadmium was injected intrapritoneally to the rats as the first treatment. The second group was treated with 0.5 mg zinc, the third one received the combined doses of cadmium (1mg) and zinc (0.5mg) and the control group received only the normal saline injection. At the end of the experiment (30 and 60 d), all rats were decapitated and sera collected to measure the serum parameters related to the thyroid and parathyroid glands.

Results: The obtained results showed that cadmium significantly (P<0.05) decreased the concentration of serum calcium, T3, T4 and calcitonin, but increased the Pi concentration and the activity of Paratormone and alkaline phosphatase. Zinc treatment in animals either maintained all the aforementioned serum parameters at their normal levels or at least showed a preventive-like role.

Conclusion: Although a long-term injection of cadmium provides hypothyroidism as well as hyperparathyroidism, zinc can be able to reduce the toxic effects of cadmium.