The effect of exposure to cadmium (Cd) on the function and structure of the thyroid with parathyroids and a relationship between Cd accumulation in these glands and their damage were studied on a male rat model corresponding to human exposure. For this purpose, male rats were treated with Cd in drinking water at concentration of 5 and 50 mg Cd/dm³ for 12 and 24 weeks. The function of the thyroid was evaluated based on the measurement of serum concentrations of triiodothyronine (T₃) and tetraiodothyronine (T₄), and immunohistochemical identification of hormones such as calcitonin (CT), calcitonin-gene related peptide (CGRP) and somatostatin (ST). To assess the parathyroid function immunohistochemical reaction for parathyroid hormone-related peptide (PTHrP) was performed. Histological structure of the thyroid and parathyroid glands was evaluated in a light microscope. Rats exposed to 5 and 50 mg Cd/dm³ showed changes in the epithelium of follicular cells, intensified remodeling of the glandular structure of the thyroid, mononuclear cell infiltrations in connective tissue and pale staining of colloid. Hypertrophy and hyperplasia of endocrine parathyroid cells were evident.The intensity of reactions for CT, ST, CGRP and PTHrP was weakened. Exposure to Cd had no effect on the T₃ and T₄ serum concentrations, except for a marked increase in the concentrations of both hormones after 24 weeks of exposure to 50 mg Cd/dm³ . All the Cd-induced changes were much more advanced at exposure to 50 mg Cd/dm³ than 5 mg Cd/dm³ . The seriously disturbed structure and function of the thyroid and parathyroids at a low Cd concentration (0.087 ± 0.005 µg/g) in these glands suggests that the damaging Cd influence may be due to its indirect rather than direct action. Based on the results it can be hypothesized that a human body chronically exposed to moderate and relatively high Cd levels may be at risk of damage to the thyroid and parathyroid glands.
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