Effect of chronic administration of cadmium on the rat thyroid: radioimmunological and immunohistochemical studies

The effect of chronic (12 months) oral cadmium (Cd) administration (5 or 50 mg Cd/dm3) to rats on the structure and function of the thyroid was evaluated. Paraffin thyroid and parathyroid sections were stained with H+E and immunocytochemically for calcitonin (CT), somatostatin (ST), synaptophysin (SPh), chromogranin A (CgA) and thyroid transcription factor-1 (TTF-1). Serum levels of thyroid hormones: triiodothyronine (T3) and tetraiodothyronine (T4) as well as levels of Cd in the blood and calcium (Ca) in the serum were estimated. CT, ST and SPh were detected in C cells of the thyroid, while CgA in both thyroid and parathyroid cells. In animals exposed to Cd, proliferation of CT- and SPh-positive thyroid C cells was observed, ST being found only in very few C cells--both in control animals and in those exposed to Cd. Serum T3 concentration was not affected by Cd, while T4 was reduced but only at the exposure to the higher Cd concentration. Moreover, the rats exposed to Cd showed a decrease in serum Ca concentration.