The effect of manganese supply on thyroid hormone metabolism in the offspring of manganese-depleted dams.

The present study was performed to investigate the effect of manganese (Mn) supply on metabolism of thyroid hormones in the rat. A study with rats was carried out over two generations. Female rats were raised with a Mn-deficient diet (0.1 mg Mn/kg), and mated to produce a second generation. The male rats of the second generation were used as subjects for the investigation. They were divided into five groups and fed diets with Mn concentrations of 0.1, 0.5, 2.2, 10, and 46 mg/kg for 40 d. For assessment of thyroid hormone metabolism, concentrations of thyroid hormones in serum and activity of hepatic type I 5'deiodinase (5'D-1) were measured. Feeding diets with 0.1 mg Mn/kg impaired growth and food conversion, influenced parameters of thyroid hormone metabolism, and changed some clinical-chemical parameters, such as concentrations of total protein, albumin, calcium (Ca) and magnesium (Mg) as well as activity of alkaline phosphatase in serum. Regarding the thyroid hormone metabolism, rats fed the diet with a Mn level of 0.1 mg/kg had a higher 5'D-I activity in liver, and consequently a higher concentration of triiodothyronine in serum than the rats fed the other diets. In contrast, the concentrations of total and free thyroxine were not influenced by the Mn intake. Growth, clinical-chemical parameters, concentrations of thyroid hormones in serum, and activity of hepatic 5'D-I were similar in the rats fed diets with Mn concentrations between 0.5 and 64 mg/kg. The present study shows that feeding a diet with a very low Mn concentration affects growth and thyroid hormone metabolism and that a dietary level of 0.5 mg Mn/kg is adequate for growth and thyroid hormone metabolism in the offspring of Mn-depleted dams.