Effects of manganese ions on thyroid function in rat.

Rats were treated with MnSO4, H2O (1 mg/100 g/day, SC) for a period of 5 weeks. Thyroxine (T4) and triiodothyronine (T3) levels were measured in thyroid by radioimmunoassay. T4, T3 and thyroid-stimulating hormone (TSH) levels were also estimated by radioimmunoassay in serum. Manganese treatment produced no change in thyroid T4 and T3 levels but induced a significant decrease in serum T4, T3 and TSH levels. This decrease can be interpreted as the result of a pituitary alteration which appears to be related to the high accumulation of manganese in the pituitary gland.