Hormonal control of manganese transport in the mouse thyroid

The present study deals with a possible mechanism controlling the transport of manganese (Mn), an essential trace element, from the circulation to the thyroid. Mice were pretreated with propylthiouracil (PTU) or triiodothyronine (T₃), and a measurement of the thyroid:serum concentration ratio (T/S) of radioactive manganese (⁵⁴Mn) was carried out. The T/S of⁵⁴Mn was greatly enhanced by PTU, but reduced by T₃. Several methods were used to demonstrate that the T/S of⁵⁴Mn depends upon the level of thyroid-stimulating hormone (TSH) in the serum. First, bovine TSH was injected into mice; an increase in the T/S resulted. Secondly, serum thyroxine and T₃ levels measured by radioimmunoassay (RIA) suggested that PTU produced an increase in serum TSH and T₃ a decrease. However, direct measurement of mouse TSH by RIA for rat TSH failed to produce proof of any changes in TSH level, owing to poor cross-reactivity. Taking all the information into account, it is concluded that Mn-transport into the thyroid is controlled by the thyroid state.