Stimulation of Na,K-ATPase by hypothyroidism in the thyroid gland

Although studies have documented the regulatory effects of thyroid hormones on the Na,K-ATPase in peripheral tissues, there is little information on the regulation of this transporter in the thyroid gland itself. Accordingly, we investigated the effects of thyroid status on Na,K-ATPase specific activity and the abundance of its constituent subunits in rat thyroid. Exogenous tri-iodothyronine (T-3) was administered daily to produce hyperthyroidism. 6n-proyyl-2-thiouracil (PTU), an inhibitor of thyroid hormone synthesis, was used to induce hypothyroidism. There was a four-fold increase in Na,K-ATPase specific activity in the follicular membranes from PTU-treated animals after 7 days. Enzymatic activities were not changed in the T-3-treated glands. Immunoblotting of membranes front T-3-treated rats revealed a 75% reduction in alpha(1) subunit abundance and a slight, but nonsignificant reduction in beta(1) abundance. On the other hand, the membranes from PTU-treated rats displayed 136 and 567% increases in the abundance of the alpha(1) and beta(1) subunits respectively. These data demonstrate that thyroid hormone status regulates Na,K-ATPase in the gland, but the effects are in direct contrast to those seen in the periphery.