Effect of Injection of Thyrotropin Upon Deiodination of Diiodotyrosine by Rat Thyroid and Liver1

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Abstract
Intravenous administration of thyrotropin in rats resulted in prompt enhancement of the deiodinating activity of thyroid tissue, as judged by the formation of labeled iodide in gland homogenates incubated with labeled diiodotyrosine. Deiodinating activity of thyroid tissue was significantly greater than in the controls within 3 hr after TSH injection, and the increased activity persisted for at least 24 hr. The deiodinating activity of liver slices and homogenates was not modified by the administration of TSH. Deiodinating activity of thyroid homogenates was greatly enhanced by addition of TPNH to the incubation medium; in such fortified homogenates, the deiodinating activity of thyroid tissue of TSH-treated rats was not appreciably different from that of the controls. The results suggest that TSH-induced stimulation of thyroidal deiodinating activity may be related to an increased glandular concentration of TPNH.