Induction of outer and inner ring monodeiodinases in human thyroid gland by thyrotropin

The effects of TSH on iodothyronine 5- and 5'-deiodinations were investigated using cultured thyroid tissues from patients with Graves' disease. The addition of TSH to the culture medium stimulated all of the iodothyronine-deiodinating activities of thyroid tissues cultured for more than 4 days. Peak TSH-induced activities were found on the fifth day of culture, and increased activities were found up to 9 days. On the fifth day of culture, TSH enhanced both outer and inner ring monodeiodinations in a dose-responsive manner between 62.5 and 250 microU/ml. This stimulation by TSH was blocked by the addition of actinomycin D or propylthiouracil. Incubation of thyroid tissues with (Bu)2cAMP mimicked the action of TSH, and theophylline potentiated the action of TSH. These results suggest that TSH, in an action probably mediated by cAMP, induces synthesis of iodothyronine deiodinases in the thyroid gland.