NCIt definition : A therapeutic formulation of the primary physiologically active form of endogenous
thyroid hormone. In vivo, triiodothyronine enters the nucleus and binds to nuclear
thyroid hormone receptors that subsequently bind to thyroid response elements (TREs)
located in target genes. Receptor binding by triiodothyronine in combination with
recruited coactivators results in maximal transcriptional activation after binding
to TREs; in general, binding of thyroid hormone receptor alone to TREs leads to repression
of gene transcription (NCI04);