3,5,3'-Triiodothyronine nuclear receptors and their role in the thyroid hormone action

Abstract

Thyroid hormones are involved in a complex arrangement of physiological and developmental responses in several tissues of higher vertebrates. Thyroxine, the main product of the thyroid gland, circulates in the blood stream being bouird either to specific plasma proteins (i.e. thyroxine binding globulin and transthyretin) or non-specifically to albumin. In the target tissue it is transported into the intracellular space by both the diffusion and energy dependent process (KRENNING et al. 198i). In the cytoplasmic space there is a "pool" of thyroid hormones containing the biologically active metabolite of thyroxine-3,5,3'-L-triiodothyronine (Tr) which originates from the monodeiodination of thyroxine. The T, enters the cell nucleus probably in the free form where it is specifically bound to nuclear receptors.