CONTEXT The substitution of liothyronine (L-T3) for levothyroxine (L-T4) is commonly employed during thyroid hormone (TH) withdrawal in preparation for diagnostic and therapeutic interventions on thyroid cancer patients. Presently, only limited data are available on the L-T3 for L-T4 therapeutic substitution. Objective To characterize the pharmcodynamic equivalence of L-T3 and L-T4. DESIGN Ra...

The present study was undertaken to determine whether the capacity for 3,5,3',5'-tetraiodothyronine (T4) conversion into 3,5,3'-tri-iodothyronine (T3), as measured by the activity of thyroxine type II 5'-monodeiodinase (T4-5'D), was altered in the brains of young Zucker fa/fa rats during the period of intense maturation of the central nervous system (i.e. from 10 to 20 days of life). From 7 to ...

Thyroxine (T4) 5'-monodeiodinating activity in rat pituitary was studied, using paper chromatography. Rat anterior pituitary homogenates were incubated with 125I-T4, dithiothreitol and unlabeled L-T4 at 37 degrees C. The incubation mixture was extracted by ethanol and the extracts were subjected to descending paper chromatography. The conversion ratio of T4 to 3, 5, 3'L-triodothyronine (T3) was...

The T4 molecule may serve as a T-cell receptor recognizing molecules on the surface of specific target cells and also serves as the receptor for the human immunodeficiency virus. To define the mechanisms of interaction of T4 with the surface of antigen-presenting cells as well as with human immunodeficiency virus, we have further analyzed the sequence, structure, and expression of the human and...

Thyroid hormone [l-thyroxine (T4)] rapidly induced phosphorylation and nuclear translocation (activation) of mitogen-activated protein kinase (MAPK) in HeLa and CV-1 cells in the absence of cytokine or growth factor. A pertussis toxin-sensitive and guanosine 5'- O-(3-thiotriphosphate)-sensitive cell surface mechanism responsive to T4 and agarose-T4, suggesting a G protein-coupled receptor, was ...

T4 bacteriophage (phage)-infected cells show a marked increase in latent-period length, called lysis inhibition, upon adsorption of additional T4 phages (secondary adsorption). Lysis inhibition is a complex phenotype requiring the activity of at least six T4 genes. Two basic mysteries surround our understanding of the expression of lysis inhibition: (i) the mechanism of initiation (i.e., how se...

Transthyretin (TTR) is the major T4-binding protein in rodents. Using a TTR-null mouse model we asked the following questions. 1) Do other T4 binding moieties replace TTR in the cerebrospinal fluid (CSF)? 2) Are the low whole brain total T4 levels found in this mouse model associated with hypothyroidism, e.g. increased 5'-deiodinase type 2 (D2) activity and RC3-neurogranin messenger RNA levels?...

BACKGROUND Data suggest symptoms of hypothyroidism persist in 5-10% of levothyroxine (L-T4)-treated hypothyroid patients with normal serum thyrotrophin (TSH). The use of L-T4 + liothyronine (L-T3) combination therapy in such patients is controversial. The ETA nominated a task force to review the topic and formulate guidelines in this area. METHODS Task force members developed a list of releva...

TSH secretion is decreased by both T4 and T3. This negative feedback control ofTSH secretion has been correlated with an increase in pituitary nuclear T3 content, and it is not clear whether T4 exerts its effect directly on the thyrotroph or after its deiodination to T3. However, levels of the pituitary enzyme catalyzing T4 to T3 conversion, 51)-II, are decreased in the presence of an increased...

Thyroid hormones are extremely important for development of the fetal central nervous system. Thyroidectomy results in severe hypothyroidism. In this study two levels of maternal hypothyroidism were reached by administration of different amounts of thyroxine (T4) and 3,5,3'-tri-iodothyronine (T3) to thyroidectomized pregnant rats. We examined the production, distribution and transport of T4 and...