A Thyroid hormones

Thyroxine (3, 5, 3,5-L-teraiodothyronine, T4) is a thyroid hormone, which is transformed in peripheral tissues by the enzyme 5 -monodeiodinase to triiodothyronine. T4 is 3-8 times less active than triiodothyronine. T4 circulates in plasma bound to plasma proteins (T4-binding globulin, T4-binding prealbumin and albumin). It is effective in its free non-protein-bound form, which accounts for less than 1%. Its half-life is about 190 h. 

Triiodothyronine (3, 5,3-L-triiodothyronine, T3) is a thyroid hormone. It is producedby outer ring deiodination of thyroxine (T4) in peripheral tissues. The biologic activity of T3 is 3-8 times higher than that of T4. T3 is 99.7% protein-bound and is effective in its free non-protein-bound form. The half-life of triiodothyronine is about 19 h. The daily tur nover of T3 is 75%. Triiodothyronine acts via nuclear receptor binding with subsequent induction of protein synthesis. Effects of thyroid hormones are apparent in almost all organ systems. They include effects on the basal metabolic rate and the metabolisms of proteins, lipids and carbohydrates. 

Once a euthyroid state is achieved, tlie primary health care provider may add a thyroid hormone to tlie therapeutic regimen to prevent or treat hypothyroidism, which may develop slowly during long-term antithyroid drug therapy or after administration of 131I. 

Thyroglobulin A thyroid hormone-containing protein, usually stored in the colloid within the thyroid follicles. 

Thyroxine one of the iodine-containing amino acids that act as a thyroid hormone. 

A number of medical conditions are associated with high rates of depression (see Table 3.4). In some instances, the distinction between MDD and depression due to a general medical condition is largely academic with little bearing on treatment selection. For example, pancreatic cancer may induce depression directly through the release of tumor-secreted substances however, depression in the pancreatic cancer patient is treated with conventional antidepressant medications. In other cases, the diagnostic distinction bears important treatment implications. One commonly cited example is depression occurring in association with hypothyroidism. Patients with depression and hypothyroidism do not respond to antidepressant treatment alone but require a thyroid hormone supplement. 

Z)-2,3-Methanothyronine 59 and its dibromo derivative 60 have comparable activity with the thyroxine 61, a thyroid hormone [66], which exhibited thyro-mimetic activities in basal metabolism and antigoiter tests (comparison of oxygen consumption and heart rate in normal and thyroidectomized rats) but did not have an inhibitory action on the metabolism developed by triiodothyronine [66]. (Z)-2,3-Methanohistidine 62, tested on rat liver, is an effective inhibitor of histidine decarboxylase, Eq. (23) [67]. 

In patients with longstanding hypothyroidism and those with ischemic heart disease, rapid correction of hypothyroidism may precipitate angina, cardiac arrhythmias, or other adverse effects. For these patients, replacement therapy should be started at low initial doses, followed by slow titration to full replacement as tolerated over several months. If hypothyroidism and some degree of adrenal insufficiency coexist, an appropriate adjustment of the corticosteroid replacement must be initiated prior to thyroid hormone replacement therapy. This prevents acute adrenocortical insufficiency that could otherwise arise from a thyroid hormone-induced increase in the metabolic clearance rate of adrenocortical hormones. 

Mechanism of Action A synthetic form of triiodothyronine (T3), a thyroid hormone involved in normal metabolism, growth, and development. Possesses catabolic and anabolic effects. Therapeutic Effect Increases basal metabolic rate, enhances gluco-neogenesis, and stimulates protein synthesis. 

The major location of calcium in the body is in the skeleton, which contains more than 90% of the body calcium as phosphate and carbonate. Bone resorption and formation keeps this calcium in dynamic equilibrium with ionized and complexed calcium in blood, cellular fluids and membranes. Homeostasis is mainly regulated by the parathyroid hormone and vitamin D which lead to increased blood calcium levels, and by a thyroid hormone, calcitonin, which controls the plasma calcium concentration J5 Increasing the concentration of calcitonin decreases the blood calcium level, hence injections of calcitonin are used to treat severe hyperalcaemia arising from hyperparathyroidism, vitamin D intoxication or the injection of too high a level of parathyroid extract. High levels of calcitonin also decrease resorption of calcium from bone. Hypocalcaemia stimulates parathyroid activity, leading to increased release of calcium from bone, reduction in urinary excretion of calcium and increased absorption of calcium from the intestine. Urinary excretion of phosphate is enhanced. 

Hyperglycemia Vitamin A Thyroid hormone AH-trans retinoic acid Forskolin Isoproterenol... 

In fact, when the primary structure of the first steroid receptor, the human glucocorticoid receptor [79] was deduced from the nucleotide sequence the homology of this central region with the product of the v-erb-A oncogene of the avian erythroblastosis virus immediately became conspicuous [80]. This similarity subsequently led to the identification of c-erb-A, the cellular counterpart of v-erb-A, as the gene for a thyroid hormone receptor [92,93]. The kinship amongst these sequences has also greatly helped to identify cDNA clones for other steroid hormone receptors. 

Correct answer = A. Triiodothyronine is a thyroid hormone that is overproduced in hyperthyroidism. 

Class II receptors are heterodimers. To this group belong receptors for non-steroidal compounds, such as the retinoids. The heterodimers are composed, for example, of a 9-m-retinoic-acid-bound monomer combined with an all-traw5-retinoic-acid-bound monomer or with a thyroid-hormone-bound monomer. These hetero-dimeric receptors bind to hexameric DNA repeats. 

Taylor AH, et al. Beneflcial effects of a novel thyromimetic on lipoprotein metabolism. Mol. Pharmacol. 1997 52 542-547. Ocasio CA, Scanlan TS. Design and characterization of a thyroid hormone receptor alpha (TRalpha)-speciflc agonist. ACS Chem. Biol. 2006 1 585-593. 

Slc21al) estrone-S, ochratoxin A, thyroid hormones, bile acids Drugs BQ123, dexamethasone, cardiac glycosides, enalapril. fexofenadine, pravastatin Drugs atorvastatin, furosemide, lovastatin, simvastatin... 

A. Thyroid hormone feeds back on the anterior pituitary and inhibits the release of TSH. This patient s TSH levels are elevated, so her thyroid hormone levels are too low, and her dose should be increased. 

Thyrer thyrotrophin-releasing hormone, thyreotrophic hormone thyrotrophin. thyrocalcitonin calcitonin. a thyrocalcitonin calcitonin (pork), thyroglobulin [inn, usan] is obtained from thyroid glands of Sus scrota (hog), and contains >0.7% total iodine. It acts as a THYROID HORMONE, and was formerly used in the treatment of hypothyroidism. 

Yuan CX, Ito M, Fondell JD, Fu ZY, Roeder RG. 1998. The TRAP220 component of a thyroid hormone receptor-associated protein (TRAP) coactivator complex interacts directly with nuclear receptors in a ligand dependent fashion. Proc. Natl. Acad Sci. USA 95 7939 14... 

Sap J, Munoz A, Schmitt J, Stunnenberg H, Vennstrom B. 1989. Repression of transcription mediated at a thyroid hormone response element by the v-erb-A oncogene product. Nature 340 242 14... 

Non cardiac effects with important consequences on the course of the ischemic heart disease are elicited in a thyroid hormone receptor iso form manner. In fact, TRal blockade by dronedarone prevented body weight gain by reducing food intake, an ef-... 

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