Thyroid hormones thyroxine

The amino acid tyrosine is the starting point in the synthesis of the catecholamines and of the thyroid hormones tetraiodothyronine (thyroxine T4) and triiodothyronine (T3) (Figure 42-2). T3 and T4 are unique in that they require the addition of iodine (as T) for bioactivity. Because dietary iodine is very scarce in many parts of the world, an intricate mechanism for accumulating and retaining T has evolved. 

C03-0144. The thyroid gland produces hormones that help regulate body temperature, metabolic rate, reproduction, the synthesis of red blod cells, and more. Iodine must be present in the diet for these thyroid hormones to be produced. Iodine deficiency leads to sluggishness and weight gain, and can cause severe problems in the development of a fetus. One thyroid hormone is thyroxine, whose chemical formula is... 

Like steroid hormones, thyroid hormones interact with receptors to alter genomic activity and affect the synthesis of specific proteins during development [25-28], As with testosterone and progesterone, metabolic transformation of thyroxine (T4) is critical to its action [25-28]. Moreover, as with steroid hormones, thyroid hormones alter brain functions in adult life in ways that both resemble and differ from their action during development [25-28]. 

Three hormones are secreted by the thyroid thyroxine (T4) and tri-iodothyronine (T3) are usually referred to as the thyroid hormones and calcitonin, a peptide, which under certain circumstances, affects calcium mobilization and is secreted from specialized so-called C cells. Only T3 and T4 will be discussed further at this point. 

Thyroid extract/thyroxine Hormone Thyroid gland... 

Thyroid-stimulating hormone (TSH) Thyrotropin-releasing hormone (TRH)(+) Thyroid Thyroxine, triiodothyronine... 

Thyroid Hormones The thyroid hormones T4 (thyroxine) and T3 (triiodothyronine) are synthesized from the precursor protein thyroglobulin (Mr 660,000). Up to 20 Tyr residues in thyroglobulin are enzymatically iodinated... 

Henry EC, Gasiewicz TA. 1987. Changes in thyroid hormones and thyroxine glucuronidation in hamsters compared with rats following treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicol Appl Pharmacol 89 165-174. 

SUCRALFATE THYROID HORMONES i thyroxine levels 1 absorption Give thyroxine 2-3 hours before sucralfate... 

The concentration of free rather than bound thyroxine is considered to be the most accurate assessment of thyroid activity as this is the fraction which can penetrate cell membranes and exert a metabolic effect. Free thyroxine exists in equilibrium with thyroxine bound to globulin, albumin, and prealbumin. Any changes in the concentration of thyroid binding proteins leading to an increase in free hormone. Thyroid binding prealbumin is reduced after all kinds of stress and the reduction is significant within 24 hours. 

Lithium affects thyroid function (52-56), and in most patients, after 4 months of treatment, there is a transient fall in serum levels of thyroxine (T4) and a rise in thyrotropic hormone (thyroid-stimulating hormone, TSH). After 1 year of treatment, these hormones have generally returned to their baseline. The mechanisms for this are obscure, but lithium inhibits both thyroxine synthesis and its release from the gland (201). Lithium may inhibit endocytosis in the thyroid gland, which results in an accumulation of colloid and thyroglobulin within the follicles, thereby reducing hormone release (202). Thyroid volume... 

Thyroglobulin. a glycoprotein, is composed of several peptide chains it also contains 0.5 to 1% iodine and 8 (o 10% carbohydrate in (he form of two types of poly.saccharide. The formation of thyroglobulin is regulated by TSH. Thyroglobulin has no hormonal properties. I( must be hydrolyzed to release the hormonal iodothyronines thyroxine and liothy-lonine (see Thyroid Hormones" in Chapter 19). 

Iodine is a powerful oxidizing agent and has a direct action on cells by precipitating proteins. The affected cells may be destroyed. In addition to the primary irritant action of iodine, this compound can act as a potent sensitizer. Iodine is an integral part of thyroid hormones (tetraiodothyronine (thyroxine) and triiodothyronine), and deficiency results in compensatory hyperplasia and hypertrophy of the thyroid gland (endemic goiter). Endemic goiter occurs naturally where soil is deficient in iodine. 

The major circulating forms of thyroid hormone are thyroxine (T ), containing four iodine atoms per molecule, and triiodothyronine (Tj), with three iodine atoms per molecule. 

---