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Thyroxine biologic effect

In plasma, over 99.95% of T4 is transported bound to proteins. Thyroxine binding globulin (TBG) carries 70% of Tj, albumin approximately 25% and transthyretin (formerly called prealbumin) around 5%. Over 99.5% of T, is transported by the same proteins. It is the unbound, or free . Tj and Tj concentrations which arc important for the biological effects of the hormones, including the feedback to the pituitary and hypothalamus. Changes in binding protein concentration complicate the interpretation of thyroid homione results, e.g. in pregnancy. [Pg.144]

Many factors are suspected to lead to an increased rate of conversion of carotene to vitamin A. For example, aureomycin increases the biological effectiveness of vitamin A, not by stimulating the absorption of the vitamin through the intestinal epithelium, but by altering the bacterial flora in such a way that the conversion of carotenes to vitamin A is favored. The administration of thyroxine increases the conversion of carotenes into vitamin A in chickens. Numerous other experiments suggest that various dietary and hormonal factors can facilitate the conversion of carotenes into vitamin A in the intestine. However, many of these experiments do not exclude other mechanisms that... [Pg.306]

Biologic Effect of the Thyroid Hormone. The thyroid gland regulates the entire metabolism of the adult organism. Disturbances of the thyroid function are reflected in the basal metabolic rate (metabolism while resting, cf. Chapt. XXII-1). In hyperthyroidism (thyrotoxicosis) the rate is elevated during hypofunction (clinical manifestation myxedema), it is lowered. This phenomenon is used frequently in judging thyroid function. Administration of thyroxine raises the basal... [Pg.342]

Its biologic effect consists in the control of the thyroid gland. Thyrotropin stimulates the elaboration of thyroxine, while the iodine content of the gland drops drastically. Circulating thyroxine has a feedback effect on the hypophysis, inhibiting the further elaboration of the stimulating hormone (compare with corticotropin, below). [Pg.348]

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. [Pg.1243]

Prealbumin is the transport protein for thyroxine and a carrier for retinol-binding protein. The body s content of prealbumin is low (10 mg/kg of body weight), and it has a very short biologic half-fife (I to 2 days). Prealbiunin may be reduced in as few as 3 days after calorie and protein intake is significantly decreased, or when hypercatabolism or severe metabolic stress (tramna or bmns) is present. Because of its short half-life, it is most useful in monitoring the shortterm, acute effects of nutrition support. As with ALB and TFN, sermn prealbumin concentrations are depressed in those with liver disease due to decreased hepatic synthesis. Increased serum prealbumin concentrations have been noted in patients with renal disease due to impaired renal excretion. [Pg.2564]

Reimers, T. J., J. P. McCann, R. G. Cowan, and P. W. Concannon. 1983. Effect of storage, hemolysis, and freezing and thawing on concentrations of thyroxine, cortisol and insulin in hlood samples. Proceedings of the Society for Experimental Biology and Medicine 170 509-516. [Pg.213]

A comparison of the affinity of the thyroxine-binding globulin for thyroxine and that of the biologically most effective of the triiodothyronines suggests that the specificity of the binding protein is directed toward the biologically active compound [24]. [Pg.445]

Investigators have for years tried to pinpoint the step in biological oxidations that is affected by thyroxine. In their attempts to solve such a problem, researchers are constantly faced with the necessity of distinguishing between effects that are primary and those that are secondary to adaptation to an increased metabolic rate. This distinction is often difficult to make. [Pg.446]

In 1914, Kendall, a scientist at the Mayo Clinic in Minnesota, crystallized thyroxin, one of the thyroid hormones. The chemical structure of thyroxin wtis described in 1927 by Harrington and Barger, British university scientists. Harrington synthesized thyroxin, thereby paving the way for a more effective therapeutic agent than thyroid extracts which were variable in biological potency. [Pg.515]


See other pages where Thyroxine biologic effect is mentioned: [Pg.392]    [Pg.71]    [Pg.54]    [Pg.1003]    [Pg.1238]    [Pg.40]    [Pg.405]    [Pg.337]    [Pg.1238]    [Pg.501]    [Pg.245]    [Pg.278]    [Pg.148]    [Pg.315]    [Pg.2537]    [Pg.348]    [Pg.39]    [Pg.417]    [Pg.222]    [Pg.362]    [Pg.1073]    [Pg.131]    [Pg.140]    [Pg.170]    [Pg.257]    [Pg.293]    [Pg.246]    [Pg.41]    [Pg.276]   
See also in sourсe #XX -- [ Pg.342 ]




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