Thyroxine and thyrotropin

Burger A, Dinichert D, Nicod P, Jenny M, Lemarchand-Beraud T, Vallotton MB. Effect of amiodarone on serum triiodothyronine, reverse triiodothyronine, thyroxin, and thyrotropin. A drug influencing peripheral metabolism of thyroid hormones. J Clin Invest 1976 58(2) 255-9. 

An analytical HPLC method for methanol involves esteriflcation with naphthylmethylamino-oxo-butanoic acid mediated by EDC and DMPA. The method can simultaneously determine methanol, ethanol and 1-propanol. Similarly, hydroxyl functions are labeled with 2-(prenyloxymethyl)benzoic acid using DCC and DMPA. Also, the simultaneous measurement of thyroxine and thyrotropin from newborn dried blood spot specimens is conducted using EDCCl and N-hydroxysuccinimide-3-sulfonate. ... 

Heidemann P, Stubbe P. 1978. Serum 3,5,3 -triiodothyronine, thyroxine, and thyrotropin in hypothyroid infants with congenital goiter and the response to iodine. J.Clin. Endocrinol.Metab. 47 189. 

Thyroid hormone production is controlled by the hypothalamic-pituitary system (see Chapter 28). Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary.17,63 TSH then travels via the systemic circulation to the thyroid gland to stimulate the production of thyroxine and triiodothyronine. 

Thyrotropin-releasing hormone, or protirelin, is a tripeptide hormone found in the paraventricular nuclei of the hypothalamus as well as in other parts of the brain. TRH is secreted into the portal venous system and stimulates the pituitary to produce thyroid-stimulating hormone (TSH, thyrotropin), which in turn stimulates the thyroid to produce thyroxine (T4) and triiodothyronine (T3). TRH stimulation of thyrotropin is blocked by thyroxine and potentiated by lack of thyroxine. 

Wang PS, Huang S-W, Tung Y-F, Pu H-F, Tsai S-C, Lau C-P, Chien EJ, Chien C-H (1994) Interrelationship between thyroxine and estradiol on the secretion of thyrotropin-releasing hormone and dopamine into hypophysial portal blood in ovariectomized-thyroidectomized rats. Neuroendocrinology 59 202-207. 

Primary hypothyroidism The thyroid gland is unable to produce sufficient quantity of thyroxine and triiodothyronine, resulting in an increased serum level of thyrotropin-releasing hormone and thyroid-stimulating hormone. 

Kabadi UM, Cech R. Normal thyroxine and elevated thyrotropin concentrations Evolving hypothyroidism or persistent euthyroidism with reset thyrostat. J Endocrinol Invest 1997 20 319-326. 

Collins WT, Capen CC. 1980a. Ultrastructural and functional alterations of the rat thyroid gland produced by polychlorinated biphenyls compared with iodide excess and deficiency, and thyrotropin and thyroxine administration. Virchow Arch B Cell Pathol 33 213-231. 

Thyrotropin-releasing factor (TRF) is produced in the hypothalamus and arrives at the pituitary via the hypophyseal portal blood system. TRF mediates the release of thyrotropin from the anterior hypophysis. The thyrotropin release is inhibited by thyroxine, presumably free thyroxine, and the inhibition is dose dependent. Thus excessive levels of thyroxine depress thyrotropin release, and lower thyroxine levels result in increased thyrotropin release from the anterior pituitary. TSH, in turn, stimulates thyroid hormone synthesis and secretion by the thyroid gland. Thyroxine and triiodothyronine are bound to specific binding proteins in the blood. The amounts and binding constants of the specific thyroid-binding proteins, together with the rate of thyroid hormone release from the thyroid, determine the amount of free thyroxine in the blood. Free thyroxine levels are determined not only by the rate of... 

B15. Bowers, C. Y., Schally, A. V., Reynolds, G. A., and Hawley, W. D., Interactions of 1,-thyroxine or L-triiodothyronine and thyrotropin-releasing factor on the release and synthesis of thyrotropin from anterior pituitary gland of mice. Endocrinology 81, 741-747 (1967). 

Thyroxine and triiodothyronine are released from thyroglobulin through the action of a series of proteases. Both the protease action and the release of the thyroid hormones into the bloodstream are stimulated by pituitary thyrotropin Like glucagon... 

Lee, D. E., V. J. Salerno, S. V. Lamb, and T. J. Reimers. 1998. Clinical evaluation of immunlite chemiluminescent immunoassays in total thyroxine (TT4) thyrotropin (TSH) and free-thyroxine (FT4) in dog serum. Clinical Chemistry 44 (SuppL) A108. 

Figure 71.12 Thyroid hormone concentrations after iodine and seienium suppiementation. Mean ( SE) serum thyroxine (T4), triiodothyronine (T3) and thyrotropin (TSH) concentrations in the piacebo-iodine suppiemented subjects (O circies), and in the seienium-iodine-suppiemented subjects ( circies). The reference range for serum TSH concentrations is within the dotted iine. For serum TSH, bars indicate the vaiues 1 SE beiow and 1 SE above the mean on the iogarithmic scaie. A significant main effect of time was observed for serum T4 (P < 0.001), T3 (P < 0.001), and TSH (P = 0.011). Significantly different from all subsequent values, P < 0.001 (Heimert contrast). For serum T3, there was a significant main effect of group (P = 0.03). Reproduced with permission from Moreno-Reyes et al., (2003). The American Society for Nutrition.

Thyrotropin releasing hormone, thyrotropic hormone releasing factor(TRF), thyroliberin Pyr-His-Pro-NH2 (Pyroglutamyi-L-hktidyl-L-prolinamide), M, 262. The identical hormone is found in all hitherto investigated species. Secretion of TRF is promoted by neurotransmitters, e.g. noradrenalin, and inhibited by serotonin. TRF stimulates the anterior pituitary to synthesize and secrete thyrotropin, which in turn stimulates the thyroid gland to secrete thyroxin and triiodothyronin. The latter two hormones exert a negative feedback on the secretion of TRF and thyrotropin. TRF also stimulates the secretion of prolactin and acts as a neurotransmitter in the central nervous system. 

From 1968 to 1975 the distributioon of iodized salt was silently interrupted in 2 small districts (Podoba, unpublished). Within one year the urinary iodine decreased from about 100 g/24h to about 40 fiq/2 h. In addition, the total iodine in thyroid and thyroxine in serum decreased, while uptake by thyroid and thyrotropin in serum increased. 

In the plasma, increased levels of /3-endorphin, epinephrine, norepinephrine, corticosterone, ACTH, renin, and angiotensin I and decreased levels of growth hormone, thyroxine, triiodothyronine, and thyrotropin were reported with high caffeine doses. The mechanisms responsible for these various effects are largely unknown, and the mediation of adenosine receptors is suggested. The antagonism of benzodiazepine at the receptor level is observed at lower caffeine concentrations (0.5-0.7mM) than those required for phosphodiesterase inhibition. 

FIGURE 41-1. Hypothalamic-pituitary-thyroid axis. Thyrotropinreleasing hormone (TRH) is synthesized in the neurons within the paraventricular nucleus of the hypothalamus. TRH is released into the hypothalamic-pituitary portal circulation and carried to the pituitary, where it activates the pituitary to synthesize and release thyrotropin (TSH). TSH activates the thyroid to stimulate the synthesis and secretion of thyroxine (T4) and triiodothyronine (T3). T4 and T3 inhibit TRH and TSH secretion, closing the feedback loop. 

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