Thyroid status

Zhou, T, John-Alder, H.B., and Weis, P. et al. (1999). Thyroidal status of mummichogs (Eundulus heteroclitus) from a polluted versus a reference habitat. Environmental Toxicology and Chemistry 18, 2817-2823. 

Fig. 33.1. Canonical variate plot for three classes with different thyroid status. The boundaries are obtained by linear discriminant analysis [2].

Duntas LH, Mantzou E, Koutras DA (2001) Lack of substantial effects of raloxifene on thyroxine-binding globulin in postmenopausal women dependency on thyroid status. Thyroid 11 779-782... 

Monitoring Treatment of patients with thyroid hormones requires the periodic assessment of thyroid status by means of appropriate laboratory tests. The TSH suppression test can be used to test the effectiveness of any thyroid preparation. 

Thyroid status can be assessed using dried blood spot specimens for epidemiological surveys. Since TSH levels (as a marker of hypothyroidism) are stable in dried blood spot specimens for months this is the preferred assay for monitoring purposes. TSH monitoring is used in this way in India, China, Zaire, Thailand and Indonesia. 

A. Approximately 5% of patients taking lithium over the long term develop hypothyroidism, and thyroid status should be followed as routine care for these patients. Mr. Smith s symptoms are classic for hypothyroidism. Impairment in glucose metabolism, hepatic function, red blood cell production, and prolactin secretion are not typical complications of lithium therapy. 

Her weight is 136 lb (61.8 kg), an increase of 10 lb (4.5 kg) in the last year. Her thyroid gland is not palpable and her reflexes are delayed. Laboratory findings include a thyroid-stimulating hormone (TSH) level of 14.9 pIU/mL and a free thyroxine level of 8 pmol/L. Evaluate the management of her past history of hyperthyroidism. Identify the available treatment options for control of her current thyroid status. 

Effects on growth and calorigenesis are accompanied by a pervasive influence on metabolism of drugs as well as carbohydrates, fats, proteins, and vitamins. Many of these changes are dependent upon or modified by activity of other hormones. Conversely, the secretion and degradation rates of virtually all other hormones, including catecholamines, cortisol, estrogens, testosterone, and insulin, are affected by thyroid status. 

It is important to monitor maternal thyroid status carefully and to use the lowest possible dose of antithyroid drug sufficient to maintain maternal euthyroidism. 

Tiihonen M, Liewendahl K, Waltimo O, Ojala M, Valimaki M. Thyroid status of patients receiving longterm anticonvulsant therapy assessed by peripheral parameters a placebo-controlled thyroxine therapy trial. Epilepsia 1995 36(ll) 1118-25. 

Feek CM, Sawers JS, Brown NS, Seth J, Irvine WJ, Toft AD. Influence of thyroid status on dopaminergic inhibition of thyrotropin and prolactin secretion evidence for an additional feedback mechanism in the control of thyroid hormone secretion. J Clin Endocrinol Metab 1980 51(3) 585-9. 

It has been suggested that thyroid status is a possible major regulator of metabolic rate. Herlihy et al. [38] found that CR reduces the 24-hour mean serum triiodothyronine (T3) level, but not the thyroxine (T4) level. CR appears to have this action because it attenuates the circadian amplitude in the concentrations of both hormones. However, Snyder et al. [39] found no effect of CR on either T4 or T3 in young rats and no consistent effect of CR on age-related changes in the concentrations of these two hormones. 

Numerous studies in rodents have reported alterations in thyroid status after exposure to 2,3,7,8-TCDD. End points commonly examined included serum levels of T4, T3, TSH, and activity of hepatic... 

Potter CL, Moore RW, Inhom SL, et al. 1986b. Thyroid status and thermogenesis in rats treated with... 

In fat cells epinephrine stimulation of cyclic AMP accumulation and lipolysis is markedly reduced in hypothyroidism but enhanced in hyperthyroidism (see Ref. 79). Similar effects of altered thyroid status on the response to two other lipolytic hormones, ACTH and glucagon, have been reported suggesting that thyroid hormones regulate similarly either the different receptors of the various lipolytic hormones and/or a common step of the lipolytic pathway [80],... 

In contrast to the type I deiodinase which shows a high preference for rT4 over T4 as the substrate (Table II), the type II enzyme is somewhat more effective in the deiodination of T4 than of rT3 (Table III). Under the conditions tested, the Km value of T4 for the type II enzyme is three orders of magnitude lower than the Km of T4 for the type I deiodinase. The Km of rT3 for the type II deiodinase is somewhat greater than that of T4 and differs less from the Km of rT3 for the type I enzyme. The Umax of the conversion of T4 to T3 by the type II enzyme depends on the tissue and the thyroid status of the animal (see below). In cerebral cortex of hypothyroid rats [82] it is roughly one-thousandth of the maximum T3 production by the hepatic type I deiodinase of euthyroid animals determined under similar conditions [32]. The VmiJKm ratio of this reaction is, therefore, similar for the type II deiodinase of hypothyroid rat brain and the type I deiodinase of euthyroid rat liver and much greater than that for the hepatic enzyme of hypothyroid rats [86], In view of the reaction kinetics of the type II deiodinase (see below), it is questionable if the Vm,JKm ratios estimated in vitro also apply to physiological conditions with unknown cofactor availability. 

Nobes, C.D., P.L. Lakin-thomas, and M.D. Brand (1989). The contribution of ATP turnover by the Na+/K+-ATPase to the rate of respiration of hepatocytes. Effects of thyroid status and fatty acids. Biochim. Biophys. Acta 976 241-245. 

Spiess J, Rivier J, Vale W (1983) Characterization of rat hypothalamic growth hormone-releasing factor. Nature 303(5917) 532-5. PMID 6406907 Szabo M, Ruestow PC, Kramer DE (1985) Growth hormone response to thyrotropin-releasing hormone in the urethane-anesthetized rat effect of thyroid status. Endocrinology 117(1) 330—7... 

Reymond MJ, Benotto W, Lemarchand-Beraud T (1987) The secretory activity of the tuberoinfundibular dopaminergic neurons is modulated by the thyroid status in the adult rat consequence on prolactin secretion. 

Because of the potential effect it may have on other body systems and the risk of toxicity, a baseline medical workup is de rigueur in every patient who is a candidate for lithium therapy. This workup includes laboratory tests aimed at evaluating kidney function, thyroid status, complete blood count, cardiac function, and so on. 

THYROID HORMONES BRONCHODILATORS- THEOPHYLLINE Altered theophylline levels (T or f) when thyroid status was altered therapeutically Uncertain Monitor theophylline levels closely during changes in treatment of abnormal thyroid function. Watch for early features of theophylline toxicity... 

The hypothalamus contains high concentrations of the monoamines dopamine and serotonin and these neurotransmitters have inhibitory or excitatory effects, respectively, on the anterior pituitary. For example, thyroid-stimulating hormone (TSH) secretion is increased by serotoninergic and decreased by dopaminergic activation. Pyridoxine deficiency in rats is associated with low levels of PLP in the hypothalamus, with no change in dopamine concentrations, but decreased levels of serotonin (Dakshinamurti et al., 1990). This correlates with decreased thyroid status and decreased pituitary TSH. Treatment with pyridoxine returns these parameters to normal. 

More information is needed on teratogenicity of PCDEs as well as the role of thyrotoxicity in the developmental toxicity of PCDEs [104], Teratogenicity caused by nitro-PCDEs has been suggested to involve alterations in thyroid hormone status [87] and transient alterations in maternal thyroid status might affect development of the fetus [143], Effects of PCDEs after prenatal exposure have been similar to those of PCBs [104]. 

In pregnancy a hypothyroid patient should be carefully assessed and monitored monthly a 50-100% increase in dose of levothyroxine may be required breast feeding is not contraindicated though the baby s thyroid status should be watched. 

Iodide effects are complex and related to dose and to thyroid status of the subject. 

An increase in thyroid hormone levels results in an increase in the basal metabolic rate (BMR). BMR measurements can be used to assess thyroid status, as discussed in detail in Chapter 5. This method for the diagnosis of hypo- or hyperthyroidism is not in coitimon use because it is cumbersome. The increase in BMR has been associated with increases in various reactions that use ATP. The increased use of ATP is matched by an increase in activity of the respiratory chain and in Oj... 

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