Thyroid function influence

The results on the effect of thyroid hormone on myelin lipid synthesis correlate well with the in vivo changes induced under altered thyroid functions, proving, thereby, the direct influence of T on brain maturation. Another in vitro system used to demonstrate such a direct effect of thyroid hormone on myelination was an explant culture of cerebella obtained from newborn rats. 

Eales, J.G. and S. Shostak. Influence of potassium thiocyanate on thyroid function of rainbow trout, Salmo gairdneri. Gen. Comp. Endocrinol. 51 39-43, 1983. 

E9. Egeberg, O., Influence of thyroid function on the blood clotting system. Scand. J. Clin. Lab. Invest. 16, 1-7 (1963). 

Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism The influence of soy-based formula. J Am Coll Nutr 1997 16 280-282. 

Mil. Miksche, L. W., and Caldwell, F. T., The influence of fever, protein metabolism and thyroid function on energy balance following bilateral fracture of the femur in the rat. Ann. Surg. 54, 455-459 (1967). 

Three- to four-day old northern bobwhite were used to evaluate the influence of ammonium perchlorate (AP) on thyroid function, as well as thyroidal hormone level systemic effects on the hypothalamic-pituitary-thyroid axis [46], The perchlorate ion competitively inhibits iodide uptake, thus with time AP has the potential to reduce... 

Daminet, S., M. Paradis, K. R. Refsal, and C. Price. 1999. Short-term influence of prednisone and phenobarbital on thyroid function in euthyroid dogs. Canadian Veterinary Journal 40 411 15. 

The available data from in vivo, as well as from in vitro, experiments clearly demonstrate that soy isoflavones act as inhibitors of TPO and thus may influence iodine incorporation in thyroid hormone biosynthesis. On the other hand, most of the cfinical trials, including our own, have shown only modest and transitory effects of soy isoflavones on circulating thyroid hormone levels. However, they may be important in the case of insufficient iodine supply. Besides thyroid hormone biosynthesis, soy isoflavones may influence other events involved in thyroid function, such as iodine transport, thyroid hormone deiodination, and signaling pathways. So far, the data available on these topics is scarce and more experiments addressing these issues are needed. 

Clinical trials, including ours, have been undertaken to ascertain whether soy food consumption can influence thyroid function, especially actual thyroid hormone biosynthesis and actual thyroid hormone levels. 

Endemic cretinism has been a common finding in the mountains or isolated regions, such as the Alps or the Himalayas and has been described or depicted in drawings over the centuries. McCarrison (1917) studied this condition in the Himalayas, describing two types of cretinism the nervous and myxedematous types. He already suspected the influence of the maternal thyroid function on the fetus. Early observations in the Alps (Hunziker-Shild, 1915) already reported that the fetus could receive the hormone from the mother, and proposed the prophylactic administration of iodine from conception. 

Therefore, based on the above Hmited evidence, we conclude that excess iodine exposure may influence maternal-fetal TH metabohsm by three mechanisms (1) excess iodine affects the maternal hormone thyroid level by inhibition of thyroid function and/or Dl activity (2) excess iodine has an effect on maternal—fetal TH transfer by affecting placental D2 and D3 activity and (3) excess iodine transferred by the placenta has a direct inhibition on the development and function of the fetal thyroid gland (Figure 88.2). 

Influence of Iodine-Containing Pharmaceuticals on Iodine Status and Thyroid Function Iodine-Induced Hyperthyroidism and Hypothyroidism... 

Factors that affect control of thyroid function in elderly persons include noncompliance with therapy, variability in absorption, variation in the biological activity of levothyroxine tablets, or the influence of drugs on TSH levels. Rapid changes in levothyroxine dose may also cause delays in the control of patients. The half life of T4 is about 1 week, but is longer in patients with hypothyroidism. This is the reason why a lapse of 3—6 weeks would be needed forT4 concentrations to reach a steady state and to evaluate the need for a change in dose. 

In summary, most evidence in the fiterature indicates that a low (and low-normal) thyroid function can influence the cardiovascular system either direcdy, as a consequence of the lack of the beneficial effect ofTH on heart and vessel physiology, or indirectly, by aggravating most of the recognized risk factors that can lead to cardiovascular damage. 

A low thyroid function can influence many of the neuro-humoral systems involved in vascular tone and plasma volume regulation. It has long been known that chronic hypothyroid patients show an increase in peripheral arterial resistance. This is principally due to the lack of direct T3-dependent vasorelaxation and to an increase in arterial wall thickness (Cappola and Ladenson, 2003 Rawat and Satyal, 2004), but enhanced sympathetic activity may also contribute significantly to peripheral vasoconstriction, probably as a powerful compensatory mechanism for the decreased cardiac contractility and intravascular volume which follows TH deprivation. The enhanced sympathetic efflux may eventually overcome a downregulation of post-synaptic vasoconstrictor a-adrenoreceptors, which is described in hypothyroid states, at variance with what is observed in normal physiology, where a positive relationship does exist between TH and the number and activities of noradrenergic receptors (Gomberg-Maitland and Frishman, 1998). 

Vozeh, S. et al.. Influence of thyroid function on theophylline kinetics, Clin. Pharmacol. Then, 36(5) 634-640, 1984. 

Singh, A., Reineke, E.P., and Ringer, R.K. 1968. Influence of thyroid status of the chick on growth and metabolism, with observations on several parameters of thyroid function. Poult. Sci. 47, 212-219. 

In normal, untreated rats, single injections of thyrotropin caused as much as a threefold rise in the thyroid-serum iodide ratio 50 hours after the injection. It appears therefore that the pituitary gland influences thyroid function at two stages the concentration of iodide and its conversion to organically bound iodine evidence for the second of these effects will be discussed in a later section. 

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