Development thyroid hormone effects

This report has briefly summarized what we now know about thyroid hormone transport to the central nervous system. The data are still sketchy and much remains to be done. Obviously the brain is a complex organ and major differences in thyroid hormone transport and metabolism are to be expected in its constituent parts, so study of different brain regions as well as different cell types is required. We also need to distinguish between findings in the mature brain and those during fetal and postnatal development. Thyroid hormones play a very different role in these stages of the organism, and possible variations in hormone delivery to cells may contribute to these differences. Finally, in the malnutrition that often accompanies iodine deficiency, we need to ask whether PA synthesis in the choroid plexus is compromised, as it is in the liver. If so, important effects in thyroid hormone delivery to the brain may be expected. 

J. Legrand, Thyroid hormone effects on growth and development,... 

Ahlgren SC, Wallace H, Bishop J, Neophytou C, Raff MC 1997 Effects of thyroid hormone on embryonic oligodendrocyte precursor cell development in vivo and in vitro. Mol Cell Neurosci 9 420-432... 

In permissiveness, one hormone enhances the responsiveness of the target tissue to a second hormone in other words, the first hormone increases the activity of the second. For example, the normal maturation of the reproductive system requires reproductive hormones from the hypothalamus, pituitary, and gonads as well as the presence of thyroid hormone. Although thyroid hormone by itself has no effect on the reproductive system, if it is absent the development of this system is delayed. Therefore, thyroid hormone is considered to have a permissive effect on the reproductive hormones, facilitating their actions causing sexual maturation. 

The Class III effects of amiodarone develop over several weeks. This time-course is similar to that seen in thyroid gland ablation [25]. It is well known that patients with hypothyroidism have long QT intervals which are indicative of prolonged action potentials. Amiodarone has been shown to inhibit the conversion of thyroxine (T4) to triiodothyronine (T3) both in human subjects [26] and in vitro [27]. It has been argued that the Class III effects of amiodarone are due to its effects on thyroid hormones [28]. Others, however, argue that there is no relationship between prolongation of ventricular refractory period by amiodarone and thyroid state [29]. 

Within a programme aimed at the development of thyroid hormone analogues as potentially useful plasma cholesterol-lowering agents, the pyrida-zinone derivative SK F L-94901 (98) has been prepared and investigated in the U.K. [419-422]. Whereas naturally occurring thyroid hormones cannot be employed for this purpose because of their undesirable effect on heart rate, (98) has been found to represent a potent thyromimetic which retains hepatic activity but lacks cardiac activity. Structural modifications and QSAR studies have been carried out [422]. 

Walpita CN, Van der Geyten S, Rurangwa E, Darras VM (2007) The effect of 3,5,3 -triiodothyronine supplementation on zebrafish (Danio rerio) embryonic development and expression of iodothyronine deiodinases and thyroid hormone receptors. Gen Comp Endocrinol 152 206-214... 

Z)-2,3-Methanothyronine 59 and its dibromo derivative 60 have comparable activity with the thyroxine 61, a thyroid hormone [66], which exhibited thyro-mimetic activities in basal metabolism and antigoiter tests (comparison of oxygen consumption and heart rate in normal and thyroidectomized rats) but did not have an inhibitory action on the metabolism developed by triiodothyronine [66]. (Z)-2,3-Methanohistidine 62, tested on rat liver, is an effective inhibitor of histidine decarboxylase, Eq. (23) [67]. 

Treatment-related altered serum th5Toid hormone levels indicate that chlorine dioxide and chlorite may exert toxic effects that are mediated through the neuroendocrine axis. Changes in thyroid hormones have been reported in laboratory animals that were either directly exposed to chlorine dioxide (repeated doses as low as 9 mg/kg/day), or exposed to chlorine dioxide or chlorite via their mothers (maternal doses of chlorine dioxide and chlorite as low as 13 and 9 mg/kg/day, respectively) during pre- and postpartum development (Bercz et al. 1982 Carlton and Smith 1985 Carlton et al. 1987, 1991 Mobley et al. 1990 Orme et al. 1985). 

Mechanism of Action A synthetic form of triiodothyronine (T3), a thyroid hormone involved in normal metabolism, growth, and development. Possesses catabolic and anabolic effects. Therapeutic Effect Increases basal metabolic rate, enhances gluco-neogenesis, and stimulates protein synthesis. 

Thyroid hormone is critical for the development and functioning of nervous, skeletal, and reproductive tissues. Its effects depend on protein synthesis as well as potentiation of the secretion and action of growth hormone. Thyroid deprivation in early life results in irreversible mental retardation and dwarfism—typical of congenital cretinism. 

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