Regulation by Thyroid Hormone

Recently Exton and co-workers [93] have proposed that adrenergic responsiveness in skeletal muscle is regulated by thyroid hormones at two levels, i.e., 1) stimulation of /3-adrenergic receptors and adenylate cyclase activity and 2) increased activity of phosphoprotein phosphatases. Such results would explain the effect of thyroid hormones on glycogen metabolism in muscle although the primary mechanism of these actions remains unknown. 

Recently Izumo et al. [100] have reported that the myosin multichain family is composed of six different myosin heavy chains that are all responsive to thyroid hormones. The same myosin heavy chain gene can be regulated differently by thyroid hormones, even in opposite directions, depending on the tissue in which it is expressed. Differential expression and regulation by thyroid hormones have been demonstrated not only in heart muscle cells (atrium and ventricle) but also in several skeletal muscles (soleus, diaphragm, masseter, etc.). 

Recent investigations of the metabolism of iodothyronines in different tissues especially of the rat have led to the recognition of at least three different iodothyron-ine-deiodinating enzymes [5-8] (Table I). These deiodinases have in common that they are located in the membrane fractions of the tissues and that they are stimulated by sulfhydryl (SH) compounds, especially dithiols [5-8]. However, important differences exist between the specificities and catalytic mechanisms of these enzymes, their tissue distribution, sensitivity to PTU and other inhibitors, and regulation by thyroid hormone [5-8]. The characteristics of the different deiodinases will be discussed in more detail in Sections 2 and 3. 

Thyroid hormone decreases hepatic hpase activity [14] deficiency of thyroid hormone does not result in significant effects on HDL levels, however. Individuals wifh hypothyroidism have either unchanged or slightly elevated HDL levels [15]. It is possible fhat EL expression in the thyroid is regulated by thyroid hormone or that EL is involved in thyroid lipid metabolism. 

Emi, Y., Ikushiro, S., and Kato, Y. (2007) Thyroxine-metabolizing rat uridine diphosphate-glucuronosyltransferase 1A7 is regulated by thyroid hormone receptor. 

A similar connection between a decrease in CL levels and the age-linked decline of rat heart mitochondrial cytochrome c oxidase activity was demonstrated. Treatment of heart mitochondria from aged rats with CL-liposomes restored their lower cytochrome c oxidase activity to the level of young control rats (Paradies et al., 1997b). Again, no restoration of activity was found after treatment with other phospholipids or with peroxidized CL. CL level in heart mitochondria was shown to be regulated by thyroid hormone (Mutter et al.,... 

Arlotto, M.P. and A. Parkinson (1989). Identification of cytochrome P450a (P45011A1) as the principal testosterone 7 alpha-hydroxylase in rat liver microsomes and its regulation by thyroid hormones. Arch. Biochem. Biophys. 270, 458—471. 

What organs and functions of the body are regulated by thyroid hormones ... 

The next set of issues on the detected iriRNAs utilizing the hyt/hvt mice were l)To identify brain and cer ral cortex iriRNAs possibly regulated by thyroid hormone in fetal and neonatal brain and 2)To try to determine vhy some iriRNAs were specifically altered. To do this, zeta probe eets for northern gel hybridizations were prepared from 1, 5 and 7 day central cortex, brain remainder, and total brain RNA from hyt/hyt and hyt/+ littermates. These sheets were hybridized to cDNA probes reflecting iriRNAs that had been detected in cerebral cortex and total brain (Figures 4 and 5). 

N.R. Bhat, L.L. Sarlieve, G. Subba Rao and R.A. Pieringer, Investigations on myelination in vitro. Regulation by thyroid hormone in cultures of dissociated brain cells from embryonic mice, J. Biol. Chem. 254 9342 (1979)-... 

G. Shanker, A.T. Campagnoni and R.A. Pieringer, Investigations on myelinogenesis in vitro developmental expression of myelin basic protein mRNA and its regulation by thyroid hormone in primary cerebral cell cultures from embryonic mice. J. Neurosci. Res. 17 220 (1987). 

Carrasco, E., Blum, M., Weickert, C. S., and Casper, D. (2003). Epidermal growth factor receptor expression is related to post-mitotic events in cerebellar development Regulation by thyroid hormone. Brain Res. Dev. Brain Res. 140, 1-13. 

N.A. Almeida, A. Cordeiro, D.S. Machado, L.L. Souza, T.M. Ortiga-Carvalho, A.C. Campos-de-Carvalho, F.E. Wondisford, C.C. Pazos-Moura, Connexin40 messenger ribonucleic acid is positively regulated by thyroid hormone (TH) acting in cardiac atria via the TH receptor. Endocrinology 150 (2009) 546-554. 

The activity of the Na+-K+ pump has been proposed to be regulated by thyroid hormones and to account for a large contribution of the increased energy expenditure in hyperthyroidism. Microcalorimetry was used to measure erythrocyte [64] and lymphocyte [62 heat production rate during ouabain-induced inhibition of ATPasc, thus estimating the importance of the sodium-potassium pump in hyperthyroidism. The results of these studies show that the raised heat production rate in this condition was not due to increased energy expenditure by the pump. This was confirmed in microcalorimetric studies with mammalian. skeletal muscle [65,66] and hcpatocytes [66,67J. 

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