Thyroid hormone hormonal effects

I realize that this is a side track issue, but relevant all the same. Cycle protocols were an approach intended to facilitate optimal growth of muscle tissue. Remember there are two main muscle fiber types Type I, which is endurance orientated, and Type II which is strength orientated. Type "Ha", "Hb", and Type "He" are responsible for most musculature size and have the greatest potential for growth. Testosterone increases the number of Type II fibers at the expense of the Type I transformation. Growth hormone, Insulin, IGF-1, and thyroid hormones effect growth and hyperplasia of both fiber types. This should be another key relating to protocols that were utilized and why. 

Mauer RA (1982b) Relationship between estradiol, ergocryptine, and thyroid hormone effects on prolactin synthesis and prolactin messenger ribonucleic acid levels. Endocrinology 770 1515-1520. 

Hallgren S, Damerud PO (2002) Polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and chlorinated paraffins (CPs) in rats testing interactions and mechanisms for thyroid hormone effects. Toxicology 177 227-243... 

Thyroid hormone effects on metabolism arc diverse. The rates of protein and carbohydrate synthesis and catabolism are inlluenced. An example of the effect of thyroid hormones on lipid metabolism is the observation of a high serum cholesterol in some hypothyroid patients. This is a consequence of a reduction in cholesterol metabolism due to down regulation of low-density lipoprotein (LDL) receptors on liver cell membranes, with a subsequent failure of sterol excretion via the gut. 

Apletalina, E.V, H.C. Li, and D.J. Waxman (2003). Evaluation of thyroid hormone effects on liver P450 reductase translation. Arch. Biochem. Biophys. 409, 172-179. 

One of the most frequent questions asked has been whether or not pure ID results in hypothyroidism (Morreale de Escobar et ai, 1997). The answer to this is especially difficult, because there are few quantitative indices of thyroid hormone action in different tissues. For this reason, we have focused on concentrations of 3,5,3 -triiodo-L-thyronine (T3), which was taken as an index of possible thyroid hormone effectiveness at the individual tissue level, as discussed elsewhere (Escobar-Morreale et ai, 1995). As will be seen, the thyroid status of rats with ID cannot be defined for the animal as a whole, because it is eminently tissue specific At all grades of ID, elevated. 

Therapy with levothyroxine is very safe, provided that thyroid hormone levels are monitored and maintained within the normal range. Excess doses of T4 are associated with a loss of bone mass. A meta-analysis of 41 controlled studies on the impact of thyroid hormone therapy on bone mineral density (Uzzan et al., 1996) has shown that doses of T4 that suppress thyrotropin (TSH) secretion are associated with a significant loss of bone in the lumbar spine and hip in postmenopausal women. Another review of the evidence of the thyroid hormone effect of on skeletal integrity concluded that hyperthyroidism and the use of thyroid hormone to suppress TSH seem to have an adverse effect on bone, especially in postmenopausal women (Greenspan and Greenspan, 1999) however, thyroid hormone replacement seems to have a minimal effect on bone. 

Thyroid hormone effects on the heart and peripheral vasculature... 

Mechanisms for Thyroid Hormone Effects on Motor Units... 

Table 1. Tissue responsiveness to thyroid hormone. Effect of thyroid hormone on oxygen consumption and malic enzyme mRNA levels compared to nuclear T3-binding capacity. Data for selected tissues in adult rats were adapted from the cited references. Oxygen consumption (cu.mm./mg wet weight/h) is the ratio in euthyroid versus thyroidectomized (Tx) rats. The fold of induction of malic enzyme mRNAs was calculated from values obtained from tissues of euthyroid rats and rats treated for 10 days with ISpg T3/IOO g b.w. The binding capacity was measured in normal rats.

Finally, it should be stressed that receptors do not as such control the expression of thyroid hormone effects. In addition to postreceptor events, the interpretation of in vitro findings should also take into account differences in cellular transport of T3 from plasma to cytosol, and from cytosol to nucleus in different tissues [63]. 

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

Bronk, J.R. Thyroid hormone Effects on electron transport. Science 153, 638-639 (1966)... 

Thyroid-stimulating hormone can be used clinically to test thyroid function but has not found practical apphcation in the treatment of human thyroid insufficiency. Direct replacement therapy with thyroid hormone is easy and effective, owing to a simple molecular stmcture. TSH has been used in the veterinary treatment of hypothyroidism, and preparations of TSH ate produced by Cooper Animal Health, Inc. and Armour Pharmaceuticals. 

Metabolic Functions. The functions of the thyroid hormones and thus of iodine are control of energy transductions (121). These hormones increase oxygen consumption and basal metaboHc rate by accelerating reactions in nearly all cells of the body. A part of this effect is attributed to increase in activity of many enzymes. Additionally, protein synthesis is affected by the thyroid hormones (121,122). 

Only small amounts of free T are present in plasma. Most T is bound to the specific carrier, ie, thyroxine-binding protein. T, which is very loosely bound to protein, passes rapidly from blood to cells, and accounts for 30—40% of total thyroid hormone activity (121). Most of the T may be produced by conversion of T at the site of action of the hormone by the selenoenzyme deiodinase (114). That is, T may be a prehormone requiring conversion to T to exert its metaboHc effect (123). 

The class III cytokine receptor family includes two TNE receptors, the low affinity NGE receptor and 7-ceU surface recognition sites that appear to play a role in proliferation, apoptosis, and immunodeficiency. TNE-a (- 17, 000 protein) is produced by astrocytes and microglia and can induce fever, induce slow-wave sleep, reduce feeding, stimulate prostaglandin synthesis, stimulate corticotrophin-releasing factor and prolactin secretion, and reduce thyroid hormone secretion. TNE-a stimulates IL-1 release, is cytotoxic to oligodendrocytes, and reduces myelination this has been impHcated in multiple sclerosis and encephalomyelitis. Astrocyte TNE-a receptors mediate effects on IL-6 expression and augment astrocytic expression of MHC in response to other stimulants such as lEN-y. 

Iodide and Other Inorganic Anions. When large doses of iodide ion are administered, a transient inhibition of synthesis and release of the thyroid hormones is brought about by the so-called Wolff-Chaikoff effect. 

Thiocyanate ion, SCN , inhibits formation of thyroid hormones by inhibiting the iodination of tyrosine residues in thyroglobufin by thyroid peroxidase. This ion is also responsible for the goitrogenic effect of cassava (manioc, tapioca). Cyanide, CN , is liberated by hydrolysis from the cyanogenic glucoside finamarin it contains, which in turn is biodetoxified to SCN. 

A large number of thyroid hormone analogues have been tested for this effect (6). Among others, i-T (3) and 3,3 -T2 (5) and their propionic acid side-chain analogues decrease oxygen consumption at molar ratios of 50—200 1 of T. Nevertheless, no potent or clinically usehil peripheral antagonists have been found. 

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