This is the mechanism whereby exogenous thyroid hormone suppresses natural thyroid hormone production. When T3 levels go up, TSH secretion is suppressed. Like the hypothalamic-pituitary-gonadal axis, the thyroid gland is under negative feedback control. Therefore in normal subjects 3,5-T2 may be the principal active metabolite of T3 (1) Studies have shown that 3,3'-T2 may be more effective in raising resting metabolic rate when hypothyroid subjects are treated with T3, than when normal (euthyroid) subjects are given T3. In addition to T3, it has recently been recognized that there exist two additional active metabolites of T3: 3,5 and 3,3' diiodothyronines, which we will collectively call T2. This is analogous to testosterone production, where GnRH from the hypothalamus causes the pituitary to release LH, which in turn stimulates the testes to produce testosterone. TSH secretion is in turn controlled through release of Thyrotropin Releasing Hormone which is produced in the hypothalamus. The secretion of T4 is under the control of Thyroid Stimulating Hormone (TSH) which is produced by the pituitary gland. The bulk of the body's T3 (about 80%) comes from this conversion. T3 is considered the physiologically active hormone, and T4 is converted peripherally into T3 by the action of the enzyme deiodinase. The thyroid gland secretes two hormones of interest to us, thyroxine (T4) and triiodothyronine (T3). The widespread underground use of T3 warrants an understanding of its mechanism of action, as well as a knowledge of how it is most effectively and safely used, with an eye to minimizing side effects.īefore jumping right into a discussion of the use of thyroid hormone for fat loss, a little review of thyroid function and physiology might be in order. Nevertheless, thyroid hormones, particularly triiodothyronine (T3) are a mainstay in the arsenal of drugs used by bodybuilders for fat loss. These deleterious effects include cardiac problems such as tachycardia and atrial arrhythmias, loss of muscle mass as well as fat, increased bone resorption and muscle weakness. This is probably due to the number of side effects observed during thyroid hormone use at the relatively high doses used in the majority of obesity treatment studies. Despite numerous clinical studies having shown that the administration of thyroid hormone induces weight loss, it is not currently indicated as a weight loss agent. Despite this great length of time, the precise mechanisms by which thyroid hormones exert their calorigenic effect are not completely characterized, and still actively debated. It has been over 100 years since the discovery by Magnus-Levy that thyroid hormones play a central role in energy homeostasis, and 75 years since the hormones were first used for weight loss. Mooi stukje over de effecten van T3 gevonden.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |