Some New Stacks for you!!!!!
- 04-02-2010, 11:14 AM
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Recently been recognized that there exist two additional active metabolites of T3: 3,5 and 3,3' diiodothyronines, which we will collectively call T2. 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. Therefore in normal subjects 3,5-T2 may be the principal active metabolite of t3.
Like the hypothalamic-pituitary-gonadal axis, the thyroid gland is under negative feedback control. When t3 levels go up, TSH secretion is suppressed. This is the mechanism whereby exogenous thyroid hormone suppresses natural thyroid hormone production. There is a difference though between the way anabolic steroids suppress natural testosterone production and the way t3 suppresses the thyroid. With steroids, the longer and heavier the cycle is, the longer your natural testosterone is suppressed. This is not the case with exogenous thyroid hormone.
An early study that looked at thyroid function and recovery under the influence of exogenous thyroid hormone was undertaken by Greer. He looked at patients who were misdiagnosed as being hypothyroid and put on thyroid hormone replacement for as long as 30 years. When the medication was withdrawn, their thyroids quickly returned to normal.
Here is a remark about Greer's classic paper from a later author:
"In 1951, Greer reported the pattern of recovery of thyroid function after stopping suppressive treatment with thyroid hormone in euthyroid [normal] subjects based on sequential measurements of their thyroidal uptake of radioiodine. He observed that after withdrawal of exogenous thyroid therapy, thyroid function, in terms of radioiodine uptake, returned to normal in most subjects within two weeks. He further observed that thyroid function returned as rapidly in those subjects whose glands had been depressed by several years of thyroid medication as it did in those whose gland had been depressed for only a few days"
These results have been subsequently verified in several studies. So contrary to what has been stated in the bodybuilding literature, there is no evidence that long term thyroid supplementation will somehow damage your thyroid gland. Nevertheless, most bodybuilders will choose to cycle their t3 (or T4 which in most cases works just as well) as part of a cutting strategy, since t3 is catabolic with respect to muscle just as it is with fat. As previously mentioned, long term t3 induced hyperthyroidism is also catabolic to bone as well as muscle.
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