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Levothyroxine is the chemical name of the manufactured version of T 4, which is metabolised more slowly than T 3 and hence usually only needs once-daily administration. Natural desiccated thyroid hormones are derived from pig thyroid glands, and are a "natural" hypothyroid treatment containing 20% T 3 and traces of T 2 , T 1 and calcitonin .
The compound migrated close to thyroxine in chromatography and they initially named it 'unknown 1' . Around that time a group led by Jean Roche in Paris described a deiodinating activity in the sheep thyroid gland, raising the possibility that 'unknown 1' is the less iodinated analogue of T4, triiodothyronine. [24]
Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, or abbreviated TSH) is a pituitary hormone that stimulates the thyroid gland to produce thyroxine (T 4), and then triiodothyronine (T 3) which stimulates the metabolism of almost every tissue in the body. [1]
T4 is a prohormone; that is, T4 is a precursor to the hormone T3. Whereas T4 is a tetraiodide, T3 is a triiodide, triiodothyronine. The T4 → T3 conversion is mediated by the selenoenzyme iodothyronine deiodinase. T3-thyroxine is a unique example of an iodine compound that is essential for human health.
Total T4 is measured to see the bound and unbound levels of T4. The total T4 is less useful in cases where there could be protein abnormalities. The total T4 is less accurate due to the large amount of T4 that is bound. The total T3 is measured in clinical practice since the T3 has decreased amount that is bound as compared to T4. [citation needed]
Desiccated thyroid has roughly a 4:1 ratio of thyroxine (T4) to triiodothyronine (T3). In humans, the ratio is 11:1. [10] A combination of various ratios of T4 and T3 might not provide benefits over T4 alone. Some controlled trials have shown inconsistent benefits of various ratios of T4 and T3. [11] [12]
[1] Triiodothyronine is formed, when diiodotyrosine is combined with monoiodotyrosine (in the colloid of the thyroid follicle ). Two molecules of DIT combine to make the thyroid hormone thyroxine ('T4' and 'T3').
Reverse triiodothyronine, also known as rT 3, is an isomer of triiodothyronine (T 3).. Reverse T 3 is the third-most common iodothyronine the thyroid gland releases into the bloodstream, at 0.9%; tetraiodothyronine (levothyroxine, T 4) constitutes 90% and T 3 is 9%.