Thyroid hormones
Thyroid hormones are two hormones produced and released by the thyroid gland, namely triiodothyronine (T) and thyroxine (T). They are tyrosine-based hormones that are primarily responsible for regulation of metabolism. T and T are partially composed of iodine. A deficiency of iodine leads to decreased production of T and T, enlarges the thyroid tissue and will cause the disease known as simple goitre. The major form of thyroid hormone in the blood is thyroxine (T), which has a longer half-life than T. In humans, the ratio of T to T released into the blood is approximately 14:1. T is converted to the active T (three to four times more potent than T) within cells by deiodinases (5'-iodinase). These are further processed by decarboxylation and deiodination to produce iodothyronamine (Ta) and thyronamine (Ta). All three isoforms of the deiodinases are selenium-containing enzymes, thus dietary selenium is essential for T production. Edward Calvin Kendall was responsible for the isolation of thyroxine in 1915.
Thyroid storm
High levels of thyroid hormone result in a hypermetabolic state, which can result in increased breakdown of cortisol, a hormone produced by the adrenal gland. This results in a state of relative adrenal insufficiency, in which the amount of cortisol is not sufficient. Guidelines recommend that corticosteroids (hydrocortisone and dexamethasone are preferred over prednisolone or methylprednisolone) be administered to all patients with thyroid storm. However, doses should be altered for each individual patient to ensure that the relative adrenal insufficiency is adequately treated while minimizing the risk of side effects.