|Thyroxine is an iodine-containing hormone, produced by attaching iodine atoms to the ring structures of tyrosine molecules. Thyroxine forms by combining the amino acid tyrosine with iodine. Thyroxine is produced by follicular cells of the thyroid gland. The thyroid gland is composed of spherical follicles that selectively absorb iodine from the bloodstream and concentrate it for
production of thyroid hormones. Thyroxine is stored in the follicle stems between thyroid cells. Thyroxine enters into the bloodstream complexed to another protein, plasma globulin. The sole function of the thyroid is to make thyroid hormone. Thyroxine and tri-iodothyronine are necessary for normal brain development and for normal metabolic rates. Thyroxine releases fats from most fat cells, increases metabolism by influencing mitochondria, and in lower vertebrates induces metamorphosis.
Every cell in the body depends upon thyroid hormones for regulation of their metabolism. The thyroid hormones act on the body to increase the basal metabolic rate, affect protein synthesis and increase the body's sensitivity to catecholamines (such as adrenaline). Thyroxine causes an increase in the rate of carbohydrate metabolism and a rise in the rate of protein synthesis and breakdown. The hormone, which excites the nervous system and leads to increased activity of the endocrine system, remains active in the body for more than a month. Thyroxine plays an important role in childhood development, metabolism regulation, and breaking down fats and proteins. Thyroxine is necessary for normal neural development and normal cellular metabolism. Thyroxine increases the metabolic rate of most cells. In amphibians it is responsible for metamorphosis. Thyroxine increases the number and activity of mitochondria in cells by binding to the cells' DNA, increasing the basal metabolic rate.
Thyroxine is the main hormone produced by the thyroid gland. Hypothyroidism is the disease state caused by insufficient thyroid hormone by the thyroid gland. Hypothyroidism is the condition that results from under-production of thyroxine by the thyroid gland either because the gland is naturally underactive or because radioiodine therapy or surgery for an overactive gland has resulted in underactivity. Thyroxine is taken to replace the deficiency which exists in such situations and therefore to restore normal metabolic activity. In humans, children born with thyroid hormone deficiency will not grow well, and brain development can be severely impaired, in the condition referred to as cretinism. Children with thyroid hormone deficiency are easily treated by supplementation with synthetic thyroxine, which enables them to grow and develop normally. Synthetically prepared thyroxine is used clinically in the treatment of thyroid gland deficiency diseases in adults and in the treatment of cretinism in children. Thyroxine medications which include combinations of levothyroxine, and/or liothronine, or dextrothyroxine, or thyroid, and one or more iodine salts, or iodine donor compounds are described, which produce a stable thyroxine medication, with a long shelf life.