Thyroid Cases in Dogs and Cats.
Specific Hormones | Functions of Thyroid Hormones
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Number 55 4, total 4 (thyroxine): indicators, criteria-find out the price of animal experiments in Moscow The synthesis of these hormones requires iodine and tyrosine. As a product of the synthesis of hormones in the thyroid, an intermediate protein-thyroglobulin is formed, which accumulates in the follicles of the glands. It is the main product of thyroid secretion, and the release of 3 is very small. In the blood, thyroid hormone binds to protein, and the binding capacity of 4 is higher than 3. Less than 1% of 4 and 3 circulate in the blood in unbound form. In dogs, thyroid binding proteins include thyroxine binding globulin, thyroxine binding prealbumin, albumin and certain plasma lipoproteins. It is the main binding protein in dogs, but it does not exist in cats. Compared to humans, the lower concentration and structural differences between species explain the lower serum levels and rapid metabolism in dogs. Only the free or unbound form of thyroid hormone can enter the cell to perform its biological function or regulate the secretion of the pituitary gland. The thyroid hormone of the binding protein plays a storage role. When the hormone is released from the binding protein and enters the cell, it will slowly enter the circulatory system. The entry of thyroid hormones into cells is mediated by transporters. 3 enters the cell faster, is activated faster, and moves several times stronger than 4. Thyroid hormone forms a hormone receptor complex with receptors in the nucleus, then penetrates into the nucleus and binds to chromatin, thereby further affecting the expression of many genes encoding enzyme synthesis. Thyroid hormones also have some non-genomic effects, which are mediated through receptors in the plasma membrane and cytoplasm.
Thyroid hormones regulate many metabolic processes by changing the concentration and activity of many enzymes. Thyroid hormones affect the metabolism of substrates, vitamins and minerals, the secretion and degradation rate of almost all hormones, and the response of target tissues to these hormones. Thyroid hormone is very important in the development of the fetus, especially in the formation of the nervous and skeletal system. Thyroid hormones have a stimulating effect on the production of calories, the synthesis of proteins and enzymes, and almost all stages of carbohydrate and lipid metabolism (including the synthesis, mobilization and degradation of substances). In addition, thyroid hormone has a time-changing and inotropic effect on the heart, increasing the number and affinity of β-adrenergic receptors for catecholamines. These hormones are essential for proper effects on the respiratory center under hypoxia and hypercapnia. Stimulates red blood cell production and bone metabolism (increases bone formation and resorption). Basically, any tissue or organ will be affected by excess or deficiency of thyroid hormone.
The iodination process plays an important regulatory role in the homeostasis of thyroid hormones and affects the intracellular 3 concentration.
The principle of negative feedback Lesage reduces the production of thyroxine (thyrotropin releasing factor), which affects the production of the pituitary gland. In turn, it regulates the production of 4 and 3 in the thyroid. If the level of 3 in the blood drops, the thyroid begins to produce more thyroxine through the hypothalamic-pituitary system. When the level of 3 in the blood or thyroid cells increases, the production of 4 and the flow into the blood will decrease. 
The thyroid itself can participate in blood regulation by producing autoantibodies, thereby reducing the production of thyroxine. Another mechanism of regulation is in the cells of the hypothalamus, where the thyroxine metabolic pathway is converted to the production of 3 (under the action of type deiodinase), which blocks the cell's 3 nuclear receptors, thereby reducing the production of thyroxine. Reverse 3 (3) has an affinity for nuclear receptors that greatly exceeds the ability of 3 to bind to receptors. In this case, it cannot be recognized by 3 receptors. Even if there is an increase in the content of 4 and free 3, the decrease of 3 in the cell and the blockade of 3 receptors will lead to an increase in the production of thyroxine and an increase in the production of thyroxine. Urine is another important way of thyroid hormone metabolism. In veterinary medicine, serum total 4 and total 3 levels are usually determined. However, studies have shown that the basic serum 4 measurement (as opposed to the basic 3 measurement) is a very reliable method for identifying clinical symptoms and palpation of thyroid nodules in hyperthyroid cats. Therefore, the study of 4 levels in cat blood can be used as a screening test. It is a disease caused by lymphocytes and plasma cells destroying thyroid tissue, or due to idiopathic thyroid atrophy. Canine hypothyroidism caused by reduced pituitary gland production and prolonged pituitary dysfunction is rare. Feline hyperthyroidism is a disease caused by autonomous secretion caused by thyroid tissue hyperplasia or adenomatous lesions. 4 Excessive levels (toxic) can cause clinical symptoms such as irritability, loss of appetite, weight loss and polyuria and polydipsia syndrome. Diseases that are not directly related to the thyroid of both animals (tumor, inflammatory etiology or related to metabolic or hormonal disorders) can be caused by changing the binding of 4 to proteins, leading to increased thyroxine clearance or affecting the production of 4 The resulting reduction. Pituitary release or production of thyroid follicular cells4. In addition, some diseases are accompanied by free 4 deiodination and 3 formation. Certain drugs can affect the physiology of the thyroid. Therefore, in dogs with euthyroidism, certain diseases or certain drugs, the level of 4 in the blood may be lower than the lower limit of the reference value. Similarly, for cats with comorbidities not directly related to the thyroid gland or hyperthyroidism in cats using certain drugs, the value 4 may be within the reference range.
Before testing, animals must eat and drink for at least 13 hours. At a storage temperature of + 2 ... + 8, the stability of thyroxine in serum is 11 days, and at a storage temperature of -18 ... -24 for 2 months. Material requirements before analysis). The results of the study only contain information for doctors. Diagnosis is based on a comprehensive evaluation of various indicators and additional information. Hyperthyroidism caused by thyroid adenoma or adenomatous hyperplasia. Specific Hormones | Functions of Thyroid Hormones