Canine hypothyroidism under the conditions of prolonged exposure to low doses of ionizing radiation
The results of thyroid gland damage features studies in clinically healthy dogs in the zone of prolonged exposure to low doses of ionizing radiation (zone III of radioactive contamination) are presented. It is established that the studied zone belongs to the biogeochemical province of iodine deficiency. The power of the exposure dose in the zone is 3 times higher than that in a relatively clean zone and is 3.1-3.8 nCl/kg/h (41-41.4 mcR/h). The specific density of the dogs' diet according to Cesium-137 in animals of the III zone exceeded by 5 times that in animals of the pure zone, and the specific activity of thyroid tissue exceeded by 6 times. The results of the clinical study determined the underdevelopment of dogs in the III zone of radioactive contamination, which was manifested in a lag in growth and weight gain, insufficient blood supply to the distal parts of the body, skin pathologies, cardiovascular insufficiency, gastroenterocolitis. The enlargement of the thyroid gland was manifested only by palpation and was determined as an increase of the I degree. Laboratory studies have established a violation of hematopoiesis (hypochromic anemia, regenerative shift of the nucleus to the left, a tendency to lymphopenia, monocytosis), liver failure in the form of damage to hepatocytes (hyperfermentation of aspartate aminotransferase and gammaglutamyltranspeptidase), renal failure in the form of a violation of the filtration and resorption function of the organ (a tendency to creatininemia), as well as a violation of lipid metabolism (cholisterinemia). A significant decrease in the level of thyroid hormones triiodothyronine and thyroxine occurs against the background of a decrease in the level of thyroid-stimulating hormone. Thus, hypothyroidism has a secondary origin, due to the depressing effect of radionuclides on the thyretropic hormone. The results of morphometric and histological studies indicate hyperplasia of the organ due to the proliferation of interfollicular tissue. The specific area of the follicles is reduced, the follicles themselves are devoid of colloid. Thyrocytes have a flattened shape and are desquamated. Hemorrhages were found in the interfollicular tissue. Such changes determine the impossibility of normal synthesis of thyroid hormones necessary for normal metabolism. The pathomorphological picture is equivalent to secondary hypothyroidism, and laboratory data determine the consequences of exposure to low doses of ionizing radiation.