SUMMARY
Introduction. Iodine as a component of thyroid hormones is accumulated in the thyroid gland. This permits to study the thyroid gland functional activity by focusing on the iodine content in its tissue.The aim of the study – to learn the effect of organic and inorganic iodine on its content in the thyroid gland under the conditions of subclinical hyperthyroidism.Research Methods. White non-linear male rats (n=90) with an initial body weight of 140–160 g were kept on a iodine-deficient isocaloric starch-casein diet with a food mixture and consumed minimally active, moderate and large doses of iodine (21, 50, 100 µg/kg body weight) with potassium iodide (inorganic iodine) or iodine-protein preparation made of the Black Sea red algae Phyllophora nervosa (D?.) Grev (organic iodine) within the period of 30 days. The iodine content in the thyroid tissue (absolute, relative, and per 100 g of body weight) was determined using the Winkler procedure principle in J. F. Sadusk, Jr., & E. G. Ball.Results and Discussion. The iodine content in the thyroid glands depended on its chemical nature and the dose. Consumption of 21 µg/kg body weight of organic iodine caused a sharp increase of its content in the thyroid glands; with the consumed dose increase, the organ’s iodine concentration ability decreased. The iodine content in the thyroid gland when consuming inorganic iodine in the dose of 21, 50 and 100 µg/kg body weight, was significantly less than in consuming the similar amounts of organic iodine. The consumption of the large (100 µg/kg body weight) dose of iodine in the both iodine-containing substances was accompanied by a decrease of the iodine content in the thyroid gland tissue.Conclusions. In the conditions of subclinical hyperthyroidism, the intake of organic iodine increases the iodine content in the thyroid gland tissue, the effect of inorganic iodine being less pronounced. The best prerequisites for the thyroid gland functional activity growth are the intake of a minimal dose (21 µg/kg body weight) of organic iodine and a minimal and moderate dose (21 and 50 µg/kg body weight) of inorganic iodine. The minimal functional activity of the thyroid gland can be expected in rats which consumed a large dose of organic and inorganic iodine (100 µg/kg body weight).