Chapter 61 - Bromide Interference with Iodine Metabolism: Goitrogenic and Whole-body Effects of Excessive Inorganic Bromide in the Rat

Abstract

This chapter reviews conclusions drawn from recent research on the interference of excessive bromide intake with iodine metabolism in the rat. The biological behavior of bromide ion, especially in the thyroid gland, is compared with the behavior of iodide and chloride. The effects of both organic and inorganic bromides on human health are briefly mentioned. The effects of an enhanced bromide intake in the rat on the thyroid function, and on the whole-body metabolism of iodine are also summarized. Inorganic, as well as organic, bromides (methyl bromide) exert toxic effects in animals and humans, especially on the CNS, with a rather steep dose–response curve. The biological behavior of bromide in the thyroid gland, in contrast to other organs and tissues, is more similar to the behavior of iodide rather than that of chloride. High bromide intake in the rat decreases the amount of iodide accumulated in the thyroid and exerts goitrogenic effects. It is suggested that high levels of bromide in the organism of experimental animals can influence their iodine metabolism in two parallel ways: by a decrease in iodide accumulation in the thyroid and skin (and in the mammary glands in lactating dams), and by a rise in iodide excretion by the kidneys. Very high bromide intake in the rat significantly shortens the biological half life of iodine in the thyroid (from about 100 to 30 h). The nature of the toxic effects of bromide on the thyroid gland and the mechanisms of its interference with the biosynthesis of thyroid hormones has not been explainded so far. It is suggested that a high surplus of bromide ions in blood can competitively inhibit the entrance of iodide into the thyroid and bromide can replace a part of iodide in the gland.