Effects of sodium bromide on the biosynthesis of thyroid hormones and brominated/iodinated thyronines

The influence of bromide on thyroid function was studied in iodine-deficient rats, fed on a diet containing 4-16 g/kg sodium bromide for 4 weeks. Measurement of total and free thyroxine and thyroid-stimulating hormone in blood, as well as the thyroid hormones in the thyroid gland, revealed typical signs of hypothyroidism, which were significantly enhanced by bromide intake. Special attention was paid to the possible formation of bromo/iodosubstituted thyronines in the thyroid. These measurements were performed by high-performance liquid chromatography with off-line radioimmunoassay detection. Such thyroid hormone analogues could be detected in all groups of animals with additional bromide intake, but the amounts were found to be too low to compensate adequately for the reduced amounts of thyroid hormones. The results of this study also indicate that bromide toxicity is dependent upon the state of the iodine supply, which should be taken into account for evaluation of acceptable daily intake values for bromide.