POTASSIUM-BROMIDE AND THE THYROID-GLAND OF THE RAT - MORPHOLOGY AND IMMUNOHISTOCHEMISTRY, RIA AND INAA ANALYSIS

The increasing environmental concentration of bromine has resulted in attempts to obtain information on its possibly deleterious effect on h umans, particularly on a major target organ of this halogen i.e. the t hyroid gland. In order to establish the morphological and functional e ffects of bromine on the thyroid, we have performed experiments on mal e rats which, in addition to a standard diet with an estimated iodine/ bromine content, were fed for periods of 16 and 66 days with the small quantities of bromide expected to be encountered in the environment ( 10, 50 and 100 mg of Br-/1 in drinking water). This treatment induced growth of the follicular epithelial component and microfollicular tiss ue rearrangement, a reduction of intrafollicular colloid, an increase in the height of the follicular cells and the number of mitoses, and i t enhanced vascularization. Image analysis revealed a significant redu ction in the volume of colloid, despite the accompanying rise in the n umber of minute follicles. The immunohistochemical positivity of the t hyroglobulin fell in the microfollicular colloid of the exposed animal s, although this was affected to a lesser extent in the larger follicl es. The concentration of bromine in the thyroid increased with the amo unt of bromine intake, while at the same time the molar ratio of iodin e/bromine decreased. The plasma level of T-4 was lowered after both 16 and 66 days of treatment, but the T-3 level only after 66 days treatm ent. The level of TSH did not exhibit any significant change. The obse rved changes, which have a parenchymatous goitre-like character, may h ave a direct relevance for human medicine, since the concentrations of bromide chosen in these experiments are readily encountered in the en vironment.