LONG-TERM ACTION OF POTASSIUM-BROMIDE ON THE RAT-THYROID GLAND

Male rats fed by a standard diet with determined of bromine and iodine content were exposed to a 133-day oral administration of KBr (100, 20 0, 400 mg Br-/l drinking water). Their thyroid glands showed increased growth of the epithelial cells reflected by a microfollicular rearran gement of the parenchyma due to proliferation of very small follicles with a low or zero content of colloid. Morphometric analysis of thyroi ds of Br--exposed animals revealed a significant decrease in the volum e of intrafollicular colloid and marked increase in the number of the smallest follicles (areas up to 100 and 100-300 mu m(2)). In addition, the nuclei of thyrocytes showed an increased number of mitoses. The v ascularization was increased as well. In the blood plasma of the Br--e xposed animals the T-4 concentration was significantly decreased in de pendence on the bromine concentrations. Thyroglobulin immunoreactivity in the colloid of Br--exposed animals decreased after administration of 400 mg Br-/l drinking water. Increasing concentrations of Br- in th e drinking water caused an increased bromine concentration in the thyr oid a decreased iodine content and a decreased I/Br molar ratio. The c hanges in the rat thyroid caused by long-term administration of 100 mg Br-/l were similar to hyperplastic parenchymal goitre and were compar able to those induced in previous experiments by the same bromine conc entration administered over a 16- and 66-day period respectively.