The effect of bromide on the ultrastructure of rat thyrocytes.

Electron microscopic examination of thyroid tissue following administration of bromide to rats showed marked hypertrophy and hyperplasia in the thyrocytes, microfollicular rearrangement and lowered volume of colloid. The luminal surface of the thyrocytes showed increased size and number of microvilli, often filling the microlumen. Most of the nuclei were irregular in shape with unusual incisions and a higher density of chromatin. Proliferation of ER was seen with significantly dilated cisterns containing low electron density material. The Golgi complex was well developed and larger in rats receiving 10 mg Br/l drinking water (16 days) and 100 mg Br/l (16 and 66 days) than in control rats. Granules and small spherical structures (50-100 nm) appeared in the subapical part of the cytoplasm and their number increased in animals after administration of 50 mg Br-/l (16 and 66 days), 100 mg Br-/l (16 and 66 days), 200 and 400 mg Br-/l (133 days). In contrast, their number was reduced in thyrocytes of rats treated with 100 mg Br/l (16, 66 and 133 days). Colloid droplets were only rarely found. There was no significant change in the amount of mitochondria, secondary lysosomes including phagolysosomes. Some thyrocytes showed signs of necrosis in animals following administration of 10 mg Br/l (16 days, 100 and 400 mg Br/l, 133 days). Clusters of thyrocytes with spongy cytoplasm and bizarre shaped nuclei were found in groups treated with 100 mg Br/l, and 400 mg Br-/l (133 days). These changes, with previously published light microscopical, radioanalytical and biochemical findings, confirm the goitrogenic effect of bromide.