Abstract
Adult male Wistar-Imamichi rats were given the drinking water containing 1-2 ppm or 200 ppm of iodine ad libitum for 5, 15 and 60 days. The thyroid gland cells were investigated light and electron microscopically. The mean value of T/S ratio was lower markedly in rats with 200 ppm of iodide intake. The peculiar big canals invaginated deeply the gland cell from the colloid lumen in most of rats given 200 ppm of iodine for 5 and 15 days, whereas they were not recognized in rats given for 60 days, therefore the occurrence of them is temporal. These canal systems extend irregularly and are complicated in shape, either dilated or constricted. The cross-sections of the canals represent huge granules and are eventually in contact with the basement membrane, invading the deepest area. The content of the canals seems to be identical with the luminal colloid and their wall is equipped with the elongated numerous microvilli. The intracellular canals in thyroid gland cells have been observed for the first time in the present electron microscopy. As to their functional significance, the possible transient reabsorption of thyroglobulin has been suggested.
