Demonstration of intracellular canals in thyroid gland cells of rats with high iodide intake.

It is the present acceptance in general that the level of dietary iodine is of paramount importance for the proper working of the thyroid gland. Remington low iodine diet is much used for studies on iodine deficiency in rats. This diet induces the hyperactive state of the thyroid gland, which is proved by the increase of I131 uptake and thyroid/serum radioiodide concentration ratio(T/S ratio)or by the change of the histological feature(Rosenberg et al., 1963), whereas the high iodine diet inhibits the release of thyroid hormone(Wolff-Chaikoff effect) and induces hypofunction of the thyroid gland(Miani, 1956). It is general consideration that hypofunction of the thyroid gland due to prolonged and excessive intake of potassium iodide takes place as the results of the decrease of hormone release, inhibition of hormone synthesis and of organic binding of iodine (Yamada et al., 1963; Frey, 1964). Morphological changes in the thyroid gland of rats due to various kinds of diets and the variations in administration of iodine were reported by Hagmuller (1958). He pointed out that low iodine diets led to signs of cell activation and the formation of parafollicular cells and that the administration of a large amount of iodine in drinking water was unable to prevent the activation of the thyroid gland, without goitrogenic response, in rats fed with low iodine diets, whereas high iodine dosage combined with a normal diet did not lead to changes in the thyroid gland. Few reports have been presented concerning the ultrafine structures of thyroid gland cells of rats fed with high iodine diets. Feldman (1961) investigated electron microscopically the changes of thyroid gland cells during the iodine deficient period. Milcu, Lupulesen and Petrovici (1963), Lupulescu and Petrovici(1964)studied the ultrastructural changes in the goitre induced by the low iodine diet in rats. In the present investigation, the particular big canals in the thyroid gland cells of rats given drinking water containing a large amount of iodine with a normal diet have been successfully observed in detail.