The effects of dietary iodine on thyroid ultrastructure

This is a morphological study of changes in thyroid cells following iodine deficiency and iodine excess. Fifteen young male Sprague-Dawley rats were divided into three groups and fed one of the following diets for 6 weeks: low iodine (LID), normal iodine (NID) and high iodine (HID). Then the thyroid glands were removed and processed for light and electron microscopy. Thyroid tissue from the NID group was normal in appearance. The most outstanding feature of HID thyroids was the presence of numerous cells which contained irregularly shaped and stained lysosomes. These displaced other cell organelles and caused the apical cell surfaces to project into the follicle lumen. Thyroids from the LID group were three times heavier than the other two groups. Their follicles were very small, contained very little colloid. They were surrounded by dilated capillaries. Mitoses were frequent. Cells were columnar and contained abundant dilated endoplasmic reticulum, numerous apical vesicles, long microvilli and many mitochondria. Mitochondria were especially abundant in greatly infolded lateral and basal cell membranes. These findings show that there is a redistribution of organelles in thyroid cells in response to iodine deficiency and iodine excess which can be related to alterations in intracellular iodine metabolism.