Autoradiographic localization of radioiodide in the thyroid gland of the mouse

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Abstract
Radioiodide was localized by autoradiographic methods in the thyroid gland of mice at short and at long time intervals after radioiodide injection. The formation of organic radioiodine was blocked by the prior injection of propylthiouracil. The image density over the cell was greater than over the lumen in less active glands at short time intervals after radioiodide injection. The image was as dense or denser over lumens than over cells in the more active glands even at short time intervals after radioiodide injection and in all glands independent of activity at long time intervals after injection. Density over small follicles was usually greater than over large ones at short time intervals after radioiodide injection, but generally was independent of follicle diameter at long time intervals after injection. The image over a lumen was uniform even at the shortest times observed, indicating that radioiodide diffuses rapidly, as might be anticipated from the diffusion constant of iodide in aqueous solutions. The results suggest that the principal site of the mechanism for the concentration of radioiodide by the follicle is the membrane at the basal end of the cell and that some follicles, usually the smaller ones, equilibrate radioiodide with blood radioiodide faster than others.