THYROGLOBULIN FORMATION IN THE THYROID FOLLICLE VISUALIZED BY THE “COATED AUTOGRAPH” TECHNIQUE

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Abstract
When tracer doses of radio-iodine are detected in the thyroid by the radioactive autograph method, the detectable radio-iodine is present as thyroglobulin. In rats receiving 22 gamma of non-radioactive iodine daily,the radioactivity is mostly present in the epithelium at 1 hour, and in the colloid at 24 hrs. after injn. In iodine-deficient rats, the deposition of radio-iodine into the colloid was much accelerated, since it was found there as early as 2 min. after injn. In hypophysectomized animals, the deposition of radio-activity into the colloid is depressed, since the radioactive material is still present in the cells at 24 hrs. after injn. These results indicate that thyroglobulin is formed in the cells and released into the colloid, this sequence being most rapid in active thyroids and slow after hypophysectomy. The secretion polarity of the thyroid cell in the direction of the colloid, suggested by the above data, is further demonstrated by the presence of a considerable amt. of radio-iodine in the colloid at 2, 7 and 15 min. after injn., although no significant amt, of protein-bound iodine can be detected in the blood at that time. The presence of radioactivity in all follicles as early as 1 hr. and in one case, 2 min. after radio-iodine injn. shows that all follicles in any gland are active at all times in fixing I. However, the rate of I fixation by the various follicles is variable; thus, in the rat less active follicles are located under the capsule and in the isthmus of the gland. From the data presented, it seems likely that circulating iodide is continuously bound to protein (i.e., thyroglobulin) in the cytoplasm of the thyroid cells. This thyroglobulin is continuously deposited in the colloid of the thyroid follicle. Excretion of the thyroid hormone itself probably results from the proteolytic breakdown of thyroglobulin in the colloid and the diffusion of the resulting fragments through the epithelial wall of the follicle.