Evidence of in vivo iodine-induced hyperthyroidism in hyperfunctional autoimmune and autonomous human thyroid tissue xenotransplanted to nude mice.

The effect of different doses of continuous iodine infusion on xenotransplanted human thyroid tissue from toxic adenoma, and Graves' disease was examined using 131I scintigraphy in athymic nude mice. In spite of pretreatment with high iodine doses (1.25 micrograms or 12.5 micrograms 131I per day via i.p. implanted minipumps, Alzet 2002), the radioactivity localized in the transplanted tissue of toxic adenoma was more than 50% of the radioactivity in the transplants of the controls without iodine pretreatment 2 h after 131I injection, which was not a significant difference. Moreover, after high iodine treatment the 131I turnover rate in the thyroid transplants of toxic adenoma increased significantly. A tendency to an increased turnover rate was already observed with the lower dose. In contrast to that the transplants of Graves' disease tissue and mouse thyroids responded to high iodine treatment with a significant decrease in 131I retention. Serum of an untreated patient with active Graves' disease or injections of TSH increased 131I retention and the 131I turnover rate in the transplanted tissue of Graves' disease significantly (P less than 0.01). Iodine turnover was still increased after high iodine treatment. These results again show that thyroid tissue of toxic adenoma remains hyperfunctional after transplantation to athymic nude mice in contrast to thyroid tissue of Graves' disease which loses all signs of hyperfunction, when no exogenous stimulator is administered. In addition, these data clearly demonstrate, for the first time under in vivo conditions, that high iodine doses accelerate iodine turnover and thus presumably hyperfunction of human toxic adenoma in a dose-dependent manner as well as of the activated thyroid in Graves' disease.