The benefits of diet supplementation to prevent iodine deficiency disorders are understood, but adverse effects also occur, including thyrotoxicosis and thyroiditis causing hypothyroidism. Previous evidence iodine-induced thyroiditis has come from experimental studies, pathological series, and cross-sectional epidemiological surveys. In the current study of three Chinese populations in regions with mildly deficient, more than adequate, and excessive iodine intake, Teng et al. have identified small, but significantly higher incidences of thyroid autoimmunity and subclinical hypothyroidism with higher iodine intakes, but no higher incidence of overt hypothyroidism. These findings are reassuring from the clinical and public health perspectives, confirming that iodization programs yield great benefits with little risk to human health.

Diagnostic and therapeutic use of radioiodine in the management of thyroid disorders depends on the ability of thyroid cells to concentrate radioiodine, a process that is regulated by the intracellular increase in cAMP. We hypothesized that theophylline, a drug known to increase intracellular cAMP via inhibition of phosphodiesterase, could increase thyroidal radioiodine uptake. We tested this effect in vivo, using C57BL/6j mice, and in vitro, using Fisher rat thyroid (FRTL-5) cells. One mouse received 2.5mg theophylline i.p., whereas a control mouse received only saline. Twenty-hours after theophylline, mice were injected with 10mu Ci Na(125)I in 0.1 mL saline through the tail vein. Mean thyroidal (125)I activity was 3.3-fold higher in theophylline-treated mice than in their respective controls. Radioiodine uptake and intracellular cAMP production of FRTL-5 cells were increased by a relatively low concentration of theophylline (1mu M). Intracellular cAMP increased up to 30 min and then declined in response to 1mu M theophylline. Sera from theophylline-treated mice stimulated (125)I uptake and intracellular cAMP production by FRTL-5 cells. These findings show that theophylline can enhance radioiodine uptake by thyrocytes in vivo and in vitro. The in vitro effects of theophylline on both radioiodine uptake and cAMP production in a dose-dependent manner are consistent with an action mediated by phosphodiesterase inhibition.
Animals ; Blood Proteins/pharmacology ; Cells, Cultured ; Cyclic AMP/metabolism ; Female ; Iodine Radioisotopes/*diagnostic use/pharmacokinetics ; Mice ; Mice, Inbred C57BL ; Theophylline/*pharmacology ; Thyroid Gland/cytology/*metabolism ; Vasodilator Agents/*pharmacology