RESUMO
BACKGROUND: To understand the mechanism of aging-related changes of the thyroid, the differentiated functions and growth of thyroid cells in response to TSH were investigated using aged or young thyrocytes. METHODS: FRTL-5 cells, with less than 10 or more than 45 passages, were used. After treatment with 1 U/L TSH or 1-100 mM NaI, the cAMP generation, iodide uptake, cellular proliferation or the expression of NIS mRNA or protein were measured. Sprague-Dawley rats were sacrificed at 5 and 16 weeks and 23 months, and their thyroids used for Northern blot analysis or immunohistochemistry of NIS. RESULTS: There were no differences in cAMP generation, iodide uptake, the proportions of G1/M or S phase, or intracellular DNA contents between the young and aged cells at basel levels. After TSH stimulation, these were increased in dose-dependent manners, with larger increments in the young cells. The changes in the NIS mRNA expression were similar in both the young and aged cells, but to a greater extent in the young cells. A similar phenomenon was observed in rat. However, the amount or intracellular distribution of NIS protein was not different. There was also no difference in the function or expression of NIS after treatment with a high dose of iodide. CONCLUSION: The aging-related decrease in the generation of cAMP might be thought of as one of the mechanisms of the decrement of iodide uptake or cellular proliferation with aging. The decreased expression of NIS mRNA seems to be the most important mechanism for the decreased iodide uptake capacity