engleski

Thyroidal conversion of thyroxine to triiodothyronine but not that to reverse triiodothyronine is increased in cold thyroid nodules

Thyroidal conversion of thyroxine(T4)to T3 and rT3 was investigated in cold thyroid nodules and paranodular tissues obtained during thyroid surgery from 10 patients with non-toxic nodular goiter.The tissues were homogenized in a glass homogenizer in 10 volumes ice-cold 50 mmol/l TRIS and 5 mmol DTT, cells and nuclei removed by centrifugation, and the particulate fraction collected as a pellet.The pellet was resuspended in a small volume of the same buffer and incubation was accomplished at 37 Celsius degree. A volume of 200 micro L 1.3 micro mol T4 was added to the thyroid tissue enzyme fraction and the reaction was stopped by adding ice-cold 95% ethanol after 5, 10 and 20 minutes.The generation of T3(pmol/mg protein) in cold nodules vs. paranodular tissues was 4.2&plusmn ; ; 0.97 (mean&plusmn ; ; SEM) vs. 3.5&plusmn ; ; 0.8 at 5 min ; 5.96&plusmn ; ; 1.49 vs. 4.0&plusmn ; ; 0.58 at 10 min ; and 8.0&plusmn ; ; 1.88 vs. 3.92&plusmn ; ; 0.65 (p<0.05) at 20 min.The respective values of rT3(pmol/mg protein) for nodular vs. paranodular tissues were 3.12&plusmn ; ; 0.48 vs. 2.47&plusmn ; ; 0.43 ; 3.43&plusmn ; ; 0.56 vs. 3.42&plusmn ; ; 1.32, and 2.87&plusmn ; ; 0.36vs. 3.39&plusmn ; ; 0.88(mean&plusmn ; ; SEM).Thyroid hormones were determined by use of commercial radioimmunoassays (from Institute of Immunology, Zagreb for T4 ; Ames for T3 ; and Biodata Serono for rT3). Variations in T4 to T3 deiodination patterns were observed in cold nodules: no conversion was detected in three nodules ; conversion patterns similar to those in paranodular tissues were found in two nodules ; and a significantly increased and sustained T4 to T3 deiodinating activity was observed in five nodules.Results suggested that an increased thyroidal T4 to T3 conversion rate in some cold thyroid nodules could be explained as a compensatory mechanism resulting in an increased delivery of the more potent T3.The conversion of T4 to rT3 was generally low, with no difference between the nodular and paranodular tissues, and probably without any effect on thyroid hormone metabolism.

thyroid tissue; cold nodules; paranodular tissue; deiodination

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