Iodine, Thyroxine (T4), Triiodothyronine (T3), 3,3′,5′-Triiodothyronine (rT3), 3,3′-Diiodothyronine (T2) in Normal Human Thyroids. Effect of Excessive Iodine Exposure

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Abstract
Twenty normal glands obtained from euthyroid subjects at autopsy were analyzed for total iodine (TI), PBI [protein bound iodine], L-thyroxine (T4), 3,3'',5-triiodothyronine (T3), 3,3'',5''-triiodothyronine (rT3) and 3,3''-diiodothyronine (T2) after pronase hydrolysis. The mean TI was 325.1 .+-. 47.2 .mu.g/g wet tissue, giving a total iodine per gland of 10.01 mg. Pretreatment with iodine containing X-ray drugs in 8 patients did not significantly affect these results with the exception of Lipiodol. The mean T4, T3, and T2 values were 93.0 .+-. 23.1 .mu.g/g, 5.25 .+-. 0.99 .mu.g/g, rT3 5.54 .+-. 1.05 .mu.g/g and 0.60 .+-. 0.19 .mu.g/g, respectively. In contrast to goitrous tissue, normal thyroid tissue showed no dependence of the T4/T3 ratio on the TI. Compared with goitrous tissue PBI consisted of much more T4-I in normal tissue. The corresponding values were 47.7 .+-. 11.8% and 12.7 .+-. 3.4%, respectively. A positive relationship was found between TI and T4, T3, rT3 but not with T2. The rT3 concentration corresponds to that of T3 in a remarkable way. The ratios of T3 to rT3 were similar, suggesting that thyroidal T3 and rT3 production is a random process. T2 represents only 0.73% of T4-I. The results in normal thyroid tissue clearly show that the difference in iodine concentrations in only 1 factor among others in comparison to goitrous tissue.