Iodine, thyroxine (T4), triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (T2) in normal human thyroids. Effect of excessive iodine exposure.

TLDR: Normal thyroid tissue showed no dependence of the T4/T3 ratio on the Tl, suggesting that thyroidal T3 and rT3 production is a random process.

Abstract: 20 Normal glands obtained from euthyroid subjects at autopsy were analysed for total iodine (Tl), PBl, L-thyroxine (T4), 3,3',5-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (T2) after pronase hydrolysis. The mean Tl was 325.1+-47.2 micrograms/g wet tissue, giving a total iodine per gland of 10.01 mg. Pretreatment of 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 micrograms/g, 5.25+-0.99 micrograms/g, 5.54+-1.05 micrograms/g and 0.60+-1.19 micrograms/g, respectively. In contrast to goitrous tissue, normal thyroid tissue showed no dependence of the T4/T3 ratio on the Tl. Compared with goitrous tissue PBI consisted of much more T4-l in normal tissue. The corresponding values were 47.7+-11.8% and 12.7+-3.4%, respectively. A positive relationship was found between Tl and T4, T3, rT3 but not with T2. The rT3 concentration corresponds to that of T3 in a remarkable way. The ratios of T3 or rT3 were similar, suggesting that thyroidal T3 and rT3 production is a random process. T2 represents only 0.73% of T4-l. Our results in normal thyroid tissue clearly show that the difference in iodine concentrations is only one factor among others in comparison to goitrous tissue.