Serum Concentrations of 3, 3’-Diiodothyronine, 3’, 5’-Diiodothyronine, and 3, 5-Diiodothyronine in Altered Thyroid States

Abstract

To investigate the thyroid hormone metabolism in altered states of thyroid function, serum concentrations of 3, 3’-diiodothyronine (3, 3’-T2), 3’, 5’-T2 and 3, 5-T2 as well as T4, T3 and rT3 were determined by specific radioimmunoassays in 17 hyperthyroid and 10 hypothyroid patients, before and during the treatment. Serum T4, T3, rT3, 3, 3’-T2 and 3’, 5’-T2 concentrations were all higher in the hyperthyroid patients than in age-matched controls and decreased to the normal ranges within 3 to 4 months following treatment with antithyroid drugs. In the hypothyroid patients, these iodothyronine concentrations were lower than in age-matched controls and returned to the normal ranges after 2 to 3 months treatment with T4. In contrast, serum 3, 5-T2 concentrations in hyperthyroid patients (mean±SE : 4.0±0.5 ng/dl) were not significantly different from those in controls (3.9±0.4 ng/dl), although they tended to decrease in 3 of 6 patients after the antithyroid drug therapy. Serum 3, 5-T2 levels in the hypothyroid patients (3.8±0.6 ng/dl) were also within the normal range and showed no significant change following the T4 replacement therapy. However, serum 3, 5-T2 as well as 3, 3’-T2 concentrations rose significantly with a marked rise in serum T3 following T3 administration, 75 μg/day for 7 days, in Graves’ patients in euthyroid state. These results indicate that serum concentrations of 3, 3’-T2 and 3’, 5’-T2 well reflect the thyroid function states, but that serum 3, 5-T2 concentrations change little in altered thyroid function states, although it is monodeiodinated from T3 in vivo. © 1983, The Japan Endocrine Society. All rights reserved.