Low thyroidal T3 in nodular goitrous tissue.

Six nodular tissues of non-treated and four of treated patients (suppressive treatment with thyroid hormones from three months to two years until the operation) with nodular non-toxic goitre contained low T3 (less than 1 ug/g w.w.). The results of iodothyronines and thyroglobulin (Tg) were compared with respective tissues containing T3 greater than 1 ug/g w.w. In non-treated patients, nodular tissues with low T3 and very high T4/T3 ratio showed T4 and Tg concentrations not different from the tissues with T3 greater than 1 ug/g w.w. In the goitres with low T3 of treated patients, T4 was also reduced but disproportionately to T3. Microscopically, nodular goitres with low T3 were characterized with gross fibrous infiltration and diffuse haemorrhage which was substantially different from histological findings in nodular goitres with T3 greater than 1 ug/g w.w. High T4/T3 ratio in the tissues with low T3 is similar to increased T4/T3 ratio in paranodular tissues of autonomously functioning adenomas. The results suggest that low T3 and high T4/T3 ratio in nodular goitrous tissue could be due to grossly impaired thyroid function or due to suppressed secretion of TSH.