Relationship between T4, T3 and T4/T3 ratio in thyroid tissue, thyroid and peripheral veins in patients with nontoxic nodular goiter.

The relationship between T4, T3 and T4/T3 ratio in thyroid nodules/paranodular tissues, thyroid and peripheral veins has been investigated in 26 patients with nontoxic nodular goiters; eleven of them were treated with l-thyroxine 150 micrograms daily. A significant correlation between iodothyronine concentrations and T4/T3 [corrected] ratio in paranodular thyroid tissues and thyroid effluents was found in both groups of patients. By contrast, the correlation between these parameters in the nodule and thyroid veins was poor, which implies that the thyroid hormone pattern in the thyroid veins on the side of nodular lesion is predominantly controlled by the release of the hormones from paranodular healthy tissue. A close dependence of the serum T4/T3 ratio on the values of iodothyronines and their ratio in thyroid tissues and thyroid veins was observed in nontreated, but not in treated patients. Conversely, in the latter group, the thyroidal T4/T3 ratio in paranodular tissue, but not in the nodule, was found to be dependent on the serum T4/T3 ratio, suggesting that paranodular thyroid tissue more readily responds to 1-thyroxine-inhibited TSH secretion. The results demonstrate that 1. the serum thyroid hormone pattern under physiological conditions is dependent on the intrathyroidal T4/T3 ratio, and 2. minor alterations in the serum thyroid hormones may secondarily change the thyroidal T4/T3 ratio, presumably by their effect on TSH secretion.