Relationship between T₄, T₃ and T₄/T₃ Ratio in Thyroid Tissue, Thyroid and Peripheral Veins in Patients with Nontoxic Nodular Goiter

Summary

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 1-thyroxine 150 μg daily. A significant correlation between iodothyronine concentrations and T₄/T₂ 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 TJT₃ 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.

Key words

Goiter - T₄/T₃ ratio - Thyroid tissues - Thyroid veins - Peripheral veins