Triiodothyronine turnover studies in euthyroid patients with autonomous thyroid nodules

Abstract

Triiodothyronine (T 3) kinetic studies were carried out using 125I-T 3 and the single injection technique in eight clinically euthyroid patients with autonomous thyroid nodules and the metabolic results were compared to those obtained in a group of 12 healthy control subjects. Plasma labeled T 3 concentration was measured by a chromatographic method based on the extraction of the hormone on Sephadex G-25 columns, followed by its elution with a specific anti-T 3 antiserum. The analysis of the experimental plasma disappearance curves of the labeled hormone was performed using the noncompartmental method. The results obtained showed a significantly increased metabolic clearance rate of T 3 in the patients with autonomous thyroid nodules, as compared to the control group. On the average, the T 3 production rates were increased more significantly than the corresponding circulating levels of the hormone, therefore, suggesting that the significant TSH inhibition observed in the euthyroid patients with autonomous thyroid nodules could be related with an increased peripheral utilization of triiodothyronine.