Thyroxine (T4) and triiodothyronine (T3): Effects of iodine on the serum concentrations and disposal rates in subjects from an endemic goiter area

Abstract

In iodine-deficient subjects the T3 and T4 peripheral metabolism was studied. A diminished disposal rate of T4 and an increase in T3 were found. Serum concentrations and disposal rates of both hormones were determined before and after KI administration. A mean initial concentration of T3 of 0.54 ± 0.014 µg/ 100 ml decreased after 6 months of treatment to 0.20 ± 0.029 µg/100 ml. T4 concentration increased from 5.3 ±0.82 µg/100 ml to 11.2 ± 1.68 µg/100 ml. Since T3 and T4 clearances were not modified by KI administration, disposal rates of both hormones changed in accordance with their serum concentration. The peripheral conversion of T4 to T3 is discussed and it is postulated that the changes observed could be the result of a modification of the thyroid secretion due to the chronic iodine deficiency. © 1974 by The Endocrine Society.