<i>In Vitro</i>Leukocyte Uptake of¹³¹I Labeled Iodide, Thyroxine and Triiodothyronine, and Its Relation to Thyroid Function1

Abstract

The human leukocyte as an end organ indicator of thyroid activity was studied by determining in vitro uptake of 131I labeled iodide (Na131I), l-thyroxine (T4-131I) and l-triiodothyronine (T3-131I) after incubating these compounds with whole blood. For the 165 subjects studied, the mean fraction of the dose localized per leukocyte was, respectively, 1.65 × 10−11 for Na131I, 5.81 × 10−11 for T4-131I. and 4.01 × 10−11 for T3-131I. The uptake by the leukocyte was very high for each compound as compared to the erythrocyte, the average ratio being 1200 for Na131I, 870 for T4-131I, and 53 for T3-131I. Exposure to air during incubation with either Na131I or T3-131I produced a marked rise in leukocyte localization. Experiments with T3-131I on blood obtained from 10 hypothyroid, 52 euthyroid and 16 hyperthyroid subjects demonstrated that the fraction of the label taken up per leukocyte is significantly related to thyroid function; the respective averages were 2.25 ±0.58 × 10−11 (SD) for hypothyroids, 3.73 ±1.63 × 10−11 for euthyroids, and 6.02±3.41 × 10–11 for hyperthyroids. Na131I and T4-131I incubation results were not significantly correlated with clinical thyroid status. It is believed that these techniques provide a useful experimental tool for studying certain aspects of peripheral thyroid hormone metabolism in man.