Kinetics of the iodide trapping mechanism in normal and pathological human thyroid slices

Kinetics of the iodide trapping mechanism in thyroid slices was studied in human and animal tissues. Slices were incubated with several medium iodide concentrations, ranging from 5 x 10(-6)M to 2 x 10(-4)M, in order to calculate in the steady state the following kinetic parameters of the iodide transport: Km, maximal capacity (C) and diffusion factor (D). Results indicated that the Km was similar in magnitude (10(-5)M) in all cases where trapping activity was present, while maximal capacity (C) values showed significant differences between those pathologies in which trapping activity was hyperstimulated (dishormonogenetic goitre, Graves' disease, toxic adenoma) and those where thyroid tissues presented focal or total alterations on its structure (non-toxic nodular goitre, Hashimoto's thyroiditis, thyroid cancer) or where thyroid tissues were not sufficiently stimulated by TSH (extranodular tissue of toxic adenoma). 'Warm' nodules were not significantly different from normal human thyroid. These results suggest that the scattered trapping values observed in the different thyroid pathologies correspond to quantitative differences between them rather than to qualitative alterations in the thyroid iodide pump.