Influence of stable iodine on the uptake of the thyroid - model vs. experiment

Aim: The influence of physiological and pharmacological amounts of iodine o n the uptake of radioiodine in the thyroid was examined in a 4-compartment model. This model allows equations to be derived describing the distributio n of tracer iodine as a function of time. The aim of the study was to compa re the predictions of the model with experimental data. Methods: Five euthy roid persons received stable iodine (200 mug, 10 mg). 1-123-uptake into the thyroid was measured with the Nal(T1)-detector of a body counter under phy siological conditions and after application of each dose of additional iodi ne. Actual measurements and predicted values were compared, taking into acc ount the individual iodine supply as estimated from the thyroid uptake unde r physiological conditions and data from the literature. Results: Thyroid i odine uptake decreased from 80% under physiological conditions to 50% in in dividuals with very low iodine supply (15 mug/d) (n = 2). The uptake calcul ated from the model was 36%. iodine uptake into the thyroid did not decreas e in individuals with typical iodine supply, i.e. for Cologne 65-85 mug/d ( n = 3). After application of 10 mg of stable iodine, uptake into the thyroi d decreased in all individuals to about 5%, in accordance with the model ca lculations. Conclusion: Comparison of theoretical predictions with the meas ured values demonstrated that the model tested is well suited for describin g the time course of iodine distribution and uptake within the body. It can now be used to study aspects of iodine metabolism relevant to the pharmaco logical administration of iodine which cannot be investigated experimentall y in humans for ethical and technical reasons.