[Changes in thyroid hormone status after injections of iodinated contrast media]

Administration of four different contrast media exerted slight but significant and prolonged effects on the hormonal thyroid status, in 53 euthyroid subjects (four subgroups), without any clinical expression of dysthyroidism. Changes in serum T3, rT3 and T4 demonstrated different trends for each iodinated compound, probably depending on the regulatory thyroid mechanisms, and CM pharmacokinetics. Plasma profiles of free fractions (FT3, FT4) slightly reflected consensual changes with circulating iodothyronines, at various time periods of study, demonstrating high correlation indexes with total fractions. The five hormones profiles correlation study suggest that different mechanisms could be responsible for some features encountered of "low T3 syndrome". These effects may be not only equivalent to giving various sources of iodide, but suggest more complex mechanisms. It is apparent that man has a remarkable and possibly unique system of homeostatic thyroid hormone regulation.