[Thyroidal autoregulation in nontoxic goiter patients: normalization of the T3/T4 ratio in serum by treatment with potassium iodide (author's transl)].

In iodine deficiency areas, an increased T3/T4 ratio in serum was reported earlier. In this study the influence of potassium iodide on the T3/T4 ratio was investigated. Treatment with 200 mug KI per day for only 4 weeks normalized the initially elevated T3/T4 ratio in 16 nontoxic goiter patients (24.6 plus or minus 9.9 times 10-3, mean plus or minus S.D., before, respectively 18.9 plus or minus 5.5 times 10-3 after KI treatment, p smaller than 0.0025). The mean basal TSH levels (1.42 plus or minus 0.68 before, respectively 1.29 plus or minus 0.52 mugU/ml after KI), and the TSH increase 30 min after 200 mug TRH i.v. (5.54 plus or minus 4.22 and 6.50 plus or minus 5.09 mugU/ml, respectively) did not change significantly. Since the normalization of the T3/T4 ratio in nontoxic goiter patients was independent from changes in the TSH levels, this effect of KI obviously represents an example of thyroidal autoregulation.