Nonhormonal Iodine Escape from the Normal and Abnormal Thyroid Gland1

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Abstract
A kinetic analysis of iodine metabolism was performed on 7 normal subjects on an iodine-restricted diet, 7 normal subjects and 7 subjects with simple goiter on the usual Japanese diet. 1) The mean intrathyroidal iodine content was 12.2, 27.6 and 43.3 mg/gland, respectively. 2) The escape of nonhormonal iodine from the thyroid gland was confirmed in all cases despite the restriction of dietary iodine. 3) After the occurrence of leveling off of the daily urinary excretion of 131I, the mean daily excretion rate of urinary 131I (E*) was 5 times greater than the mean daily degradation rate of labeled hormonal iodine in the extrathyroidal organic iodine pool (D*) and was 3 times greater than the mean daily secretion rate of the labeled hormonal iodine from the gland (H*). 4) The ratio of the mean daily excretion rate of urinary 131I (E*) to the mean daily secretion rate of PB131I from the gland (H*) was used as one of the indices for the release of nonhormonal iodine. The relationship in 19 subjects between the intrathyroidal iodine content (Q) and the index of E*/H* was Q =2.19 × (E*/H*)1.14; in other words, the greater the intrathyroidal iodine content, the greater the release of nonhormonal iodine. 5) Functional heterogeneity of iodine metabolism in the thyroid was observed in 2 cases.