Observations were made on the deiodination of I¹³¹-labeled L-diiodotyrosine (L-DIT I¹³¹) in 71 patients with various thyroid diseases. Of these patients 19 had simple goiter, 13 hyperthyroidism, 9 myxedema without goiter, 2 hypothyroidism with goiter, 5 cretinism with dysgenesis of the thyroid, 10 nodular goiter, 6 thyroid cyst, 3 thyroid cancer, 2 Hashimoto's struma, 1 Riedel's struma and 1 subacute thyroiditis.
1. Simple goiter
Thyroid tissues from the patients with simple goiter could deiodinate L-DIT I¹³¹ normally. All patients with simple goiter reported here had a normal rate of deiodination of administered L-DIT I¹³¹.
2. Hyperthyroidism
The iodotyrosine deiodinating activity of the thyroid in hyperthyroidism, though slightly higher than in simple goiter, was not significantly so. In the patients with hyperthyroidism, the rate of deiodination of administered L-DIT was similar to that in control subjects.
3. Myxedema
Many of the myxedematous subjects had a slow rate of deiodination of injected L-DIT I¹³¹ The percentage of labeled iodine which was present as L-DIT I¹³¹ in urine was distinctly higher in these patients than in control subjects. The percentage of the administered dose of L-DIT I¹³¹ which was excreted unchanged was higher in these patients than in any of the control subjects. This percentage was reduced by thyroid therapy. The results showed that these patients had a peripheral defect in deiodination of L-DIT I¹³¹, and that this defect was probably caused by hypothyroidism.
On the other hand, some of the patients with myxedema had a normal rate of deiodination of administered L-DIT I¹³¹ This finding might suggest that myxedema itself does not cause a defect in peripheral deiodination.
4. Hypothyroidism with goiter
Thyroid tissues from the 2 patients with goitrous hypothyroidism could not deiodinate L-DIT I¹³¹ in vitro. In these patients, the rate of deiodination of injected L-DIT I¹³¹ persisted after thyroid therapy. Thyroid tissue from one of these left the L-DIT I¹³¹ unchanged after thyroid therapy. Thus, it seemed that these patients had a deiodination defect in the thyroid, but not in the periphery.