Activity of Iodotyrosine deshalogenase in “Normal” and Diseased Human Thyroids*

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Abstract
Iodotyrosine deshalogenase assays were performed on 40 surgical specimens from 39 human thyroid glands. Histologically normal thyroid tissue from 8 patients with thyroid cancer served as "normal" controls. The iodotyrosine deshalogenase activity of thyroid tissue from 10 patients with colloid adenomatous goiter and 5 patients with Hashimoto''s struma was within the range of activity found in "normal" thyroid tissue. Iodotyrosine deshalogenase activity was significantly lower (P<0.02) than "normal" in the thyroid glands of 2 patients with nonspecific thyroiditis. A clearcut difference from "normal" activity was not found in the thyroid glands of 8 thyrotoxic patients rendered euthyroid with propylthiouracil and Lugol''s solution. The Michaelis-Menten constant for iodotyrosine deshalogenase in the thyroids of these thyrotoxic patients did not differ significantly from "normal" (2.3X10-5 [image] and 1.8X10-5 [image] respectively.) The mean iodotyrosine deshalogenase activity in carcinomatous tissue from the thyroids of 8 patients was less than "normal" and tended to be lower in undifferentiated thyroid carcinoma than in the well differentiated form. The normal iodotyrosine deshalogenase activity found in Hashimoto''s struma, despite numerical reduction in follicles, is consistent with the hypothesis of an increased effect of TSH in this disorder. Because of preoperative preparation of the thyrotoxic patients with iodine, failure to find a clearcut increase above normal deshalogenase activity in the thyroids of this group cannot be considered evidence against the hypothesis of an increased action of TSH in thyrotoxicosis. The findings in thyroid carcinoma are consistent with a correlation between loss of differentiation and loss of function.