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Inhibition of Organic Binding of Iodine with Graded Doses of Iodide in Euthyroid Men

Medical Service, Veterans Administration Research Hospital
Department of Medicine, Northwestern University Medical School Chicago, Illinois 60611

The inhibition of thyroidal organic binding of iodine by iodide (Wolff-Chaikoff effect) was studied in 15 euthyroid men. The subjects received 5 U thyrotropin im for 3 consecutive days and varying doses of iodide for 48 hr before measuring the thyroid uptake of 132I. After the determination of the 3 hr thyroid ¹³²I uptake, serum iodide, and thyroid iodide uptake, 1 g potassium perchlorate was given orally and thyroid ¹³²I was measured 1 hr later. A positive response indicative of inhibition of organic binding was defined as a loss of 15% ¹³²I in the thyroid at 3 hr. The base line thyroid uptake (5.00 ± 0.96%) and thyroid iodide uptake (4.48 ± 0.53 µg/hr) increased 3-fold with the administration of thyrotropin. As iodide intake increased, the serum iodide increased, the thyroid ¹³²I uptake fell, but the thyroid iodide uptake increased progressively. A positive perchlorate response occurred in 11 subjects at iodide doses ranging from 1 to 16 mg daily, serum iodide concentrations of 2.5 to 36.9 µg/100 ml, and thyroid iodide uptakes of 17.4 to 135 µg/hr. Although inhibition of binding did not occur in many instances in which the serum iodide and thyroid iodide uptake were in these ranges, for a given individual, inhibition of binding occurred at a higher thyroid iodide uptake and serum iodide concentration than that at which inhibition did not occur.

Supported in part by USPHS Research Grant AM 09599 from the National Institute of Arthritis and Metabolic Diseases.

¹ Veterans Administration Clinical Investigator.

Present address: Department of Medicine, University of Alabama Medical Center, Birmingham, Ala, 35233.

Received March 9, 1967.

Accepted July 20, 1967.