Effect of Methimazole Upon Thyroid Clearance of Circulating Iodide

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Abstract
Thyroid glandular clearance of iodide was studied in the dog by serial measurements of arterial and thyroid venous plasma l3lI concentration and thyroid venous flow before and after the intravenous injection of methimazole. A prompt, transient increase in measured clearance was observed 10–30 min after methimazole in 9 of 10 experiments in which a large quantity of iodide carrier had been given with the tracer iodide131I, while there was no increase in observed clearance in 5 of 6 experiments in which carrier-free iodide-l31I was given. The results suggest that methimazole decreases the rate at which iodide within the gland enters the circulation but has little effect upon the rate at which circulating iodide enters the gland. This response to methimazole would appear to be distinct from its well-known effect on inhibiting organic binding of iodine. (Endocrinology75: 89, 1964)