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Turnover and Urinary Excretion of Circulating Diiodotyrosine^*

Thyroid Research Group, Department of Nuclear Medicine, and Endocrine Department, Klinikum Steglitz, Free University Berlin Berlin, West Germany
The Division of Clinical Endocrinology, Department of Medicine, University Essen Berlin, West Germany
Small Animal Clinic of the Free University Berlin Berlin, West Germany

Address all correspondence and requests for reprints to: Dr. H. Meinhold, Department of Nuclear Medicine, Klinikum Steglitz, Free University Berlin, Hindenburgdamm 30, D-1000 Berlin 45, West Germany.

The MCR of diiodotyrosine (DIT) was determined by measuring serum DIT concentrations by RIA after a single injection of 200 µg DIT and noncompartmental analysis. Comparison of the stable DIT method with the tracer DIT technique in dogs yielded good agreement of measured DIT MCRs. The mean (±SD) MCR and blood production rate of DIT were 122 ± 29 L/day·70 kg and 24.2 ± 12.7 nmol/day·70 kg (10.5 µg/day·70 kg), respectively, in 10 normal subjects.

Urinary DIT was measured by RIA after its immunoprecipitation from urine. Acid hydrolysis had no effect on measured urinary DIT concentrations, suggesting the presence of predominantly unconjugated DIT. Mean urinary DIT excretion was 1.23 ± 0.43 (±SD) nmol/24 h (533 ng/24 h) or 0.108 ± 0.048 nmol/mmol creatinine in 32 normal individuals. In patients with defective thyroidal iodine metabolism, urinary DIT was extremely elevated, ranging from 1.2–17.7 nmol/mmol creatinine. Comparison of normal production and excretion rates suggests that about 5% of the daily extrathyroidal DIT turnover is excreted in the urine unchanged or in a DIT-like form.

^* Presented in part at the 14th Annual Meeting of the European Thyroid Association, Rotterdam, The Netherlands, September 1984, and at the 30th Symposium of the German Society of Endocrinology, Munich, West Germany, February 1986. This work was supported by the Deutsche Forschungsgemeinschaft (Me 582/5–3).

Received July 24, 1986.

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