Metabolism. 1980 Oct;29(11):1031-6. doi: 10.1016/0026-0495(80)90212-7.

Labeled metabolites appearing in human serum after 125I-triiodothyronine (T3) administration: a quantitative reappraisal.

Metabolism: clinical and experimental

G C Zucchelli, A Pilo, D Giannessi, R Bianchi, F Cazzuola, N Molea

PMID: 7432167 DOI: 10.1016/0026-0495(80)90212-7

Abstract

The appearance in human serum of labeled iodothyronines arising from 3,5,3'-triiodothyronine (T3) catabolism was measured after bolus administration of 125I-T3. The use of column chromatography made it possible to separate in the plasma samples iodoproteins, iodide, T3 and a fourth peak ("pre-T3") eluting just before T3. The radioactivity associated with this pre-T3 peak was found to be 0.5% of T3 activity 30 min after injection, and reached a plateau value of 5.6% +/- 1.2 (mean +/- SD) from the 10th hr onward. From these data, we calculated that a maximal 5% underestimation in T3 metabolic clearance rate is inherent in those analytical methods that do not completely separate pre-T3 from T3 radioactivity. The MCR of 3,3'-diiodothyronine (T2) was also measured from the plasma disappearance curve after single injection of 125I-3,3'-T2. From these data and the mean disappearance curve of T3, the appearance curve of 3,3'-T2 in plasma was reconstructed by convolution under the assumption of a 100% conversion of T3 to 3,3'-T2. A plateau value of 4.6% of T3 activity was computed, very comparable to the experimentally determined 5.6%. This suggest that, if labeled 3,3'-T2 is the main component of the pre-T3 peak, the conversion into 3,3'-T2 represents a major pathway of T3 metabolism in man.

Substances

• Diiodothyronines
• Thyronines
• Triiodothyronine

MeSH terms

• Chromatography, Gel
• Diiodothyronines / blood
• Humans
• Kinetics
• Metabolic Clearance Rate
• Thyronines / blood
• Triiodothyronine / blood

Publication Types

• Journal Article

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