Characteristics of 3,5,3'-triiodothyronine sulfate metabolism in euthyroid man
- University of Southern California, School of Medicine, Department of Medicine, LA (United States)
The sulfated conjugate of T3 (T3S) has long been recognized as a normal product of peripheral thyroid hormone metabolism. In order to better understand the role that T3S may play in this process, the metabolic handling of T3S was studied in euthyroid man. After the iv administration of (125I)T3S in man, T3S was found to be rapidly metabolized with estimated mean MCR of 135 {plus minus} 15 liters/day (L/D) after a bolus injection and 127 {plus minus} 8 L/D employing a constant infusion. The primary route of T3S disposal was by deiodination with an efficiency of 92%. The administration of propylthiouracil (PTU, 300 mg every 6 h {times} 5 days) and iopanoic acid (IA, 500 mg every day {times} 5 days), both inhibitors of deiodination, decreased clearance compared to control (87 {plus minus} 9 L/D, P less than 0.01 and 46 {plus minus} 10 L/D, P less than 0.002, respectively). A 3-day fast also reduced the clearance of T3S (56 {plus minus} 10 L/D, P less than 0.002). All three maneuvers decreased the total urinary deiodination fraction of tracer T3S (control 91 {plus minus} 2%, PTU 70 {plus minus} 9%, P less than 0.04, IA 26 {plus minus} 3%, P less than 0.0001, and fasting 58 {plus minus} 6%, P less than 0.01). A strong correlation between T3S clearance and deiodination was noted for fasting and IA only (r = 0.78, P less than 0.003). However, no relationship between clearance and deiodination was noted with PTU administration presumably as a result of a compensatory increase in biliary losses of T3S. The urinary thyronine excretion pattern demonstrated the presence of small amounts of labeled T3,3,3{prime}-T2, and 3,3{prime}-T2S with the major metabolite being T3S itself. TSH levels were not influenced by the infusion of stable T3S designed to achieve a serum value greater than 50 ng/dL. No absorption of intact T3S was detected after its oral ingestion.
- OSTI ID:
- 5077843
- Journal Information:
- Journal of Clinical Endocrinology and Metabolism; (United States), Vol. 73:4; ISSN 0021-972X
- Country of Publication:
- United States
- Language:
- English
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THYROID
BIOLOGICAL FUNCTIONS
TRIIODOTHYRONINE
METABOLISM
FASTING
IODINE 125
ORAL ADMINISTRATION
TRACER TECHNIQUES
BETA DECAY RADIOISOTOPES
BODY
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
ENDOCRINE GLANDS
GLANDS
HORMONES
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANS
PEPTIDE HORMONES
PROTEINS
RADIOISOTOPES
THYROID HORMONES
550501* - Metabolism- Tracer Techniques