Radioimmunoassay for 3,5-diiodothyronine and evidence for dependence on conversion from 3,5,3'-triiodothyronine

Journal Article · Sun Jun 01 04:00:00 EDT 1980 · J. Clin. Endocrinol. Metab.; (United States)

DOI:https://doi.org/10.1210/jcem-50-6-1075· OSTI ID:5220896

Pangaro, L; Burman, K D; Wartofsky, L; Cahnmann, H J; Smallridge, R C; O'Brian, J T; Wright, F D; Latham, K

The present report describes a RIA for 3,5-diiodothyronine (3,5T/sub 2/) which uses inner ring-labeled 3,5-(/sup 125/I)T/sub 2/ as the ligand and has a lower limit of detectability of 0.5 ng/dl. Cross-reaction was 0.14% with T/sub 3/, less than 0.001% with T/sub 4/, 1.2% with 3,3',5-triiodothyroacetic acid, and 6.1% with 3,5-diiodothyroacetic acid. No cross-reaction was detectable for iodothyronines within their physiological ranges. Intraassay variation ranged from 2.2 to 7.8%, and interassay variation ranged from 12.7 to 14%. The mean (+-SE) serum 3.5T/sub 2/ concentration in 70 normal subjects was 4.3 +- 0.2 ng/dl. The mean (+-SE) 3.5T/sub 2/ in 14 hyperthyroid patients was increased to 18.4 +- 2.3 ng/dl (P < 0.001), and all but 1 patient had an elevated level. In 10 hypothyroid patients the mean (+-SE) 3,5T/sub 2/ level was decreased to 1.4 +- 0.3 ng/dl (P < 0.001). In 4 patients, levels overlapped with the normal range. In 4 hypothyroid subjects treated with L-T/sub 1/, 3,5T/sub 2/ levels were normal, suggesting that the majority of 3,5T/sub 2/ originates from extrathyroidal conversion from T/sub 3/. Studies in fasting obese subjects demonstrated that serum 3,5T/sub 2/ (mean +- SE) levels fell from 3.4 +- 0.3 to 2.5 +- 0.7 ng/dl during fasting. This fall was significant (P < 0.001) and in parallel with the fall in T/sub 3/ levels of 182 +- 20 to 126 +- 12 ng/dl. In fasting subjects given 100 ..mu..g oral L-T/sub 3//day T/sub 3/ levels rose from 138 +- 11 to 362 +- 26 ng/dl. 3,5T/sub 2/ levels (corrected for cross-reaction and for contamination of oral T/sub 3/ with 3,5T/sub 2/) rose from 2.2 +- 0.7 to 6.4 +- 1.0 ng/dl. In fasting subjects given 25 ..mu..g oral L-T/sub 3//day, T/sub 3/ levels fell from 165 +- 5.1 to 139 +- 6.9 ng/dl. Corrected 3,5T/sub 2/ levels changed from 3.7 +- 0.4 to 2.5 +- 0.3 ng/dl. Neither change were significant.

• Research Organization: Walter Reed Army Medical Center, Washington, DC
• OSTI ID: 5220896
• Journal Information: J. Clin. Endocrinol. Metab.; (United States), Journal Name: J. Clin. Endocrinol. Metab.; (United States) Vol. 50:6; ISSN JCEMA
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
62 RADIOLOGY AND NUCLEAR MEDICINE
AMINO ACIDS
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BIOSYNTHESIS
CARBOXYLIC ACIDS
DAYS LIVING RADIOISOTOPES
DIAGNOSIS
DIAGNOSTIC USES
DISEASES
ELECTRON CAPTURE RADIOISOTOPES
ENDOCRINE DISEASES
HORMONES
HYDROXY ACIDS
HYPERTHYROIDISM
HYPOTHYROIDISM
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
PEPTIDE HORMONES
PRECURSOR
RADIOASSAY
RADIOIMMUNOASSAY
RADIOISOTOPES
REACTION KINETICS
SYNTHESIS
THYROID HORMONES
THYRONINE
TRACER TECHNIQUES
TRIIODOTHYRONINE
USES