Interactions of thyroxine with thyroxine-binding globulin of low binding capacity

Journal Article · Tue Sep 01 04:00:00 EDT 1987 · J. Nucl. Med. Technol.; (United States)

OSTI ID:5995015

Cuaron, A

The physico-chemical interactions between thyroxine (T/sub 4/) and thyroxine-binding globulin (TBG) of low binding capacity were investigated by radioimmunoassay, equilibrium dialysis, and reverse flow electrophoresis. Knowledge of total and free T/sub 4/ (FT/sub 4/) concentrations in serum, and of the total binding capacity of the protein carrier (TTBG), allowed the determination of the association constant ruling these interactions (K/sub tbg/). Correlation between T/sub 4/ and FT/sub 4/ varies with TTBG, shifting the normal range for T/sub 4/. The level of FT/sub 4/ in serum is a function of the fractional saturation of TBG by endogenous hormones, which depends on T/sub 4/ and TTBG. Data on T/sub 4/, TTBG, and K/sub tbg/ were integrated into the general equation of the law of mass action and the results showed a very significant linear correlation with the values of FT/sub 4/ measured by equilibrium dialysis. It is concluded that the misleading results of serum T/sub 4/ measurements and of the free T/sub 4/ index, obtained in euthyroid individuals with low TTBG, cannot be ascribed to a reduction of the intrinsic sensitivity of the assay due to oversaturation of TBG by endogenous T/sub 4/, as previously postulated by others, but to a shift of their normal ranges produced by abnormal variations of TTBG. These results stress the need for data regarding TTBG for the proper interpretation of T/sub 4/, and for the calculation of the fractional saturation of TBG and the FT/sub 4/ concentration in serum. The authors have solved this problem by using an empirical equation relating TTBG to T/sub 4/ and triiodothyronine (T/sub 3/) uptake, which was previously derived by other workers.

• Research Organization: National Institute of Cardiology, Mexico City, MX
• OSTI ID: 5995015
• Journal Information: J. Nucl. Med. Technol.; (United States), Journal Name: J. Nucl. Med. Technol.; (United States) Vol. 15:3; ISSN JNMTB
• Country of Publication: United States
• Language: English

Related Subjects

550601* -- Medicine-- Unsealed Radionuclides in Diagnostics
62 RADIOLOGY AND NUCLEAR MEDICINE
AMINO ACIDS
BIOCHEMISTRY
BODY
CARBOXYLIC ACIDS
CHEMISTRY
CONFIGURATION INTERACTION
ELECTROPHORESIS
ENDOCRINE GLANDS
GLANDS
GLOBULINS
HORMONES
IMMUNOASSAY
IMMUNOGLOBULINS
IMMUNOLOGY
ISOTOPE APPLICATIONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC IODINE COMPOUNDS
ORGANS
PATIENTS
PEPTIDE HORMONES
PROTEINS
RADIOASSAY
RADIOIMMUNOASSAY
RADIOIMMUNOLOGY
THYROID
THYROID HORMONES
THYROXINE
TRACER TECHNIQUES