Fasting induces the generation of serum thyronine-binding globulin in Zucker rats
Five-month-old lean and obese Zucker rats were fasted for up to 7 days (lean rats) or 28 days (obese rats), and serum total and free T4 and T3 concentrations, percent free T4 and T3 by equilibrium dialysis, and the binding of (/sup 125/I) T4 to serum proteins by gel electrophoresis were measured. In the lean rats, a 4- or 7-day fast resulted in significant decreases in serum total and free T4 and T3 concentrations. There was a decrease in the percent free T3 after 7 days of starvation. In contrast, a 4- or 7-day fast did not alter any of these variables in the obese rats. However, after 14 or more days of starvation, serum total T4 and T3 concentrations increased, and the percent free T4 and T3 decreased, resulting in no change in the serum free T4 or T3 concentrations in the obese rats. The percent of (/sup 125/I)T4 bound to serum thyronine-binding globulin increased and the percent bound to thyronine-binding prealbumin decreased with the duration of the fast in both the lean and obese rats. The increase in serum thyronine-binding globulin binding of T4 can explain the increase in serum total T4 and T3 concentrations, the decrease in percent free T4 and T3, and the normal free hormone concentration in the long term fasted obese rats. The findings in the lean rats appear to be due to a combination of the known central hypothyroidism that occurs during 4-7 days of fasting and the fasting-induced changes in T4 binding in serum. Changes in T4 and T3 binding in serum during fasting in the rat must be considered when the effects of fasting on serum concentrations of the thyroid hormones, thyroid hormone kinetics, and the peripheral action of the thyroid hormones are evaluated.
- Research Organization:
- Univ. of Massachusetts Medical School, Worcester
- OSTI ID:
- 5483532
- Journal Information:
- Endocrinology; (United States), Journal Name: Endocrinology; (United States) Vol. 116:4; ISSN ENDOA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
ANIMALS
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL ADAPTATION
BLOOD CHEMISTRY
CARBOXYLIC ACIDS
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
ELECTROPHORESIS
FASTING
GLOBULINS
HORMONES
HYDROXY ACIDS
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
MAMMALS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
PEPTIDE HORMONES
PROTEINS
RADIOISOTOPES
RATS
REACTION KINETICS
RODENTS
THYROID HORMONES
THYRONINE
TRACER TECHNIQUES
TRIIODOTHYRONINE
VERTEBRATES