Production rates and turnover of triiodothyronine in rat-developing cerebral cortex and cerebellum. Responses to hypothyroidism
Local 5'-deiodination of serum thyroxine (T4) is the main source of triiodothyronine (T3) for the brain. Since we noted in previous studies that the cerebral cortex of neonatal rats tolerated marked reductions in serum T4 without biochemical hypothyroidism, we examined the in vivo T4 and T3 metabolism in that tissue and in the cerebellum of euthyroid and hypothyroid 2-wk-old rats. We also assessed the contribution of enhanced tissue T4 to T3 conversion and decreased T3 removal from the tissues to the T3 homeostasis in hypothyroid brain. Congenital and neonatal hypothyroidism was induced by adding methimazole to the drinking water. Serum, cerebral cortex (Cx), cerebellum (Cm), liver (L) and kidney (R) concentrations of 125I-T4, 125I-T3(T4), and 131I-T3 were measured at various times after injecting 125I-T4 and 131I-T3. The rate of T3 removal from the tissues was measured after injecting an excess of anti-T3-antibody to rats previously injected with tracer T3. In hypothyroidism, the fractional removal rates and clearances were reduced in all tissues, in cortex and cerebellum by 70%, and in liver and kidney ranging from 30 to 50%. While greater than 80% of the 125I-T3(T4) in the brain tissues of euthyroid rats was locally produced, in hypothyroid cerebral cortex and cerebellum the integrated concentrations of 125I-T3(T4) were 2.7- and 1.5-fold greater than in euthyroid rats.
- Research Organization:
- Department of Medicine, Harvard Medical School, Boston, Massachusetts
- OSTI ID:
- 6184564
- Journal Information:
- J. Clin. Invest.; (United States), Journal Name: J. Clin. Invest.; (United States) Vol. 74:3; ISSN JCINA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMISTRY
BODY
BRAIN
CENTRAL NERVOUS SYSTEM
CEREBELLUM
CHEMISTRY
DAYS LIVING RADIOISOTOPES
DISEASES
ELECTRON CAPTURE RADIOISOTOPES
ENDOCRINE DISEASES
HORMONES
HYPOTHYROIDISM
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE 131
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
MAMMALS
METABOLISM
NERVOUS SYSTEM
NUCLEI
ODD-EVEN NUCLEI
ONTOGENESIS
ORGANS
PEPTIDE HORMONES
RADIOISOTOPES
RATS
RODENTS
THYROID HORMONES
TRACER TECHNIQUES
TRIIODOTHYRONINE
VERTEBRATES