Cold-increase in brown fat thyroxine 5'-monodeiodinase is attenuated in Zucker obese rat
In this study the authors examined the possibility that the reduced brown adipose tissue (BAT) thermogenesis in the Zucker obese rat may result from a limited capacity for enzymic conversion of thyroxine (T/sub 4/) to triiodothyronine (T/sub 3/) in BAT. A total of 34 lean and obese rats, approx.4 mo old were divided into three treatment groups: group 1 (5 lean and 6 obese) was fed Purina rat chow for 21 days, and group two (5 lean and 6 obese) was fed a cafeteria diet for 21 days, and groups 3 (6 lean and 6 obese) was fed Purina rat chow and maintained in the cold (8 +/- 1/sup 0/C) for 7 days. Activity of T/sub 4/ 5'-deiodinase was determined as the rate of T/sub 3/ production from added T/sub 4/ under controlled in vitro conditions. Serum T/sub 4/ and T/sub 3/ were determined by radioimmunoassay. The rate of T/sub 4/-to-T/sub 3/ conversion in BAT was similar in the lean and obese rats maintained at room temperature, whether fed rat chow or a cafeteria diet. However, expressed per scapular BAT depot, lean rats exposed to cold displayed about a fivefold increase in BAT T/sub 3/ production whereas only a small increase was observed in the cold-exposed obese rats. Serum T/sub 3/ levels tended to be reduced in the Zucker obese rats. The data indicate a reduced capacity for T/sub 3/ production of Zucker rat BAT exposed to cold. This defect may account for the reduced tolerance of the obese animals to cold, but it does not account for their reduced diet-induced BAT thermogenesis.
- Research Organization:
- Univ. of California, Davis
- OSTI ID:
- 6352381
- Journal Information:
- Am. J. Physiol.; (United States), Vol. 252:1
- Country of Publication:
- United States
- Language:
- English
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ADIPOSE TISSUE
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THYROXINE
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TRIIODOTHYRONINE
METABOLIC DISEASES
OXIDOREDUCTASES
RATS
AMINO ACIDS
ANIMAL TISSUES
ANIMALS
BODY
CARBOXYLIC ACIDS
CHEMISTRY
CONNECTIVE TISSUE
DISEASES
ENZYMES
HORMONES
IMMUNOASSAY
IMMUNOLOGY
ISOTOPE APPLICATIONS
MAMMALS
ORGANIC ACIDS
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RADIOASSAY
RADIOIMMUNOLOGY
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THYROID HORMONES
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550601* - Medicine- Unsealed Radionuclides in Diagnostics