Effects of thyroxine on rat brown fat and muscle thermogenesis in the cold.
We studied whether the activation of rat brown adipose tissue (BAT) by cold exposure or by the administration of beta-3-noradrenergic agonist CGP-12177 could be prevented by the inhibition of thyroxine (T4) to triiodothyronine (T3) conversion. Hypothyroid rats were treated with replacement doses of T4, T4 plus iopanoic acid (IA) or T3. Groups of rats were placed at 4 degrees C for 24 h or kept at room temperature. Cold exposure induced a significant increase in guanosine diphosphate (GDP) binding to BAT mitochondrial proteins in T4-treated rats, an effect not abolished by IA. No significant changes were seen in T3-treated rats. In rats maintained at room temperature and injected with CGP-12177, T4 induced a significant rise in GDP binding which was not blocked by IA. T3 also induced a significant increase in binding. The study of mitochondrial oxygen consumption in muscle from cold-exposed rats showed a marked decrease in consumption in T3-treated rats as compared to values in the warm. Normal oxygen consumption was restored with 2-fold doses of T3 replacement, whereas 5-fold doses increased consumption above normal. The data suggest that in states with low or absent T3, T4 can stimulate heat production and preserve normothermia.
Hospital de Clínicas and Ingebi, University of Buenos Aires, Argentina.
A A
AA
Zaninovich
I
I
Rebagliati
M
M
Raíces
C
C
Ricci
K
K
Hagmüller
D002001:Adipose Tissue, Brown / Q000187:drug effects* / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D003080:Cold Temperature; D006153:Guanosine Diphosphate / Q000378:metabolism; D007480:Iopanoic Acid / Q000494:pharmacology; D008297:Male; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D022722:Thermogenesis / Q000187:drug effects*; D013974:Thyroxine / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D011412:Propanolamines; D014284:Triiodothyronine; D006153:Guanosine Diphosphate; D007480:Iopanoic Acid; D013974:Thyroxine; C033394:CGP 12177