title: Effects of thyroid hormones on mitochondrial oxygen consumption in brown adipose tissue and heart from cold-exposed hypothyroid rats.
abstract: The present work measured brown adipose tissue and heart mitochondrial oxygen consumption in hypothyroid rats treated with replacement doses of T3, T4 or T4 plus iopanoic acid and kept at 4 degrees C for 24 h. Heart oxygen consumption in normal, untreated hypothyroid and T4-treated hypothyroid rats was unaffected by cold exposure. In rats treated with T4 plus iopanoic acid, rates of oxygen consumption were normal in those maintained at 4 degrees C as well as in those kept at room temperature, despite serum T3 concentration being significantly decreased. The cold-exposed T3-treated hypothyroid rats showed a marked decrease in oxygen consumption (p less than 0.02) and alpha-glycerophosphate dehydrogenase activity, a T3-dependent enzyme. Mitochondrial oxygen consumption in brown fat from normal (p less than 0.01), T4 (p less than 0.02) and T4 plus iopanoic acid-treated (p less than 0.01) rats rose more than twofold in response to cold. In the T3-treated group, oxygen consumption at room temperature was higher (p less than 0.02) than in any other group at similar temperatures. However, the T3-treated group showed no changes in oxygen consumption in response to cold, perhaps because this group reached the maximal response at room temperature. The untreated and the T3-treated hypothyroid rats (both groups devoid of T4) did not survive at 4 degrees C unless T4 or several-fold replacement amounts of T3 were administered. The data demonstrate the crucial role of T4 in thermogenesis during cold exposure.
authors.affiliation: CONICET, Hospital de Clinicas, Buenos Aires, Argentina.
authors.forename: L F
authors.initials: LF
authors.lastname: Cageao
authors.forename: I R
authors.initials: IR
authors.lastname: Mignone
authors.forename: C R
authors.initials: CR
authors.lastname: Ricci
authors.forename: C C
authors.initials: CC
authors.lastname: Brignone
authors.forename: J A
authors.initials: JA
authors.lastname: Brignone
authors.forename: A A
authors.initials: AA
authors.lastname: Zaninovich
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism* / Q000648:ultrastructure; D002001:Adipose Tissue, Brown / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology; D003080:Cold Temperature; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D007037:Hypothyroidism / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D007480:Iopanoic Acid / Q000494:pharmacology; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D009929:Organ Size; D010101:Oxygen Consumption / Q000187:drug effects* / Q000502:physiology; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013974:Thyroxine / Q000378:metabolism / Q000494:pharmacology*; D014284:Triiodothyronine / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D014284:Triiodothyronine; D005993:Glycerolphosphate Dehydrogenase; D007480:Iopanoic Acid; D013974:Thyroxine