title: Cold tolerance in hypothyroid rabbits: role of skeletal muscle mitochondria and sarcoplasmic reticulum Ca2+ ATPase isoform 1 heat production.
abstract: Brown adipose tissue (BAT) is involved in rat and mice thermoregulation, and heat produced by BAT depends on the concerted action of thyroid hormones and catecholamines. Little is known about cold-induced thermogenesis in mammals that have little or no BAT, such as rabbits. In these animals, thermogenesis primarily occurs in skeletal muscle. In this work, we have studied the effect of cold acclimation (4 C for 10 d) in normal and hypothyroid rabbits. It is known that hypothyroid rats die after a few hours of cold exposure. We now show that, different from rats, hypothyroid rabbits sustain their body temperature and survive after 10 d cold exposure. When compared with rabbits kept at room temperature, the muscles of cold-exposed rabbits showed a dark red color characteristic of oxidative muscle fibers. According to this pattern, we observed that in both normal and hypothyroid rabbits, cold exposure promotes an increase in oxygen consumption by skeletal muscle mitochondria. Moreover, in red muscle, cold acclimation induces an increase in the expression and activity of sarcoplasmic reticulum Ca(2+) ATPase isoform 1 (SERCA1), one of the muscle enzymes involved in heat production. We conclude that rabbit cold tolerance is probably related to increased muscle oxidative metabolism and heat production by SERCA1 and that these changes are not completely dependent on normal thyroid function.
authors.affiliation: Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro 21941-590, Brazil.
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Arruda
authors.forename: Luisa A
authors.initials: LA
authors.lastname: Ketzer
authors.forename: Mariana
authors.initials: M
authors.lastname: Nigro
authors.forename: Antonio
authors.initials: A
authors.lastname: Galina
authors.forename: Denise P
authors.initials: DP
authors.lastname: Carvalho
authors.forename: Leopoldo
authors.initials: L
authors.lastname: de Meis
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001835:Body Weight; D003080:Cold Temperature; D004435:Eating; D007037:Hypothyroidism / Q000097:blood / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D008931:Mitochondria, Muscle / Q000378:metabolism* / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D011817:Rabbits; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*; D022722:Thermogenesis; D013974:Thyroxine / Q000097:blood; D013997:Time Factors; D014284:Triiodothyronine / Q000097:blood
chemical_list: D014284:Triiodothyronine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013974:Thyroxine