title: Exogenous thyroid hormones regulate the activity of citrate synthase and cytochrome c oxidase in warm- but not cold-acclimated lake whitefish (Coregonus clupeaformis).
abstract: Thermal acclimation is known to elicit metabolic adjustments in ectotherms, but the cellular mechanisms and endocrine control of these shifts have not been fully elucidated. Here we examined the relationship between thermal acclimation, thyroid hormones and oxidative metabolism in juvenile lake whitefish. Impacts of thermal acclimation above (19°C) or below (8°C) the thermal optimum (13°C) and exposure to exogenous thyroid hormone (60µg T4/g body weight) were assessed by quantifying citrate synthase and cytochrome c oxidase activities in liver, red muscle, white muscle and heart. Warm acclimation decreased citrate synthase activity in liver and elevated both citrate synthase and cytochrome c oxidase activities in red muscle. In contrast, induction of hyperthyroidism in warm-acclimated fish stimulated a significant increase in liver citrate synthase and heart cytochrome c oxidase activities, and a decrease in the activity of both enzymes in red muscle. No change in citrate synthase or cytochrome c oxidase activities was observed following cold acclimation in either the presence or absence of exogenous thyroid hormones. Collectively, our results indicate that thyroid hormones influence the activity of oxidative enzymes more strongly in warm-acclimated than in cold-acclimated lake whitefish, and they may play a role in mediating metabolic adjustments observed during thermal acclimation.
authors.affiliation: Department of Biology, University of Regina, Regina, Saskatchewan S4S 0A2, Canada.
authors.forename: Megan A
authors.initials: MA
authors.lastname: Zak
authors.affiliation: U.S. Geological Survey, Leetown Science Center, Conte Anadromous Fish Research Laboratory, Turner Falls, MA 01376, USA.
authors.forename: Amy M
authors.initials: AM
authors.lastname: Regish
authors.affiliation: U.S. Geological Survey, Leetown Science Center, Conte Anadromous Fish Research Laboratory, Turner Falls, MA 01376, USA.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: McCormick
authors.affiliation: Department of Biology, University of Regina, Regina, Saskatchewan S4S 0A2, Canada. Electronic address: richard.manzon@uregina.ca.
authors.forename: Richard G
authors.initials: RG
authors.lastname: Manzon
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D002950:Citrate (si)-Synthase / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D060106:Lakes; D009928:Organ Specificity / Q000187:drug effects; D010084:Oxidation-Reduction / Q000187:drug effects; D012487:Salmonidae / Q000378:metabolism*; D013696:Temperature; D013963:Thyroid Hormones / Q000494:pharmacology*
chemical_list: D013963:Thyroid Hormones; D003576:Electron Transport Complex IV; D002950:Citrate (si)-Synthase
keywords: Citrate synthase; Cytochrome c oxidase; Lake whitefish (Coregonus clupeaformis); Oxidative metabolism; Thermal acclimation; Thyroid hormones