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Increased resistance to hydrogen peroxide‐induced cardiac contracture is associated with decreased myocardial oxidative stress in hypothyroid rats
Authors:Alex Sander da Rosa Araujo  Madalena Freitas Silva de Miranda  Ubirajara Oliveira de Oliveira  Tânia Fernandes  Susana Llesuy  Luiz Carlos Rios Kucharski  Neelam Khaper  Adriane Belló‐Klein
Affiliation:1. Physiology Department, Basic Health Sciences Institute at Federal University of Rio Grande do Sul, Porto Alegre, Brazil;2. Catedra de Quimica General y Inorgánica. Facultad de Farmacia y Bioquimica, Universidad de Buenos Aires, Buenos Aires, Argentina;3. Northern Ontario School of Medicine, Medical Sciences Division, Lakehead University, Thunder Bay, Ontario, Canada
Abstract:The purpose of this study was to determine whether decreased oxidative stress would increase the resistance to cardiac contracture induced by H2O2 in hypothyroid rats. Male Wistar rats were divided into two groups: control and hypothyroid. Hypothyroidism was induced via thyroidectomy. Four weeks post surgery, blood samples were collected to perform thyroid hormone assessments, and excised hearts were perfused at a constant flow with or without H2O2 (1 mmol/L), being divided into two sub‐groups: control, hypothyroid, control + H2O2, hypothyroid + H2O2. Lipid peroxidation (LPO) was evaluated by chemiluminescence (CL) and thiobarbituric acid reactive substances (TBARS) methods, and protein oxidation by carbonyls assay in heart homogenates. Cardiac tissue was also screened for superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities, and for total radical‐trapping antioxidant potential (TRAP). Analyses of SOD and glutathione‐S‐transferase (GST) protein expression were also performed in heart homogenates. Hypothyroid hearts were found to be more resistant to H2O2‐induced contracture (60% elevation in LVEDP) as compared to control. CL, TBARS, carbonyl, as well as SOD, CAT, GPx activities and TRAP levels were reduced (35, 30, 40, 30, 16, 25, and 33%, respectively) in the cardiac homogenates of the hypothyroid group as compared to controls. A decrease in SOD and GST protein levels by 20 and 16%, respectively, was also observed in the hypothyroid group. These results suggest that a hypometabolic state caused by thyroid hormone deficiency can lead to an improved response to H2O2 challenge and is associated with decreased oxidative myocardial damage. Copyright © 2009 John Wiley & Sons, Ltd.
Keywords:thyroid hormones  protein expression  antioxidant enzymes  oxidative damage  heart function
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