Circulating Irisin Concentrations in Rat Models of Thyroid Dysfunction - Effect of Exercise

Objectives. The speculation that the myokine irisin could regulate whole body energy expenditure led to the anticipation that irisin may have therapeutic potential in metabolic diseases. Regulation of irisin under conditions of metabolic derangements in altered thyroid status, and the changes in irisin response to exercise remain to be investigated. Methods. Serum irisin concentration was measured in sixty male Wistar rats subjected to either sedentary life or 8-week chronic swimming exercise after induction of hyper- or hypothyroidism (10 rats/group). The effect of acute exercise on serum irisin was assessed in 10 additional rats subjected once to forced swimming against a load (5% of body weight) and compared to sedentary rats. Results. Serum irisin was significantly higher in both sedentary hyper- and hypothyroid rats (by 45%, p < 0.001, and 30%, p < 0.001, respectively) versus euthyroid controls. Serum irisin also increased after acute exercise (p < 0.001 versus sedentary control). Chronic training episodes failed to significantly alter serum irisin in all thyroid hormone profiles. Serum irisin correlated positively with serum creatine kinase (r = 0.45, p < 0.001) and with muscle and liver concentrations of malondialdehyde (r = 0.50 and r = 0.47 respectively, p < 0.001 for both), and negatively with muscle and liver content of reduced glutathione (r = 0.34, p = 0.003 and r = -0.28, p = 0.018 respectively) in pooled groups. However, significance of these associations was waived when analyzing each group separately. Serum irisin was not associated with skeletal muscle mass, insulin resistance, blood glucose, lipids or TSH. Conclusions. Both hyper- and hypothyroidism are associated with up-regulation of serum irisin in male rats, possibly as a response to oxidative damage and/or myopathy observed in both conditions. Acute exercise, which is also associated with oxidative stress, increases serum irisin. No obvious association was detected linking serum irisin to metabolic abnormalities in thyroid dysfunction. (C) 2015 Elsevier Inc. All rights reserved.