Purpose Irisin is a newly discovered adipo-myokine known for having significant effects on body metabolism. Currently, there is a discussion regarding the relation between thyroid function and irisin concentration. This study was designed to evaluate the influential role of levothyroxine replacement therapy on circulating levels of irisin in patients with recently onset hypothyroidism following total thyroidectomy. Methods Circulating levels of thyroid hormones, irisin and other metabolic parameters, were assessed in 40 recently thy-roidectomized patients (34 females, mean age 50.1 ± 15.2 years) at baseline (5-7 day after surgery) and after 2 months under replacement therapy with levothyroxine. Results At baseline, circulating levels of thyroid hormones were indicative of hypothyroidism (TSH 12.7 ±5.0 μU/mL, FT3 1.9 ±0.7 pg/mL, FT4 8.7 ± 3.6 pg/mL). Mean serum irisin concentrations significantly increased after 2 months under replacement therapy with levothyroxine (from 2.2 ±0.6 to 2.9 ±0.6 μg/mL,p< 0.0001). Variations of circulating levels of irisin under levothyroxine replacement therapy were directly correlated with those of FT3 (Rho = 0.454, p = 0.0033) and FT4 (Rho = 0.451, p= 0.0035). Multivariate regression analysis revealed that changes in thyroid hormones concentrations explained up to 10% of the variations of serum irisin levels under levothyroxine replacement therapy (FT3 R~2 = 0.098, FT4 R~2 = 0.103). Conclusion Our study suggests that levothyroxine replacement therapy mildly influences irisin metabolism in patients with recently onset hypothyroidism following total thyroidectomy.
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