Abstract Background: Hyperthyroidism (Hy) is an endocrine disorder, in which the thyroid hormones markedly alter the cardiac function. Increased myocardial contractility and cardiac output, improvement in diastolic relaxation, changes in electrical activity, increments in ventricular mass, and arrhythmias have been reported. However, the influences of thyroid hormones upon molecular mechanisms of cardiac functions have not yet been fully understood. Objectives: To evaluate changes in cardiac contractile parameters and the Na+/Ca2+ exchanger (NCX) function in induced hyperthyroid rats. Methods: Hy was induced by intraperitoneal injections of T3 (15 μg/100 g) for 10 days. Contractile parameters and NCX function were evaluated in the isolated papillary muscle. Data normality was confirmed by the Shapiro-Wilk test. The comparison between groups was performed through an unpaired Student’s t-test. Results are expressed as mean ± SD. The accepted significance level was p < 0.05. Results: Our data revealed, in the Hy group, an increase of 30.98% in the maximum speed of diastolic relaxation (–284.64 ± 70.70 vs. –217.31 ± 40.30 mN/mm2/sec (p = 0.027)) and a boost of 149% in the NCX function in late phase of relaxation (20.17 ± 7.90 vs. 50.22 ± 11.94 minutes (p = 0.002)), with no changes in the maximum twitch force (p = 0.605) or maximum speed of systolic contraction (p = 0.208) when compared to the control. Conclusion: The improvement in relaxation parameters is hypothetically attributed to an increase in Sarco-Endoplasmic Reticulum Ca2+ATPase isoform 2 (SERCA2) expression and an increased calcium flow through L-type channels that boosted the NCX function.

Resumo Introdução: Atletas profissionais e recreativos utilizam suplementos nutricionais diariamente para melhorar a performance física. Os ácidos graxos poliinsaturados (PUFA) têm sido usados nesse sentido. Os n-3 PUFA, particularmente os ácidos eicosapentaenoicos (EPA) e docosaexaenoico (DHA), são relacionados com importantes funções fisiológicas e os benefícios da suplementação são demonstrados em diversas populações. O óleo de fígado de tubarão (OFT) é fonte natural de n-3 PUFA. Objetivo: Avaliar o efeito da suplementação com OFT na contratilidade de músculos esqueléticos com diferentes características metabólicas, sóleo e extensor longo de dedos (EDL) de ratos submetidos a oito semanas de treinamento intervalado de intensidade progressiva em esteira motorizada. No grupo suplementado, os animais foram suplementados com OFT (1 g/kg) cinco vezes por semana por oito semanas. Método: Parâmetros contráteis como produção de força isométrica máxima (Tmax), velocidade máxima de contração (+dF/dt), velocidade máxima de relaxamento (-dF/dt), força tetânica máxima (Fmax) e resistência à fadiga foram analisados em músculos isolados. Resultados: Comparados ao grupo controle, os músculos EDL dos animais do grupo suplementado reduziram Tmax no primeiro (10.82 ± 0.89 vs 14.30 ± 0.67 mN/mm2. p < 0.01) e no segundo minutos de experimentação (9.85 ± 0.63 vs 13.12 ± 0.70 mN/mm2. p < 0.01), entretanto, aumentaram a resistência à fadiga (22.80 ± 0.97 vs 18.60 ± 0.51 segundos. p = 0.005). Conclusão: Nenhuma diferença foi observada no músculo sóleo.

Abstract Introduction: Professional and recreational athletes make daily use of nutritional supplements to improve physical performance. Polyunsaturated fatty acids (PUFAs) have been used in this sense. N-3 PUFA, particularly eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids are involved in important physiological functions and the benefits of supplementation are demonstrated in several types of users. Shark liver oil (SLO) is a natural source of n-3 PUFA. Objective: To evaluate the effect of supplementation with SLO on contractility of skeletal muscles with different metabolic characteristics, soleus and extensor digitorum longus (EDL) from rats submitted to eight weeks of interval training of progressive intensity on a motorized treadmill. In the supplemented group, animals were supplemented with SLO (1 g/kg) five times a week for eight weeks. Method: Contractile parameters as maximum isometric twitch force (Tmax), maximum speed of force development (+dF/dt), maximum speed of force decrease (-dF/dt), maximum tetanic force (Fmax) and resistance to fatigue were analyzed in isolated muscle. Results: Compared to the control group, EDL muscles from the supplemented group reduced Tmax at the first (10.82 ± 0.89 vs 14.30 ± 0.67 mN/mm2. p < 0.01) and second minutes of experimentation (9.85 ± 0.63 vs 13.12 ± 0.70 mN/mm2. p < 0.01). However, it increased resistance to fatigue (22.80 ± 0.97 vs 18.60 ± 0.51 seconds. p = 0.005). Conclusion: No difference was observed in the soleus muscle.

Resumen Introducción: Los atletas profesionales y recreativos utilizan suplementos nutricionales diariamente para mejorar el rendimiento físico. Los ácidos grasos poliinsaturados (PUFA) se han utilizado en este sentido. Los n-3 PUFA, particularmente los ácidos eicosapentaenoicos (EPA) y el docosaexáenoico (DHA), se relacionan con importantes funciones fisiológicas y los beneficios de la suplementación se demuestran en diversas poblaciones. El aceite de hígado de tiburón (AHT) es fuente natural de n-3 PUFA. Objetivo: Evaluar el efecto de la suplementación con AHT en la contractilidad de músculos esqueléticos con diferentes características metabólicas, sololeo y extensor largo de dedos (EDL) de ratas sometidas a ocho semanas de entrenamiento intervalado de intensidad progresiva en estera motorizada. En el grupo suplementario, los animales fueron suplementados con AHT (1 g/kg) cinco veces por semana durante ocho semanas. Método: Parámetros contráctiles como producción de fuerza isométrica máxima (Tmax), velocidad máxima de contracción (+dF/dt), velocidad máxima de relajación (-dF/dt), fuerza tetánica máxima (Fmax) y resistencia a la fatiga se analizaron en músculos aislados. Resultados: En comparación con el grupo control, los músculos EDL de los animales del grupo suplementado redujeron Tmax en el primer (10.82 ± 0.89 vs 14.30 ± 0.67 mN/mm2. p < 0.01) y en el segundo minuto de experimentación (9.85 ± 0.63 vs 13.12 ± 0.70 mN/mm2. p < 0.01), sin embargo, aumentaron la resistencia a la fatiga (22.80 ± 0.97 vs 18.60 ± 0.51 segundos. p = 0.005). Conclusión: No se observó ninguna diferencia en el músculo sóleo.