ß2-Adrenergic Signaling Modulates Mitochondrial Function and Morphology in Skeletal Muscle in Response to Aerobic Exercise.

The molecular mechanisms underlying skeletal muscle mitochondrial adaptations induced by aerobic exercise (AE) are not fully understood. We have previously shown that AE induces mitochondrial adaptations in cardiac muscle, mediated by sympathetic stimulation. Since direct sympathetic innervation of neuromuscular junctions influences skeletal muscle homeostasis, we tested the hypothesis that ß2-adrenergic receptor (ß2-AR)-mediated sympathetic activation induces mitochondrial adaptations to AE in skeletal muscle. Male FVB mice were subjected to a single bout of AE on a treadmill (80% Vmax, 60 min) under ß2-AR blockade with ICI 118,551 (ICI) or vehicle, and parameters of mitochondrial function and morphology/dynamics were evaluated. An acute bout of AE significantly increased maximal mitochondrial respiration in tibialis anterior (TA) isolated fiber bundles, which was prevented by ß2-AR blockade. This increased mitochondrial function after AE was accompanied by a change in mitochondrial morphology towards fusion, associated with increased Mfn1 protein expression and activity. ß2-AR blockade fully prevented the increase in Mfn1 activity and reduced mitochondrial elongation. To determine the mechanisms involved in mitochondrial modulation by ß2-AR activation in skeletal muscle during AE, we used C2C12 myotubes, treated with the non-selective ß-AR agonist isoproterenol (ISO) in the presence of the specific ß2-AR antagonist ICI or during protein kinase A (PKA) and Gαi protein blockade. Our in vitro data show that ß-AR activation significantly increases mitochondrial respiration in myotubes, and this response was dependent on ß2-AR activation through a Gαs-PKA signaling cascade. In conclusion, we provide evidence for AE-induced ß2-AR activation as a major mechanism leading to alterations in mitochondria function and morphology/dynamics. ß2-AR signaling is thus a key-signaling pathway that contributes to skeletal muscle plasticity in response to exercise.

Strength training prior to muscle injury potentiates low-level laser therapy (LLLT)-induced muscle regeneration.

We evaluated whether strength training (ST) performed prior to skeletal muscle cryolesion would act as a preconditioning, improving skeletal muscle regeneration and responsiveness to low-level laser therapy (LLLT). Wistar rats were randomly assigned into non-exercised (NE), NE plus muscle lesion (NE + LE), NE + LE plus LLLT (NE + LE + LLLT), strength training (ST), ST + LE, and ST + LE + LLLT. The animals performed 10 weeks of ST (climbing ladder; 3× week; 80% overload). Forty-eight hours after the last ST session, tibialis anterior (TA) cryolesion was induced and LLLT (InGaAlP, 660 nm, 0.035 W, 4.9 J/cm2/point, 3 points, spot light 0.028 cm2, 14 J/cm2) initiated and conducted daily for 14 consecutive days. The difference between intergroups was assessed using Student's t test and intragroups by two-way analysis of variance. Cryolesion induced massive muscle degeneration associated with inflammatory infiltrate. Prior ST improved skeletal regeneration 14-days after cryolesion and potentiated the regenerative response to LLLT. Cryolesion induced increased TNF-α levels in both NE + LE and ST + LE groups. Both isolated ST and LLLT reduced TNF-α to control group levels; however, prior ST potentiated LLLT response. Both isolated ST and LLLT increased IL-10 levels with no additional effect. In contrast, increased TA IL-6 levels were restricted to ST and ST + LE + LLLT groups. TA myogenin mRNA levels were not changed by neither prior ST or ST + LLLT. Both prior ST and LLLT therapies increased MyoD mRNA levels and, interestingly, combined therapies potentiated this response. Myf5 mRNA levels were increased only in ST groups. Taken together, our data provides evidences for prior ST potentiating LLLT efficacy in promoting skeletal muscle regeneration.

Influência da ordem de execução de exercícios resistidos na hipotensão pós-exercício em idosos hipertensos / Influence of resistance exercises order performance on post-exercise hypotension in hypertensive elderly

Existem evidências de que exercícios resistidos contribuem para o controle de hipertensão arterial sistêmica, porém, são necessários estudos que indiquem a melhor forma de utilizá-los. O objetivo deste estudo foi analisar a influência da ordem de execução de exercícios resistidos na hipotensão pós-exercício em idosos com hipertensão arterial bem controlada. A amostra foi composta por oito idosos com hipertensão arterial sistêmica bem controlada (quatro homens e quatro mulheres). No protocolo 1 (P1) foram realizados inicialmente três exercícios para membros superiores e, posteriormente, três exercícios para membros inferiores. No protocolo 2 (P2) a sequência foi inversa. Já no protocolo 3 (P3) os exercícios foram realizados de forma alternada. Todos os exercícios foram realizados em três séries de 12 RM. Após cada protocolo a pressão arterial (PA) foi verificada em intervalos de 10 minutos, até 60 minutos pós-exercício. Os dados obtidos foram analisados através da ANOVA de fator duplo e fator único com post-hoc de Tukey e teste t de Student pareado com distribuição bicaudal (p < 0,05). Em relação ao repouso, as seis verificações de PA pós-exercício de P1 não apresentaram diferenças significativas; no P2 foram significantemente diferentes apenas as verificações de 20 e 40 minutos na PAS; no P3 foram observadas diferenças significativas em todas as seis verificações da PAS e nas de 10, 20, 30 e 60 minutos da PAD. A verificação de 20 minutos na PAD do P3 demonstrou-se significantemente diferente das de 20 minutos de P1 e P2. Conclui-se que a ordem de realização de exercícios resistidos em idosos com hipertensão arterial bem controlada influenciou na duração da resposta hipotensiva, mas não diretamente em sua magnitude.

There is evidence that resistance training can help to control hypertension, although further studies are needed to show the best way to perform it. The objective of this study was to analyze the influence of the resistance exercises order performance in post-exercise hypotension in elderly with controlled hypertension. The study sample consisted of eight elderly with controlled hypertension (four men and four women). In exercise protocol 1 (P1), they performed three upper limb exercises and then three lower limb exercises. In exercise protocol 2 (P2) the sequence was reversed. In exercise protocol 3 (P3) the subjects performed the same exercises in an alternate way. All exercises were performed in three sets of 12RM. Blood pressure (BP) was measured after each protocol at every 10 min until 60 min post-exercise. The data obtained were assessed using two-way ANOVA with post-hoc Tukey and paired Student's t test (p<0.05). Concerning rest values, P1 did not show statistically significance in any moment; however, in P2 at 20 and 40 min Systolic Blood Pressure (SBP) values were statistically significant. Moreover, P3 showed differences in all SBP moments and also in the 10, 20, 30 and 60 min of Diastolic Blood Pressure (DBP). When all the moments in the three protocols were compared just in the 20 min moment, P3 showed statistically difference compared with P1 and P2. It was concluded that the performed order of resistance exercises in elderly with controlled hypertension has influenced on the duration, but not directly on its magnitude.