Is the silvering process similar to the effects of pressure acclimatization on yellow eels?

International audienceTo reproduce eels need to migrate over 6000 km and at pressure but before this migration they metamorphose into silver eels (silvering). The question raised in this study is to determine whether and how the silvering process contributes to pressure resistance. As migration represents a long swimming activity mainly performed with slow muscles, the red muscle energetics of pressure exposed silver eels was studied. By comparing these results to what has already been shown in yellow eels, we point out that the effects of the silvering process on pressure resistance are similar to the effects of pressure acclimatization in yellow eels. As previously shown, success of pressure acclimatization depends on membrane fluidity, but we raise the hypothesis that the high-pressure resistance of silver eels is due to more fluid membranes

In vitro effect of hydrostatic pressure exposure on hydroxyl radical production in fish red muscle.

International audienceThe effects of hydrostatic pressure on reactive oxygen species (ROS) production have been studied in vitro on fish red muscle fibres. In the eel, Anguilla anguilla, previous studies have shown that hydrostatic pressure acclimatization improves oxidative phosphorylation efficiency together with a supposed concomitant decrease in electron leak and ROS production. In order to test the hypothesis of an electron leak decrease under pressure, hydroxyl radical (HO*) production and oxygen consumption were measured on fish red muscle fibres directly exposed to hydrostatic pressure. Experiments were performed under two conditions--atmospheric pressure and hydrostatic pressure (16.1 MPa)--on eel and trout (which exhibit low- and high-pressure sensitivity, respectively). This work has permitted, first, the validation of an indirect HO* measurement (in vitro) on fish red muscle and the documentation of reference values for fish. Second, at atmospheric pressure, results show higher oxygen consumption for trout (+40%) than for eel which is accompanied by higher HO* production (+90%); in addition, both species present a positive relationship between HO* production and oxygen consumption. Hydrostatic pressure exposure reverses this relationship for eel but not for trout. These preliminary results only partially verify the proposed hypothesis and further experiments are needed

Effect of induced mild hypothermia on two pro-inflammatory cytokines and oxidative parameters during experimental acute sepsis.

International audienceThis study aimed to determine the effect of induced mild hypothermia (34°C) on the production of two cytokines (interleukin (IL-6) and tumor necrosis factor (TNF)alpha) and reactive nitrogen and oxygen species in plasma and the heart of acutely septic rats. After anesthesia and in conditions of normothermia (38°C) or mild hypothermia (34°C), acute sepsis was induced by cecal ligation and perforation. For each temperature three groups were formed: (1) baseline (blood sample collected at T0 hour), (2) sham (blood sample at T4 hours) and (3) septic (blood sample at T4 hours). At either temperature sepsis induced a significant increase in plasma IL-6, TNF-alpha and HO* concentration, compared with the sham groups (P≤0.016). Compared with the normothermic septic group, septic rats exposed to mild hypothermia showed a mild decrease in TNF-alpha concentration (104±50 pg/ml vs. 215±114 pg/ml; P>0.05) and a significant decrease in IL-6 (1131±402 pg/ml vs. 2494±691 pg/ml, P=0.038). At either temperature sepsis induced no enhancement within the heart of lipoperoxidation (malondialdehyde content) or antioxidant activities (superoxide dismutase and catalase). In conclusion, during acute sepsis, induced mild hypothermia appears to reduce some pro-inflammatory and oxidative responses. This may, in part, explain the beneficial effect of hypothermia on survival duration of septic rats

Effect of exercise training on respiration and reactive oxygen species metabolism in eel red muscle.

International audienceThis paper deals with the effects of exercise training on oxygen consumption (MO(2)) and ROS metabolism in the red muscle of trained and untrained female silver eels. Their critical swimming speed (U(crit)) was determined before and after a 4-day training (10h of swimming at 70% of U(crit) and 14 h at 50%, every day). The U(crit) of trained eels increased significantly (by about 7%). The in vitro MO(2) and ROS production by the red fibres were higher (not significant) in trained than in untrained eels, but the ROS production/MO(2) ratio was alike in both groups. The antioxidant-enzyme activities and lipoperoxidation index in trained eels were both lower than those of the untrained ones. These biochemical changes related to the increase in U(crit) suggest that such a training session could maintained or even increased aerobic power of the red muscle without deleterious impact by ROS. These regulations could play a role in the eel's swimming performance efficiency

Training protocols differently affect AMPK–PGC-1α signaling pathway and redox state in trout muscle

International audienceBeneficial effects of physical exercise training are in part related to enhancement of muscle mitochondrial performance. The effects of two different trainings were investigated on transcripts and proteins of theAMPK–PGC-1α signaling pathway, the mitochondrial functioning (citrate synthase (CS), oxidative phosphorylationcomplexes, uncoupling proteins (UCP)) and the antioxidant defenses (superoxide dismutase (SOD),glutathione peroxidase (GPx), catalase) in rainbow trout red and white skeletal muscles. One group of troutsswam for 10 days at a moderate intensity (approximately 57% Ucrit or 2.0 body lengths/s, 23.5 h/day) andanother group at a high intensity (approximately 90% Ucrit or 3.2 body lengths/s, 2 h/day). In the red muscle,the increase of Cs mRNA levels was significantly correlated with the transcripts of Ampkα1, Ampkα2, Pgc-1α, theoxidative phosphorylation complexes, Ucp2α, Ucp2β, Sod1, Sod2 and Gpx1. After 10 days of training, high intensitytraining (HIT) stimulates more the transcription of genes involved in this aerobic pathway than moderateintensity training (MIT) in the skeletal muscles, and mainly in the red oxidative muscle. However, no changes inCS, cytochrome c oxidase (COX) and antioxidant defenses activities and in oxidative stress marker (isoprostaneplasmatic levels) were observed. The transcriptomic responses are fiber- and training-type dependent whenproteins were not yet expressed after 10 days of training. As in mammals, our results suggest that HIT couldpromote benefit effects in fish

How do exercise training variables stimulate processes related to mitochondrial biogenesis in slow and fast trout muscle fibres?

International audienceExercise is known to be a powerful way to improve health through the stimulation of mitochondrial biogenesis in skeletal muscle, which undergoes cellular and molecular adaptations. One of the current challenges in human is to define the optimal training stimulus to improve muscle performance. Fish are relevant models for exercise training physiology studies mainly because of their distinct slow and fast muscle fibres. Using rainbow trout, we investigated the effects of six different training protocols defined by manipulating specific training variables (such as exercise intensity, volume, duration and frequency), on mRNAs and some proteins related to four sub- systems (AMP-activated protein kinase–peroxisome proliferator-activated receptor γ coactivator-1α signalling pathway, mitochondrial function, antioxidant defences and lactate dehydrogenase (LDH) metabolism) in both red and white muscles (RM and WM, respectively). In both muscles, high-intensity exercise stimulated more mRNA types and enzymatic activities related to mitochondrial biogenesis than moderate-intensity exercise. For volume, duration and frequency variables, we demonstrated fibre type- specific responses. Indeed, for high-intensity interval training, RM transcript levels are increased by a low training volume, but WM transcript responses are stimulated by a high training volume. Moreover, transcripts and enzymatic activities related to mitochondria and LDH show that WM tends to develop aerobic metabolism with a high training volume. For transcript stimulation, WM requires a greater duration and frequency of exercise than RM, whereas protein adaptations are efficient with a long training duration and a high frequency in both muscles

In vitro aerobic and anaerobic muscle capacities in the European eel, Anguilla anguilla: effects of a swimming session.

International audienceIn order to have a general view of metabolic requirements during swimming, in vitro aerobic and anaerobic fluxes were measured in red and white muscles from silver eels and yellow eels which differ in activity levels and nutritional states. These measurements were performed in control eels and after a 4 day swimming session (70% U(crit) in yellow eels, 80% U(crit) in silver eels). A swimming session significantly increases U(crit) from 12% to 18%, depending on the stage, with a significantly higher in vitro energy cost during the yellow stage at the muscle level. In vitro, the swimming session brings about a gain in anaerobic capacities rather than in aerobic ones. Some in vivo hypotheses are proposed

Exercise training changes mitochondrial function and its vulnerability to reactive oxygen species exposure differently in male and female silver European eels

International audienceThe effects of sex and training on mitochondrialfunction and its sensitivity to in vitro reactiveoxygen species (ROS) exposure were investigated inmale and female silver European eels. The critical swimmingspeed (Ucrit) was used as an index of trainingintensity and of overall swimming performance. Afterfour days of training (10 h at 70% and 14 h at 50% oftheir Ucrit before training), Ucrit increased significantlyin trained eels for both sexes. In untrained eels, basalmitochondrial respiration (V0) measured in the absenceofADP in permeabilized cardiac fibreswas significantlyhigher and more resistant to in vitro ROS exposure inmales than in females. No difference in ATP production(VATP) or hydroxyl radical release (V●OH ) was observedbetween male and female eels. In trained male eels,V●OH decreased in red muscle fibres concomitantly to atrend in an increased ATP production. In trained femaleeels, a different trend in ATP decrease was observed.Training significantly enhanced respiratory rate Vmaxand resistance to in vitro ROS exposure in cardiac fibresof male silver eels but not females. In male silver eels,but not females, training could induce an improvementof energy efficiency in red muscle and a greater resistanceof mitochondrial function to ROS exposure incardiac fibres. These beneficial effects could contributeto the highly efficient swimming performance of themale eel, which could serve to compensate their smallersize, helping them to achieve their transoceanic migrationand synchronized arrival with the females at theirreproduction area

Moderate intensity continuous versus high intensity interval training: Metabolic responses of slow and fast skeletal muscles in rat.

The healthy benefits of regular physical exercise are mainly mediated by the stimulation of oxidative and antioxidant capacities in skeletal muscle. Our understanding of the cellular and molecular responses involved in these processes remain often uncomplete particularly regarding muscle typology. The main aim of the present study was to compare the effects of two types of exercise training protocol: a moderate-intensity continuous training (MICT) and a high-intensity interval training (HIIT) on metabolic processes in two muscles with different typologies: soleus and extensor digitorum longus (EDL). Training effects in male Wistar rats were studied from whole organism level (maximal aerobic speed, morphometric and systemic parameters) to muscle level (transcripts, protein contents and enzymatic activities involved in antioxidant defences, aerobic and anaerobic metabolisms). Wistar rats were randomly divided into three groups: untrained (UNTR), n = 7; MICT, n = 8; and HIIT, n = 8. Rats of the MICT and HIIT groups ran five times a week for six weeks at moderate and high intensity, respectively. HIIT improved more than MICT the endurance performance (a trend to increased maximal aerobic speed, p = 0.07) and oxidative capacities in both muscles, as determined through protein and transcript assays (AMPK-PGC-1α signalling pathway, antioxidant defences, mitochondrial functioning and dynamics). Whatever the training protocol, the genes involved in these processes were largely more significantly upregulated in soleus (slow-twitch fibres) than in EDL (fast-twitch fibres). Solely on the basis of the transcript changes, we conclude that the training protocols tested here lead to specific muscular responses