Aerobic and anaerobic energy production in juvenile roach (Rutilus rutilus): regulation of glycolytic process by ethofumesate at two temperatures.

The aim of this study was to evaluate the coupled impact of an herbicide, ethofumesate, and temperature on the cellular energy metabolism of juvenile roach, especially on the glycolysis pathway. Juvenile roach were exposed to 0, 0.5, 5, and 50 µg/L of ethofumesate for 7 days in laboratory conditions at two temperatures (10 and 17 °C). The energy reserves (carbohydrate, lipid, and protein) were quantified, since the availability of substrates regulates the glycolysis. Then, the glycolysis was studied at the biochemical level by the measurement of the glycolytic flux and at the molecular level with the measurement of the relative expression of four genes encoding for glycolysis enzymes. This study revealed different effect of ethofumesate on the glycolysis pathway according to the temperature of exposure. Indeed, at 10 °C, it appeared that only the molecular regulation level was affected, whereas, at 17 °C, ethofumesate acted on the biochemical level. The differences observed between the two exposures imply the establishment of different strategies in order to maintain to cope with stress according to the temperature of exposure.

Sex-related differences in aerobic capacities and reactive oxygen species metabolism in the silver eel.

Silver European eels (Anguilla anguilla L.) need to develop important aerobic capacities to cope with their long fasting spawning migration at depth, particularly males which are about half the size of females. Moreover, they have to face potential oxidative stress because reactive oxygen species (ROS) production is linked to the increase in metabolic rate. Thus, aerobic metabolism was globally evaluated in male and female silver eels exposed to a 10.1 MPa hydrostatic pressure (1,000 m depth). Oxygen consumption (MO(2)), ROS production and antioxidant enzyme activities were measured in the muscle fibres. Males showed a trend in both higher rate of aerobic metabolism and ROS production than females. After pressure exposure, ROS production was inversely correlated to metabolic rate only in males. By facilitating MO(2) rise with no harmful effects by ROS, the supposed enhanced aerobic capacities of males could speed up the sustained swimming. In females, the tendency to lower metabolic rate and higher catalase activity would make them less vulnerable to ROS effects. These results are in agreement with the hypothesis for different migration depths between genders.

Pressure and temperature interactions on aerobic metabolism in migrating silver eels: results in vitro.

The European eel (Anguilla anguilla) migrates (6000 km) from European coast towards the supposed spawning area: the Sargasso Sea. This intensive and sustained swimming activity is performed without feeding and by using essentially red muscle i.e. aerobic metabolism. Temperature and hydrostatic pressure vary during migration and have known effects on energy metabolism, mainly on mitochondrial functioning. We raise the question about the existence of a pressure-temperature combination that optimizes energy metabolism. We have measured the maximal oxygen consumption (MO2) of red muscle fibres of silver eel (migrating stage) in a temperature range (5 to 25 degrees C) covering what can be reasonably expected during the migration. We have combined (random order) three temperatures (5, 15, 25 degrees C) with 5 different pressures steps from 0.1 to 10.1 MPa (corresponding to depths from surface to 1000 m). The results show that when an adequate temperature is chosen as a reference, pressure effects and pressure sensitivity depend on the temperature. Based on the fact that energy budget is limited in migrating eels, we consider that the best conditions are low temperature and high pressure.

Does hydrostatic pressure have an effect on reactive oxygen species in the eel?

Eels are submitted to hydrostatic pressure (HP) during their spawning migration (about 6000 Km). Before migration, they change from the yellow to the silver stage (silvering process). The effects of HP in relation to the silvering process have been studied on aerobic metabolism and more precisely on reactive oxygen species (ROS) metabolism. HP acclimatization of yellow eels improves oxidative phosphorylation together with supposed concomitant changes in electron leak and ROS production. Therefore hydroxyl radical (OH*) production, superoxyde dismutase and catalase activities, malondialdehyde content and in parallel oxygen consumption were measured in the red muscle of long-term pressure exposed and control group yellow and silver eels. At atmospheric pressure, yellow eels exhibited significantly higher oxygen consumption and OH* production than silver eels; and significantly lower malondialdehyde content. This could be due to the increase in membrane fluidity induced by the silvering process. Long-term HP exposure decreases yellow eel oxygen consumption which becomes similar to that of the silver stage. In parallel there is a decrease in OH* production and concomitantly antioxidant enzyme activities follow the same tendency. Thus the respiratory chain improvement in pressure acclimatized yellow eels is accompanied by a ROS production decrease which could mean an electron leak decrease.

A comparative study of reactive oxygen species in red muscle: pressure effects.

In ectotherms as well as in endotherms, the mitochondrial respiratory chain is the major source of reactive oxygen species (ROS) including the highly reactive, hydroxyl radical (OH*). It is known that the different steps involved in ROS production and the antioxidant systems are comparable in ectotherms and endotherms. But regulatory mechanisms in ROS production are less known especially in fish submitted to environmental changes. Firstly, we performed a ROS muscle metabolism interspecies study, using trout and eels as ectotherms and rats as endotherms, measuring OH* production, superoxide dismutase and catalase activities and in parallel oxygen consumption (MO2). Secondly, we studied the effects of an environmental factor (hydrostatic pressure) on ROS metabolism in both fish species. The results show that, at atmospheric pressure, fish have a higher OH*/MO2 ratio than rats which exhibit a higher superoxide dismutase activity. In fish exposed to hydrostatic pressure, this ratio is reversed so that for the same MO2 value, fish produce less OH* under hydrostatic pressure than at atmospheric pressure.

Hydrostatic pressure effects on eel mitochondrial functioning and membrane fluidity.

Aerobic metabolism which is required for long swimming activities during the eel's spawning migration at depth, is a potential target for pressure effects due to its components located in the inner mitochondrial membrane (respiratory chain and oxidative phosphorylation). Previous studies have evidenced that eels are able to acclimatize to pressure through membrane fluidity adjustment. However these studies were performed on the premigratory stage (yellow stage), which never encounters high pressure. Metamorphosis (silvering) seems to preadapt eels (at the silver stage) to most of the environmental changes they will encounter during migration. Is it also true for pressure resistance? This study shows that yellow eels exhibit a higher pressure sensitivity than silver eels (compression effects). The acclimatization period (21 days at 10.1 MPa) cancels the differences in pressure sensitivity and in aerobic metabolism observed at 0.1 MPa between the two stages. The mechanisms, which take place in yellow eels during acclimatization to high pressure, appear to be already present in silver eels before pressure exposure. Indeed at 0.1 MPa, silver eels exhibit higher membrane fluidity and proportions of membrane polyunsaturated fatty acids. Metamorphosis, by improving membrane fluidity, seems to allow silver eels to cope with hydrostatic pressure without spending energy in acclimatization processes.

Genetic differences in hypothalamic-pituitary-adrenal axis activity and food restriction-induced hyperactivity in three inbred strains of rats.

We used three inbred rat strains known for significant differences in the activity and reactivity of their hypothalamic-pituitary-adrenal (HPA) axis to stress [Fischer 344 (F344), Brown Norway (BN) and Lewis (Lew) rats] to search for a strain difference in the paradoxical increase in running activity induced by food restriction and to explore the role of the HPA axis in this behaviour. Rats were randomly assigned to either an ad lib sedentary group (AL), a control wheel activity group (ACT), a food restriction-induced hyperactivity group (FR-ACT) group (1.5 h/day ad lib food, 22.5 h/day ad lib wheel access) or a pair-fed group (FR). The BN and Lew rats reached the 25% body weight-loss criterion of FR-ACT (strain effect: F(2,132) = 45.58, P < 10-6) faster than the F344 strain due to higher food restriction-induced running activity (strain effect: F(2,65) = 17.43, P = 0.00001). FR and FR-ACT decreased thymus weight (marker of integrated HPA axis activation) in all strains. In Lew and BN strains, FR-ACT induced a further decrement on thymus weight compared to their FR group. Prefeeding corticosterone levels (15.00 h) increased during the study in BN and Lew FR-ACT rats, but not in F344. Total wheel turns were correlated to both final adipose weight (r = -0.49, P = 0.002) and thymus weight decrement (r = 0.59, P = 0.0001), emphasizing the relationship between fat mass and HPA axis activation in excessive running activity. Increased running in conditions of food restriction and HPA axis activation may be linked at the level of the central nervous system. However, the involvement of corticotrophin-releasing hormone, agouti-related peptide or cocaine- and amphetamine-regulated transcript in behavioural disturbances of FR-ACT rats was excluded (in situ hybridization). We propose that corticosterone may be the link between initial low levels of fat mass and/or rate of fat mass loss (peripheral energy stores) and increased wheel activity, favouring fueling through lipolysis and proteolysis and reinforcing the self starvation via reward mechanisms, thus establishing a deleterious vicious cycle.

Pressure and temperature interactions on cellular respiration: a review.

Thermodynamic equations show that pressure and temperature can, theoretically, act in synergy or in opposite directions depending on their respective variations. Hence, they interact to establish rates of biological processes (pressure/temperature interactions, PTI). For such studies, it is interesting to use aquatic ectotherms, in particular fish, because it is easy to submit them to temperature and/or pressure changes. This review focuses on the effects of temperature and pressure changes on the energy metabolism of fish, mitochondrial oxygen consumption and functioning, showing that the observed effects do not always match the predictions made by equations or models. Unpublished results concerning the mitochondrial function of eels acclimatised at two temperatures and two pressures show that the mitochondrial targets of pressure and temperature are probably not the same. The possible mechanisms and consequences of PTI are discussed.