Optimization of embryonic thermal programming confirms increased liver fattening in mule ducks and changes in lipid metabolism.

Introduction: The embryonic thermal programming (TM) in birds has been shown to impact several physiological parameters such as resistance to thermal stress, muscle growth or immunity. In mule ducks, it has recently been shown that TM can induce metabolic programming resulting in increased liver weight and fat storage after overfeeding. However, a decrease in hatchability and foie gras quality was also observed, suggesting that this technique needs to be optimized. Here, we tested a new thermal manipulation condition determined with the objective of avoiding negative impacts while maintaining or improving liver properties. Methods: The eggs of the control group were incubated at 37.6°C during the whole incubation period while those of the experimental group (TM group) were incubated at 39.3°C 16 h/24 h from the 11th day of incubation to the 21st. After hatching, all the animals were fed and raised under the same conditions until the age of 12 weeks. At this stage, one part of the animals was overfed and then slaughtered 2 h (to measure rapid changes in metabolism) or 10 h after the last meal (to obtain the best technological yields), while the other part was ration-fed and slaughtered 2 h after the last meal, at the same age. Results: An 8% increase in foie gras production was measured in the TM group compared to the control group without altering the quality of the final product (nor hatchability), confirming the successful optimization of the metabolic programming. Interestingly, these results allowed us not to reject the previously suggested hypothesis of a potential delay in metabolic processes involved in liver fattening in programmed animals, in particular by measuring a trend reversal regarding the amount of total hepatic lipids in both groups at 2 h and then 10 h after the last meal. Discussion: This study therefore validates the optimization of metabolic programming by embryonic thermal manipulation for duck liver fattening. The understanding of the mechanisms of embryonic thermal programming in birds remains today very incomplete and the search for epigenetic marks (main hypothesis of the concept of programming) at the origin of the observed phenotypes could be the next step of this work.

Identification of different critical embryonic periods to modify egg incubation temperature in mule ducks.

Egg incubation of mule ducks, mainly used for fatty liver production, is one of the critical phases in this sector. Based on hatching rate, the best incubation parameters have already been well described for poultry, but the literature on ducks is lacking. In this study, we tested different incubation conditions by varying two important factors, temperature and relative humidity, in mule ducks. These variations were applied at different periods during embryogenesis in order to measure the impact of environmental disturbances on different zootechnical performances. The temperature was increased by 1.5 °C (16 h/24) and the relative humidity was set up to 65%, during 10 days. Six 10-day developmental windows were tested, from embryonic day 9 to embryonic day 14. Our results are in line with previous reports showing that increasing incubation temperature, even when relative humidity is adjusted, can have a negative impact on duck embryonic mortality up to 24.5% for the condition E10-E20 (P < 10-5). However, the hatchability can be maintained at the level of the control groups when these modifications are applied on the latest windows (from the 11th embryonic day). Sex ratio, hatching BW, and internal temperature are also sensitive to these incubation changes, and their modification could have a major impact on later zootechnical performance. These results should contribute to the development or embryonic temperature programming approaches, especially for the fatty liver production industry.

Glucose injection into the yolk influences intermediary metabolism in adult Nile tilapia fed with high levels of carbohydrates.

Nutritional programming is a concept proposed to be applied in the field of fish nutrition to improve the use of new diets in aquaculture. This study aimed to investigate for the first time the effects of a glucose injection into the yolk at the alevin stage on intermediary metabolism and growth in adult Nile tilapia (Oreochromis niloticus) at 32-37 weeks later in the life. The early stimulus was performed through direct microinjection of 2 M glucose into yolk sacs of Nile tilapia alevin. Subsequently, in adult tilapia, the long-term effects of glucose stimulus on growth performance, blood metabolites, chemical composition in the liver and muscle, expression of genes involved in glucose transport and metabolism (glycolysis and gluconeogenesis) and related pathways (amino acid catabolism and lipogenesis) were investigated. Our results showed that, even though early glucose injection had no effect on growth performance in adult fish, very few significant effects on glucose metabolism were observed. Furthermore, to evaluate the potential metabolic programming after a dietary challenge, a 2 × 2 factorial design with two early stimuli (0.85% NaCl or 2 M glucose) and two different dietary carbohydrate intakes (medium-carbohydrate diet, CHO-M; high-carbohydrate diet, CHO-H) was performed between weeks 33 and 37. As expected, compared with the CHO-M diet, the CHO-H diet led to decreased growth performance, higher glyceamia and triglyceridemia, higher glycogen and lipid levels in the liver as well as down-regulation of gluconeogenesis and amino acid catabolism gene expressions. More interestingly, although early glucose injection had no significant effect on growth performance, it enhanced the capacities for lipogenesis, glycolysis and gluconeogenesis, particularly in fish that were fed the CHO-H diet. Thus, the nutritional programming of tilapia linked to glucose injection into the yolk of alevins is always visible at the adult stage albeit less intense than what we previously observed in juvenile.

Pck-ing up steam: Widening the salmonid gluconeogenic gene duplication trail.

Rainbow trout have, as salmonid fish species, undergone sequential genome duplication events in their evolutionary history. In addition to a teleost-specific whole genome duplication approximately 320-350 million years ago, rainbow trout and salmonids in general underwent an additional salmonid lineage-specific genome duplication event approximately 80 million years ago. Through the recent sequencing of salmonid genome sequences, including the rainbow trout, the identification and study of duplicated genes has become available. A particular focus of interest has been the evolution and regulation of rainbow trout gluconeogenic genes, as recent molecular and gene expression evidence points to a possible contribution of previously uncharacterized gluconeogenic gene paralogues to the rainbow trout long-studied glucose intolerant phenotype. Since the publication of the initial rainbow trout genome draft, resequencing and annotation have further improved genome coverage. Taking advantage of these recent improvements, we here identify a salmonid-specific genome duplication of ancestral mitochondrial phosphoenolpyruvate carboxykinase 2 isoenzyme, we termed pck2a and pck2b. Cytosolic phosphoenolpyruvate carboxykinase (Pck1) and, more recently mitochondrial Pck2, are considered to be the rate-limiting enzymes in de novo gluconeogenesis. Following in silico confirmation of salmonid pck2a and pck2b evolutionary history, we simultaneously profiled cytosolic pck1 and mitochondrial pck2a and pck2b expression in rainbow trout liver under several experimental conditions known to regulate hepatic gluconeogenesis. Cytosolic pck1 abundance was increased by nutritional (diets with a high protein to carbohydrate ratio compared to diets with a low carbohydrate to protein ratio) and glucoregulatory endocrine factors (glucagon and cortisol), revealing that the well-described transcriptional regulation of pck1 in mammals is present in rainbow trout. Conversely, and in contrast to mammals, we here describe endocrine regulation of pck2a (decrease in abundance in response to glucagon infusion), and nutritional, social-status-dependent and hypoxia-dependent regulation of pck2b. Specifically, pck2b transcript abundance increased in trout fed a diet with a low protein to carbohydrate ratio compared to a diet with a high protein to carbohydrate ratio, in dominant fish compared to subordinate fish as well as hypoxia. This specific and differential expression of rainbow trout pck2 ohnologues is indicative of functional diversification, and possible functional consequences are discussed in light of the recently highlighted gluconeogenic roles of mitochondrial pck2 in mammalian models.

New Insights on Intermediary Metabolism for a Better Understanding of Nutrition in Teleosts.

The rapid development of aquaculture production throughout the world over the past few decades has led to the emergence of new scientific challenges to improve fish nutrition. The diet formulations used for farmed fish have been largely modified in the past few years. However, bottlenecks still exist in being able to suppress totally marine resources (fish meal and fish oil) in diets without negatively affecting growth performance and flesh quality. A better understanding of fish metabolism and its regulation by nutrients is thus mandatory. In this review, we discuss four fields of research that are highly important for improving fish nutrition in the future: ( a) fish genome complexity and subsequent consequences for metabolism, ( b) microRNAs (miRNAs) as new actors in regulation of fish metabolism, ( c) the role of autophagy in regulation of fish metabolism, and ( d) the nutritional programming of metabolism linked to the early life of fish.

Effect of food shortage and temperature on age 0+ salmonids: a contribution to predict the effects of climate change.

Brown trout Salmo trutta alevins were maintained at 8 and 11° C at three conditions over a 9 day period from yolk sac exhaustion: fed ad libitum, starved or fed ad libitum after starvation. Whole-body gene expressions for proteins involved in energy metabolism and the two primary proteolytic pathways were assessed. This study is the first to show an over-expression of proteasome and autophagy-related genes in young stages of salmonids, particularly at 11° C.

How Tom Moon's research highlighted the question of glucose tolerance in carnivorous fish.

Fifteen years ago, Tom Moon wrote a review on this journal in order to propose some explanations to the exacerbated glycaemic response after a glucose load or a carbohydrate meal intake observed in fish, the so-called intolerance to glucose. Before, but in most of cases after this paper, several laboratories worldwide started to make important efforts in order to better understand this strange phenotype observed in fish and that so far seemed to belong to diabetic humans only. Tom had been worked on fish metabolism for at least 30years when he proposed that mini-review and the paths opened by him in 2001 were followed by tens of fish researchers, making this paper a breaking point on the field. Fifteen years later, we propose not only to have a look to the answers given to the questions rose in that paper, but also to summarize how his career over all these years impacted the domain of glucose metabolism in fish. In the review, we will show how Tom Moon analysed at different levels (from genes up to the whole organism), using distinct experimental tools (cells, hormone or glucose injection, pumps, drugs) the questions of glucose metabolism, tolerance and nutrition in fish species.

High or low dietary carbohydrate:protein ratios during first-feeding affect glucose metabolism and intestinal microbiota in juvenile rainbow trout.

Based on the concept of nutritional programming in mammals, we tested whether an acute hyperglucidic-hypoproteic stimulus during first feeding could induce long-term changes in nutrient metabolism in rainbow trout. Trout alevins received during the five first days of exogenous feeding either a hyperglucidic (40% gelatinized starch + 20% glucose) and hypoproteic (20%) diet (VLP diet) or a high-protein (60%) glucose-free diet (HP diet, control). Following a common 105-day period on a commercial diet, both groups were then challenged (65 days) with a carbohydrate-rich diet (28%). Short- and long-term effects of the early stimuli were evaluated in terms of metabolic marker gene expressions and intestinal microbiota as initial gut colonisation is essential for regulating the development of the digestive system. In whole alevins (short term), diet VLP relative to HP rapidly increased gene expressions of glycolytic enzymes, while those involved in gluconeogenesis and amino acid catabolism decreased. However, none of these genes showed persistent molecular adaptation in the liver of challenged juveniles (long term). By contrast, muscle of challenged juveniles subjected previously to the VLP stimulus displayed downregulated expression of markers of glycolysis and glucose transport (not seen in the short term). These fish also had higher plasma glucose (9 h postprandial), suggesting impaired glucose homeostasis induced by the early stimulus. The early stimulus did not modify the expression of the analysed metabolism-related microRNAs, but had short- and long-term effects on intestinal fungi (not bacteria) profiles. In summary, our data show that a short hyperglucidic-hypoproteic stimulus during early life may have a long-term influence on muscle glucose metabolism and intestinal microbiota in trout.

Regulation of de novo hepatic lipogenesis by insulin infusion in rainbow trout fed a high-carbohydrate diet.

Carbohydrate energy intake in excess of total energy expenditure is converted to fat. In fish, the liver is considered to be the main lipogenic tissue. Its regulation by insulin is not fully understood, and some of the available in vivo findings are contradictory. In this study, bovine insulin was infused for 5 d into rainbow trout fed a high-carbohydrate diet, and variables of de novo hepatic lipogenesis were measured. We found that hepatic lipogenesis in trout is stimulated by insulin, reflected in enhanced mRNA and protein abundance and enzyme activity of ATP-citrate lyase, acetyl-CoA carboxylase, and fatty acid synthase. These results were further supported by parallel changes in enzymes acting as NAD phosphate donors, especially those participating in the pentose phosphate pathway. This is the first time that the main enzymes involved in de novo hepatic lipogenesis have been studied at the molecular, protein, and activity levels in fish. We hypothesize that some of the delayed changes found in the different levels of regulation were probably related to the insulin resistance achieved by the trout liver after 5 d of insulin infusion. We assessed enzyme activity and mRNA abundance of lipid oxidation-related enzymes in the livers of insulin-infused fish in which paradoxically increased ß-oxidation potential was found. The insulin-stimulated de novo hepatic lipogenesis in carbohydrate-fed trout reinforces the hypothesis that this pathway may act as an important sink for excess glucose, which could ultimately contribute to improved glucose homeostasis in this carnivorous and glucose-intolerant species when fed high-carbohydrate diets.

Insulin stimulates lipogenesis and attenuates Beta-oxidation in white adipose tissue of fed rainbow trout.

As lipid deposition tissue in fish, the white adipose tissue (WAT) has important functions related to reproduction and the challenges of long-term fasting. In the study reported here, we infused fish fed a high-carbohydrate diet with two doses of insulin for 5 days in order to explore the effects of this hormone on lipogenesis and beta-oxidation-related enzymes. We demonstrated the presence of some of the main lipogenic enzymes at molecular, protein and activity levels (ATP-citrate lyase and fatty acid synthase). However, while ATP-citrate lyase was unexpectedly down-regulated, fatty acid synthase was up-regulated (at protein and activity levels) in an insulin dose-dependent manner. The main enzymes acting as NADPH donors for lipogenesis were also characterized at biochemical and molecular levels, although there was no evidence of their regulation by insulin. On the other hand, lipid oxidation potential was found in this tissue through the measurement of gene expression of enzymes involved in ß-oxidation, highlighting two carnitine palmitoyltransferase isoforms, both down-regulated by insulin infusion. We found that insulin acts as an important regulator of trout WAT lipid metabolism, inducing the final stage of lipogenesis at molecular, protein and enzyme activity levels and suppressing ß-oxidation at least at a molecular level. These results suggest that WAT in fish may have a role that is important not only as a lipid deposition tissue but also as a lipogenic organ (with possible involvement in glucose homeostasis) that could also be able to utilize the lipids stored as a local energy source.

Glucose homeostasis in rainbow trout fed a high-carbohydrate diet: metformin and insulin interact in a tissue-dependent manner.

Carnivorous fish species such as the rainbow trout (Oncorhynchus mykiss) are considered to be "glucose intolerant" because of the prolonged hyperglycemia experienced after intake of a carbohydrate-enriched meal. In the present study, we use this species to study glucose homeostasis in fish chronically infused with the hypoglycemic agents, insulin, and metformin, and fed with a high proportion of carbohydrates (30%). We analyzed liver, skeletal muscle, and white adipose tissue (WAT), which are insulin- and metformin-specific targets at both the biochemical and molecular levels. Trout infused with the combination of insulin and metformin can effectively utilize dietary glucose at the liver, resulting in lowered glycemia, increased insulin sensitivity, and glucose storage capacity, combined with reduced glucose output. However, in both WAT and skeletal muscle, we observed decreased insulin sensitivity with the combined insulin + metformin treatment, resulting in the absence of changes at the metabolic level in the skeletal muscle and an increased potential for glucose uptake and storage in the WAT. Thus, the poor utilization by rainbow trout of a diet with a high proportion of carbohydrate can at least be partially improved by a combined treatment with insulin and metformin, and the glucose intolerance observed in this species could be, in part, due to some of the downstream components of the insulin and metformin signaling pathways. However, the predominant effects of metformin treatment on the action of insulin in these three tissues thought to be involved in glucose homeostasis remain exclusive in this species.

Effects of insulin infusion on glucose homeostasis and glucose metabolism in rainbow trout fed a high-carbohydrate diet.

The origin for the poor glucose utilization in carnivorous fish species fed high carbohydrate diets remains under debate. In the present study, we have fed rainbow trout a diet containing 30% carbohydrate for 1 or 5 days. In both cases, fish were implanted with mini-osmotic pumps releasing 0.7 i.u. kg(-1) day(-1) bovine insulin, and mRNA transcripts and the protein phosphorylation status of proteins controlling glycemia and glucose-related metabolism were studied in fish killed 6 h after the last meal. We demonstrate that when the exposure occurs over a short term (30 h), insulin exerts beneficial actions on trout glucose homeostasis, including a lowered glycemia and increased hepatic lipogenic and glycogenic potentials. However, when trout were fed for 5 days, these beneficial actions of insulin infusion were no longer observed. Thus, the increased lipogenic potential observed after one single meal was not present, and this together with the increased glycogenesis and the decreased glucose exported to the blood from the liver explains the lack of hypoglycemic action of insulin. The fact that insulin improved glucose homeostasis when administrated over a short time period implies that endogenous insulin secretion is inadequate in trout to deal with this amount of dietary carbohydrates. Moreover, the fact that a longer exposure to insulin resulted in a reduced response indicates that the rainbow trout is sensitive to insulin, re-enforcing the hypothesis that the hyperglycemia observed following a high carbohydrate meal is an insulin secretion issue rather an insulin action issue.

Molecular regulation of lipid metabolism in liver and muscle of rainbow trout subjected to acute and chronic insulin treatments.

Although the metabolic actions of insulin in fish have been investigated widely in the past several years, lipid metabolism has received little attention, especially in tissues like the liver or white muscle. In the present study, rainbow trout received insulin treatments both acutely (intraperitoneal injection) and chronically (through mino-osmotic pumps) to elucidate hormone metabolic actions at molecular levels on the 2 main insulin target tissues in trout, namely, liver and muscle. Plasma and free fatty acid concentrations in plasma, as well as mRNA measurements of some key enzymes involved in lipid metabolism, were assessed in these tissues after 6h and 4 d of acute and chronic insulin treatments, respectively. Our results showed that although fish received the same final total amount of hormone in both treatments, the actions of insulin on lipid metabolism were both time and tissue dependent. After the acute insulin treatment, the main anabolic role of insulin was reflected in decreased plasma free fatty acid concentrations linked to enhanced hepatic lipogenesis. We also found that insulin increased the mRNA levels of enzymes involved in lipid oxidation, perhaps to counteract insulin-induced hypoglycemia. In contrast, our data show that after chronic insulin treatment, liver and muscle exhibit different metabolic strategies: whereas in the liver chronic insulin-induced hypoglycemia may stimulate lipolytic processes to spare glucose stores, the muscle responds directly to the anabolic hormone action by increasing its lipogenic capacity and by inhibiting pathways of lipid oxidation.

Glucose homeostasis is impaired by a paradoxical interaction between metformin and insulin in carnivorous rainbow trout.

Utilizing rainbow trout (Oncorhynchus mykiss) as a known model of a "glucose-intolerant" and poor dietary glucose user, we assessed glucose utilization in fish chronically receiving two molecules able to improve glucose homeostasis: insulin and metformin. Our objectives were to assess the ability of rainbow trout to deal with a glucose load and to improve glucose utilization in fish receiving a chronic administration of insulin plus metformin treatments. Fish received (implanted miniosmotic pumps) saline, insulin, metformin, and insulin plus metformin solution for 4 days and then were subjected to a glucose challenge (intraperitoneal injection) to study glucose homeostasis, analyzing plasma glycemia, mRNA levels of glucose metabolism-related proteins, insulin signaling, and glycogen levels in liver and muscle. Control fish received a saline pump implantation and saline intraperitoneal injection. We found no evidence that the "glucose intolerance" in this species could be linked to any of the molecular markers of metabolism in the tissues analyzed. By contrast, very interestingly, we show for the first time, that metformin is not only unable to improve glucose homeostasis in trout, but, in fact, its counteracts the effects of insulin, creating an "insulin resistance," especially in the muscle. These results make trout an attractive original model to study both insulin and metformin effect on biological systems.

Metformin improves postprandial glucose homeostasis in rainbow trout fed dietary carbohydrates: a link with the induction of hepatic lipogenic capacities?

Carnivorous fish are poor users of dietary carbohydrates and are considered to be glucose intolerant. In this context, we have tested, for the first time in rainbow trout, metformin, a common anti-diabetic drug, known to modify muscle and liver metabolism and to control hyperglycemia in mammals. In the present study, juvenile trout were fed with very high levels of carbohydrates (30% of the diet) for this species during 10 days followed by feeding with pellets supplemented with metformin (0.25% of the diet) for three additional days. Dietary metformin led to a significant reduction in postprandial glycemia in trout, demonstrating unambiguously the hypoglycemic effect of this drug. No effect of metformin was detected on mRNA levels for glucose transporter type 4 (GLUT4), or enzymes involved in glycolysis, mitochondrial energy metabolism, or on glycogen level in the white muscle. Expected inhibition of hepatic gluconeogenic (glucose-6-phosphatase, fructose-1,6-bisphosphatase, and phosphoenolpyruvate carboxykinase) mRNA levels was not found, showing instead paradoxically higher mRNA levels for these genes after drug treatment. Finally, metformin treatment was associated with higher mRNA levels and activities for lipogenic enzymes (fatty acid synthase and glucose-6-phosphate dehydrogenase). Overall, this study strongly supports that the induction of hepatic lipogenesis by dietary glucose may permit a more efficient control of postprandial glycemia in carnivorous fish fed with high carbohydrate diets.

Nutritional regulation of hepatic glucose metabolism in fish.

Glucose plays a key role as energy source in the majority of mammals, but its importance in fish appears limited. Until now, the physiological basis for such apparent glucose intolerance in fish has not been fully understood. A distinct regulation of hepatic glucose utilization (glycolysis) and production (gluconeogenesis) may be advanced to explain the relative inability of fish to efficiently utilize dietary glucose. We summarize here information regarding the nutritional regulation of key enzymes involved in glycolysis (hexokinases, 6-phosphofructo-1-kinase and pyruvate kinase) and gluconeogenesis (phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase and glucose-6-phosphatase) pathways as well as that of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. The effect of dietary carbohydrate level and source on the activities and gene expression of the mentioned key enzymes is also discussed. Overall, data strongly suggest that the liver of most fish species is apparently capable of regulating glucose storage. The persistent high level of endogenous glucose production independent of carbohydrate intake level may lead to a putative competition between exogenous (dietary) glucose and endogenous glucose as the source of energy, which may explain the poor dietary carbohydrate utilization in fish.

Rearing temperature enhances hepatic glucokinase but not glucose-6-phosphatase activities in European sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata) juveniles fed with the same level of glucose.

The aim of this work was to elucidate if the previous results observed in hepatic glucokinase (GK) and glucose-6-phosphatase (G6Pase) activities in European sea bass and gilthead sea bream are due to temperature per se or to differences in feed intake at different water temperatures. For that purpose triplicate groups of fish (30 g initial body weight) were kept at 18 degrees C or 25 degrees C during two weeks and fed a fixed daily ration of a glucose-free or 20% glucose diet. At the end of the experimental period, plasma glucose levels in both species were not influenced by water temperature but were higher in fish fed the glucose diet. Higher hepatic GK activity was observed in the two fish species fed the glucose diet than the glucose-free diet. In the glucose fed groups, GK activity was higher at 25 degrees C than at 18 degrees C. Glucose-6-phosphatase activities in both species were not influenced by water temperature. In European sea bass and in contrast to gilthead sea bream it was observed an effect of dietary composition on G6Pase activities with surprising higher activities recorded in fish fed the glucose diet than in fish fed the glucose-free diet. Overall, our data strongly suggest that European sea bass and gilthead sea bream are apparently capable to strongly regulate glucose uptake by the liver but not glucose synthesis, which is even enhanced by dietary glucose in European sea bass. Within limits, increasing water temperature enhances liver GK but not G6Pase activities, suggesting that both species are more able to use dietary carbohydrates at higher rearing temperatures.

Liver and muscle metabolic changes induced by dietary energy content and genetic selection in rainbow trout (Oncorhynchus mykiss).

We combined genetic selection and dietary treatment to produce a model to study metabolic pathways involved in genetic and nutritional control of fat deposition in fish muscle. Two experimental lines of rainbow trout, selected for a lean (L) or fat (F) muscle, were fed with diets containing either 10 or 23% lipids from the first feeding, up to 6 mo. At the end of the feeding trial, trout were distinguished by very different muscle fat content (from 4.2 to 10% wet weight), and line x diet interactions were observed for parameters related to fat storage. We analyzed the activity and gene expression of key enzymes involved in lipid metabolism (fatty acid synthase, hydroxyacyl-CoA dehydrogenase, carnitine palmitoyltransferase 1 isoforms, and peroxisome proliferator-activated receptor alpha) and glycolysis (hexokinase 1 and pyruvate kinase) as well as energy production (isocitrate dehydrogenase, citrate synthase, and cytochrome oxidase) in the liver and the white muscle of rainbow trout. The lipid-rich diet repressed the activity of the lipogenic enzymes and stimulated enzymes involved in fatty acid oxidation and glycolysis in liver but had little effect on muscle enzymes assessed in this study. Regarding the selection effect, enzyme activity and expression suggest that compared with the L line, the F line presented reduced hepatic fatty acid oxidation as well as reduced mitochondrial oxidative capacities and enhanced glucose utilization in both liver and muscle. Very few line x diet interactions were found, suggesting that the two factors (i.e., dietary energy content and selection) used in this study to modify muscle lipid content exerted some additive but mostly independent effects on these metabolic actors.

Hepatic glucokinase and glucose-6-phosphatase responses to dietary glucose and starch in gilthead sea bream (Sparus aurata) juveniles reared at two temperatures.

The effects of carbohydrate sources/complexity and rearing temperature on hepatic glucokinase (GK) and glucose-6-phosphatase (G6Pase) activities and gene expression were studied in gilthead sea bream juveniles. Two isonitrogenous (50% crude protein) and isolipidic (19% crude lipids) diets were formulated to contain 20% waxy maize starch or 20% glucose. Triplicate groups of fish (63.5 g initial body weight) were fed each diet to near satiation during four weeks at 18 degrees C or 25 degrees C. Growth, feed intake, feed efficiency and protein efficiency ratio, were higher at the higher water temperature. At each water temperatures fish growth and feed efficiency were higher with the glucose diet. Plasma glucose levels were not influenced by water temperature but were higher in fish fed the glucose diet. Hepatosomatic index and liver glycogen were higher at the lower water temperature and within each water temperature in fish fed the glucose diet. No effect of water temperature on enzymes activities was observed, except for hexokinase and GK which were higher at 25 degrees C. Hepatic hexokinase and pyruvate kinase activities were not influenced by diet composition, whereas glucose-6-phosphate dehydrogenase activity was higher in fish fed the glucose diet. Higher GK activity was observed in fish fed the glucose diet. GK gene expression was higher at 25 degrees C in fish fed the waxy maize starch diet while in fish fed the glucose diet, no temperature effect on GK gene expression was observed. Hepatic G6Pase activities and gene expression were neither influenced by dietary carbohydrates nor water temperature. Overall, our data suggest that in gilthead sea bream juveniles hepatocytes dietary carbohydrate source and temperature affect more intensively GK, the enzyme responsible for the first step of glucose uptake, than G6Pase the enzyme involved in the last step of glucose hepatic release.

Early feeding of carnivorous rainbow trout (Oncorhynchus mykiss) with a hyperglucidic diet during a short period: effect on dietary glucose utilization in juveniles.

Based on the concept of nutritional programming in higher vertebrates, we tested whether an acute hyperglucidic stimulus during early life could induce a long-lasting effect on carbohydrate utilization in carnivorous rainbow trout. The trout were fed a hyperglucidic diet (60% dextrin) at two early stages of development: either at first feeding (3 days, stimulus 1) or after yolk absorption (5 days, stimulus 2). Before and after the hyperglucidic stimulus, they received a commercial diet until juvenile stage (>10 g). Fish that did not experience the hyperglucidic stimuli served as controls. The short- and long-term effects of the stimuli were evaluated by measuring the expression of five key genes involved in carbohydrate utilization: alpha-amylase, maltase (digestion), sodium-dependent glucose cotransporter (SGLT1; intestinal glucose transport), and glucokinase and glucose-6-phosphatase, involved in the utilization and production of glucose, respectively. The hyperglucidic diet rapidly increased expressions of maltase, alpha-amylase, and glucokinase in stimulus 1 fish and only of maltase in stimulus 2 fish, probably because of a lower plasticity at this later stage of development. In the final challenge test with juveniles fed a 25% dextrin diet, both digestive enzymes were upregulated in fish that had experienced the hyperglucidic stimulus at first feeding, confirming the possibility of modification of some long-term physiological functions in rainbow trout. In contrast, no persistent molecular adaptations were found for the genes involved in glucose transport or metabolism. In addition, growth and postprandial glycemia were unaffected by the stimuli. In summary, our data show that a short hyperglucidic stimulus during early trout life may permanently influence carbohydrate digestion.