Muscle insulin binding and plasma levels in relation to liver glucokinase activity,glucose metabolism and dietary carbohydrates in rainbow trout

Rainbow trout were fed for 10 weeks with either a carbohydrate-free diet (C-free) or with four experimental diets containing various levels (20 or 40%) and sources of starch (extruded wheat or peas) in order to examine metabolic utilisation of dietary vegetable carbohydrates and its endocrine control. The study was focused on the parameters described as limiting in glucose metabolism in fish. Feeding trials were conducted at 8 and 18 degrees C to establish whether carbohydrate-rich diets can be used in trout farming irrespective of water temperature. At both temperatures, pea diets (especially the highest level) resulted in a feed efficiency as high as the C-free diet. Fish had similar growth rates except when fed the low wheat content diet. Glycaemia values 6 h after feeding were significantly higher in trout fed carbohydrate diets than those given the C-free diet, whereas plasma insulin levels were similar independently of the levels of dietary starch. This study provides the first evidence that glucokinase (GK) activity and mRNA level in trout liver increase in proportion to the content of dietary starch. Nevertheless, these changes were not correlated with plasma insulin levels. Insulin-like growth factor-I (IGF-I) binding and number of receptors in skeletal muscle were consistently higher than those for insulin but no diet-induced differences were found for any of these parameters. Temperature clearly affected the postprandial profile of glucose and insulin, which both showed lower levels 6 h after feeding at 8 degrees C than at 18 degrees C, which was consistent with a lower feed intake. Glucose and insulin levels decreased markedly 24 h after feeding at 18 degrees C, while they were still high at 8 degrees C, an observation concordant with delayed transit rate. These findings indicate satisfactory adaptation of rainbow trout to diets with a relatively high vegetable starch content, especially when provided as extruded peas, and indicate that diets with increased levels of carbohydrates can be used in this species even when it is reared at low temperature.     

Effect of normal and waxy maize starch on growth, food utilization and hepatic glucose metabolism in European sea bass (Dicentrarchus labrax) juveniles

We determined the effect of dietary starch on growth performance and feed utilization in European sea bass juveniles. Data on the dietary regulation of key hepatic enzymes of the glycolytic, gluconeogenic, lipogenic and amino acid metabolic pathways (hexokinase, HK; glucokinase, GK; pyruvate kinase, PK; fructose-1,6-bisphosphatase, FBPase; glucose-6-phosphatase, G6Pase; glucose-6-phosphate dehydrogenase, G6PD; alanine aminotransferase, ALAT; aspartate aminotransferase, ASAT and glutamate dehydrogenase, GDH) were also measured. Five isonitrogenous (48% crude protein) and isolipidic (14% crude lipids) diets were formulated to contain 10% normal starch (diet NS10), 10% waxy starch (diet WS10), 20% normal starch (diet NS20), 20% waxy starch (diet WS20) or no starch (control diet). Another diet was formulated with no carbohydrate, and contained 68% crude protein and 14% crude lipids (diet HP). Each experimental diet was fed to triplicate groups of 30 fish (initial weight: 23.3 g) on an equivalent feeding scheme for 12 weeks. The best growth performance and feed efficiency were achieved with fish fed the HP diet. Neither the level nor the nature of starch had measurable effects on growth performance of sea bass juveniles. Digestibility of starch was higher with waxy starch and decreased with increasing levels of starch in the diet. Whole-body composition and plasma metabolites, mainly glycemia, were not affected by the level and nature of the dietary starch. Data on enzyme activities suggest that dietary carbohydrates significantly improve protein utilization associated with increased glycolytic enzyme activities (GK and PK), as well as decreased gluconeogenic (FBPase) and amino acid catabolic (GDH) enzyme activities. The nature of dietary carbohydrates tested had little influence on performance criteria.     

Hepatic glucokinase is induced by dietary carbohydrates in rainbow trout, gilthead seabream, and common carp

Glucokinase (GK) plays a central role in glucose homeostasis in mammals. The absence of an inducible GK has been suggested to explain the poor utilization of dietary carbohydrates in rainbow trout. In this context, we analyzed GK expression in three fish species (rainbow trout, gilthead seabream, and common carp) known to differ in regard to their dietary carbohydrate tolerance. Fish were fed for 10 wk with either a diet containing a high level of digestible starch (>20%) or a diet totally deprived of starch. Our data demonstrate an induction of GK gene expression and GK activity by dietary carbohydrates in all three species. These studies strongly suggest that low dietary carbohydrate utilization in rainbow trout is not due to the absence of inducible hepatic GK as previously suggested. Interestingly, we also observed a significantly lower GK expression in common carp (a glucose-tolerant fish) than in rainbow trout and gilthead seabream, which are generally considered as glucose intolerant. These data suggest that other biochemical mechanisms are implicated in the inability of rainbow trout and gilthead seabream to control blood glucose closely.     

High Dietary Lipid Level Is Associated with Persistent Hyperglycaemia and Downregulation of Muscle Akt-mTOR Pathway in Senegalese Sole (Solea senegalensis)

High levels of dietary lipids are incorporated in feeds for most teleost fish to promote growth and reduce nitrogen waste. However, in Senegalese sole (Solea senegalensis) previous studies revealed that increasing the level of dietary lipids above 8% negatively affect growth and nutrient utilization regardless of dietary protein content. It has been shown that glucose regulation and metabolism can be impaired by high dietary fat intake in mammals, but information in teleost fish is scarce. The aim of this study was to assess the possible effect of dietary lipids on glucose metabolism in Senegalese sole with special emphasis on the regulation of proteins involved in the muscle insulin-signalling pathway. Senegalese sole juveniles (29 g) were fed two isonitrogenous diets (53% dry matter) for 88 days. These two diets were one with a high lipid level (∼17%, HL) and a moderate starch content (∼14%, LC), and the other being devoid of fish oil (4% lipid, LL) and with high starch content (∼23%, HC). Surprisingly, feeding Senegalese sole the HL/LC diet resulted in prolonged hyperglycaemia, while fish fed on LL/HC diet restored basal glycaemia 2 h after feeding. The hyperglycaemic phenotype was associated with greater glucose-6-phosphatase activity (a key enzyme of hepatic glucose production) and lower citrate synthase activity in the liver, with significantly higher liver glycogen content. Sole fed on HL/LC diet also had significantly lower hexokinase activity in muscle, although hexokinase activity was low with both dietary treatments. The HL/LC diet was associated with significant reductions in muscle AKT, p70 ribosomal S6-K1 Kinase (S6K-1) and ribosomal protein S6 (S6) 2 h after feeding, suggesting down regulation of the AKT-mTOR nutrient signalling pathway in these fish. The results of this study show for the first time that high level of dietary lipids strongly affects glucose metabolism in Senegalese sole.     

Effect of dietary carbohydrate type on lipoprotein lipase, hepatic lipase, and lecithin:cholesterol acyltransferase activities in cynomolgus monkeys

The effects of dietary sucrose and starch with and without exogenous cholesterol on postheparin plasma lipoprotein lipase (PHLA) and hepatic lipase (HLA) were studied in cynomolgus monkeys. Serum triglyceride levels were higher in sucrose-fed animals than starch and exogenous cholesterol lowered serum triglyceride levels when added to sucrose diet but not starch diets. Sucrose markedly increased insulin levels, more so than starch; however, dietary cholesterol lowered insulin levels in sucrose diet but increased the levels in starch diet. PHLA activity was increased two- to threefold greater in sucrose than in starch diets. Exogenous cholesterol lowered PHLA activity in sucrose diet but increased PHLA activity in starch diet. HLA activity was increased with sucrose more than starch. Lecithin:cholesterol acyltransferase (LCAT) activity was significantly higher in sucrose diets than in the starch diet. Addition of cholesterol to either of these diets lowered the LCAT activity. These results indicate that PHLA, HLA, and LCAT activities not only are affected by the nature of carbohydrates, but also are related to triglyceride metabolism. The interaction of carbohydrates and cholesterol in the diet by influencing these selected enzymes plays an integrated role in lipoprotein particle interconversion processes.     

Insulin and glucagon family peptides in relation to activities of hepatic hexokinase and other enzymes in fed and starved Atlantic salmon (Salmo salar) and cod (Gadus morhua).

1. Plasma levels of insulin, glucagon, and glucagon-like peptide (Glp) were all reduced by starvation of salmon and cod. In the salmon the drop in Glp was larger than in insulin and glucagon. 2. After starvation the activity of hexokinase (EC 2.7.1.1) was increased in salmon liver, but decreased in cod liver. The salmon hepatic hexokinase activity was inversely correlated with the Glp/insulin ratio. 3. Activities of hepatic glycogen phosphorylase (EC 2.4.1.1) and phosphofructokinase (EC 2.7.1.11) were increased in starved as compared to fed salmon. In cod, starvation resulted in decreased or unchanged activity of phosphorylase. This discrepancy may be related to different degrees of environmental and handling stress. 4. Intraperitoneal injection of human insulin in salmon gave increased hepatic phosphorylase and hexokinase activities and reduced plasma levels of glucagon, Glp and endogenous fish insulin at sampling after 30 hr. 5. No differences in hepatic hexokinase activities or plasma hormone levels were observed between cod fed low and high carbohydrate diets. Apparently, regulation of glucose phosphorylation by dietary carbohydrate does not occur.     

Dietary carbohydrates induce changes in glucosensing capacity and food intake of rainbow trout

We hypothesize that variations in dietary carbohydrate levels produce changes in glucosensor parameters in previously characterized glucosensing areas (hypothalamus and hindbrain) related with the regulation of food intake of a carnivorous fish species like rainbow trout. Therefore, we fed trout with standard, carbohydrate-free (CF) or high-carbohydrate (HC) diets for 10 days to assess changes in glucosensing system and food intake. Fish fed CF diet displayed hypoglycemia and increased food intake. Fish fed a HC diet displayed hyperglycemia and decreased food intake. Changes in food intake due to dietary carbohydrates were accompanied in hypothalamus and hindbrain of fish fed with HC diet by changes in parameters involved in glucosensing, such as increased glucose, glucose 6-phosphate, and glycogen levels and increased glucokinase (GK), glycogen synthase, and pyruvate kinase activities as well as increased GK and GLUT2 expression. All those results address for the first time in fish, despite the relative intolerance to glucose of carnivorous species, that dietary carbohydrates are important regulators of the glucosensing system in carnivorous fish, suggesting that the information generated by this system can be associated with the changes observed in food intake.     

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.     

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.     

The Effect of Dietary Organic Chromium on Specific Growth Rate, Tissue Chromium Concentrations, Enzyme Activities and Histology in Common Carp, Cyprinus carpio L.

A 63-day feeding trial was carried out to investigate the effect of three levels of Cr yeast (0.5, 1.0 and 2.0?mg Cr/kg) on the utilization of diets containing 38.5?% of maize starch or dextrin in common carp, Cyprinus carpio L. (initial mean body mass 14?±?0.3?g) in an auto circulator system at 25?±?0.5?°C. A two-way analysis of variance (ANOVA) showed that the final body mass (FBM), percentage mass gain (%MG), specific growth rate (SGR) and feed conversion ratio (FCR) were significantly (P?<?0.05) affected by the two sources of variation (carbohydrate source and Cr level). In general, fish fed on a diet containing starch and fortified with 0.5?mg Cr/kg performed significantly higher FBM (47.23?g), %MG (225.11), SGR (1.91) and lower value of FCR (1.24) compared to fish fed on the other diets. Carp fed on 2.0?mg Cr/kg with maize starch and 1.0?mg Cr/kg with dextrin-based diet showed a significant reduction (P?<?0.05) in whole body lipid content as confirmed by a two-way ANOVA. Fish fed on a maize starch-based diet supplemented with 0.5 and 1.0?mg Cr/kg recorded the highest activities for hexokinase enzyme. Glucose-6-phosphate dehydrogenase activity was neither affected by Cr concentration nor by dietary carbohydrate source. Fish fed on dextrin-based diets accumulated higher Cr in the whole tissue compared to fish fed on starch-based diets. Normal histological structures in the liver and gut tissues were observed in all groups. The present data clearly showed that dietary Cr yeast was safe in the fish diet at the levels tested.     

Factorial effects of salinity, dietary carbohydrate and moult cycle on digestive carbohydrases and hexokinases in Litopenaeus vannamei (Boone, 1931)

Litopenaeus vannamei were reared in close cycle over seven generations and tested for their capacity to digest starch and to metabolise glucose at different stages of the moulting cycle. After acclimation with 42.3% of carbohydrates (HCBH) or 2.3% carbohydrates (LCBH) diets and at high salinity (40 g kg(-1)) or low salinity (15 g kg(-1)), shrimp were sampled and hepatopancreas (HP) were stored. Total soluble protein in HP was affected by the interaction between salinity and moult stages (p<0.05). Specific activity of alpha-amylase ranged from 44 to 241 U mg protein(-1) and a significant interaction between salinity and moult stages was observed (p<0.05), resulting in highest values at stage C for low salinity (mean value 196.4 U mg protein(-1)), and at D0 in high salinity (mean value 175.7 U mg protein(-1)). Specific activity of alpha-glucosidase ranged between 0.09 and 0.63 U mg protein(-1), an interaction between dietary CBH and salinity was observed for the alpha-glucosidase (p<0.05) and highest mean value was found in low salinity-LCBH diet treatment (0.329 U mg protein(-1)). Hexokinase specific activity (range 9-113 mU mg protein(-1)) showed no significant differences when measured at 5 mM glucose (p>0.05). Total hexokinase specific activity (range 17-215 mU mg protein(-1)) showed a significant interaction between dietary CBH and salinity (p<0.05) with highest value (mean value 78.5 mU mg protein(-1)) found in HCBH-high salinity treatment, whereas in the other treatments the activity was not significantly different (mean value 35.93 mU mg protein(-1)). A synergistic effect of dietary CBH, salinity and moult stages over hexokinase IV-like specific activity was also observed (p<0.05). As result of this interaction, the highest value (135.5+/-81 mU mg protein(-1)) was observed in HCBH, high salinity at D0 moult stage. Digestive enzymes activity is enhanced in the presence of high starch diet (HCBH) and hexokinase can be induced at certain moulting stages under the influence of blood glucose level. Perspectives are opened to add more carbohydrates in a growing diet, exemplifying the potential approach for less-polluting feed.     

Dietary carbohydrate composition modifies the milk N efficiency in late lactation cows fed low crude protein diets

Nitrogen emissions from dairy cows can be readily decreased by lowering the dietary CP concentration. The main objective of this work was to test whether the milk protein yield reduction associated with low N intakes could be partially compensated for by modifying the dietary carbohydrate composition (CHO). The effects of CHO on digestion, milk N efficiency (milk N/N intake; MNE) and animal performance were studied in four Jersey cows fed 100% or 80% of the recommended protein requirements using a 4×4 Latin square design. Four iso-energetic diets were formulated to two different CHO sources (starch diets with starch content of 34.3% and NDF at 32.5%, and fiber diets with starch content of 5.5% and NDF at 49.1%) and two CP levels (Low=12.0% and Normal=16.5%). The apparent digestible organic matter intake (DOMI) and the protein supply (protein digestible in the small intestine; PDIE) were similar between starch and fiber diets. As planned, microbial N flow (MNF) to the duodenum, estimated from the urinary purine derivatives (PD) excretion, was similar between Low and Normal CP diets. However, the MNF and the efficiency of microbial synthesis (g of microbial N/kg apparently DOMI) were higher for starch v. fiber diets. Milk and milk N fractions (CP, true protein, non-protein N (NPN)) yield were higher for starch compared with fiber diets and for Normal v. Low CP diets. Fecal N excretion was similar across dietary treatments. Despite a higher milk N ouput with starch v. fiber diets, the CHO modified neither the urinary N excretion nor the milk urea-N (MUN) concentration. The milk protein yield relative to both N and PDIE intakes was improved with starch compared with fiber diets. Concentrations of β-hydroxybutyrate, urea and Glu increased and those of glucose and Ala decreased in plasma of cows fed starch v. fiber diets. On the other hand, plasma concentration of albumin, urea, insulin and His increased in cows fed Normal compared with Low CP diets. This study showed that decreasing the dietary CP proportion from 16.5% to 12.0% increases and decreases considerably the MNE and the urinary N excretion, respectively. Moreover, present results show that at similar digestible OM and PDIE intakes, diets rich in starch improves the MNE and could partially compensate for the negative effects of Low CP diets on milk protein yield.     

芙蓉鲤鲫幼鱼饲料适宜淀粉含量

实验以鱼粉和酪蛋白为主要蛋白源、以鱼油和豆油为主要脂肪源(鱼油/豆油, 1/1), 设计了7组不同玉米淀粉水平(6%、12%、18%、24%、30%、36%和42%)的等氮(35%)等脂(8%)饲料来饲喂芙蓉鲤鲫(Carassiusauratus var Furong carp ♀Cyprinus carpio red crucian carp ♂)幼鱼(8.940.59) g以确定其最适饲料淀粉水平。实验周期为61d。结果表明, 随饲料玉米淀粉水平的增加实验鱼增重率、特定生长率和饲料效率先上升(P0.05)而后趋于稳定, 18%42%饲料玉米淀粉组之间差异不显著(P0.05)。鱼体蛋白沉积率随饲料玉米淀粉水平的增加而增加, 30%和42%处理组显著高于6%和12%处理组(P0.05)。血浆葡萄糖没有受饲料玉米淀粉水平的影响(P0.05), 血浆总胆固醇含量在30%处理组最高(P0.05), 血浆甘油三酯随饲料玉米淀粉水平的增加而上升(P0.05)。肝糖原随饲料玉米淀粉水平的增加而上升, 36%处理组显著高于6%和12%处理组(P0.05)。肌糖原和肠道淀粉酶活性随饲料玉米淀粉水平增加而显著上升(P0.05)。通过特定生长率和饲料淀粉水平的折线法分析表明, 芙蓉鲤鲫幼鱼达到最大生长时饲料淀粉水平为27.47%。     

饲料不同水平淀粉对全养殖周期异育银鲫“中科3号”生长和糖代谢的影响

研究探讨了饲料淀粉对全养殖周期异育银鲫(Carassius auratus gibelio)生长性能和糖代谢的影响。实验以玉米淀粉为主要糖源, 分别设计淀粉水平为3% (S3)、13% (S13)、23% (S23)、33% (S33)和43% (S43)的5种等氮等脂饲料, 在长江故道江面网箱中饲养初始体重为(12.0±0.1) g的异育银鲫幼鱼340d, 期间根据鱼体养成阶段共取样5次, 生长阶段分为63d(D63, 幼鱼期)、110d(D110, 养成前期)、223d(D223, 越冬期)、275d(D275, 越冬后)和340d(D340, 养成中后期)。研究结果表明, 幼鱼期D63异育银鲫后肠淀粉酶活力较低且对饲料淀粉水平变化不敏感, 自养成前期D110之后鱼体后肠淀粉酶活力增强且随饲料淀粉水平的变化产生波动。幼鱼期D63异育银鲫glut2 mRNA相对表达量无显著差异, 其他阶段异育银鲫glut2 mRNA相对表达量水平随饲料淀粉水平升高而升高。各个生长阶段异育银鲫糖酵解的敏感度高于糖异生代谢, 幼鱼期D63与养成前期D110异育银鲫糖脂转化能力较强。幼鱼期D63异育银鲫适宜饲料淀粉水平为23%; 养成前期D110异育银鲫适宜饲料淀粉水平减为13%; 越冬后D275组异育银鲫整体代谢旺盛, 43%淀粉组生长最好; 而在养成中后期D340异育银鲫饲料淀粉需求则再次降到33%。研究结果表明, 异育银鲫在养殖周期的不同阶段对饲料淀粉的需求和利用存在显著的差异, 可以为异育银鲫不同养殖阶段特有饲料配方的设计提供支撑。     

The role of hepatic, renal and intestinal gluconeogenic enzymes in glucose homeostasis of juvenile rainbow trout

Rainbow trout is unable to utilize high levels of dietary carbohydrates and experiences hyperglycemia after consumption of carbohydrate-rich meals. Carbohydrates stimulate hepatic glycolytic activity, but gene expression of the rate-limiting gluconeogenic enzymes glucose-6-phosphatase (G6Pase), fructose-1,6-bisphosphatase (FBPase) and phosphoenolpyruvate carboxykinase (PEPCK) remains high. Although there is significant mRNA expression and activity of gluconeogenic enzymes in trout intestine and kidney, the regulation of these enzymes by diet is not known. We tested the hypothesis that dietary carbohydrate modulates intestinal and renal G6Pase, FBPase and PEPCK. Fish were either fasted or fed isocaloric carbohydrate-free (CF) or high carbohydrate (HC) diets for 14 days. As expected, fish fed HC exhibited postprandial hyperglycemia and enhanced levels of hepatic glucokinase mRNA and activity. Dietary carbohydrates had no significant effect on the expression and activity of PEPCK, FBPase and G6Pase in all three organs. In contrast, fasting enhanced the activity, but not the mRNA expression of both hepatic and intestinal PEPCK, as well as intestinal FBPase. Therefore, the activity of rate-limiting gluconeogenic enzymes in trout can be modified by fasting, but not by the carbohydrate content of the diet, potentially causing hyperglycemia when fed high levels of dietary carbohydrates. In this species consuming low carbohydrate diets at infrequent intervals in the wild, fasting-induced increases in hepatic and intestinal gluconeogenic enzyme activities may be a key adaptation to prevent perturbations in blood glucose during food deprivation. Presented in part at Experimental Biology, April 2006, San Francisco, CA [Kirchner S., Panserat S., Kaushik S. and Ferraris R. FASEB-IUPS-2006 A667.6].     

Influence of dietary fibre on nutrient digestibility and energy utilisation in growing pigs fed diets varying in soluble and insoluble fibres from co-products

The co-products from the industry are used to reduce costs in pig diets. However, the co-products used in pig diets are limited because of a high fibre content which is not digested by endogenous enzymes and is resistant to degradation in the small and large intestines. The aim of this study was to investigate digestibility of nutrients and energy, and energy utilisation in pigs fed diets with various soluble and insoluble dietary fibre (DF) from co-products. The experiment was performed as a 4 × 4 Latin square design (four diets and four periods) using four growing pigs (66.2 ± 7.8 kg) surgically fitted with a T-cannula in the end of the small intestine. The pigs were fed four experimental diets: low-fibre control (LF), high-fibre control (HF), high-soluble fibre (HFS) and high-insoluble fibre (HFI) diets. The apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of ash, organic matter, CP, fat, carbohydrates, starch and non-starch polysaccharides (NSP) divided into cellulose and soluble and insoluble non-cellulosic polysaccharide residues were measured using chromic oxide as marker. The recovery of total solid materials, organic matter and total carbohydrates in ileal digesta in pigs fed the HF and HFS diets was higher than in pigs fed LF and HFI, whereas recovery of organic matter and total carbohydrates in faecal materials in the HFS diet was lowest (P < 0.05). AID of organic matter, total carbohydrates and starch was lowest for HFS diet (P < 0.05). ATTD of organic matter and CP was higher for LF diet compared with other diets (P < 0.05), whereas total NSP, cellulose and non-cellulosic polysaccharides residues were highest for HFS diet (P < 0.05). Lactic acid in ileal digesta was influenced by dietary composition (P < 0.05) whereas neither type nor level of DF affected short chain fatty acids. The digestible energy, metabolisable energy, net energy and retained energy intake were similar among diets without influence of DF inclusion (P > 0.05). The metabolisable energy:digestible energy ratio was lower when feeding the HFS diet because of a higher fermentative methane loss. Faecal nitrogen and carbon were positively correlated with DM intake and insoluble DF in the diets (P < 0.05), but nitrogen and carbon (% of intake) were similar among diets. The present findings suggest that high-DF co-products can be used as ingredients of pig diets when features of DF are considered.     

A review of processing of feed ingredients to enhance diet digestibility in finfish

Replacement of fish meal with plant proteins in aquaculture diets presents several problems. Firstly, aquaculture diets, particularly diets for carnivorous fish species, are nutrient dense and may contain up to 450 g crude protein (CP)/kg. Such diets preclude the use of ingredients with only moderate CP content, such as pulses including peas and faba beans or oilseed meals including canola/rapeseed meal and flax. Secondly, virtually all crops contain heat-labile and heat-stable secondary compounds including protease inhibitors, tannins, lectins, phytate, dietary fibre and starch. Removal of heat-labile secondary compounds may be accomplished by extrusion or other heat treatment. However, elimination of heat-stable secondary compounds, and increasing the nutrient concentration of diets, requires fractionation of crops. Fractionation technologies range from low technology processes such as dehulling to medium technologies such as air classification to sophisticated technologies such as aqueous and solvent protein purification. Studies on the nutritional value of processed plant proteins in various fish species have consistently shown improved digestibility and growth compared to feeding unprocessed ingredients. This review examines effects of processing technologies on nutritional properties of soybean meal, canola meal, peas, lupins and flax in aquaculture diets.     

Fructose metabolizing enzymes in the rat liver and metabolic parameters: Interactions between dietary copper,type of carbohydrates,and gender

This study was conducted to determine the effects of nutrient interactions between dietary carbohydrates and copper levels on fructose-metabolizing hepatic enzymes in male and female rats. Male and female rats were fed diets for 5 weeks that were either adequate or deficient in copper that contained either starch or fructose. Rats of both sexes fed fructose as compared with those fed starch showed higher activity of hepatic fructose metabolizing enzymes. There were also significant differences in fructose metabolism of liver between the male and female rats. Female rats had lower hepatic ketohexokinase and triose kinase but higher triosephosphate isomerase activities compared with male rats. Male rats fed copper-deficient diets had lower aldolase B activity compared with those fed copper-adequate diets. Female rats fed copper-deficient diets had higher triosephosphate isomerase activity compared with rats fed copper-adequate diets. Our data suggest that gender differences in hepatic fructose metabolism may not be the primary reason for the severity of copper deficiency syndrome in male rats fed copper-deficient diet with fructose.     

饲料脂肪水平对长养殖周期异育银鲫“中科3号”生长和脂代谢的影响

实验以初重为(11.33±0.03) g的异育银鲫(Carassius auratus gibelio)为研究对象,分别投喂脂肪水平为4%(L4)、8%(L8)、12% (L12)、16% (L16)和20% (L20)的5种等氮饲料进行为期340d的长养殖周期实验,以探究饲料脂肪水平对长养殖周期异育银鲫生长性能、消化酶活性和脂代谢的影响。期间共取样5次,生长阶段分为63d(D63,幼鱼期)、110d(D110,养成前期)、223d(D223,越冬期)、275d(D275,越冬后)和340d(D340,养成中后期)。实验结果显示,以增重率为评价指标,幼鱼期D63的异育银鲫适宜脂肪水平为8%,养成前期D110的异育银鲫适宜脂肪水平为12%,而其他生长阶段饲料脂水平对增重率无显著影响。饲料脂肪水平对幼鱼期异育银鲫肠道消化酶活性有显著影响,脂肪酶活性随脂肪水平的升高呈现先降低后升高的趋势,幼鱼期(D63)异育银鲫肠道胰蛋白酶和淀粉酶活性高于越冬期和养成中后期的异育银鲫,表明幼鱼期的异育银鲫对脂肪的利用较低。幼鱼期(D63)异育银鲫脂肪合成相关基因pparγ和fas的表达量饲料脂肪水平升高呈先升高后下降的趋势,且在L8组表达量最高,而脂解基因lpl和cpt1a的表达量在低脂组L4显著低于其他各组。pparγ和cpt1a在越冬后期(D275)的表达量随饲料脂肪水平的升高呈现先上升后下降,而fas表达量在L4组显著高于其他组,表明不同生长阶段异育银鲫对饲料脂肪摄入的响应策略不一致,摄入过高或过低均会导致代谢紊乱。适宜的脂水平(8%—12%)可促进幼鱼期和养成前期异育银鲫的生长,增强脂肪利用率和脂代谢能力,而较大规格的异育银鲫对脂肪的变化不敏感。     

Lack of significant long-term effect of dietary carbohydrates on hepatic glucose-6-phosphatase expression in rainbow trout (Oncorhynchus mykiss)

Hepatic glucose-6-phosphatase (G6Pase) plays an important role in glucose metabolism because it catalyzes the release of glucose to the circulatory system in the processes of glycogenolysis and gluconeogenesis. The present study was initiated to analyze the regulation of hepatic G6Pase expression by dietary carbohydrates in rainbow trout. The first step in our study was the identification of a partial G6Pase cDNA in rainbow trout that was highly homologous to that of mammals. Hepatic G6Pase activities and mRNA levels were measured in trout fed one of the experimental diets, with or without carbohydrates. We found no significant effect of intake of dietary carbohydrates on G6Pase expression (mRNA and activity) 6 hours and 24 hours after feeding. These results suggest that there is no control of G6Pase synthesis by dietary carbohydrates in rainbow trout and that the lack of regulation of gluconeogenesis by dietary carbohydrates could at least partially explain the postprandial hyperglycemia and the low dietary glucose utilization observed in this species.