Metabolism In Rainbow Trout Research Articles

Effects of dichlorvos and formalin on fatty acid metabolism of rainbow trout (Oncorhynchus mykiss) skin cells in primary culture

The effects of sub-lethal doses of dichlorvos and formalin, antimicrobial/parasitic agents used in aquaculture, on lipid composition and metabolism of rainbow trout skin cells in primary culture were investigated. [1-14C]Stearic (18:0), [1-14C]lin 18:2n-6) and [1-14C]linolenic (18:3n-3) acids were used as tracers to determine effects on fatty acid incorporation and metabolism. Formalin increased cell numbers and reduced the lipid content of the cells and the incorporation of radioactive fatty acids. The effects of dichlorvos were qualitatively similar but quantitatively less. Formalin induced relatively small but significant changes in lipid class composition including a decreased proportion of phosphatidycholine with increased proportions of sphatidylethanolamine and phosphatidylserine. Dichlorvos had no significant effect on lipid class compositions. The trout primary skin cells expressed substantial Δ9, Δ6 and Δ5 fatty acyl desaturase activities. Although, as expected, the cells were m active towards [1-14C]18:3n-3, the cells were unusually active towards [1-14C]18:2n-6. Both dichlorvos and, especially, formalin appeared to significantly inhibit Δ9 and Δ6 desaturation. Changes in the distribution of radioactivity between individual spholipid classes was also influenced by formalin and dichlorvos, and this may be related to changes in desaturase activity. This study has shown that topically active agents used in aquaculture, formalin and dichlorvos, had a range of effects on the rainbow trout skin cell cultures that may affect cell proliferation and lipid and fatty acid metabolism. Both agents significantly inhibited desaturation of fatty acids, particularly of 18:2n-6 to 20:4n-6 and, as 20:4n-6 is a major eicosanoid precursor ish and considering the importance of eicosanoids in the biochemistry of skin, it is suggested that these agents may have direct effects on fish skin that could have important consequences for fish health in general.

Dose-dependent effects of acute melatonin treatments on brain carbohydrate metabolism of rainbow trout

The levels of glycogen, lactate, acetoacetate and β-hydroxybutyrate in brain as well as glycogen and lactate levels in liver, and glucose levels in plasma were evaluated in rainbow trout, Oncorhynchus mykiss, injected with ethanol/saline (5/95; v/v) alone (controls) or containing melatonin at three different doses 0.25, 0.5 and 1 mg kg-1. The results obtained demonstrate, for the first time in a teleost fish, the existence of changes in brain carbohydrate and ketone body metabolism due to melatonin treatment. Thus, a clear dose-dependent decrease was observed in brain and liver glycogen levels, whereas a clear dose-response increase was observed in brain for lactate, acetoacetate and β-hydroxybutyrate levels, and in plasma for glucose levels. CO2 production from glucose was also tested in brains of pooled fish and these rates were not altered by melatonin treatment. Altogether, these results suggest that melatonin may play an indirect role, possibly through alterations in insulin physiology, in the regulation of carbohydrate and ketone body metabolism in brain of rainbow trout.

Bioaccumulation of dehydroabietic acid in rainbow trout (Oncorhynchus mykiss): role of biotransformation enzymes

The role of Phase I and Phase II metabolism in rainbow trout on the bioaccumulation of dehydroabietic acid, an abundant and persistent compound found in pulp and paper mill effluents, was investigated using known inducer/inhibitor compounds for cytochromes P450 (P450s), ethoxyresorufin O-deethylase (EROD) and uridine diphosphoglucuronosyltransferase (UDPGT). The inducer/inhibitor compounds consisted of piperonyl butoxide (PBO), salicylamide (SAL) and β-naphthoflavone (βNF). PBO induced EROD, SAL had no effect on the measured biotransformation enzyme activities and βNF induced EROD and UDPGT. Treatment of trout with these compounds altered the bioaccumulation and distribution of dehydroabietic acid (DHAA) between bile, liver, and muscle in trout exposed to both the pure compound and an untreated mill effluent indicating that biotransformation enzyme activities may directly influence these bioconcentration processes in recipient biota.

Bioaccumulation of dehydroabietic acid in rainbow trout (Oncorhynchus mykiss): Role of biotransformation enzymes

The role of Phase I and Phase II metabolism in rainbow trout on the bioaccumulation of dehydroabietic acid, an abundant and persistent compound found in pulp and paper mill effluents, was investigated using known inducer/inhibitor compounds for cytochromes P450 (P450s), ethoxyresorufin O-deethylase (EROD) and uridine diphosphoglucuronosyltransferase (UDPGT). The inducer/inhibitor compounds consisted of piperonyl butoxide (PBO), salicylamide (SAL) and R-naphthoflavone (BNF). PBO induced EROD, SAL had no effect on the measured biotransformation enzyme activities and 13NF induced EROD and UDPGT. Treatment of trout with these compounds altered the bioaccumulation and distribution of dehydroabietic acid (DHAA) between bile, liver, and muscle in trout exposed to both the pure compound and an untreated mill effluent indicating that biotransformation enzyme activities may directly influence these bioconcentration processes in recipient biota.

Effects of seasonal temperature acclimatization on muscle metabolism in rainbow trout , Oncorhynchus mykiss

Maximal enzyme activities in cardiac and swimming muscles of rainbow trout (Oncorhynchus mykiss) were estimated during the natural progression of environmental temperature, between seasonal extremes of 4 and 18°C. Specific activity of marker enzymes were measured at a common temperature of 11°C to determine the potential for metabolic acclimatization. The results confirm an increased oxidative capacity in the cold, with little or no expansion in glycolytic capacity of slow muscle: citrate synthase (CS) activity was 23, 15 and 3 µmoles min-1 g wet wt-1 and pyruvate kinase (PK) 15, 23 and 17 µmoles min-1 g wet wt-1 from 4, 11 and 18°C acclimatized groups, respectively. Expansion of lipid metabolism was limited, with increased carnitine palmitoleoyltrasferase (CPT) seen only in the coldest group. Cardiac and fast muscle showed a similar response for CS but not PK or CPT which were greatest at 11 and 18°C, respectively. When compared with previous laboratory acclimation studies, these data suggest that environmental factors other than temperature are likely to influence the nature of metabolic acclimatization.

Long-term nutritional effects on the primary liver and kidney metabolism in rainbow trout (Oncorhynchus mykiss). II. Adaptive response of glucose 6-phosphate dehydrogenase activity to high-carbohydrate/low-protein and high-fat/non-carbohydrate diets

: The influence of long-term administration of high-carbohydrate/low-protein and high-fat/non-carbohydrate diets were studied in relation to kinetic behaviour of glucose 6-phosphate dehydrogenase in liver and kidney of rainbow trout. In all cases studied, the saturation curves of these enzyme showed typical hyperbolic kinetics without evidence of sigmoidicity. After 30 days of feeding with a high-fat diet (170 g kg−1), there was a significant decrease in Vmax and specific activity (45%) as well as catalytic efficiency (39%) without changes in Km or activity ratio of hepatic glucose 6-phosphate dehydrogenase. These changes agree more with a clearly decreased cell concentration than with an inhibition of the pre-existing enzyme. The administration of a high-carbohydrate diet (60 g kg−1), contrary to what was previously thought, decreased Vmax by 21% and specific activity and catalytic efficiency by 30%, without significant changes in the other kinetic parameters of the hepatic enzyme. The kinetic behaviour under these nutritional conditons was due to the rejection of this diet by the fish and thus could be considered a low-feeding situation. On the other hand, no variations in the kinetics of renal glucose 6-phosphate dehydrogenase were found, clearly demonstrating that in this organ, the pentosephosphate pathway showed no adaptive response related to fattyacid and other lipid synthesis. The activity of the renal enzyme was consistently half that of the hepatic enzyme.

Long-term nutritional effects on the primary liver and kidney metabolism in rainbow trout, Oncorhynchus mykiss (Walbaum): adaptive response to a high-protein/non-carbohydrate diet and starvation of glucose 6-phosphate dehydrogenase activity

The adaptive response of the kinetics of glucose 6-phosphate dehydrogenase (G6PDH) was studied in trout liver and kidney after feeding (control or high-protein/non-carbohydrate diet) or starving for 30 days, as well as influences on growth and other nutritive parameters. Typical Michaelis-Menten kinetics were found for the hepatic catalysis of G6PDH under all conditions studied, without evidence of sigmoidicity. The administration of a high-protein/non-carbohydrate diet (61.0% protein, 7.9% lipids) produced no significant changes in specific activity or other kinetic parameters of the liver enzyme. This nutritional situation caused a significant daily increase in relative growth (20%) and feed efficiency (13.5%), as well as a 13% decrease in the protein-conversion efficiency, with respect to the control diet (46% protein, 8% lipids, 22% carbohydrates). On the other hand, long-term starvation (30 days), as a lipolytic condition, significantly decreased the activity and catalytic efficiency of hepatic G6PDH, by almost 45%, without significant changes in the Km and activity-ratio values. These changes agree with a fall in the intracellular concentration of the enzyme as a consequence of a protein-repression process. The activity of the renal G6PDH was less than in the liver of control fish, and no variation in kinetics was found under the high-protein diet or starvation. This behaviour clearly demonstrates that the kidney pentose-phosphate pathway showed no adaptive response in relation to synthesis of fatty acids and other lipids.

Biotransformation of di(2‐ethylhexyl)phthalate by rainbow trout

AbstractThe biotransformation of di(2‐ethylhexyl)phthalate (DEHP) was studied in rainbow trout (Oncorhynchus mykiss) following intravascular administration. Methyl‐esterified metabolites were identified using rodent‐derived standards and nonlinear gradient elution HPLC; metabolites were confirmed by gas chromatography. Similarities between the biotransformation of DEHP by rainbow trout and mammalian species included (a) mono‐ethylhexyl phthalate (MEHP) appeared to be the obligatory first step in DEHP metabolism; (b) the phthalate ring was not oxidized; (c) phthalic acid was a minor metabolite; and (d) several metabolites contained multiple oxidations of the 2‐ethylhexyl moiety of MEHP. No metabolites unique to rainbow trout were identified. However, fewer oxidized metabolites were identified in rainbow trout than in mammalian species, possibly due to limited mitochondrial metabolism of MEHP in rainbow trout. The amount of biliary MEHP glucuronide after intravascular administration of DEHP was substantially less than reported in rainbow trout exposed to DEHP via the water. Results confirmed that DEHP metabolism in rainbow trout proceeds by initial rapid formation of MEHP, followed by excretion or extensive oxidation by microsomal P450.

The effect of gradual transfer to sea water on muscle carbohydrate metabolism of rainbow trout

An assessment of the levels of glycogen and glucose, as well as of the activity of several key enzymes of glycogenolysis, glycolysis, gluconeogenesis and the pentose phosphate shunt were performed in white and red muscle of rainbow trout (Oncorhynchus mykiss) of two different sizes, 97.03 ± 3.03 g (small, n=67) and 165.69 ± 5.01 g (large, n= 68) during gradual transfer to sea water using salinities of 0, 9, 18 and 28 ppt. The results indicate the existence of changes in carbohydrate metabolism in both white and red muscle. Glycogenolysis was observed for both types of muscle associated with increased salinity. The glucose obtained from glycogen breakdown appears to be used in situ in the white muscle of both sizes of animal through increased glycolysis, this is also the case for the red muscle but only for small animals. In neither white or red muscle, were major changes detected in gluconeogenesis, the pentose phosphate shunt or in the use of exogenous glucose. The metabolic changes described are indirectly related to the increased energetic demand occurring during adaptation of rainbow trout to sea water. No main differences were observed between size for the parameters studied except in red muscle probably reflecting a better adaptation of large animals to sea water.

Influence of tank design and hydraulic loading on the behavior, growth, and metabolism of rainbow trout ( Oncorhynchus mykiss)

Subadult rainbow trout ( Oncorhynchus mykiss) stocked at 48 kg/m 3 (3 lb/ft 3) were subjected to treatments of tank design (rectangular plug flow, circular, and cylindrical cross flow) and water exchange rate (1·5 and 2·5 exchanges/h) to determine their effects on fish behavior, growth, and metabolism. Ambient light levels and current velocities were also measured in each of three tank sectors (upstream, middle, and downstream) to determine their relative contributions to behavioral effects. Tank design significantly affected fish orientation to current, contact time with tank surfaces, and frequency of agonistic encounters, though aggression levels were relatively low overall. Gradients in fish distribution by sector were greatest in plug-flow tanks. Effects were either modified or eliminated by increasing the water exchange rate from 1·5 to 2·5/h. Multiple-regression analysis showed the following hieararchy of independent-variable effects on fish distribution: tank type > exchange rate > aggression level > current velocity > light level. Significant effects of tank design were also observed on fish growth in terms of biomass gain (cross flow > plug flow > circular). These results were matched in metabolic studies, where both oxygen consumption and ammonia excretion were highest in circular and lowest in cross-flow tanks. Reduction (cross-flow compared with circular tanks) in oxygen consumption averaged 13·6%, ammonia excretion 17·5%. These results were also modified by an increase in water exchange rate. Tank-design effects on fish metabolism and growth may be mediated, at least partly, through changes in fish behavior.

Effect of Vitamin C on Lipid and Carnitine Metabolism in Rainbow Trout

Effect of Vitamin C on Lipid and Carnitine Metabolism in Rainbow Trout

Effects of somatostatin-25 on lipid mobilization from rainbow trout, Oncorhynchus mykiss, liver and adipose tissue incubated in vitro. Comparison with somatostatin-14

The physiological effects of the pancreatic peptides somatostatin-14 and somatostatin-25 on lipid metabolism in rainbow trout were evaluated by in vitro culture of liver and adipose tissue. The culture medium was subsequently analyzed for glycerol and fatty acid content and triacylglycerol lipase activity was measured within the tissues. Both somatostatin-14 and somatostatin-25 stimulated hepatic fatty acid and glycerol release within 3 h after treatment. Liver triacylglycerol lipase activity was elevated following treatment with somatostatin-14 (76% above control) or somatostatin-25 (94% above control). Somatostatin-14 and somatostatin-25 also significantly stimulated the release of fatty acid and glycerol from adipose tissue. Triacylglycerol lipase activity in adipose tissue also was enhanced by both somatostatins. These results indicate that somatostatin-14 and somatostatin-25 directly stimulate the mobilization of triacylglycerol from liver and adipose tissue, suggesting that these peptides are important systemic modulators of lipid metabolism in fish.

Hormonal stimulation of hepatocyte metabolism in rainbow trout following an acute handling stress

Abstract In juvenile rainbow trout subjected to a 3-min handling stress, plasma cortisol and lactate concentrations showed an initial rapid rise, but returned to near-resting levels after 1 and 3 hr post-stress, respectively. Plasma glucose concentration showed a more gradual increase and was higher than the pre-stress level at 3 and 6 hr post-stress. No significant differences in hepatocyte glycogen content, total glucose production and alanine oxidation after stress were apparent from those of the pre-stress values; alanine gluconeogenesis increased at 3 hr post-stress, but not at any other time periods. Hepatocyte responsiveness to epinephrine (1 hr post-stress) and glucagon stimulation of total glucose production was abolished after stress, while hepatocyte responsiveness to insulin stimulation increased at 3 and 6 hr post-stress. Hepatocyte response to hormonal stimulation of alanine oxidation was also modified by acute stress, but there was no hormonal effect on alanine gluconeogenesis after stress. The results show that acute handling stress alters hepatocyte responsiveness to hormonal stimulation in rainbow trout. The changes are indicative of a control mechanism that may be partly responsible for conserving hepatic glycogen in stressed fish.

Hormonal stimulation of hepatocyte metabolism in rainbow trout following an acute handling stress

In juvenile rainbow trout subjected to a 3-min handling stress, plasma cortisol and lactate concentrations showed an initial rapid rise, but returned to near-resting levels after 1 and 3 hr post-stress, respectively. Plasma glucose concentration showed a more gradual increase and was higher than the pre-stress level at 3 and 6 hr post-stress. No significant differences in hepatocyte glycogen content, total glucose production and alanine oxidation after stress were apparent from those of the pre-stress values; alanine gluconeogenesis increased at 3 hr post-stress, but not at any other time periods. Hepatocyte responsiveness to epinephrine (1 hr post-stress) and glucagon stimulation of total glucose production was abolished after stress, while hepatocyte responsiveness to insulin stimulation increased at 3 and 6 hr post-stress. Hepatocyte response to hormonal stimulation of alanine oxidation was also modified by acute stress, but there was no hormonal effect on alanine gluconeogenesis after stress. The results show that acute handling stress alters hepatocyte responsiveness to hormonal stimulation in rainbow trout. The changes are indicative of a control mechanism that may be partly responsible for conserving hepatic glycogen in stressed fish.

Differential Effects of Somatostatin-14 and Somatostatin-25 on Carbohydrate and Lipid Metabolism in Rainbow Trout Oncorhynchus mykiss

Previous studies have indicated that teleost fish appear to have two somatostatin genes. In salmonid fish, it is purported that gene I encodes for somatostatin-14 (SS-14), while gene II encodes for somatostatin-25 (sSS-25). In the present study, the physiological effects of SS-14 and sSS-25 on carbohydrate and lipid metabolism in rainbow trout, Oncorhynchus mykiss, were evaluated by in vivo administration of hormone and measuring resulting levels of specific metabolites and hormones present within tissues and plasma. Somatostatin-14 administration caused hyperglycemia without affecting liver glycogen content and increased plasma fatty acid (FA) levels in association with enhanced activity of the lipid mobilizing enzyme, triacylglycerol lipage (TG lipase). Somatostatin-14 injection also resulted in reduced hepatic glucose-6-phosphate dehydrogenase activity, which may indicate a decrease in glucose channeling through the pentose phosphate shunt. In addition, SS-14 reduced plasma glucagon concentration, while having no effect on plasma insulin levels. Salmon SS-25 elevated plasma glucose levels in association with reduced glycogen content and resulted in increased plasma FA levels accompanied by increased hepatic TG lipase activity. Salmon SS-25 injection also resulted in a reduction in plasma glucagon and insulin levels. These results indicate that SS-14 and sSS-25 are important regulators of carbohydrate and lipid metabolism in rainbow trout and that modulation of metabolic activity by these peptides may be accomplished, in part, by alterations in insulin and glucagon levels circulating in the plasma.

Effects of growth hormones on bone formation and resorption in rainbow trout ( Oncorhynchus mykiss), as examined by histomorphometry of the pharyngeal bone

Effects of salmon and eel growth hormones (GHs) on bone metabolism in rainbow trout ( Oncorhynchus mykiss) were studied using histomorphometry of their pharyngeal bones. When salmon GH (sGH) was injected intraperitoneally at a dose of 0.01 or 0.1 μg/g/week for 10 times into fed trout, body growth in both length and weight was accelerated. Formation and resorption of bone were enhanced only by the higher dose of sGH. When a cholesterol pellet containing recombinant eel GH (reGH-pellet) was implanted subcutaneously into starved trout for 1 week (37 μg reGH/18 g fish), formation and resorption of bone increased, although activity of bone formation was low. The results indicate that the GHs increased both formation and resorption of bone, regardless of the nutritional status of the fish.

Control of Red Blood Cell Metabolism in Rainbow Trout After Exhaustive Exercise

Metabolic responses (rates of CO2 production from 14C-labelled glucose or lactate, and total O2 consumption) of red blood cells were monitored in rainbow trout (Oncorhynchus mykiss) at rest and during 12 h of recovery from exhaustive exercise. Extracellular acid-base status, red blood cell intracellular pH (pHi), and plasma metabolite and catecholamine levels were recorded simultaneously. Despite a post-exercise rise in plasma glucose level, glucose oxidation was depressed, at least partly because of a rise in plasma lactate level. However, lactate oxidation was stimulated markedly, especially at 0-2 h post-exercise. Subsequent multifactorial experiments in vitro demonstrated that augmentation of lactate oxidation was due partly to increased plasma lactate, and partly to separate stimulatory effects of elevated PCO2 and catecholamine levels. Changes in pH and HCO3- level were not directly involved, but the stimulatory effects of catecholamines occurred only under acidotic conditions. Total red cell O2 consumption (MO2) remained generally stable after exercise. Similar multifactorial experiments in vitro demonstrated that respiratory, metabolic and mixed acidoses all inhibited MO2, an effect largely attributable to the lowered pH. This inhibition was reversed by typical post-exercise levels of epinephrine and norepinephrine; again, catecholamines had no effect under control conditions. Red cell pHi regulation was achieved without an increase in MO2 above resting levels. Our results indicate a complex sensitivity of red cell metabolism to acid-base status and a shift in substrate preference for oxidation after strenuous exercise. The mobilization of catecholamines plays an important coordinating role and helps sustain normal rates of oxidative metabolism by red cells in the face of post-exercise blood acidosis.

Characterization of Red Blood Cell Metabolism in Rainbow Trout

Red blood cell metabolism was studied in vitro using whole blood obtained by catheter from resting rainbow trout (Oncorhynchus mykiss). Preparations were viable as shown by stable NTP, metabolite and catecholamine levels and acid-base status, all of which remained at in vivo levels over the 2 h incubation period. Enzymes diagnostic of glycolysis, the tricarboxylic acid (TCA) cycle and phosphagen metabolism were all present in significant amounts in red blood cells. In direct comparisons of 14C-labelled substrates at normal resting plasma concentrations, rates of CO2 production were in the order: glucose greater than lactate greater than alanine greater than oleate. Total CO2 production rates from these four oxidative substrates did not equal directly measured O2 consumption rates, indicating that other substrates may also be important in vivo. Oxidative pathway Km values for glucose (8.4 mmol l-1), lactate (3.3 mmol l-1) and alanine (0.8 mmol l-1) were well within the normal physiological ranges of plasma concentrations. Glucose concentration did not affect lactate oxidation rates, but there was some inhibition (27%) of glucose oxidation by high lactate concentrations (20 mmol l-1). The observed Km values and competitive interactions suggest that changes in plasma concentrations associated with environmental stresses can considerably alter the relative rates of oxidation of glucose and lactate in vivo. Considerable pentose-phosphate shunt activity was detected in red cells, as indicated by high activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and high CO2 production rates from (1-14C)-labelled glucose. Even in the presence of normal O2 levels, a significant percentage (28%) of glucose metabolism was directed to lactate production. Taken together, these results demonstrate that rainbow trout whole blood incubated in vitro constitutes a dynamic and viable system for metabolic studies at the pathway level.

Effect of digestible carbohydrates on protein/energy utilization and on glucose metabolism in rainbow trout ( Salmo gairdneri R.)

Diplicate groups of rainbow trout were fed low-protein (38%) diets containing high levels (38%) of five different carbohydrate sources (raw starch, extruded corn, extruded wheat, extruded corn starch or extruded wheat starch). A modified pair-feeding method was used to allow equal intakes of protein and of digestible energy by each group of fish. Growth parameters were followed over a period of 18 weeks; the digestibility of the diets, nitrogen and energy balances, and the respiratory and ammonia quotients of fish fed the different diets were determined. To study the long-term effects of dietary carbohydrates, plasma glucose profile and its control by bovine insulin was followed in fish fed over 30 weeks with selected test diets. The results show that inclusion of extruded cereals or extruded starch improves availability of dietary energy. High levels of carbohydrates to not adversely affect overall growth or nutrient retention efficiencies. Long-term feeding with carbohydrate-rich d diets does not confer on trout any adaptive capacity to regulate postprandial glycemia levels. Respirometric measurements appear to provide interesting data on the metabolic utilization of body substrates.

Long-term effect of a high-protein/non-carbohydrate diet on the primary liver and kidney metabolism in rainbow trout ( Salmo gairdneri)

Several aspects of the metabolic adaptation of trout liver and kidney to a high-protein diet were studied. Under this nutritional situation there were significant increases in the activities of the glycolytic enzymes phosphofructokinase (PFK) and pyruvate kinase (PK) from both tissues but with a different molecular basis. PFK activity was increased at subsaturating substrate concentrations, with a decrease in Michaelis constant ( K m) values of about 70% in both tissues and without changes in the maximum velocity ( V max). The activity of PK was increased all along the saturation curve, approximately 70% and 20% in liver and kidney respectively. However, no changes in the activities of glucose 6-phospate dehydrogenase (G6PDH) were detected. On the other hand, the activity of the gluconeogenic enzyme fructose 1,6-bisphosphatase (FBPase) from both tissues was increased only at cellular substrate concentrations. With respect to amino acid metabolism, liver alanine aminotransferase (AAT) was enhanced at all substrate concentrations, with a significant increase of almost 50% in the V max, without changes in the renal activity. Glutamate dehydrogenase (GDH) activity was almost 300% and 100% of control values, in liver and kidney respectively, observations which are in good agreement with the role of this enzyme in the two tissues.