Effects of fasting and feeding various diets on hepatic lipogenic enzyme activities in coho salmon (Oncorhynchus kisutch (Walbaum))

Postprandial pattern of digestive enzymes and protein turnover in meagre (Argyrosomus regius) juveniles

After a meal, a sequence of physiological changes occurs in animals in response to digestion, absorption and assimilation of the ingested nutrients. These processes are very important for the aquaculture sector since they will define the efficiency by which food is converted into growth, thus contributing to reduce the production costs and also undigested food in the effluents. Here we investigated the activity of digestive enzymes in the midgut and the protein degradation systems following a single meal to define postprandial patterns of action in hepatic and muscle tissues of meagre juveniles. Fish were fed with a single meal followed by a period of 24 h without feed. The activity of several digestive enzymes (α-amylase, trypsin, aminopeptidase, alkaline and acid phosphatases) plus the analysis of key players of the ubiquitin-proteasome (UPS) and autophagy-lysosomal (ALS) systems were examined just before feeding (0 h, basal point) and 2, 4, 6, 8 and 24 h after food ingestion. Digestion was activated around 4 h after food ingestion and nutrients available for protein degradation 2 h later. This work provided information about the short-term physiological effects induced by a single meal to support scientists' decision when planning a specific study involving digestion and protein degradation, and also to fish farmers on how to better manage feeding protocols when producing A. regius juveniles. Our results suggested that meagre juveniles, under the experimental conditions used, can be fed every 4 h, time when digestion starts, however further studies should be addressed to find the optimal feeding regime for this juvenile species.

Effect of Quercetin Nanoparticles on Hepatic and Intestinal Enzymes and Stress-Related Genes in Nile Tilapia Fish Exposed to Silver Nanoparticles

Recently, nanotechnology has become an important research field involved in the improvement of animals’ productivity, including aquaculture. In this field, silver nanoparticles (AgNPs) have gained interest as antibacterial, antiviral, and antifungal agents. On the other hand, their extensive use in other fields increased natural water pollution causing hazardous effects on aquatic organisms. Quercetin is a natural polyphenolic compound of many plants and vegetables, and it acts as a potent antioxidant and therapeutic agent in biological systems. The current study investigated the potential mitigative effect of quercetin nanoparticles (QNPs) against AgNPs-induced toxicity in Nile tilapia via investigating liver function markers, hepatic antioxidant status, apoptosis, and bioaccumulation of silver residues in hepatic tissue in addition to the whole-body chemical composition, hormonal assay, intestinal enzymes activity, and gut microbiota. Fish were grouped into: control fish, fish exposed to 1.98 mg L−1 AgNPs, fish that received 400 mg L−1 QNPs, and fish that received QNPs and AgNPs at the same concentrations. All groups were exposed for 60 days. The moisture and ash contents of the AgNP group were significantly higher than those of the other groups. In contrast, the crude lipid and protein decreased in the whole body. AgNPs significantly increased serum levels of ALT, AST, total cholesterol, and triglycerides and decreased glycogen and growth hormone (*** p < 0.001). The liver and intestinal enzymes’ activities were significantly inhibited (*** p < 0.001), while the oxidative damage liver enzymes, intestinal bacterial and Aeromonas counts, and Ag residues in the liver were significantly increased (*** p < 0.001, and * p < 0.05). AgNPs also significantly upregulated the expression of hepatic Hsp70, caspase3, and p53 genes (* p < 0.05). These findings indicate the oxidative and hepatotoxic effects of AgNPs. QNPs enhanced and restored physiological parameters and health status under normal conditions and after exposure to AgNPs.

Short-Term Effect of a Low-Protein High-Carbohydrate Diet on Mature Female and Male, and Neomale Rainbow Trout

Rainbow trout are considered as a poor user of dietary carbohydrates, displaying persistent postprandial hyperglycaemia when fed a diet containing high amounts of carbohydrates. While this phenotype is well-described in juveniles, less attention was given to broodstock. Our objective was to assess for the first time the short-term consequences of feeding mature female and male, and neomale trout with a low-protein high-carbohydrate diet on glucose and lipid metabolism. Fish were fed for two days with a diet containing either no or 32% of carbohydrates. We analysed plasma metabolites, mRNA levels and enzymatic activities of glycolysis, gluconeogenesis, de novo lipogenesis and β-oxidation in the liver. Results demonstrated that the glucose and lipid metabolism were regulated by the nutritional status in all sexes, irrespective of the carbohydrate intake. These data point out that carbohydrate intake during a short period (5 meals) at 8 °C did not induce specific metabolic changes in broodstock. Finally, we demonstrated, for the first time, sex differences regarding the consequences of two days of feeding on glucose and lipid metabolism.

Glucose metabolism and gene expression in juvenile zebrafish (Danio rerio) challenged with a high carbohydrate diet: effects of an acute glucose stimulus during late embryonic life

Knowledge on the role of early nutritional stimuli as triggers of metabolic pathways in fish is extremely scarce. The objective of the present study was to assess the long-term effects of glucose injection in the yolk (early stimulus) on carbohydrate metabolism and gene regulation in zebrafish juveniles challenged with a high-carbohydrate low-protein (HC) diet. Eggs were microinjected at 1 d post-fertilisation (dpf) with either glucose (2 M) or saline solutions. Up to 25 dpf, fish were fed a low-carbohydrate high-protein (LC) control diet, which was followed by a challenge with the HC diet. Survival and growth of 35 dpf juveniles were not affected by injection or the HC diet. Glucose stimulus induced some long-term metabolic changes in the juveniles, as shown by the altered expression of genes involved in glucose metabolism. On glycolysis, the expression levels of hexokinase 1 (HK1) and phosphofructokinase-6 (6PFK) were up-regulated in the visceral and muscle tissues, respectively, of juveniles exposed to the glucose stimulus, indicating a possible improvement in glucose oxidation. On gluconeogenesis, the inhibition of the expression levels of PEPCK in fish injected with glucose suggested lower production of hepatic glucose. Unexpectedly, fructose-1,6-bisphosphatase (FBP) expression was induced and 6PFK expression reduced by glucose stimulus, leaving the possibility of a specific regulation of the FBP-6PFK metabolic cycle. Glucose metabolism in juveniles was estimated using a [¹⁴C]glucose tracer; fish previously exposed to the stimulus showed lower retention of [¹⁴C]glucose in visceral tissue (but not in muscle tissue) and, accordingly, higher glucose catabolism, in comparison with the saline group. Globally, our data suggest that glucose stimulus at embryo stage has the potential to alter particular steps of glucose metabolism in zebrafish juveniles.

Comparison of glucose and lipid metabolic gene expressions between fat and lean lines of rainbow trout after a glucose load

Two experimental rainbow trout lines developed through divergent selection for low (Lean ‘L’ line) or high (Fat ‘F’ line) muscle fat content were used as models to study the genetic determinism of fat depots. Previous nutritional studies suggested that the F line had a better capability to use glucose than the L line during feeding trials. Based on that, we put forward the hypothesis that F line has a greater metabolic ability to clear a glucose load effectively, compared to L line. In order to test this hypothesis, 250 mg/kg glucose was intraperitoneally injected to the two rainbow trout lines fasted for 48 h. Hyperglycemia was observed after glucose treatment in both lines without affecting the phosphorylation of AMPK (cellular energy sensor) and Akt-TOR (insulin signaling) components. Liver glucokinase and glucose-6-phosphate dehydrogenase expression levels were increased by glucose, whereas mRNA levels of β-oxidation enzymes (CPT1a, CPT1b, HOAD and ACO) were down-regulated in the white skeletal muscle of both lines. Regarding the genotype effect, concordant with normoglycemia at 12 h after glucose treatment, higher muscle glycogen was found in F line compared to L line which exhibited hyperglycemia. Moreover, mRNA levels of hepatic glycolytic enzymes (GK, 6PFK and PK), gluconeogenic enzyme PEPCK and muscle fatty acid oxidation enzymes (CPT1a, CPT1b and HOAD) were concurrently higher in the F line. Overall, these findings suggest that F line may have a better ability to maintain glucose homeostasis than L line.

Fasting ameliorates metabolism, immunity, and oxidative stress in carbon tetrachloride-intoxicated rats

Background:

Fasting has been recently discovered to improve overall health, but its beneficial effects in the presence of hepatic insufficiency have not been proven.

Aim:

The influence of fasting on the metabolism, immunological aspects, and oxidative stress of 40 male carbon tetrachloride (CCl4)-intoxicated Wistar rats was investigated in the present study.

Methods:

The rats were divided into four groups, including a placebo group, CCl4-intoxicated rats, which were injected subcutaneously with 1.0 ml/kg of CCl4 solution, a fasting group, which was fasted 12 h/day for 30 days, and a fourth group, which was injected with CCl4 and fasted.

Results:

The metabolism, immunity, and oxidative stress improved in CCl4-intoxicated rats fasted for 12 h/day for 30 days, as evidenced in significant increase ( p < 0.05) in total protein, globulin, immunoglobulin M (IgM) and IgG levels, and total antioxidant capacity. In contrast, significant decrease ( p < 0.05) in blood glucose, total cholesterol, low-density lipoprotein-cholesterol, alanine aminotransferase, C-reactive protein, and malondialdehyde levels were observed. Compared with CCl4-intoxicated rats, significant differences in the albumin, triacylglycerol, high-density lipoprotein-cholesterol, very low-density lipoprotein-cholesterol, cardiovascular risk factor, calcium and magnesium levels were not detected.

Conclusions:

The results of the present study showed that fasting improved metabolism, immunity, and oxidative stress in CCl4-intoxicated rats. Thus, fasting during Ramadan is safe for patients with hepatic disorders, as the prophet Mohammed (S) said “Keep the fast, keep your health”.

Induction of autophagy by amino acid starvation in fish cells

Autophagy is well established as a starvation-induced process in yeast and mammalian cells and tissues. To elucidate the cellular mechanisms induced by starvation in fish, we characterized the induction of autophagy in cultured zebrafish cells under starvation conditions. As an autophagic marker protein, the microtubule-associated protein 1-light chain 3B protein (MAP1-LC3B) was cloned from the fish cells, and its expression and localization were characterized. In zebrafish embryonic (ZE) cells, posttranslational modifications produced two distinct forms of MAP1-LC3B, i.e., a cytosolic form and a membrane-bound form (types I and II, respectively). Immunofluorescence microscopy revealed fluorescently labeled autophagosomes in cells stably transfected with a green fluorescent protein (GFP)–MAP1-LC3B fusion protein and showed that this protein accumulated in punctate dots in a time-dependent manner in response to amino acid starvation. Starvation also induced the degradation of long-lived proteins. Treatment with 3-methyladenine and wortmannin, two class-III inhibitors of phosphoinositide 3-kinase (PI3K), repressed autophagy under starvation conditions, indicating that the PI3K class-III pathway regulates starvation-induced autophagy in fish.

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 β-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 β-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 β-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.

Role of the PGC-1 family in the metabolic adaptation of goldfish to diet and temperature

In mammals, the peroxisome proliferator-activated receptor (PPAR) gamma coactivator-1 (PGC-1) family members and their binding partners orchestrate remodelling in response to diverse challenges such as diet, temperature and exercise. In this study, we exposed goldfish to three temperatures (4, 20 and 35 degrees C) and to three dietary regimes (food deprivation, low fat and high fat) and examined the changes in mitochondrial enzyme activities and transcript levels for metabolic enzymes and their genetic regulators in red muscle, white muscle, heart and liver. When all tissues and conditions were pooled, there were significant correlations between the mRNA for the PGC-1 coactivators (both alpha and beta) and mitochondrial transcripts (citrate synthase), metabolic gene regulators including PPARalpha, PPARbeta and nuclear respiratory factor-1 (NRF-1). PGC-1beta was the better predictor of the NRF-1 axis, whereas PGC-1alpha was the better predictor of the PPAR axis (PPARalpha, PPARbeta, medium chain acyl CoA dehydrogenase). In contrast to these intertissue/developmental patterns, the response of individual tissues to physiological stressors displayed no correlations between mRNA for PGC-1 family members and either the NRF-1 or PPAR axes. For example, in skeletal muscles, low temperature decreased PGC-1alpha transcript levels but increased mitochondrial enzyme activities (citrate synthase and cytochrome oxidase) and transcripts for COX IV and NRF-1. These results suggest that in goldfish, as in mammals, there is a regulatory relationship between (i) NRF-1 and mitochondrial gene expression and (ii) PPARs and fatty acid oxidation gene expression. In contrast to mammals, there is a divergence in the roles of the coactivators, with PGC-1alpha linked to fatty acid oxidation through PPARalpha, and PGC-1beta with a more prominent role in mediating NRF-1-dependent control of mitochondrial gene expression, as well as distinctions between their respective roles in development and physiological responsiveness.

Changes in lipid composition and lipogenic enzyme activities in liver of lambs fed omega-6 polyunsaturated fatty acids

Twenty-four lambs (Ovis aries) were used in a 45-day finishing study to evaluate the effects of feeding diets high in linoleic acid (C(18:2), omega-6) on liver lipid composition and on lipogenic enzyme activities in subcellular fractions of liver. Lambs were fed either a 5% safflower oil (SO, high linoleic acid) supplemented diet or a control diet without added oil. SO feeding caused a reduction in the amount of serum and liver triacylglycerols and cholesterol, whereas the level of phospholipids in both tissues was hardly affected. In liver of SO-treated lambs an increase in the levels of C(18:2) and arachidonic acid (C(20:4), omega-6), together with a simultaneous decrease of saturated fatty acids, was observed. In comparison to rat liver, rather low activities of enzymes in the pathway for de novo fatty acid synthesis, i.e. acetyl-CoA carboxylase and fatty acid synthase, were found in lamb-liver cytosol. Both enzyme activities, as well as those of the NADPH-furnishing enzymes, were significantly reduced by SO feeding. In contrast, microsomal and especially mitochondrial fatty acid chain elongation activity, the latter being much higher than that of rat liver, were significantly increased in SO-treated lambs. In these animals, a stimulation of triangle up(9)-desaturase activity was observed in liver microsomes.

Effect of DHA supplementation on digestible starch utilization by rainbow trout

Rainbow trout has a limited ability to utilize digestible carbohydrates efficiently. Trout feeds generally contain high levels of DHA, a fatty acid known to inhibit a number of glycolytic and lipogenic enzymes in animals. A study was conducted to determine whether carbohydrate utilization by rainbow trout might be affected by dietary DHA level. Two low-carbohydrate (<4% digestible carbohydrate) basal diets were formulated to contain 1 (adequate) or 4 (excess)g/100g DHA diet respectively. The two basal diets were diluted with increasing levels of digestible starch (0%, 10%, 20% and 30%, respectively) to produce eight diets. These diets were fed to fish for 12 weeks at 15°C according to a pair-fed protocol that consisted of feeding the same amount of basal diet but different amounts of starch. Live weight, N and lipid gains, hepatic glycogen and plasma glucose values significantly increased, whereas feed efficiency (gain:feed) significantly decreased, with increasing starch intake (P<0·05). The retention efficiency of N (N gain/digestible N intake) improved with starch supplementation but was not affected by DHA level (P>0·05). Starch increased the activity of glucokinase, pyruvate kinase, glucose 6-phosphate dehydrogenase and fatty acid synthase (P<0·05) but did not affect hexokinase and malic enzyme activity. DHA had no effect on growth but increased plasma glucose and reduced carcass lipid and liver glycogen contents (P<0·05). Glycolytic and lipogenic enzymes were not affected by DHA level, except for pyruvate kinase, which was reduced by increasing DHA level. These results suggest only a marginal effect of dietary DHA on the ability of fish to utilize carbohydrate.

Improving estimates of trophic shift in Nile tilapia, Oreochromis niloticus (L.), using measurements of lipogenic enzyme activities in the liver

To test whether the measurement of selected enzyme activities could be used to estimate more precisely the trophic shift of C isotopes, Nile tilapia (Oreochromis niloticus) were fed semi-synthetic diets differing in their lipid contents (1.7%, 5.0%, 10.8% and 20.0%). The diets were formulated to contain the same amount of nitrogen and metabolizable energy and were made from casein, wheat starch, corn germ oil supplemented with vitamins, minerals and L-arginine. The influence of the different diets on the activity of two lipogenic enzymes, ATP-citrate lyase and malic enzyme, on delta13C values in the whole fish, the liver and their correlation was investigated. There was a strong positive correlation between delta13C values in the lipids of whole fish and those of their livers. The activities of lipogenic enzymes increased significantly with increasing trophic shift of C isotopes (Deltadelta13Cdiet-fish values) in the lipids. If the relationship between trophic shift and enzyme activity can be confirmed in situations where feed quantity and quality are not known, the determination of enzyme activities would enable better estimates of the trophic shift to be made thus significantly improving back-calculation of diets from stable isotope data.

Dietary lipid content influences the activity of lipogenic enzymes in the liver and on whole body delta13C values of Nile tilapia, Oreochromis niloticus (L.)

The use of stable isotope techniques for the reconstruction of diets has increased over the last decade. However, isotopic ratios in an animal are not only affected by the composition of the feed, but also by the amount of feed consumed. An uncertainty of up to 1 per thousand for both delta13C and delta15N values has been observed when the feeding level is unknown. This may have substantial effects on the results of back-calculation. As the feeding level of animals is unknown in nature, an additional indicator for their nutritional status is needed. High feeding levels and a consequent surfeit of dietary energy lead to the synthesis of lipids. In order to test whether the level of lipogenesis could be used as an indicator, Nile tilapia (Oreochromis niloticus) were fed four isonitrogenous and isoenergetic wheat-based semi-synthetic diets with different lipid contents (2.0 %, 4.5 %, 9.5 % and 13.3 %) for eight weeks. Body composition, gross energy content and delta13C values in the lipids and the lipid-free material were determined in diets and fish bodies. The livers of three fish per feeding group were assayed for the activity of two lipogenic enzymes, ATP-citrate lyase and malic enzyme. There was a strong negative correlation between delta13C values in the lipids of the individual fish and the apparent lipid conversion. The activities of lipogenic enzymes decreased with rising lipid content in the diet. The delta13C values in the lipids decreased significantly with increasing specific activity for both enzymes. In this experiment where lipogenesis was influenced by the composition of the diet, it was possible to determine the exact value for the trophic shift in relation to the enzyme activities. Further experiments to investigate the use of enzyme activities in situations where the feeding level of an animal is unknown are recommended.

Dogmas and controversies in the handling of nitrogenous wastes: expression of arginase Type I and II genes in rainbow trout: influence of fasting on liver enzyme activity and mRNA levels in juveniles

Through analysis of a cDNA library and third-party annotation of available database sequences, we characterized the full-length coding regions of rainbow trout (Oncorhynchus mykiss) Type I, Onmy-ARG01, and Type II, Onmy-ARG02, arginase genes. Two partial related arginase sequences, Onmy-ARG01b and Onmy-ARG02b, and a full-length zebrafish arginase coding region (Danio rerio), Dare-ARG02, are also reported. Comparison of vertebrate arginase sequences shows that both Type I and Type II genes in bony fishes contain a mitochondrial targeting N-terminal domain. This suggests that the cytosolic Type I arginase found in ureotelic vertebrates arose in the common ancestor of amphibia and mammals. Onmy-ARG01 and Onmy-ARG02 mRNA was detected in liver, kidney, gill, intestine, red muscle and heart tissues. Onmy-ARG01 was expressed at a significantly higher level relative to Onmy-ARG02 in liver and red muscle tissue. To investigate whether there was differential regulation of Onmy-ARG01 and Onmy-ARG02, juvenile trout were fasted for 6 weeks and hepatic enzyme activities and mRNA levels were compared with those of fed control fish. There was a 3-fold increase in liver arginase activity and a 2-fold increase in Onmy-ARG02 mRNA levels but no change in Onmy-ARG01 mRNA levels in fasted fish relative to fed fish. These findings indicate that both types of arginase genes are present and expressed in rainbow trout and that the pattern of expression varies between tissues. The increase in liver arginase activity after a 6-week fast is due, in part, to an increase in the expression of Onmy-ARG02 mRNA levels.

Short- and long-term nutritional modulation of acetyl-CoA carboxylase activity in selected tissues of rainbow trout (Oncorhynchus mykiss)

Acetyl-CoA carboxylase (ACoAC) catalyses the carboxylation of acetyl-CoA into malonyl-CoA. This product plays a pivotal role in the regulation of energy metabolism since it is both a substrate for fatty acid synthesis and an inhibitor of the oxidative pathway. The present study was initiated to analyse the modulation of ACoAC activity in liver and selected extrahepatic tissues of rainbow trout (Oncorhynchus mykiss) by dietary changes as a contribution to the understanding of the nutritional control of lipid metabolism in fish. Short-term effects of food intake were studied by measuring ACoAC activity in the liver and dorsal white muscle at different time intervals after a meal. Only slight variations were observed in the muscle during the period 2-72 h after the meal. The long-term effects of an increase in dietary lipids or carbohydrates levels were examined by measuring ACoAC activity in the liver, adipose tissue, intestine, kidney, red muscle, dorsal and ventral white muscles of trout after 3 months of feeding with different diets. ACoAC activity is stimulated by a high-digestible starch diet in the abdominal adipose tissue and the white muscle. A high-lipid diet decreases ACoAC activity in the liver and the intestine, but not in other tissues. Contrary to mammals, a rapid adaptation of ACoAC activity to food supply is not effective in rainbow trout. However, a long-term nutritional control of ACoAC activity does occur in this species, but the target tissue differs with the predominant non-protein energy sources in the diet. The present results suggest the potential existence of two ACoAC isoforms with different tissue distribution as has been observed in mammals and birds.

Protein synthesis in trout liver is stimulated by both feeding and fasting

The response of protein synthesis in the liver of the rainbow trout to feeding and fasting was investigated in 3 experiments. In the first experiment, the fractional rate of protein synthesis (k s ), %/day) appeared to cycle with daily feeding events being increased by 46%, 123%, and 72% at 1.5h, 3h, and 6h, after a meal. In Experiment 2, liver protein synthesis fell progressively with fasting to a basal level at 4d which was only 20% of the value at 3h after feeding. Liver weight (hepatosomatic index, HSI, % body weight), total RNA and total protein also fell gradually. Between 4d and 6d, both the RNA/protein ratio and the rate of protein synthesis were significantly increased (11% and 74%). At this time, however, there was also a large loss of liver protein suggesting a concomitant increase in protein breakdown. In the last experiment, when trout were pre-fed a low ration (0.6%/d for 2 wks, LR group), the HSI and liver total RNA and protein were largely unaffected by the 6d fast (i.e., relative to the body weight). In this group, however, protein synthesis at 3h was significantly higher than in fish pre-fed a high ration (1.5%/d, HR group). In addition, at 6d after feeding, protein synthesis had increased back to fed levels in the LR group only. It is concluded that protein synthesis in the liver of the trout is influenced both by feeding events and by ration size and also by the degree to which the trout is fasted.

Biochemical parameters as a measure of food availability and growth in immature rainbow trout (Oncorhynchus mykiss)

1. Rainbow trout held in brackish water (15 parts per thousand) were starved or fed different amounts of food. 2. A significant correlation was found between the growth rates of the different animals and the feed rates. 3. The RNA:DNA ratio in the white epaxial muscle is lowest in starved fish and increases in proportion to the feed rate and individual specific growth rate. The correlations are significant at the P less than 0.01 level. 4. Liver metabolism varies according to food availability. 5. The protein synthesis capacity of the liver (RNA:DNA ratio) and liver somatic index increase as the feeding rate increases. It also correlates significantly with the specific growth rates of the different animals. 6. The intermediary metabolism of the central metabolic organ, the liver, varies in the same way. 7. The activities of the NADPH producing liver enzymes glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), isocitrate dehydrogenase (IDH) and malic enzyme (ME) increase as the feed rate (and therefore the specific growth rate) increases. 8. G6PDH and IDH activity in the kidney is influenced to a much lower degree by food intake. 9. Summarizing, it can be stated that biochemical parameters can be used to describe comprehensively the metabolic status and growth of rainbow trout.

Long-term starvation in Xenopus laevis Daudin--III. Effects on enzymes in several tissues

1. Adult, female Xenopus laevis were subjected to 12 months of starvation. 2. Starvation resulted in a continuous reduction in the activity of both hepatic and renal glucose-6-phosphate dehydrogenase. 3. Fructose-1,6-diphosphatase was significantly reduced at months 10 and 12 in the liver, and at months 4, 10, and 12 in the kidney. 4. Pyruvate kinase activity of muscle and liver decreased during the experimental period whereas the renal enzyme remained essentially unchanged. 5. Both hepatic and renal glutamate-pyruvate transaminase (GPT) and hepatic glutamate-oxaloacetate transaminase (GOT) showed a reduction of activity after 2 and 4 months of starvation followed by an increase in GPT but not in GOT.

Effects of temperature, food deprivation and salinity on growth, RNA/DNA ratio and certain enzyme activities in rainbow trout (Salmo gairdneri Richardson)

1. The connection between feeding regime (food deprivation and restricted diet) and thermal acclimation (1-2, 6, 11 and 16 degrees C) was studied in rainbow trout held in diluted seawater (20% S). 2. At 1 degree C, food deprivation effects on all parameters are slight, and on RNA and certain enzymes they are masked by thermal acclimation effects. 3. At a salinity of 20% rainbow trout on a restricted diet and held at 11 degrees C have the highest growth rate. 4. Owing to increasing RNA levels, the RNA/DNA quotient is significantly higher than normal in rainbow trout held at 1 degree C although the fishes do not grow at this temperature. 5. Temperature and feeding both affect the enzymes we studied (liver: G1DH, AspT, arginase, G6PDH, and 6PGDH; kidney: G1DH, AspT, arginase, and Na/K-ATPase; white muscle: AspT and A1T; gill: Na/K-ATPase) differently. Interactions between these two factors also occur in some cases.

Influence of salinity and ratio of lipid to protein in diets on certain enzyme activities in rainbow trout (Salmo gairdneri Richardson)

The connection between metabolic and sea water adaptation of the rainbow trout was investigated. The rainbow trout were kept in fresh water and diluted sea water of 8 and 20 0/00 S at 16 degrees C and fed on three different diets for 51 days. Hyperosmotic salinity (20 0/00) tends to inhibit growth in rainbow trout by reducing the food conversion efficiency. A higher protein concentration in the diet can partly compensate for this effect. The liver IDH, G6PDH and 6PGDH activities of the rainbow trout are influenced only by food quality, whereas the liver G1DH, AspT and A1T activities, like the muscle A1T, are also affected by salinity. The salinity had no significant effect on the activities of the kidney enzymes we investigated (Na/K-ATPase, G1DH, A1T, AspT) or of the muscle AspT in these experiments.

Uptake studies in adipocytes isolated from rainbow trout (Salmo gairdnerii). A comparison with adipocytes from rat and cat

Adipocytes were isolated from mesenteric adipose tissue of rainbow trout (Salmo gairdnerii) by incubation of tissue slices at 20 degrees C in a buffer containing 3 mg collagenase per ml. These cells were compared to adipocytes from the cat and the rat, isolated by conventional technique (1 mg collagenase per ml buffer, incubation temperature 37 degrees C). Uptake studies of some metabolites were performed with fish, rat and in some cases cat adipocytes. At a glucose concentration of 0.33 mM, the glucose uptake into rat cells was more than twice as fast as in cells from the cat, and more than five times as fast as in trout cells. 2-Amino butyrate resembled glucose in relative uptake rates between species. Metabolite uptake into rat cells was specific, with different uptake rates for different metabolites. The uptake into trout adipocytes proceeded at similar rates for all metabolites tested, provided the concentrations were the same. The uptake rate of glucose into rat cells was stimulated by insulin. Insulin had no effect on glucose uptake into adipocytes from trout.

Comparative study of lipogenic enzymes in several vertebrates

The liver lipogenic enzymes are compared among rats, chickens, frogs and fish. Although the apparent Km values of glucose-6-phosphate dehydrogenase for glucose-6-phosphate are not much different among all the species, those of malic enzyme for malate are much higher in chickens and fish than in rats and frogs. Glucose-6-phosphate dehydrogenase showed very high activities compared with malic enzyme in fish liver, and malic enzyme showed high activities in chicken liver. Although the apparent Km values of acetyl-CoA carboxylase and fatty acid synthetase for substrates are in the same range among all the animals, the activity of acetyl-CoA carboxylase seems to be extremely low in fish and frog livers, and that of fatty acid synthetase is low in frog livers only. In addition, the apparent Km values of alpha-glycerophosphate acyltransferase of fish liver are very high, and the enzyme activity appears to be extremely low compared to the others. Therefore, the enzymes at the first steps of both fatty acid and glycerolipid syntheses of poikilothermos animals appear to be very low. On the other hand, the Ouchterlony double-diffusion patterns showed that the lipogenic enzymes of chickens, frogs and fish are immunologically different from those of rats, with the exception of acetyl-CoA carboxylase in chickens. Therefore, it is suggested that the fatty acid and glycerolipid forming systems of poikilothermos animals are quite different from those of homoiothermos and the lipogenesis is very low in poikilothermos.

Effect of specific dietary fatty acids on lipogenesis in the livers and mammary glands of lactating mice

The effects of linoleic, linolenic and columbinic acids fed as 4% of a high carbohydrate (50% glucose) diet on the activities and the amounts of several enzymes associated with fatty acid synthesis in livers and mammary glands of lactating mice were compared with those for stearic and oleic acids. Fatty acid synthesis, measured in vivo, was significantly lower in livers of mice ingesting all 3 polyunsaturated fatty acids (PUFA), whereas in mammary glands synthesis was lower only in mice receiving columbinic acid. The activities of fatty acid synthetase (FAS) and acetyl CoA carboxylase were significantly reduced in liver by all 3 PUFA, as wee activities of glucose-6-phosphate dehydrogenase, malic enzyme (ME) and citrate cleavage enzyme (CCE), also associated with lipogenesis. In mammary gland, on the other hand, the activities of these enzymes were unaffected by dietary PUFA. The tissue contents of FAS, ME and CCE, measured by rocket immunoelectrophoresis, were found to be significantly reduced in liver by linoleate, linolenate and columbinate but were not significantly altered in mammary gland. The decrease in hepatic lipogenesis observed was principally due to a decrease in the amounts of these enzymes induced by the dietary PUFA but the inhibition in mammary gland caused by columbinate could not be accounted for by a reduction in enzyme contents and therefore may be due to allosteric effects which occur when fatty acid synthesis is measured with 3H2O. The fatty acid composition in liver and mammary gland of dams and in liver and kidney of pups completely reflected dietary fatty acids. Columbinate made up ca. 20% of the total fatty acids in both tissues of the columbinic acid-fed mice and ca. 15% in the pup tissues. This suggests that columbinate is incorporated into milk lipids of dams and is easily absorbed by pups. The elevated ratios of 16/16:1 and 18/18:1 in liver and mammary gland of dams and liver and kidney of the pups from dams fed linoleate, linolenate and columbinate suggest that each of these polyunsaturated fatty acids in the diet can inhibit the activity of delta 9 desaturase.