Effects of exercise on L-carnitine and lipid metabolism in African catfish (Clarias gariepinus) fed different dietary L-carnitine and lipid levels

African catfish (Clarias gariepinus) were fed four isonitrogenous diets (34 % crude protein), each containing one of two lipid (100 or 180 g/kg) and two L-carnitine (15 or 1000 mg/kg) levels. After 81 d of feeding, thirty-two fish (body weight 32 g) from each dietary group were randomly selected, sixteen fish were induced to a 3-h swim (speed of 1.5 body length (BL)/s), while the other sixteen fish were kept under resting condition. Fish fed 1000 mg L-carnitine accumulated 3.5 and 5 times more L-carnitine in plasma and muscle, respectively, than fish fed the 15 mg L-carnitine. Muscle L-carnitine content was significantly lower in exercised fish than in rested fish. High dietary lipid level (fish oil) led to an increase in muscle n-3 PUFA content and a decrease in SFA and MUFA content. In liver, the increase in dietary lipid level resulted in an increased levels of both n-6 and n-3 PUFA. L-carnitine supplementation significantly decreased n-3 PUFA content. Exercise decreased n-3 PUFA in both muscle and liver. Plasma lactate and lactate dehydrogenase, normally associated with increased glycolytic processes, were positively correlated with exercise and inversely correlated with dietary L-carnitine level. L-carnitine supplementation reduced significantly the RQ from 0.72 to 0.63, and an interaction between dietary L-carnitine and lipid was observed (P < 0.03). Our results indicate that an increase in fatty acids (FA) intake may promote FA oxidation, and both carnitine and exercise might influence the regulation of FA oxidation selectivity.

Enzymatic capacities for beta-oxidation of fatty fuels are low in the gill of teleost fishes despite presence of fatty acid-binding protein

A variety of circulating fuels can support the work of the teleost gill. Previous work indicates, however, that unlike other aerobic tissues from teleosts, the gill may have a limited capacity to oxidize fatty fuels. We determined capacities for catabolism of carbohydrate, fatty acids, and amino acids in four species of temperate marine or euryhaline teleosts representing distinct lineages. In addition, we assessed the capacity for fatty acid oxidation in the gill from an Antarctic species. Activities of rate-limiting or regulatory enzymes from pathways of energy metabolism were measured at physiological temperatures (15 degrees or 1 degrees C). In the temperate species, ATP yields from glucose are 3- to 30-fold greater (varying with species) than ATP yields from a monounsaturated fatty acid, while ATP generation from glutamate is 2-50 times greater than similar capacities for the lipid fuel. Like the temperate species, capacity for beta-oxidation of fatty acids is limited in the Antarctic species. A positive linear correlation between activities of citrate synthase (central pathway of oxidative metabolism) and hexokinase (glycolysis) adds further support to the hypothesis that glucose is a preferred metabolic fuel in gill. Our results also demonstrate that fatty acid-binding protein is present in the gill of teleost fishes. It is likely that this protein plays a more important role facilitating anabolic pathways in lipid metabolism rather than fatty acid oxidation in the gill of teleost fishes.

Mechanisms of signal transduction in the stress response of hepatocytes

Adaptation of animals to stress is a unique property of life which allows the survival of the species. The stress response of hepatocytes is a very complex phenomenon, sometimes involving a cascade of events. The general stress signals are elucidated by mobilization of carbohydrate stores and akin to the insulin mediators. Oxidative signals are generated by pesticides, heavy metals, drugs, and alcohol which may or may not be under the purview of peroxisomes. Peroxisomal responses are well-defined involving specific receptors, whereas nonperoxisomal responses may be signaled by calcium, the Ah receptor, or built-in antioxidant systems. The intoxication signals are generally thought to be membrane defects induced by xenobiotics which then lead to highly nonspecific responses of hepatocytes. Detoxication signals, on the other hand, are specific responses of hepatocytes triggering de novo syntheses of detoxifier proteins or enzymes. Evidence reveals the existence of two distinct mechanisms of signal transduction in stressed hepatocytes--one involving the peroxisome and the other the plasma membrane.

Effect of recovery parameters on critical swimming speed of juvenile rainbow trout (Oncorhynchus mykiss)

Critical swimming speed (Ucrit) is commonly measured to evaluate the influence of particular parameters on the swimming ability and physiological status of fish. Prior to experiments, fish are often forced to swim at low speed for a period of time to allow them to recover from handling stress. In the past, recovery times and speeds have varied from study to study but their possible effects on Ucrithave not been thoroughly examined. Therefore, hatchery-reared juvenile rainbow trout (Oncorhynchus mykiss) were forced to swim at a velocity of 26.5 cm/s for 0, 0.5, 1, 2, 4, 8, or 16 h or at a velocity of 0, 17.0, 21.8, 26.5, 36.0, or 45.5 cm/s for 0.5 h prior to being subjected to the Ucritprotocol (5-min intervals and 2.5 cm/s increments were used). Fish were tested at 6 and 18 °C. Mean Ucritvalues were independent of recovery time and speed at both temperatures, suggesting that the recovery phase of the protocol may not be required and that inconsistencies in Ucritvalues among studies are probably not attributable to differences in recovery parameters used.

Distribution and properties of lactate dehydrogenase isoenzymes in red and white muscle of freshwater fish

The distribution and kinetics of LDH isoenzymes in red and white muscles of 5 species of salmonids, 4 species of cyprinids and one coregonid species were studied. In all species the white muscles are characterized by the occurrence of only the most cathodic isoenzymes, or groups of isoenzymes. The red muscles contained either the full set of isoenzymes (cyprinids) or a selection in which the anodic forms dominated (salmonids, coregonid). The most striking difference between the two types of muscle was met inCoregonus sp. The temperature profiles of pyruvate affinity are similar in all species of fish studied. On the other hand, Km(pyr) values and degree of pyruvate inhibition are closely related and vary greatly with temperature, with the taxonomic position (and thus biology) of the species, and with electrophoresic mobility of the isoenzyme. Highest affinity and strongest inhibition occurred in the anodic (H4) isoenzymes of cyprinids at low temperature; lowest affinity and zero inhibition in the cathodic isoenzymes (Mα4 → Mβ4) of salmonids and coregonids at high temperature. In salmonids the more recently duplicated loci of the M-group of isoenzymes possess identical Km values at all temperatures, whereas the two older M and H loci differ greatly in this respect. Thus the more recent duplication of LDH loci in salmonids and coregonids may be seen as a mechanism by which the tetramers required for LDH activity can be constructed from more closely related subunits than are provided by the older M and H loci.Some problems in connection with the determination of the kinetic constants of the lactate oxidase reaction are discussed and it is suggested that an alkaline, pyruvate trapping system provides conditions which are more realistic than those of other assay systems. The Km(lactate) values found are in the biological range and, at 20°C, provide further circumstantial evidence that the red muscles of fish should be capable of oxidizing the lactate produced by the white muscles during strenuous exercise. At 4°C the Km(lactate) values are abnormally high in all muscle preparations and thus are not correlated with the Km(pyruvate) values which are lowest at this temperature.

Temperature dependence of lipogenesis in isolated hepatocytes from rainbow trout (Salmo gairdneri)

Temperature dependence of lipogenesis in trout liver cells was investigated in the presence of 5 mM lactate using either [14C]lactate or [3H]water. A ratio of 3H/14C-incorporation greater than one is found, irrespective of temperature. Acclimation of fish to 4, 10 or 16 degrees C affects neither the height of lipid synthesis nor its temperature sensitivity. The distribution of [14C]lactate between the main lipid classes and the capacities for cholesterol- and triacylglycerol-synthesis are correlated to the glycogen stores of the hepatocytes. A comparison of fatty acid synthesis and cholesterogenesis in livers of normal fed rat and of trout suggests a capability for lipogenesis in trout somewhat similar to that in mammals.

Effects of exercise stress on acid-base balance and respiratory function in blood of the teleost Tinca tinca

We measured the effects of severe, short-term exercise stress on the acid-base balance, the O2 transporting properties and the cofactors for O2 binding in the blood of tench, Tinca tinca. Short-term severe exercise resulted in a drastic decrease in arterial blood pH which is attributed to a mixed respiratory and metabolic acidosis. Concomitantly arterial PO2 rose in apparent compensation for the detrimental effects of the acidosis on O2 transport by the blood.

Bioenergetics of acclimation to permethrin (NRDC-143) by rainbow trout

Metabolic rates associated with sustained, prolonged and critical swimming speeds were examined in 10 g trout exposed to 5% 96 hr LC50 (0.75 microgram X l-1) and 10% 96 hr LC50 (1.50 micrograms X l-1) at 12 degrees C. Permethrin did not influence the metabolic cost for swimming at sustained and prolonged speeds. Basal metabolic rate increased on initial exposure to permethrin reaching maximum values after 7 days and declined to the control level after 13 days in 5% and after 32 days in 10% 96 hr LC50. Critical swimming speeds were adversely affected in a manner reflective of the effects of permethrin on basal metabolic rate. Elevation in basal metabolic rate in fish exposed to permethrin was a result of increased energy requirements due to physiological stress, detoxication and tissue repair.

Hydrogen shuttles in gills of water versus air breathing osteoglossids

1. Using subcellular preparations of gills from Arapaima, an obligate air breather, and aruana, a related osteoglossid that is an obligate water breather, a comparison was made of the relative roles of the malate-aspartate cycle and the alpha-glycerophosphate (alpha-GP) cycle in transferring reducing equivalents from the cytosol to the mitochondria. 2. In aruana gill preparations, the alpha-GP cycle could be most clearly demonstrated by reconstructing it with purified isolated mitochondria, using the oxidation rate of exogenous NADH as a measure of the cycling activity. 3. Subcellular preparations of Arapaima gill, in contrast to the aruana gill, were not responsive to exogenous alpha-glycerophosphate, but a glutamate-malate stimulated O2 uptake was sensitive to aminooxyacetate, an aminotransferase inhibitor, a result that would be expected if the respiration were based on malate-aspartate cycling. 4. It was concluded that, compared to the alpha-glycerophosphate cycle, the malate-aspartate cycle was relatively more active in Arapaima gill than in aruana gill, and possible implications were discussed.

The effect of dietary composition and of insulin on gluconeogenesis in rainbow trout (Salmo gairdneri)

1. The activities at 15° of three gluconeogenic enzymes,d-fructose-1,6-diphosphate, 1-phosphohydrolase (EC3.1.3.11), pyruvate carboxylase (EC6.4.1.1) and phosphoenolpyruvate carboxykinase (4.1.1.32), were determined in liver, kidney, gill and muscle of rainbow trout (Salmo gairdneri) given a commercial diet. The results indicated that liver and kidney are the main sites of gluconeogenesis.

2. Glucose formation from pyruvate was approximately 6 μmol/h per g wet weight at 15° in liver slices of trout given a commercial diet.

3. Glucose diffusion space in trout was measured by the dilution principle after intravascular injection of a trace dose of [U-14C]glucose. Glucose space was found to be 13.7% of the body-weight. Gluconeogenesis in vivo amounted to approximately 45 μmol/kg body-weight per h.

4. Intraperitoneally injected [U-14C]alanine was quickly converted to glucose. Maximal incorporation of alanine into glucose occurred 6 h after alanine administration.

5. Rainbow trout given a high-protein diet gained in weight significantly during a 4-week period. Those given a high-carbohydrate diet did not make a significant weight gain over the same period. Gluconeogenesis from alanine was markedly reduced in fish given the high-carbohydrate diet. There was no significant difference in gluconeogenesis from alanine in fish given a high-protein diet and fish which were fasted for 21 d.

6. Gluconeogenesis from alanine in trout was suppressed by intravenous injection of insulin. This effect was found both in trout given a high-protein diet and in fasted trout.