Muscle Lactate Concentration Research Articles

Skeletal Muscle Pyruvate Dehydrogenase Phosphorylation and Lactate Accumulation During Sprint Exercise in Normoxia and Severe Acute Hypoxia: Effects of Antioxidants.

Compared to normoxia, during sprint exercise in severe acute hypoxia the glycolytic rate is increased leading to greater lactate accumulation, acidification, and oxidative stress. To determine the role played by pyruvate dehydrogenase (PDH) activation and reactive nitrogen and oxygen species (RNOS) in muscle lactate accumulation, nine volunteers performed a single 30-s sprint (Wingate test) on four occasions: two after the ingestion of placebo and another two following the intake of antioxidants, while breathing either hypoxic gas (PIO2 = 75 mmHg) or room air (PIO2 = 143 mmHg). Vastus lateralis muscle biopsies were obtained before, immediately after, 30 and 120 min post-sprint. Antioxidants reduced the glycolytic rate without altering performance or VO2. Immediately after the sprints, Ser293- and Ser300-PDH-E1α phosphorylations were reduced to similar levels in all conditions (~66 and 91%, respectively). However, 30 min into recovery Ser293-PDH-E1α phosphorylation reached pre-exercise values while Ser300-PDH-E1α was still reduced by 44%. Thirty minutes after the sprint Ser293-PDH-E1α phosphorylation was greater with antioxidants, resulting in 74% higher muscle lactate concentration. Changes in Ser293 and Ser300-PDH-E1α phosphorylation from pre to immediately after the sprints were linearly related after placebo (r = 0.74, P < 0.001; n = 18), but not after antioxidants ingestion (r = 0.35, P = 0.15). In summary, lactate accumulation during sprint exercise in severe acute hypoxia is not caused by a reduced activation of the PDH. The ingestion of antioxidants is associated with increased PDH re-phosphorylation and slower elimination of muscle lactate during the recovery period. Ser293 re-phosphorylates at a faster rate than Ser300-PDH-E1α during the recovery period, suggesting slightly different regulatory mechanisms.

Short‐term Physiological Response Profiles of Tagged Migrating Adult Sockeye Salmon: A Comparison of Gastric Insertion and External Tagging Methods

AbstractA variety of electronic tag types are routinely applied to fish to better understand migration biology. However, tagging procedures have the potential to affect the postrelease behaviour and survival of tagged individuals. In this study, wild adult Sockeye Salmon Oncorhynchus nerka from the Harrison River, British Columbia, were radio‐tagged by gastric insertion or external attachment techniques immediately after capture to understand the short‐term physiological response to these two tagging methods. Plasma cortisol, glucose, lactate, sodium, and potassium levels, as well as white muscle lactate and glycogen concentrations, were measured in samples obtained from fish upon capture (0 h) as well as 1 or 4 h after the tagging treatment. The effects of key biological variables, such as sex and proximity to spawn, on the physiological response to the tagging events were also evaluated. Tagging occurred during two distinct time periods representing fish of different maturation states and durations of freshwater residency. Overall, the physiological response to the tagging scenarios was characteristic of the disturbance associated with exhaustive exercise. There were no significant differences detected in the response profiles following gastric or external tagging procedures. This was despite procedural differences such as stomach perforations observed in 68% of the gastric insertions in the late sampling period, and external attachments taking three times longer (43 s) than gastric insertion (15 s). Moreover, the tagged fish showed similar response profiles to control fish that were handled but not tagged. These results suggest that the capture and handling associated with a tagging event induced physiological disturbance, and that the addition of a quick tagging procedure appeared to be nonadditive over the 4‐h assessment period. Sex and proximity to spawn had significant main and interaction effects on some of the physiological response variables, indicating that biological context is important for interpreting physiological assessments in experiments that manipulate exercise and stress responses in migrating adult Pacific salmon.

Maximal-intensity exercise does not fully restore muscle pyruvate dehydrogenase complex activation after 3 days of high-fat dietary intake

Exercise activates muscle pyruvate dehydrogenase complex (PDC), but moderate intensity exercise fails to fully activate muscle PDC after high-fat diet [1]. We investigated whether maximal intensity exercise overcomes this inhibition. Quadriceps femoris muscle biopsy samples were obtained from healthy males at rest, and after 46 and 92 electrically-evoked maximal intermittent isometric contractions, which were preceded by 3 days of either low- (18%) or high- (69%) isocaloric dietary fat intake (LFD and HFD, respectively). The ratio of PDCa (active form) to total PDCt (fully activated) at rest was 50% less after HFD (0.32±0.01 vs 0.15±0.01; P<0.05). This ratio increased to 0.77±0.06 after 46 contractions (P<0.001) and to 0.98±0.07 after 92 contractions (P<0.001) in LFD. The corresponding values after HFD were less (0.54±0.06; P<0.01 and 0.70±0.07; P<0.01, respectively). Resting muscle acetyl-CoA and acetylcarnitine content was greater after HFD than LFD (both P<0.05), but their rate of accumulation in the former was reduced during contraction. Muscle lactate content after 92 contractions was 30% greater after HFD (P<0.05). Muscle force generation during contraction was no different between interventions, but HFD lengthened muscle relaxation time (P<0.05). Daily urinary total carnitine excretion after HFD was 2.5-fold greater than after LFD (P<0.01). A bout of maximal intense exercise did not overcome dietary fat-mediated inhibition of muscle pyruvate dehydrogenase complex activation, and was associated with greater muscle lactate accumulation, as a result of lower PDC flux, and increased muscle relaxation time.

Agonistic behaviour and energy metabolism of bold and shy swimming crabs Portunus trituberculatus.

The metabolism and behaviour of crustaceans are highly flexible, and the inter-individual variation in these traits is evolutionarily and ecologically significant. We analysed the relationships among personality traits (boldness, activity and hesitancy), agonistic behaviour and energy status (glycogen, glucose and lactate) in the swimming crab Portunus trituberculatus The main results were as follows. (1) Boldness was significantly correlated with activity and hesitancy. Bold crabs were more likely to initiate and win a fight. In bold individuals, the frequencies of 'move to', 'cheliped display', 'grasp' and 'contact' were significantly higher than those of shy individuals, whereas the frequency of 'move away' was significantly lower than that of shy individuals. (2) Before fighting, the glucose concentrations in the haemolymph of bold individuals were significantly lower than those of shy individuals, whereas the concentrations of lactate showed the opposite trend. There were no significant differences in glycogen and lactate concentrations in the claw muscle between bold and shy individuals. (3) After fighting, the glucose and lactate concentrations in the haemolymph of both bold and shy individuals were significantly higher than those before fighting. The glucose concentrations in the haemolymph were significantly higher in bold individuals than shy individuals. In addition, bold individuals showed a larger increase in glucose in the haemolymph but a smaller increase in lactate compared with shy individuals. (4) After fighting, the glycogen concentrations in the claw muscle were significantly lower than those before fighting; however, there were no significant differences in the concentrations of lactate in the claw muscle. These results indicated that the agonistic behaviour of the swimming crab is related to its behavioural type. Energy reserves may be one of the factors affecting the personality traits and agonistic behaviour in crabs. These results should lay a foundation for in-depth understanding of the relationships among crustacean personality, agonistic behaviour and metabolic physiology.

How does the snakehead Channa argus survive in air? The combined roles of the suprabranchial chamber and physiological regulations during aerial respiration.

ABSTRACTThis study aimed to test the hypothesis that the aerial survival of the northern snakehead is involved not only with suprabranchial chamber respiration but also with physiological regulations. The aerial survival time and oxygen consumption rate (VO2) were determined in snakeheads with either normal or injured suprabranchial organs. Some hematological and biochemical parameters were assessed during aerial exposure. The results showed that resting VO2 decreased when switching from water to air in both the control and the suprabranchial organ-injured fish, with decreases of 22.4% and 23.5%, respectively. Resting VO2 in air was not different between the control and the suprabranchial organ-injured fish. The red blood cell (RBC) count and hemoglobin concentration showed no marked changes, while RBC size increased when exposed to air. The liver lactate concentration remained unchanged, and the white muscle lactate concentration decreased when switching from water to air. The blood ammonia concentration tended to increase during aerial respiration. These results suggest that the aerial survival of the snakehead is positively associated with a combination of factors, including respiration of suprabranchial organs and other accessory organs, depressed metabolic demands and increased oxygen transport, and negatively associated with the accumulation of blood ammonia but not anaerobic metabolism.

Microdialysis as a Part of Invasive Cerebral Monitoring During Porcine Septic Shock.

Metabolic changes in critically ill patients with endotoxin-induced septic shock are measured primarily by techniques that afford organ-specific metabolic monitoring based on interstitial fluid samples. The present study was designed to evaluate the role of cerebral microdialysis (MD) as a part of invasive neuromonitoring during endotoxemia in a porcine model. Continuous endotoxin infusion was administered to 7 female pigs and, in addition to hemodynamic monitoring and blood chemistry, interstitial lactate, pyruvate, glucose and glycerol concentrations in muscle, liver, and cerebral tissue were measured via in vivo MD for an observation period of 180 minutes. The cerebral concentrations of lactate and glycerol showed no significant increases, whereas the hepatic and muscular levels rose dramatically under endotoxemia. However, the lactate/pyruvate ratio and especially the lactate/glucose ratio showed a profound and significant increase in brain tissue as well. Cerebral perfusion pressure decreased from 77 to 50 mm Hg without reaching pathologic values. Although our results confirm the special protection of the brain during endotoxemia compared with other organs, early metabolic changes become evident by increasing lactate/pyruvate ratio and lactate/glucose ratio. MD appears to be a suitable additional technique in invasive neuromonitoring for obtaining early information about metabolic deterioration in the brain during septic shock.

Bioenergetic status and oxidative stress during escape response until exhaustion in whiteleg shrimp Litopenaeus vannamei

The escape response in some decapod crustaceans through tail-flipping represents an excellent model of short-term, exhausting muscular activity to understand the role of energy depletion and oxidative stress in muscle fatigue. In this study indicators of oxidative stress and changes in energy metabolism were measured during escape response until fatigue in whiteleg shrimp Litopenaeus vannamei. The escape response of individual shrimp was elicited in a tank by prodding the shrimp with a stick until exhaustion (no further response). A control group consisted of undisturbed shrimp, and a third group was allowed to recover. Arginine phosphate (ArgP) and adenylic energy charge (AEC) were measured by reverse phase HPLC, while fuels, reserves, antioxidant enzyme activities (superoxide dismutase, catalase, glutathione peroxidase-GPx), thiobarbituric acid reactive substances, and protein carbonyl content were analyzed by spectrophotometric methods. Shrimp reached fatigue after 31 tail-flips, which decreased abdominal muscle ArgP by 75% and AEC by 18%. Hemolymph lactate levels increased 5 times and muscle GPx activity by 2.7 times. After 1h of recovery, ArgP and AEC base levels were re-established, while hemolymph lactate concentration and GPx activity were still increased, and glucose hemolymph content increased 1.8 times. The drastic decrease in ArgP levels prevents a drop of AEC to a critical level, in accordance with a situation of non-lethal stress. Although no significant changes were observed in muscle glycogen or lactate concentrations, the increase in hemolymph lactate levels indicates an important contribution of muscle glycolysis to prevent a more pronounced decrease in ATP and AEC. The increase in GPx activity in abdominal muscle suggests an increase in reactive oxygen species production during intensive muscular activity, which was adequately neutralized, for no signs of oxidative damage occurred, as indicated by the lack of lipid and protein oxidation. These responses suggest adequate energy efficiency and prevention of oxidative damage during the escape response, in accordance with the adaptative value of such behavior to avoid instantaneous danger, with a capacity of rapid recovery.

Heart Failure Impairs Muscle Blood Flow and Endurance Exercise Tolerance in COPD

Heart failure, a prevalent and disabling co-morbidity of COPD, may impair cardiac output and muscle blood flow thereby contributing to exercise intolerance. To investigate the role of impaired central and peripheral hemodynamics in limiting exercise tolerance in COPD-heart failure overlap, cycle ergometer exercise tests at 20% and 80% peak work rate were performed by overlap (FEV1 = 56.9 ± 15.9% predicted, ejection fraction = 32.5 ± 6.9%; N = 16), FEV1-matched COPD (N = 16), ejection fraction-matched heart failure patients (N = 15) and controls (N = 12). Differences (Δ) in cardiac output (impedance cardiography) and vastus lateralis blood flow (indocyanine green) and deoxygenation (near-infrared spectroscopy) between work rates were expressed relative to concurrent changes in muscle metabolic demands (ΔO2 uptake). Overlap patients had approximately 30% lower endurance exercise tolerance than COPD and heart failure (p < 0.05). ΔBlood flow was closely proportional to Δcardiac output in all groups (r = 0.89–0.98; p < 0.01). Overlap showed the largest impairments in Δcardiac output/ΔO2 uptake and Δblood flow/ΔO2 uptake (p < 0.05). Systemic arterial oxygenation, however, was preserved in overlap compared to COPD. Blunted limb perfusion was related to greater muscle deoxygenation and lactate concentration in overlap (r = 0.78 and r = 0.73, respectively; p < 0.05). ΔBlood flow/ΔO2 uptake was related to time to exercise intolerance only in overlap and heart failure (p < 0.01). In conclusion, COPD and heart failure add to decrease exercising cardiac output and skeletal muscle perfusion to a greater extent than that expected by heart failure alone. Treatment strategies that increase muscle O2 delivery and/or decrease O2 demand may be particularly helpful to improve exercise tolerance in COPD patients presenting heart failure as co-morbidity.

A 3-day EGCG-supplementation reduces interstitial lactate concentration in skeletal muscle of overweight subjects

Green tea, particularly epigallocatechin-3-gallate (EGCG), may affect body weight and composition, possibly by enhancing fat oxidation. The aim of this double-blind, randomized placebo-controlled cross-over study was to investigate whether 3-day supplementation with EGCG (282mg/day) stimulates fat oxidation and lipolysis in 24 overweight subjects (age = 30 ± 2yrs, BMI = 27.7 ± 0.3 kg/m2). Energy expenditure, substrate metabolism and circulating metabolites were determined during fasting and postprandial conditions. After 6 h, a fat biopsy was collected to examine gene expression. In 12 subjects, skeletal muscle glycerol, glucose and lactate concentrations were determined using microdialysis. EGCG-supplementation did not alter energy expenditure and substrate oxidation compared to placebo. Although EGCG reduced postprandial circulating glycerol concentrations (P = 0.015), no difference in skeletal muscle lipolysis was observed. Fasting (P = 0.001) and postprandial (P = 0.003) skeletal muscle lactate concentrations were reduced after EGCG-supplementation compared to placebo, despite similar tissue blood flow. Adipose tissue leptin (P = 0.05) and FAT/CD36 expression (P = 0.08) were increased after EGCG compared to placebo. In conclusion, 3-day EGCG-supplementation decreased postprandial plasma glycerol concentrations, but had no significant effects on skeletal muscle lipolysis and whole-body fat oxidation in overweight individuals. Furthermore, EGCG decreased skeletal muscle lactate concentrations, which suggest a shift towards a more oxidative muscle phenotype.

Paradoxical anaerobism in desert pupfish.

In order to estimate metabolic demands of desert pupfish for conservation purposes, we measured oxygen consumption in fish acclimated to the ecologically relevant temperatures of 28 or 33°C. For these experiments, we used fish derived from a refuge population of Devils Hole pupfish (Cyprinodon diabolis). Measurement of routine oxygen consumption (V̇O2,routine) revealed some 33°C-acclimated fish (10% of 295 assayed fish) periodically exhibited periods of no measurable oxygen consumption despite available ambient oxygen tensions that were above the critical PO2. We call this phenomenon paradoxical anaerobism. The longest observed continuous bout with no oxygen consumption was 149 min, although typical bouts were much shorter. Fish maintained normal posture and ventilation rate (>230 ventilations per minute) during paradoxical anaerobism. Fish rarely demonstrated a compensatory increase in oxygen use following a period of paradoxical anaerobism. In contrast, only one out of 262 sampled fish acclimated at 28°C spontaneously demonstrated paradoxical anaerobism. Muscle lactate concentration was not elevated during periods of paradoxical anaerobism. However, the amount of ethanol released by the 33°C-acclimated fish was 7.3 times greater than that released by the 28°C acclimation group, suggesting ethanol may be used as an alternative end product of anaerobic metabolism. Exposure to exogenous ethanol, in concentrations as low as 0.1%, produced periods of paradoxical anaerobism even in 28°C-acclimated fish.

Flesh Shear Force, Cooking Loss, Muscle Antioxidant Status and Relative Expression of Signaling Molecules (Nrf2, Keap1, TOR, and CK2) and Their Target Genes in Young Grass Carp (Ctenopharyngodon idella) Muscle Fed with Graded Levels of Choline.

Six groups of grass carp (average weight 266.9 ± 0.6 g) were fed diets containing 197, 385, 770, 1082, 1436 and 1795 mg choline/kg, for 8 weeks. Fish growth, and muscle nutrient (protein, fat and amino acid) content of young grass carp were significantly improved by appropriate dietary choline. Furthermore, muscle hydroxyproline concentration, lactate content and shear force were improved by optimum dietary choline supplementation. However, the muscle pH value, cooking loss and cathepsins activities showed an opposite trend. Additionally, optimum dietary choline supplementation attenuated muscle oxidative damage in grass carp. The muscle antioxidant enzyme (catalase and glutathione reductase did not change) activities and glutathione content were enhanced by optimum dietary choline supplementation. Muscle cooking loss was negatively correlated with antioxidant enzyme activities and glutathione content. At the gene level, these antioxidant enzymes, as well as the targets of rapamycin, casein kinase 2 and NF-E2-related factor 2 transcripts in fish muscle were always up-regulated by suitable choline. However, suitable choline significantly decreased Kelch-like ECH-associated protein 1 a (Keap1a) and Kelch-like ECH-associated protein 1 b (Keap1b) mRNA levels in muscle. In conclusion, suitable dietary choline enhanced fish flesh quality, and the decreased cooking loss was due to the elevated antioxidant status that may be regulated by Nrf2 signaling.

Effects of decreased lactate accumulation after dichloroacetate administration on exercise training-induced mitochondrial adaptations in mouse skeletal muscle.

Recent studies suggested that lactate accumulation can be a signal for mitochondrial biogenesis in skeletal muscle. We investigated whether reductions in lactate concentrations in response to dichloroacetate (DCA), an activator of pyruvate dehydrogenase, attenuate mitochondrial adaptations after exercise training in mice. We first confirmed that DCA administration (200 mg/kg BW by i.p. injection) 10 min before exercise decreased muscle and blood lactate concentrations after high-intensity interval exercise (10 bouts of 1 min treadmill running at 40 m/min with a 1 min rest). At the same time, exercise-induced signal cascades did not change by pre-exercise DCA administration. These results suggested that DCA administration affected only lactate concentrations after exercise. We next examined the effects of acute DCA administration on mRNA expressions involved with mitochondrial biogenesis after same high-intensity interval exercise and the effects of chronic DCA administration on mitochondrial adaptations after high-intensity interval training (increasing intensity from 38 to 43 m/min by the end of training period). Acute DCA administration did not change most of the exercise-induced mRNA upregulation. These data suggest that lactate reductions by DCA administration did not affect transcriptional activation after high-intensity interval exercise. However, chronic DCA administration attenuated, in part, mitochondrial adaptations such as training-induced increasing rates of citrate synthase (P = 0.06), β-hydroxyacyl CoA dehydrogenase activity (P < 0.05), cytochrome c oxidase IV (P < 0.05) and a fatty acid transporter, fatty acid translocase/CD36 (P < 0.05), proteins after exercise training. These results suggest that lactate accumulation during high-intensity interval exercise may be associated with mitochondrial adaptations after chronic exercise training.

Estimation of pork quality traits using exsanguination blood and postmortem muscle metabolites.

The current study was designed to estimate the pork quality traits using metabolites from exsanguination blood and postmortem muscle simultaneously under the Korean standard pre- and post-slaughter conditions. A total of 111 Yorkshire (pure breed and castrated male) pigs were evaluated under the Korean standard conditions. Measurements were taken of the levels of blood glucose and lactate at exsanguination, and muscle glycogen and lactate content at 45 min and 24 h postmortem. Certain pork quality traits were also evaluated. Correlation analysis and multiple regression analysis including stepwise regression were performed. Exsanguination blood glucose and lactate levels were positively correlated with each other, negatively related to postmortem muscle glycogen content and positively associated with postmortem muscle lactate content. A rapid and extended postmortem glycolysis was associated with high levels of blood glucose and lactate, with high muscle lactate content, and with low muscle glycogen content during postmortem. In addition, these were also correlated with paler meat color and reduced water holding capacity. The results of multiple regression analyses also showed that metabolites in exsanguination blood and postmortem muscle explained variations in pork quality traits. Especially, levels of blood glucose and lactate and content of muscle glycogen at early postmortem were significantly associated with an elevated early glycolytic rate. Furthermore, muscle lactate content at 24 h postmortem alone accounted for a considerable portion of the variation in pork quality traits. Based on these results, the current study confirmed that the main factor influencing pork quality traits is the ultimate lactate content in muscle via postmortem glycolysis, and that levels of blood glucose and lactate at exsanguination and contents of muscle glycogen and lactate at postmortem can explain a large portion of the variation in pork quality even under the standard slaughter conditions.

Effect of L-carnitine supplementation on the body carnitine pool, skeletal muscle energy metabolism and physical performance in male vegetarians.

More than 95% of the body carnitine is located in skeletal muscle, where it is essential for energy metabolism. Vegetarians ingest less carnitine and carnitine precursors and have lower plasma carnitine concentrations than omnivores. Principle aims of the current study were to assess the plasma and skeletal muscle carnitine content and physical performance of male vegetarians and matched omnivores under basal conditions and after L-carnitine supplementation. Sixteen vegetarians and eight omnivores participated in this interventional study with oral supplementation of 2 g L-carnitine for 12 weeks. Before carnitine supplementation, vegetarians had a 10% lower plasma carnitine concentration, but maintained skeletal muscle carnitine stores compared to omnivores. Skeletal muscle phosphocreatine, ATP, glycogen and lactate contents were also not different from omnivores. Maximal oxygen uptake (VO2max) and workload (P max) per bodyweight (bicycle spiroergometry) were not significantly different between vegetarians and omnivores. Sub-maximal exercise (75% VO2max for 1 h) revealed no significant differences between vegetarians and omnivores (respiratory exchange ratio, blood lactate and muscle metabolites). Supplementation with L-carnitine significantly increased the total plasma carnitine concentration (24% in omnivores, 31% in vegetarians) and the muscle carnitine content in vegetarians (13%). Despite this increase, P max and VO2max as well as muscle phosphocreatine, lactate and glycogen were not significantly affected by carnitine administration. Vegetarians have lower plasma carnitine concentrations, but maintained muscle carnitine stores compared to omnivores. Oral L-carnitine supplementation normalizes the plasma carnitine stores and slightly increases the skeletal muscle carnitine content in vegetarians, but without affecting muscle function and energy metabolism.

Hand-held lactate analyzer as a tool for the real-time measurement of physical fatigue before slaughter and pork quality prediction

The objectives of this study were to assess the relationship between blood lactate variation measured at the plant, and pork quality variation on a large sample size and under commercial preslaughter handling conditions. A total of 600 pigs were randomly chosen on arrival at a commercial slaughter plant and blood samples taken from the ear vein at unloading (UN), after lairage (LA), in the restrainer (RE; before stunning) and at exsanguination (EX) were analysed for lactate content using a Lactate Scout Analyzer (LSA). In order to have a large range of measures, pigs were distributed into two groups; one kept in lairage overnight (G1) and the other for 2 to 3 h (G2) before slaughter. Meat quality was assessed in the Longissimus thoracis (LT), Semimembranosus (SM) and Adductor (AD) muscles by measuring the pH 30 min postmortem (pH1) and at 24 h postmortem (pHu), the colour and the drip loss. Blood lactate levels did not differ between G1 and G2 (P>0.05). A reduced muscle lactate and glucose contents (P=0.02 and P=0.004, respectively) resulting in a lower (P<0.001) glycolytic potential (GP) was observed in the LT muscle of G1 pigs when compared with G2 loins. In the LT muscle of G1 pigs, the lower GP resulted in an increased pHu (r=−0.67; P<0.001), decreased drip loss (r=0.57; P<0.001) and darker colour (r=0.50; P<0.001) compared with G2. In both G1 and G2 pigs, the lower GP was correlated to higher pHu value in the SM and AD muscles (r=−0.73; P<0.001). The greatest correlation was observed in G2 between blood lactate levels at LA and pHu value of the SM and AD muscles (r=0.46 and r=0.44, respectively; P<0.001 for both muscles). The second greatest correlation was found between blood lactate levels at EX and pH1 value in the SM muscle in both groups (r=−0.37 and r=−0.41, respectively; P<0.001 for both groups). Based on the results of this study, it appears that blood lactate levels, as measured by the LSA, reliably reflect the physiological response of pigs to perimortem stress and may help explain the variation in pork quality.

수송밀도가 넙치(Paralichthys olivaceus) 근육의 물리화학적 변화에 미치는 영향

The effects of transport stocking density (500, 600 and 700 kg of olive flounder Paralichthys olivaceus/per water tank) on the physicochemical characteristics of muscle were investigated. Transport of the animals took, on average, 10 days from Busan, Korea, to Long Beach, CA, USA. There was no significant difference in the breaking strength of muscle among the three groups. There was also no significant difference in the ATP, lactate, or glycogen content of muscle from the 500 and 600 kg/tank stocking density groups at the beginning and after transport. However, the ATP content decreased sharply while the lactate content increased in muscle from fish transported at a density of 700 kg/tank at the beginning of transport, and the ATP and lactate contents in this group were stable after transport.

Genetic variants in glucocorticoid and mineralocorticoid receptors are associated with concentrations of plasma cortisol, muscle glycogen content, and meat quality traits in male Nellore cattle

The glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) are key components in the regulation of the hypothalamic-pituitary-adrenal neuroendocrine axis and coordinate the physiological response to stress agents to reestablish homeostasis. Genetic variations of GR (NR3C1) and MR (NR3C2) genes could explain the alterations in animals to adapt to challenges, and therefore, their influence on production traits. The present study aimed to identify single-nucleotide polymorphisms (SNPs) in the bovine NR3C1 and NR3C2 genes and explore their associations to relevant traits of beef cattle production. Genotypes and phenotypes were collected from 241 male Nellore cattle (119 noncastrated and 122 castrated surgically) with an average of 24 ± 1.2 mo of age and live weight of 508 ± 39 kg. The traits evaluated were concentrations of plasma adrenocorticotropic hormone (ACTH) and cortisol, muscle glycogen and lactate content, and pH, color, cooking loss, and shear force of longissimus thoracis measured on the 1st, 7th, and 14th days postmortem. Five SNPs were identified, 2 in the NR3C1 gene and 3 in the NR3C2 gene. There was an associative relationship between the SNP NR3C1_1 g.3293A>G and postmortem plasma concentration of cortisol (P = 0.0008). The SNPs NR3C2_1 g.115T>C and NR3C2_2 g.570T>C were associated with muscle glycogen content (P = 0.0306 and P = 0.0158), postmortem plasma concentration of ACTH (P = 0.0118 and P = 0.0095), and cooking loss of the steak aged 1 d (P = 0.0398 and P = 0.0423). Haplotype analysis showed associations of GR haplotypes with postmortem plasma concentrations of cortisol and MR haplotypes with meat color, cooking losses, muscle glycogen content, and plasma concentrations of ACTH. The associations observed in the present study show that SNPs in GR and MR genes are related with changes of hypothalamic-pituitary-adrenal axis activity and metabolic profile in cattle, leading to individual variation in meat quality traits.

Flesh quality loss in response to dietary isoleucine deficiency and excess in fish: a link to impaired Nrf2-dependent antioxidant defense in muscle.

The present study explored the impact of dietary isoleucine (Ile) on fish growth and flesh quality and revealed a possible role of muscle antioxidant defense in flesh quality in relation to dietary Ile. Grass carp (weighing 256.8±3.5 g) were fed diets containing six graded levels of Ile (3.8, 6.6, 9.3, 12.5, 15.2 and 18.5 g/kg) for eight weeks. The results indicated that compared with Ile deficiency (3.8 g/kg diets) and excess (18.5 g/kg diets) groups, 9.3–15.2 g Ile/kg diet supplementations promoted fish growth and muscle fat deposition, whereas 6.6–15.2 g Ile/kg diets supplementation enhanced muscle nutrients (protein and total EAAs) deposition. Furthermore, muscle shear force, pH value, and hydroxyproline concentration were improved by 9.3–12.5, 9.3 and 9.3 g Ile/kg diet supplementations, respectively. However, muscle cooking loss, lactate content, and activities of cathepsin B and L were decreased by 6.6–15.2, 9.3–12.5, 9.3–12.5 and 9.3–15.2 g Ile/kg diet supplementations, respectively. Additionally, 6.6–15.2 and 6.6–12.5 g Ile/kg diet supplementations attenuated malondialdehyde and protein carbonyl contents, respectively. The activities of copper/zinc superoxide dismutase (Cu/Zn-SOD) and glutathione peroxidase (GPx), and glutathione content were enhanced by 6.6–9.3, 6.6–12.5 and 6.6–15.2 g Ile/kg diet supplementations, respectively. Moreover, the relative mRNA expressions of antioxidant enzymes, including Cu/Zn-SOD (6.6–12.5 g/kg diets) and GPx (12.5 g/kg diets), as well as antioxidant-related signaling molecules, including NF-E2-related factor 2 (Nrf2) (6.6–12.5 g/kg diets), target of rapamycin (6.6–12.5 g/kg diets), ribosomal S6 protein kinase 1 (9.3–12.5 g/kg diets) and casein kinase 2 (6.6–12.5 g/kg diets), were up-regulated when Ile diet supplementations were administered at these levels, respectively, whereas the relative mRNA expression of Kelch-like ECH-associated protein 1 was down-regulated with 9.3 g Ile/kg diet supplementations. Collectively, the present study indicated that optimum isoleucine improved flesh quality, partly due to the activation of antioxidant defense through the Nrf2 signaling pathway.

Blood ammonia and lactate as markers of muscle metabolites during leg press exercise.

To examine whether blood lactate and ammonia concentrations can be used to estimate the functional state of the muscle contractile machinery with regard to muscle lactate and adenosine triphosphate (ATP) levels during leg press exercise. Thirteen men (age, 34 ± 5 years; 1 repetition maximum leg press strength 199 ± 33 kg) performed either 5 sets of 10 repetitions to failure (5×10RF), or 10 sets of 5 repetitions not to failure (10×5RNF) with the same initial load (10RM) and interset rests (2 minutes) on 2 separate sessions in random order. Capillary blood samples were obtained before and during exercise and recovery. Six subjects underwent vastus lateralis muscle biopsies at rest, before the first set and after the final exercise set. The 5×10RF resulted in a significant and marked decrease in power output (37%), muscle ATP content (24%), and high levels of muscle lactate (25.0 ± 8.1 mmol·kg wet weight), blood lactate (10.3 ± 2.6 mmol·L), and blood ammonia (91.6 ± 40.5 μmol·L). During 10×5RNF no or minimal changes were observed. Significant correlations were found between: (a) blood ammonia and muscle ATP (r = -0.75), (b) changes in peak power output and blood ammonia (r = -0.87) and blood lactate (r = -0.84), and (c) blood and muscle lactate (r = 0.90). Blood lactate and ammonia concentrations can be used as extracellular markers for muscle lactate and ATP contents, respectively. The decline in mechanical power output can be used to indirectly estimate blood ammonia and lactate during leg press exercise.

Cerebral metabolism during experimental endotoxin shock and after preconditioning with monophosphoryl lipid A

PurposePreconditioning with low doses of monophosphoryl lipid A (MPL) has been shown to induce endotoxin tolerance and to reduce the metabolic and hemodynamic consequences of endotoxin shock. However, no data are available about the effects of endotoxin preconditioning on cerebral metabolism during endotoxemia. The study was designed to determine the effects of endotoxin preconditioning with MPL on cerebral metabolism via microdialysis compared to muscle tissue metabolism during experimental endotoxemia. MethodsIn a controlled animal study, continuous endotoxin infusion (1μg/kg b.w. per h) was administrated to 7 female mixed-breed pigs after pretreatment with MPL in incremental doses of endotoxin during days 5–2 before the experiments. In the control group, 7 animals received a saline pretreatment. In addition to hemodynamic monitoring and blood gas analyses, interstitial lactate, pyruvate, glucose and glycerol concentrations in muscle and cerebral tissue were measured using in vivo microdialysis. ResultsThere were no significant differences between the two groups with respect to hemodynamic parameters, while mixed venous oxygen saturation (SvO2), arterial blood pH and mean pulmonary arterial pressure (MPAP) were significantly higher in the preconditioned group. Cerebral perfusion pressure (CPP) and brain tissue oxygen pressure (ptiO2) values stayed stable throughout the experiment with no inter-group differences. While interstitial concentrations of lactate and glycerol as well as the lactate/pyruvate (LP) and the lactate/glucose (LG) ratio in muscle tissues were significantly increased in control animals compared to those who had been pretreated with MPL; the results of cerebral microdialysis showed no significant changes in interstitial lactate or glycerol levels in both groups. However, the lactate/glucose (LG) ratio in the control group showed a significantly higher increase than in the preconditioned group. ConclusionsPreconditioning with low doses of MPL ameliorates the negative metabolic effects of endotoxin shock in muscle tissue. With regard to cerebral metabolism, the present study suggests that MLP preconditioning provides moderate advantages, at least in an experimental model of endotoxin shock.