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PubMed1986

Mammalian metabolite flux rates in a teleost: lactate and glucose turnover in tuna.

Lactate and glucose turnover rates were measured by bolus injection of [U-14C]lactate and [6-3H]glucose in cannulated lightly anesthetized skipjack tuna, Katsuwonus pelamis. Our goals were to find out whether the high rates of lactate clearance reported during recovery from burst swimming in tuna could be accounted for by high blood lactate fluxes; to extend the observed correlation between lactate turnover and lactate concentration in mammals to a nonmammalian system, and to assess the importance of lactate and glucose as metabolic fuels in tuna and to compare their flux rates with values reported for mammals. Measured lactate turnover rates ranged from 112 to 431 mumol X min-1 X kg-1 and were correlated with blood lactate concentration. Glucose turnover rate averaged 15.3 mumol X min-1 X kg-1. When correcting for body mass and temperature, skipjack tuna has at least as high or even higher lactate turnover rates than those recorded for mammals. Tuna glucose turnover rate is similar to that of mammals but much higher than levels found in other teleosts. Even the highest lactate turnover rate measured in tuna cannot fully account for the rate of blood lactate clearance observed during recovery, suggesting that some of the lactate produced in skeletal muscle must be metabolized in situ. After injection of [U-14C]lactate, less than 5% of the total blood activity was recovered in glucose, suggesting that the Cori cycle is not an important pathway of lactate metabolism in tuna.

Analysis of Variance↗
PubMed1994

Factors affecting L-lactate utilization by Selenomonas ruminantium.

Studies were conducted to evaluate factors that affect L-lactate utilization by the ruminal bacterium Selenomonas ruminantium HD4. L-Lactate uptake decreased over time both in the presence and absence of 10 mM L-malate. Compared with uptake in the absence of malate, 10 mM L-malate increased L-lactate uptake at 30 s and 45 min. Because L-malate had little effect on L-lactate uptake for cells grown on soluble carbohydrates compared to lactate-grown cells, it seems that the stimulation due to L-malate is inducible. Sodium concentrations between 25 and 100 mM stimulated long-term (45 min) L-lactate uptake in the presence of 10 mM L-malate, whereas uptake in the absence of L-malate was low regardless of the Na+ concentration. Monensin inhibited L-lactate uptake by 42%, and this is consistent with the involvement of Na+ in L-lactate utilization. Initial uptake (30 s) of L-lactate was not dependent on Na+. L-Lactate uptake was stimulated by 10 mM L-malate at extracellular pH values between 4.0 and 8.0. No inhibition of L-lactate uptake was observed in the presence of 10 mM glucose, maltose, sucrose, xylose, or D-lactate. The metabolic inhibitors carbonyl cyanide m-chlorophenyl-hydrazone, 2,4-dinitrophenol, and NaF inhibited L-lactate uptake (> 79%), suggesting that protons may be involved in L-lactate uptake by this bacterium. Collectively, these experiments show that L-lactate uptake by S. ruminantium HD4 is stimulated in the presence of 10 mM L-malate at pH values and Na+ concentrations commonly found in the rumen.

Animals↗
PubMed1983

Growth of guinea pig mammary glands through their first six lactations.

Guinea pigs were killed on day 5 of lactation. Each of lactations one through six was represented by six animals. Body weight was measured, and mammary glands were removed. Wet weight of mammary gland, dry weight of fat-free tissue, and weight and percent (relative to dry fat-free tissue) of deoxyribonucleic acid, ribonucleic acid, and hydroxyproline were measured. Collagen and noncollagenous dry fat-free tissues were estimated. Body weight increased from 800 g in first lactation to 1035 g in fifth and 975 g in sixth lactation. Mammary wet weight increased quadratically from 20 g for first lactation to 31 g for fifth and 26 g for sixth lactation. Dry fat-free tissue followed a similar pattern, increasing from 2330 mg first lactation to 3647 mg fifth and 3242 mg sixth lactation. Deoxyribonucleic acid rose linearly from 70 mg first lactation to 121 mg fifth and 110 sixth lactation. Ribonucleic acid followed a similar pattern, increasing from 182 mg first lactation to 289 mg sixth lactation. Ratio of ribonucleic acid to deoxyribonucleic acid was constant at 2.2. Amount of collagen was also constant at 257 mg. However, percent collagen decreased linearly from 12% first lactation to 7.1% sixth lactation. Mammary gland increases in size over subsequent lactations to five and then decreases slightly. The increase is not of connective tissue or stroma, as measured by hydroxyproline, but is an increase in parenchyma or cells involved with milk secretion and harvest.

Animals↗
PubMed1991

Production losses from mastitis: carry-over from the previous lactation.

The study examined whether elevation in SCC in the second lactation was associated with reduced milk production in the third lactation. Lactation records from 10,705 Holstein cows from 770 herds were taken from the Dairy Records Processing Center at Raleigh. Cows in the data set were selected so that no SCC test in the first lactation was elevated above a linear score of 4.5 (no mastitis in the first lactation). Using actual and mature equivalent milk production in the first lactation as a baseline, effects of elevated SCC on production in the second and third lactations were examined using linear regression. The effect of high SCC during a cow's current lactation was found to be essentially the same as previously reported by other investigators. An increase in the lactation average linear score of 1.0 was associated with a decrease of approximately 200 kg of milk per lactation. Limited carry-over effect of elevated SCC during the second lactation was found in the third lactation. For third lactation milk production, the effect of increased SCC during the preceding (second) lactation was only about 20 to 30% as much as the effect of SCC increases in the third lactation.

Animals↗
PubMed2001

Hypothalamic neuropeptide Y mRNA in pregnant, lactating and suckling rats.

Blood glucose, plasma insulin and luteinizing hormone levels were studied in pregnant wistra rats and those in early and late stages of lactation. NPY mRNA was also measured in whole hypothalamic tissue of these rats which were either fed ad libitum or food deprived to 80% of the relative controls. When fed ad libitum, hypothalamic NPY mRNA was not significantly elevated in the pregnant rats (111 +/- 2.1%). By the 5th and 4th days of lactation the mRNA had increased progressively (141 +/- 4.7% of control, p<0.01; 186 +/- 9%, p<0.001) respectively. Blood glucose levels were unchanged in pregnancy and lactation, however, insulin levels dropped significantly by the ]4th day of lactation (control 322.3 +/- 3.2; lactating 298.6 +/- 4.8 pmol/l; p<0.05). Luteinizing hormone was significantly reduced in the lactating rats (control 2.2 +/- 0.21, lactating 0.81 +/- 0.2 ng/ml;p<0.05). In food restriction, NPY mRNA was increased moderately in the non-pregnant state and enormously in late lactation (non-pregnant 157 +/- 21%, lactating 333 +/- 35%, p<0.001). In a lactation, blood glucose was unchanged while plasma insulin and LH were reduced to 20% and 50% of controls respectively (insulin: control 110.3 +/- 2.0; lactating 18.3 pmol/l; LH. control 1.3 +/- 0.1; lactating 0.59 +/- 0.4 ng/ml p<0.01). Orexigenic effect of hypothalamic NPY is possibly responsible for the hyperphagia in lactating. Food restriction and lactation had additive lowering effect on plasma insulin but an additive increase on hypothalamic NPYmRNA. NPY message may be partially responsible for the anovulatory effect of lactation.

Analysis of Variance↗
PubMed1988

A proton gradient is the driving force for uphill transport of lactate in human placental brush-border membrane vesicles.

The characteristics of lactate transport in brush-border membrane vesicles isolated from normal human full-term placentas were investigated. Lactate transport in these vesicles was Na+-independent, but was greatly stimulated when the extravesicular pH was made acidic. In the presence of an inwardly directed H+ gradient ([H+]o greater than [H+]i), transient uphill transport of lactate could be demonstrated. This H+ gradient-dependent stimulation was not a result of a H+ diffusion potential. Transport of lactate in the presence of the H+ gradient was not inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid or by furosemide, ruling out the participation of an anion exchanger in placental lactate transport. Many monocarboxylates strongly interacted with the lactate transport system, whereas, with the single exception of succinate, dicarboxylates did not. The monocarboxylates pyruvate and lactate, but not the dicarboxylate succinate, when present inside the vesicles, were able to exert a trans-stimulatory effect on the uptake of radiolabeled lactate. Kinetic analyses provided evidence for a single transport system with a Kt of 4.1 +/- 0.4 mM for lactate and a Vmax of 54.2 +/- 9.9 nmol/mg of protein/30 s. Pyruvate inhibited lactate transport competitively, by reducing the affinity of the system for lactate without altering the maximal velocity. It is concluded that human placental brush-border membranes possess a transport system specific for lactate and other monocarboxylates and that this transport system is Na+-independent and is energized by an inwardly directed H+ gradient. Lactate-H+ symport rather than lactate-OH- antiport appears to be the mechanism of the H+ gradient-dependent lactate transport in these membranes.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1995

L(+)- and D(-)-lactate modulate rat renal tubular accumulation of amantadine in the presence and absence of bicarbonate.

The effect of L(+)-, D(-)- and racemic (DL)-lactate on the energy-dependent renal uptake of the achiral organic cation amantadine was determined with purified proximal and distal cortical tubule fragments isolated from rat kidneys. Kinetic parameters for uptake of amantadine were measured, under constant pH, in bicarbonate buffer (Krebs-Henseleit [KHS]), and in lactate buffers (5 mM) with different proportions of the enantiomers. Km for amantadine uptake increased in all lactate buffers compared with KHS for both proximal and distal tubules. Km for uptake in DL-lactate was similar to that in D(-)-lactate for proximal tubules and to L(+)-lactate in distal tubules, but Km in L(+)-lactate was higher than in D(-)-lactate for both tubules. Maximal transport capacity (Vmax) in DL-lactate and mixtures of enantiomers were similar to KHS but higher than in pure L(+)- and D(-)-lactate. In KHS, lactate inhibited energy-dependent amantadine uptake in a biphasic manner. Graded competitive inhibition of amantadine uptake was observed between 1 and 15 mM lactate for both proximal and distal tubules. This first phase (1-15 mM) inhibited 60% of amantadine uptake. The second phase (15-20 mM lactate) showed a much steeper slope and inhibited the remaining amantadine uptake. There were no differences in inhibitory potencies of the lactate enantiomers for either proximal tubules or distal tubules amantadine tubule uptake. Our present studies suggest that L(+)- and D(-)-lactate modulate amantadine transport by interacting directly with the bicarbonate-dependent transport mechanism(s).

Amantadine↗
PubMed1996

Continuous enzyme-linked fluorometric detection of L-(+)-lactate released from rat brain vesicles under anoxic conditions.

A method is described for the on-line detection of L-(+)-lactate released from brain vesicles under physiological conditions. The principle of L-lactate detection is based on the reversible oxidation of L-lactate catalysed by L-lactate dehydrogenase (LDH, EC 1.1.1.27) employing 3-acetylpyridine-adenine-dinucleotide (APAD) as analogue of NAD according to the reaction: L-lactate + APAD reversible pyruvate + APADH. In practical terms, L-lactate synthesis of vesicles incubated in the presence of LDH and APAD was continuously followed by the fluorescence (490 nm) of APADH excited at 410 nm. Addition of a L-lactate standard (10 mumol/l) enhanced APADH fluorescence with a half-life of 6.0 +/- 0.6 s allowing us to uncover a short-term alteration of L-lactate synthesis. This method was applied to evaluate a prospective change of L-lactate generation caused by the anoxia-induced increase in intravesicular Na+ and Ca2+ concentration ([Na+]i, [Ca2+]i), both fluorometrically determined by SBFI and Fura, respectively. Upon anoxia, [Na+]i and [Ca2+]i increased continuously up to 40 mmol/l Na+ and 900 nmol/l Ca2+ within 400 s. Concurrently, intravesicular NADH ([NADH]i) and basal L-lactate synthesis were enhanced within a few seconds, the latter from 4.2 +/- 1.5 to 15.8 +/- 1.5 nmol L-lactate/min per mg protein. Incubation of vesicles in the presence of 10 mumol/l tetrodotoxin (TTX) suppressed the increase in [Na+]i and [Ca2+]i but failed to influence L-lactate synthesis. The data indicate a continuous Na+ influx via voltage-dependent Na+ channels accompanied by an increase in [Ca2+]i during anoxia which did not affect anaerobic L-lactate synthesis. The method of fluorometric L-lactate determination was confirmed to be suitable for the detection of L-lactate released under physiological conditions from brain vesicles and seems to be applicable to various cell models.

Animals↗
PubMed2004

Two separate pathways for d-lactate oxidation by Saccharomyces cerevisiae mitochondria which differ in energy production and carrier involvement.

In this work we looked at whether and how mitochondria isolated from Saccharomyces cerevisiae (SCM) oxidize d-lactate. We found that: (1). externally added d-lactate causes oxygen uptake by SCM with P/O ratio equal to 1.5; in the presence of antimycin A (AA), P/O ratio was 1.8, differently in the presence of the non-penetrant alpha-cyanocinnamate (alpha-CCN-) no P/O ratio could be measured. Consistently, mitochondrial electrical membrane potential (deltapsi) generation was found, due to externally added d-lactate in the presence of antimycin A, but not of alpha-CCN-. (2). SCM oxidize d-lactate in two different manners: (i). via inner membrane d-lactate dehydrogenase which leads to d-lactate oxidation without driving deltapsi generation and ATP synthesis and (ii). via the matrix d-lactate dehydrogenase, which drives deltapsi generation and ATP synthesis by using taken up d-lactate. (3). Pyruvate newly synthesised in the mitochondrial matrix is exported via the novel d-lactate/pyruvate antiporter. d-Lactate/pyruvate antiport proved to regulate the rate of pyruvate efflux in vitro. (4). The existence of the d-lactate/H+ symporter is also proposed as shown by mitochondrial swelling. The d-lactate carriers and d-lactate dehydrogenases could account for the removal of the toxic methylglyoxal from cytosol, as well as for the d-lactate-dependent gluconeogenesis.

Adenosine Triphosphate↗
PubMed2001

Glucose and lactate metabolism during brain activation.

The dependence of brain function on blood glucose as a fuel does not exclude the possibility that lactate within the brain might be transferred between different cell types and serve as an energy source. It has been recently suggested that 1) about 85% of glucose consumption during brain activation is initiated by aerobic glycolysis in astrocytes, triggered by demand for glycolytically derived energy for Na+ -dependent accumulation of transmitter glutamate and its amidation to glutamine, and 2) the generated lactate is quantitatively transferred to neurons for oxidative degradation. However, astrocytic glutamate uptake can be fueled by either glycolytically or oxidatively derived energy, and the extent to which "metabolic trafficking" of lactate might occur during brain function is unknown. In this review, the potential for an astrocytic-neuronal lactate flux has been estimated by comparing rates of glucose utilization in brain and in cultured neurons and astrocytes with those for lactate release and uptake. Working brain tissue and isolated brain cells release large amounts of lactate. Cellular lactate uptake occurs by carrier-mediated facilitated diffusion and is normally limited by its dependence on metabolism of accumulated lactate to maintain a concentration gradient. The rate of this process is similar in cultured astrocytes and glutamatergic neurons, and, at physiologically occurring lactate concentrations, lactate uptake corresponds at most to 25% of the rate of glucose oxidation, which accordingly is the upper limit for "metabolic trafficking" of lactate. Because of a larger local release than uptake of lactate and the necessity for rapid lactate clearance to maintain the intracellular redox state to support lactate production in the presence of normal oxygen levels, brain activation in vivo is probably, in many cases, accompanied by a substantial overflow of glycolytically generated lactate, both to different brain areas and under some conditions (spreading depression, hyperammonemia) to circulating blood.

Animals↗
PubMed1997

Competition between lactate and fatty acids as sources of ATP in the isolated working rat heart.

Fatty acid oxidation is generally considered the major source of energy in the heart, although lactate oxidation can be a major contributor to ATP production, depending on the concentration and availability of other competing substrates. In this study, isolated working rat hearts were used to directly determine the relationship between lactate and fatty acid oxidation to overall ATP production from exogenous sources. A range of lactate from 0.5 to 8.0 mM lactate was added to hearts perfused with buffer containing 5.5 mM glucose, and either 0.4 or 1.2 mM palmitate over a 100 min period. Rates of glycolysis, glucose oxidation, lactate oxidation, and palmitate oxidation were determined. In the presence of 0.5 mM lactate and 0.4 mM palmitate, lactate oxidation provided 17% of the ATP production and palmitate oxidation provided 68%, with the remainder coming from glucose oxidation and glycolysis. In the presence of 0.4 mM palmitate, an increase in lactate from 0.5 to 8.0 mM increased the steady state rates of lactate oxidation from 1239+/-236 to 5247+/-940 nmol/min/g dry weight, respectively. The contribution of lactate oxidation to total ATP production increased to 37%, with palmitate oxidation now contributing only 52% of the total ATP produced. At 8.0 mM lactate and 1.2 mM palmitate, lactate oxidation contributed 13% of the total ATP production, while palmitate oxidation contributed 81%. This data demonstrates that under near physiological conditions of lactate (0.5 mM) and fatty acids (0.4 mM), the preferred energy substrate of the heart remains to be fatty acids, and that only at high levels of lactate, such as can be observed during exercise or severe stress, does lactate oxidation become a significant source of ATP production.

Adenosine Triphosphate↗
PubMed1999

Lactate determination in exercise testing using an electrochemical analyser: with or without blood lysis?

The practical use of lactate electrochemical analysers in exercise testing has not been adequately examined. Initial studies have reported differences in lactate concentration between that measured spectrophotometrically and that measured electrochemically. The study described here was undertaken to compare, using the statistical technique of Bland and Altman (1986), two widely available methods of measuring lactate using lysed and non-lysed blood samples and the lactate thresholds derived from the measured lactate values using a log-log transform technique. Thirteen normal, healthy young adults (11 male) undertook progressive exercise tests to exhaustion. Arterialised venous blood samples were taken each minute and the lactate concentration therein was measured both spectrophotometrically and electrochemically and either with or without lysis of the blood samples. The lactate concentrations measured in lysed blood using both methods (182 pairs) were in close agreement. The electrochemical values obtained using non-lysed blood were systematically lower than spectrophotometric values (206 pairs), the difference becoming progressively greater at higher lactate concentrations. Results for the lactate threshold comparisons are given as mean difference (limits of agreement with 95% probability). Lactate thresholds (12 pairs) derived from lysed blood lactate concentrations measured spectrophotometrically and electrochemically were not significantly different -30 (240) ml O2 x min(-1). Lactate thresholds (11 pairs) derived from lysed spectrophotometric and non-lysed electrochemical measurements were also not significantly different + 20 (250) ml O2 x min(-1). Thus, despite the difference in the measured lactate concentrations, the derived lactate thresholds are in agreement and, therefore, electrochemical analysers can be used for lactate threshold determination using the log-log transform technique without sample lysis.

Adult↗
PubMed2003

Serum lactate and base deficit as predictors of mortality and morbidity.

OBJECTIVES: To determine whether lactate levels and base deficits in critically ill surgical intensive care unit (SICU) patients correlate and whether either measure is a significant indicator of mortality and morbidity. METHODS: A review was made of 137 SICU patients who had serial lactate and blood gas measurements. Patients were stratified by absolute lactate and base deficit values as well as time to lactate clearance. RESULTS: Initial and 24-hour lactate level was significantly elevated in nonsurvivors versus survivors (P = 0.002). Initial base deficit was not significantly different; 24-hour base deficit did achieve statistical significance (P = 0.02). Subgroup analysis among trauma patients (n = 36) and major abdominal surgery (n = 101) confirmed the significant correlation between lactate levels and survival. There was poor correlation between initial and 24-hour lactate and base deficit among all patients (r = -0.3 and -0.5). Mortality if lactate normalized within 24 hours was 10%, compared with 24% for >48 hours and 67% if lactate failed to normalize. Physical status at discharge was related to initial lactate (P = 0.05), as well as to lactate clearance time (P = 0.01). CONCLUSIONS: Elevated initial and 24-hour lactate levels are significantly correlated with mortality and appear to be superior to corresponding base deficit levels. Lactate clearance time may be used to predict mortality and is associated with outcome at discharge. Initial base deficit is a poor predictor of mortality and did not correlate with lactate levels except in trauma nonsurvivors. In addition to being used as an endpoint for resuscitation, lactate may be predictive of certain morbidities and patient outcome at discharge.

APACHE↗
PubMed1996

Pulmonary lactate release in patients with sepsis and the adult respiratory distress syndrome.

PURPOSE: Elevated arterial lactate concentrations in patients with sepsis have been interpreted as evidence of peripheral, nonpulmonary tissue hypoxia. These patients often develop pulmonary failure manifested by the acute respiratory distress syndrome (ARDS). As the result of tissue hypoxia or inflammation, the lungs of patients with sepsis and ARDS may become a source of lactate release into the circulation. MATERIALS AND METHODS: Pulmonary lactate release was measured in 19 patients with sepsis, arterial lactate > or = 2.2 mm, and gastric mucosal pH > 7.30. A normal gastric mucosal pH served as a marker of adequate splanchnic oxygenation. Pulmonary lactate release was computed as the product of the cardiac index and the difference in plasma L-lactate concentration in simultaneously obtained arterial and mixed venous blood samples. Lung injury was graded with the Lung Injury Score using radiographic and physiologic data. RESULTS: The lungs of patients with minimal or no lung injury (lung injury score <1) produced significantly less lactate than those with moderate or severe lung injury (lung injury score > or = 1) (P < .005). The Lung Injury Score correlated with pulmonary lactate release (r2 = .73; P < .0001). This relationship resulted primarily from increases in mixed venous-arterial lactate differences (r2 = .59). The Lung Injury Score correlated weakly with the cardiac index (r2 = .32). Arterial lactate concentration did not correlate with pulmonary lactate release, systemic oxygen transport, or systemic oxygen consumption. CONCLUSIONS: The lungs of patients with sepsis and ARDS may produce lactate. Pulmonary lactate release correlates with the severity of lung injury. The contribution of pulmonary lactate release should be considered when interpreting arterial lactate concentration as an index of systemic hypoxia.

Acidosis, Lactic↗
PubMed2001

Dairy goat performance with different dietary concentrate levels in late lactation.

Alpine yearling doelings (22; 44+/-1.0kg) and mature does (25; 59+/-1.7kg) were used in an experiment with 16 weeks in late lactation, 8-13 weeks dry and 12 weeks in the subsequent lactation. Diets of 20, 35, 50 or 65% concentrate and 2.18, 2.34, 2.49 and 2.62Mcal/kg ME, respectively (20C, 35C, 50C and 65C treatments, respectively), were consumed ad libitum in late lactation, with a 35% concentrate diet (2.18Mcal/kg ME) in the first 4 weeks of the dry phase and 50% concentrate (2.65Mcal/kg ME) until kidding. Other goats consuming 20 or 35% concentrate in late lactation received 65 (2.65Mcal/kg ME) or 50% concentrate, respectively, in the dry phase (20A and 35A treatments, respectively). All goats consumed a 50% concentrate diet (2.42Mcal/kg ME) in the subsequent early lactation. DM intake in late lactation was similar among treatments (1.95, 2.21, 2.17, 2.10, 1.99 and 2.00kg per day for 20C, 35C, 50C, 65C, 20A and 35A, respectively; S.E.=0.098) and greater (P<0.05) for does versus doelings (2.16 versus 1.98kg per day; S.E.=0.058); DM intake in the dry phase was similar among treatments. Relative to BW, DM intake was greater (P<0.05) for doelings than for does in late lactation (4.16 versus 3.43% BW) and early lactation (4.56 versus 3.80% BW). The effect of dietary treatment on milk production in late lactation varied with parity (P<0.05); milk production by doelings was 1.39, 1.49, 1.43, 1.57, 1.29 and 1.52kg per day and by does was 1.01, 1.89, 2.38, 1.63, 1.17 and 1.34kg per day for 20C, 35C, 50C, 65C, 20A and 35A, respectively; S.E.=0.200). BW change during the entire 16 weeks late lactation phase was greater (P<0.05) for 65C than for other treatments except 50C (6.9, 5.6, 9.1, 10.4, 5.8 and 4.0kg for 20C, 35C, 50C, 65C, 20A and 35A, respectively; S.E.=1.28), although BW at kidding and litter weight were similar among treatments. BW, DM intake and milk production in the first 12 weeks of the subsequent lactation were not affected by dietary treatment or parity. In conclusion, with moderate to high quality forage in late lactation and a moderate level of concentrate in the dry period, the level of concentrate fed in late lactation and in the dry period may not affect subsequent lactation performance regardless of parity. Milk production by doelings in late lactation appears relatively less responsive to dietary concentrate level than that by does.

Journal Article↗
PubMed2002

D-Lactate transport and metabolism in rat liver mitochondria.

In the present study we investigated whether isolated rat liver mitochondria can take up and metabolize D-lactate. We found the following: (1) externally added D-lactate causes oxygen uptake by mitochondria [P/O ratio (the ratio of mol of ATP synthesized to mol of oxygen atoms reduced to water during oxidative phosphorylation)=2] and membrane potential (Delta(psi)) generation in processes that are rotenone-insensitive, but inhibited by antimycin A and cyanide, and proton release from coupled mitochondria inhibited by alpha-cyanocinnamate, but not by phenylsuccinate; (2) the activity of the putative flavoprotein (D-lactate dehydrogenase) was detected in inside-out submitochondrial particles, but not in mitochondria and mitoplasts, as it is localized in the matrix phase of the mitochondrial inner membrane; (3) three novel separate translocators exist to mediate D-lactate traffic across the mitochondrial inner membrane: the D-lactate/H(+) symporter, which was investigated by measuring fluorimetrically the rate of endogenous flavin reduction, the D-lactate/oxoacid antiporter (which mediates both the D-lactate/pyruvate and D-lactate/oxaloacetate exchanges) and D-lactate/malate antiporter studied by monitoring photometrically the appearance of the D-lactate counteranions outside mitochondria. The D-lactate translocators, in the light of their different inhibition profiles separate from the monocarboxylate carrier, were found to differ from each other in the V(max) values and in the inhibition and pH profiles and were shown to regulate mitochondrial D-lactate metabolism in vitro. The D-lactate translocators and the D-lactate dehydrogenase could account for the removal of the toxic methylglyoxal from cytosol, as well as for D-lactate-dependent gluconeogenesis.

Animals↗
PubMed2001

Umbilical cord blood lactate in normal infants: comparison between two methods of measurement.

OBJECTIVES: Firstly, to determine the accuracy of the Radiometer ABL 625 lactate electrode (Radiometer Medical Pty Ltd, Nunawading, Victoria, Australia) by comparing the lactate values obtained by this method to those obtained with the Hitachi 917 lactate analyser (Boehringer Mannheim Corporation, Charlottetown, Prince Edward Island, Canada). Secondly, to determine the effect of delay in measurement on blood lactate levels. METHODOLOGY: Umbilical venous (UCV) blood samples were obtained from healthy term infants delivered vaginally. Lactate levels were measured with the Radiometer ABL 625 lactate electrode in the Neonatal Intensive Care Unit, Westmead Hospital and with the Hitachi 917 lactate analyser in 49 paired samples. In addition 26 UCV blood samples were placed in ice slurry and a further 26 samples at room temperature and blood lactate was measured at 5-min intervals for 30 min to determine the change of lactate levels with time. RESULTS: The lactate levels obtained from the Radiometer ABL 625 lactate electrode were consistently lower than the levels obtained from the Hitachi 917 lactate analyser (mean difference - 0.24), but the correlation was high (r = 0.97). The blood lactate levels increased at the rate of 0.012 mmol/L per min if the blood was left at room temperature. The lactate levels remained stable for 20 min if the blood was placed in ice slurry. CONCLUSION: The Radiometer ABL 625 lactate electrode was easy to use and there was high correlation with the values obtained by the standard laboratory method. The blood specimen must be place in an ice slurry if a delay in analysis is anticipated.

Analysis of Variance↗
PubMed1999

Artifactual elevation of measured plasma L-lactate concentration in the presence of glycolate.

OBJECTIVES: To determine whether glycolate, a toxic metabolite of ethylene glycol that is chemically similar to lactate, can cause artifactual elevation of measured L-lactate concentrations. DESIGN: Prospective in vitro study. SETTING: Intensive care unit and chemical pathology laboratory in a university-affiliated hospital. SUBJECTS: Heparinized normal human blood and four commercially available L-lactate analyzers. INTERVENTIONS: Four analyzers were tested, three of which used L-lactate oxidase and one of which used L-lactate dehydrogenase. Glycolic acid (10 g/L) in saline was added to blood in a series of aliquots. Corresponding plasma L-lactate concentrations and blood pH, PCO2, and hemoglobin concentrations were measured and base excess was calculated initially and after the addition of each aliquot. One of the two L-lactate oxidase-type analyzers, which was found to show interference, was then used to measure plasma L-lactate and glucose concentrations in blood with glycolic, oxalic, or formic acid added until the base excess was reduced by >15 mmol/L. MEASUREMENTS AND MAIN RESULTS: Artifactual plasma L-lactate elevations were observed in two analyzers, both of the L-lactate oxidase type. Small concentrations of glycolic acid (causing reductions of base excess of 2-5 mmol/L) were accompanied by artifactual plasma L-lactate elevations of 4-8 mmol/L. Artifactual plasma L-lactate elevations increased with further glycolic acid-induced reductions in base excess. Oxalate and formate did not interfere with plasma L-lactate measurements, and measured plasma glucose concentrations were unaffected by all three acids. CONCLUSIONS: Glycolate causes large artifactual elevations in plasma L-lactate measurements by two analyzers in common use, with potential for misdiagnosis of lactic acidosis in ethylene glycol poisoning. A possible cause of the interference is incomplete specificity of the analytical reagent L-lactate oxidase, allowing cross-reaction with glycolate.

Acidosis, Lactic↗