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PubMed2001

Prolonged stage duration during incremental cycle exercise: effects on the lactate threshold and onset of blood lactate accumulation.

The aim of this study was to investigate whether increasing the duration of workloads from 3 min to 8 min during incremental exercise would influence workload (W), oxygen consumption (VO2) and heart rate (HR) at the lactate threshold (LT) and the onset of blood lactate accumulation (OBLA). Two groups of six male cyclists were assigned to a well-trained (WT) and recreational (REC) group on the basis of their performance in a maximal incremental ramp test. Each subject then performed two incremental lactate tests (EXT) consisting of six workloads of either 3 min (EXT3-min) or 8 min (EXT8-min) duration. At the completion of each workload whole capillary blood samples were obtained for the determination of blood lactate (BLa) concentration (mM). Power output (Watts, W), HR and VO2 were averaged in the final minute of each workload as well as in the third minute of the EXT8-min. The workload, HR and VO2 at the LT and OBLA were subsequently determined from the data of EXT3-min and EXT8-min. The results demonstrate that workload and VO2, but not HR, at the LT and OBLA were higher in the WT cyclists. At the same time, the workload at the LT obtained from the results of the EXT3-min was significantly (P < 0.05) higher then the value obtained in the EXT8-min in the WT subjects but not the REC subjects. However, the workload, VO2 and HR at the OBLA, together with the VO2 and HR at the LT were not significantly different when calculated from data obtained from EXT3-min or EXT8-min. The data obtained in this study suggest that incremental exercise protocols using workloads of duration longer than 3 min have the effect of increasing the workload at the LT in well-trained cyclists. However, the OBLA determined in exercise tests using stage increments of either 3 min or 8 min is similar in cyclists of different training status.

Adaptation, Physiological↗
PubMed2004

Training effect on performance, substrate balance and blood lactate concentration at maximal lactate steady state in master endurance-runners.

Training effects on time-to-exhaustion, substrate and blood lactate balances at the maximal lactate steady state velocity (MLSSv) were examined. Eleven male, veteran, long-distance runners performed three tests before and after 6 weeks of training at MLSSv: an incremental test to determine maximum O2 uptake (VO(2,max)) and the velocity at the lactate threshold (vLT), a sub-maximal test of two stages of 20 min at 95 and 105% of vLT separated by 40 min rest to determine the MLSSv and the corresponding lactate concentration (MLSSc) and a time-to-exhaustion run at MLSSv for which the substrate balance was calculated. Duration and distance run at MLSSv increased dramatically respectively from 44+/-10 to 63+/-12 min and from 10.4 to 15.7 km respectively (P<0.01). MLSSv increased significantly with training but the relative fraction of VO(2,max) remained the same (85.2+/-4.5 vs. 85.3+/-5.2%, P=0.93). MLSSc was unaffected by training as determined from the percentage of energy yielded by carbohydrates (80%) during the exhaustive run at MLSSv. These findings show that training at MLSS elicits small increases in MLSSv and VO(2,max), but enhances time-to-exhaustion (endurance) at MLSSv substantially (+50%). Training does not change the proportion of carbohydrate oxidized, which is the major substrate used during an exhaustive run at MLSS lasting 1 h.

Adult↗
PubMed1995

L-lactate oxidase and L-lactate monooxygenase: mechanistic variations on a common structural theme.

Properties of L-lactate oxidase from Aerococcus viridans are described. The gene encoding the enzyme has been isolated. From its cDNA sequence the amino acid sequence has been derived and shown to have high similarity with those of other enzymes catalyzing oxidation of L-alpha-hydroxy acids, including flavocytochrome b2, lactate monooxygenase, glycolate oxidase, mandelate dehydrogenases and a long chain alpha-hydroxy acid oxidase. The enzyme is expressed in Escherichia coli, and is a flavoprotein containing FMN as prosthetic group. It shares many properties of other alpha-hydroxy acid oxidizing enzymes, eg stabilization of the anionic semiquinone form of the flavin, facile formation of flavin-N(5)-sulfite adducts and a set of conserved amino acid residues around the bound flavin. Steady-state and rapid reaction kinetics of the enzyme have been studied and found to share many characteristics with those of L-lactate monooxygenase, but to differ from the latter in quantitative aspects. It is these quantitative differences between the two enzymes which account for the differences in the overall reactions catalyzed. These differences arise from different stabilities of a common intermediate of reduced flavin enzyme and pyruvate. In the case of the monooxygenase this complex is very stable and is the form that reacts with O2 to give a complex in which the oxidative decarboxylation occurs, yielding the products, acetate, CO2, and H2O (Lockridge O, Massey V, Sullivan PA (1972) J Biol Chem 247, 8097-8106). With lactate oxidase, the complex dissociates rapidly, with the result that it is the free reduced flavin form of the enzyme that reacts with O2, to give the observed products, pyruvate and H2O2.

Amino Acid Sequence↗
PubMed2007

Application of lactate amperometric sol-gel biosensor to sequential injection determination of L-lactate.

This work describes the construction and evaluation of lactate sol-gel biosensors to accomplish the determination of lactate in pharmaceutical products. Lactate oxidase was incorporated in a porous sol-gel film placed onto a platinum-based electrode. Acid and basic catalysis were assessed. When coupled to a sequential injection system (SIA) the biosensor, based on (3-aminopropyl)trimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl-trimethoxysilane, deionised water, polyethylene glycol 6000 and acid catalyst, presented a range of linearity of 5x10(-5) to 5x10(-3)M. The analytical usefulness of the developed biosensor was evaluated through analysis of commercial pharmaceutical products containing lactate with a sampling rate of 40 samples h(-1). The enzyme remained active for at least 30 days, enabling about 700 determinations without sensitivity decrease.

Biosensing Techniques↗
PubMed2001

Effect of training intensity on muscle lactate transporters and lactate threshold of cross-country skiers.

The training intensity may affect the monocarboxylate transporters MCT1 and MCT4 in skeletal muscle. Therefore, 20 elite cross-country skiers (11 men and nine women) trained hard for 5 months at either moderate (MIG, 60-70% of VO2max) or high intensity (HIG, 80-90%). The lactate threshold, several performance parameters, and the blood lactate concentration (cLa) after exhausting treadmill running were also determined. Muscle biopsies taken from the vastus lateralis muscle before and after the training period were analysed for the two MCTs and for muscle fibre types and six enzymes. The concentration of MCT1 did not change for HIG (P=0.3) but fell for MIG (-12 +/- 3%, P=0.01); the training response differed between the two groups (P=0.05). The concentration of MCT4 did not change during the training period (P > 0.10). The concentration of the two MCTs did not differ between the two sexes (P=0.9). The running speed at the lactate threshold rose for HIG (+3.2 +/- 0.9%, P=0.003), while no change was seen for MIG (P=0.54); the training response differed between the two groups (P=0.04). The cLa after long-lasting exhausting treadmill running correlated with the concentration of MCT1 (rs=0.69, P=0.002), but not with that of MCT4 (rs=0.2, P=0.2). There were no other significant correlations between the concentrations of the two MCTs and the performance parameters, muscle fibre types, or enzymes (r < or = 0.36, P > 0.10). Thus, the training response differed between MIG and HIG both in terms of performance and of the effect on MCT1. Training at high intensity may be more effective for cross-country skiers. Finally, MCT1 may be important for releasing lactate to the blood during long-lasting exercise.

Adolescent↗
PubMed2000

Time-pattern of lactate and lactate to pyruvate ratio in the first 24 hours of intensive care emergency admissions.

Blood lactate elevation in critically ill patients commonly is taken as a sign of impaired tissue perfusion. Simultaneous elevation of lactate to pyruvate ratio (L/P ratio) may be helpful in discriminating between different mechanisms of hyperlactatemia and thus in determining the relevance of the finding. We studied prospectively the prevalence and the time pattern of hyperlactatemia and simultaneous L/P ratio elevation in 98 consecutive emergency admission patients in a 23-bed surgical-medical University Hospital intensive care unit. Blood lactate, L/P ratio, and blood gases were measured at 2-h intervals during the initial 24 h of intensive care unit admission. Hyperlactatemia (blood lactate over 2 mmol/L) was found in 48 (49%) patients, and the median peak value of the non-survivors was higher than that of the survivors [5.3 (interquartile range 1.9-7.5) vs. 1.9 (1.3-2.9) mmol/L, respectively, p = 0.003]. Hyperlactatemia at admission (n = 31) was associated with a higher hospital mortality than hyperlactatemia developing later (n = 17) (29.0% vs. 5.9%, P = 0.003). Sustained admission hyperlactatemia (>6 h) was associated with higher mortality than short-lasting hyperlactatemia (36.8% vs. 0%, P = 0.008). Simultaneously elevated L/P ratio (L/P ratio > 18; n = 16) was associated with higher mortality than hyperlactatemia with normal L/P ratio (n = 32; 37.5% vs. 12.5%, respectively, P = 0.03) and was found mainly in patients who had severe circulatory failure. The hyperlactatemia of patients with sepsis was not associated with L/P ratio elevation. We conclude that hyperlactatemia is common in emergency admission patients. Hyperlactatemia with L/P ratio elevation and lactic acidosis is likely to be associated with inadequate tissue perfusion. Hyperlactatemia persisting more than 6 h and simultaneous elevation of L/P ratio are associated with increased mortality.

APACHE↗
PubMed1984

Control of lactate dehydrogenase, lactate glycolysis, and alpha-amylase by o(2) deficit in barley aleurone layers.

After 4 days in an atmosphere of N(2), aleurone layers of barley (Hordeum vulgare L. cv Himalaya) remained viable as judged by their ability to produce near normal amounts of alpha-amylases when incubated with gibberellic acid (GA(3)) in air. However, layers did not produce alpha-amylase when GA(3) was supplied under N(2), apparently because alpha-amylase mRNA failed to accumulate.When an 8-hour pulse of [U-(14)C]glucose was supplied under N(2) to freshly prepared aleurone layers, both [(14)C]lactate and [(14)C]ethanol accumulated; the [(14)C]lactate/[(14)C]ethanol ratio was about 0.3. Prior incubation of layers for 1 day under N(2) changed this ratio to about 0.8, indicating an increase in the relative importance of the lactate branch of glycolysis.l(+)Lactate dehydrogenase (LDH) activity was low in freshly prepared aleurone layers and increased 10-fold during 2 days under N(2), whereas alcohol dehydrogenase activity (ADH) was high initially and rose by 60%. The responses of LDH and ADH activities to O(2) tension were dissimilar; when layers were incubated in various O(2)/N(2) mixtures, LDH activity peaked at 2 to 5% O(2) whereas ADH activity was highest at 0% O(2). The LDH activity was resolved into several enzymically active bands by native polyacrylamide gel electrophoresis.We conclude that barley aleurone layers are highly adapted to O(2) deficiency, that they possess an inducible LDH system as well as an ADH system, and we infer that the LDH and ADH systems are independently regulated.

Journal Article↗
PubMed1998

Evaluation of a lactate sensor for rapid repeated measurements of blood lactate concentration.

In critically ill patients, serial measurements of blood lactate may indicate adequacy of therapy and predict development of multi-organ failure. We studied the accuracy, precision, and repeatability of the newly developed 800 Series Lactate Sensor (Ciba Corning Diagnostic Corp., Medfield, U.S.A.). Lactate levels determined with the sensor were compared with the standard laboratory method (Abbott TDX) in 75 paired arterial blood samples from 20 patients. Agreement between methods was determined and the mean coefficient of variation calculated for repeated measurements. The bias of the sensor was -0.38 mmol/l (CI -0.23 to -0.53), and the precision +/- 0.67. The coefficient of variation for repeated measurements was 1.95% with the sensor, and 11.5% with the TDX (P = 0.007). The new sensor offers a more reproducible, rapid method of measuring lactate, vital for serial measurements. The relatively wide limits of agreement between the methods reflect the greater variability of the TDX assay.

Biosensing Techniques↗
PubMed2005

The relationship between onset of blood lactate accumulation, critical velocity, and maximal lactate steady state in soccer players.

The objective of this study was to analyze the validity of the velocity corresponding to the onset of blood lactate accumulation (OBLA) and critical velocity (CV) to determine the maximal lactate steady state (MLSS) in soccer players. Twelve male soccer players (21.5 +/- 1.0 years) performed an incremental treadmill test for the determination of OBLA. The velocity corresponding to OBLA (3.5 mM of blood lactate) was determined through linear interpolation. The subjects returned to the laboratory on 7 occasions for the determination of MLSS and CV. The MLSS was determined from 5 treadmill runs of up to 30-minute duration and defined as the highest velocity at which blood lactate did not increase by more than 1 mM between minutes 10 and 30 of the constant velocity runs. The CV was determined by 2 maximal running efforts of 1,500 and 3,000 m performed on a 400-m running track. The CV was calculated as the slope of the linear regression of distance run versus time. Analysis of variance revealed no significant differences between OBLA (13.6 +/- 1.4 km.h(-1)) and MLSS (13.1 +/- 1.2 km.h(-1)) and between OBLA and CV (14.4 +/- 1.1 km.h(-1)). The CV was significantly higher than the MLSS. There was a significant correlation between MLSS and OBLA (r = 0.80), MLSS and CV (r = 0.90), and OBLA and CV (r = 0.80). We can conclude that the OBLA can be utilized in soccer players to estimate the MLSS. In this group of athletes, however, CV does not represent a sustainable steady-state exercise intensity.

Adult↗
PubMed2003

Activities of enzymes in the malate-aspartate shuttle and the isoenzyme pattern of lactate dehydrogenase in plasma and peripheral leukocytes of lactating Holstein cows and riding horses.

The activities of the enzymes involved in the malate-aspartate shuttle and lactate dehydrogenase (LDH) and the pattern of the isoenzymes of LDH were determined in plasma and peripheral leukocytes of lactating Holstein cows and thoroughbred riding horses as representative herbivorous animals. In the horse plasma, LDH activities were significantly lower and AST activities were significantly higher than those in the cow plasma. The specific activities of cytosolic malate dehydrogenase (MDH), LDH and AST in the horse leukocytes were higher than those in the cows. The cytosolic ratio of MDH/LDH activity (ML ratio) in the horse leukocytes was significantly lower than that in the cow leukocytes owing to significantly higher activities of LDH. The ML ratio was considered to reflect the difference in energy metabolism in leukocytes between cows and horses. The plasma LDH isoenzyme patterns of cow and horse showed the characteristic as herbivorous animals with dominance of LDH-1, -2 and -3. The LDH isoenzyme patterns with dominance of LDH-3 and -4 in the horse leukocytes were remarkably different from those in the cow leukocytes. There were significant differences in activities of malate-aspartate shuttle enzymes, ML ratio and LDH isoenzyme patterns in the cytosolic fractions of leukocytes between the lactating cows and the riding horses.

Amino Acid Oxidoreductases↗
PubMed1968

D-lactate specific pyridine nucleotide lactate dehydrogenase in animals.

A survey of representative invertebrates has revealed the presence of pyridine nucleotide-linked (D)-lactate dehydrogenase in a number of groups. All species studied contained either D(D)-or (L)L-lactate dehydrogenase, but no species contained both enzymes. The (D)-lactate dehydrogenase from Limulus polyphemus has been purified and has a molecular weight of 65,000.

Animals↗
PubMed1988

Net portal-drained visceral and hepatic metabolism of glucose, L-lactate, and nitrogenous compounds in lactating holstein cows.

Net portal-drained visceral and hepatic flux of glucose, L-lactate, alpha-amino N, NH3N, urea N, glutamate, and glutamine were measured in four Holstein cows. Cows were fed a 60:40 corn silage: concentrate diet ad libitum and milked at 12-h intervals. Six to 16 d postpartum chronic catheters were established in hepatic portal, hepatic, and mesenteric veins and a carotid artery was elevated. Twelve Measurements of net flux, the mathematical product of blood flow (measured by p-aminohippurate dilution) and venous-arterial concentration difference, were obtained for each cow at hourly intervals during 1 d of wk 4 and 8 postpartum. Dry matter, N, and energy digestion trials began 1 to 2 d after blood sampling. Dry matter intake and milk yield averaged 15.6 and 32.2 kg/d. Portal-drained visceral blood flow averaged 80% of hepatic blood flow (2041 L/h). Net flux of NH3N, urea N, and alpha-amino N across portal-drained viscera represented 68, 54, and 51% of N apparently digested. There was net use of glucose by portal-drained viscera. Hepatic glucose production (3.1 kg/d) exceeded calculated mammary glucose requirements. Net hepatic removal of L-lactate, alpha-amino N, and NH3N represented 115, 43, and 101%, respectively, of their net absorption by portal-drained viscera. Net hepatic L-lactate and alpha-amino N removal could account maximally for 17.4 and 16.5% of glucose produced.

Ammonia↗
PubMed1986

Cerebrospinal fluid lactate and lactate dehydrogenase activity in the rapid diagnosis of bacterial meningitis.

The value of cerebrospinal fluid (CSF) lactate and lactate dehydrogenase (LD) activity in the rapid diagnosis of meningitis was investigated in three groups of patients--a 'no meningitis', an aseptic meningitis and a bacterial meningitis group. The sensitivity achieved in the detection of bacterial meningitis by CSF lactate values of 2.85 mmol/l (93.8%) and 3.9 mmol/l (89.6%) was greater than that reached by conventional chemical investigations using a CSF protein value of 1 g/l (81.5%) or a CSF glucose value of 2.2 mmol/l (68.8%) as the indicator. The sensitivity of an absolute CSF LD value of 40 U/l (86.3%) in the detection of bacterial meningitis was slightly lower than that of a CSF protein value of 1 g/l (87%) and better than the sensitivity of either a CSF/serum LD ratio of 0.1:1.0 (83.9%) or a CSF glucose level of 2.2 mmol/l (76.3%). As with conventional CSF chemistry, both investigations may give normal values in the presence of bacterial meningitis.

Child↗
PubMed1985

Cerebrospinal fluid lactate and lactate dehydrogenase levels as diagnostic aids in tuberculous meningitis.

The value of cerebrospinal fluid (CSF) lactate and lactate dehydrogenase (LD) values as aids in differentiating tuberculous meningitis (TBM) from aseptic meningitis has been investigated. Using an upper limit of normal for CSF lactate levels of 2,75 mmol/l resulted in detection of 24 out of 26 cases of TBM (a sensitivity of 92%). If, however, a level of 3,85 mmol/l was taken as the upper limit of normal, then 18 out of 26 cases were detected (a sensitivity of 69%). Using 40 U/l as the upper limit of normal for LD levels detected 21 out of 38 cases of TBM (a sensitivity of 55%). Both tests may give normal values in the presence of TBM, but this should not cause specific antituberculosis therapy to be withheld. Neither test appears to hold marked advantages over conventional chemical analysis of CSF in differentiating TBM from aseptic meningitis.

Child↗
PubMed1984

Characterization of apparent lactate dehydrogenase isoenzyme 6: a lactate-independent dehydrogenase.

We found in a prospective study of lactate dehydrogenase isoenzyme 6 (LD6) in human tissues obtained at autopsy that LD6 was usually present in liver when death was preceded by prolonged hypotension or impaired ventilation but not in cases of sudden death. Other organs containing LD6 were kidney and spleen. LD6 is heat stable, differs from H-subunit-containing LD isoenzymes by pyruvate resistance, differs from M-subunit-containing LD isoenzymes by immunoprecipitation, and is distinct from spermatic LDX. LD6 from liver extracts acted without lactate as substrate and could be enhanced by ethanol added to the substrate. These results indicate that LD6 is not a true lactate dehydrogenase, and that it frequently appears in severe liver injury.

Adult↗
PubMed2002

Significance of the initial arterial lactate level and transpulmonary arteriovenous lactate difference after open-heart surgery.

PURPOSE: This study was conducted to determine the clinical significance of the initial lactate level and its transpulmonary difference after open-heart surgery in adult patients. METHODS: The initial postoperative lactate levels were obtained from both radial and pulmonary arteries (La, Lv) in 65 consecutive patients undergoing coronary (n = 46), valve (n = 8), and aortic (n = 11) surgery. We analyzed the relationships between the perioperative factors and La and transpulmonary arteriovenous lactate difference (%La-v = 100(La - Lv)/Lv). RESULTS: La and % La-v were not correlated with the preoperative factors of age, pulmonary function, or emergency surgery. La significantly correlated with the cardiopulmonary bypass time, initial arterial pH, initial PaO2/FiO2, SvO2, O2 consumption, O2 extraction rate, and the peak value of creatine phosphokinase. The %La-v significantly correlated with the aortic cross-clamp time, the lowest rectal temperature, the duration of intubation, and PaO2/FiO2 after extubation. CONCLUSION: La may be an indicator of the invasiveness of the surgery, while %La-v may be a predictor of postoperative pulmonary function. Both La and %La-v, as an initial value in the intensive care unit, may play an important role in planning the postoperative management of patients undergoing open-heart surgery.

Adult↗
PubMed1992

Consummatory behaviors and weight regulation in pregnant, lactating, and pregnant-lactating mice.

Pregnant Rockland-Swiss (R-S) albino mice consumed significantly more food and water and gained significantly more weight between gestation days 8-17 compared to virgin R-S females maintained in isolation for a comparable period. Postpartum (days 1-10) patterns of ingestion and weight change among thelectomized (nipple-deprived) mouse dams provided with young did not differ significantly from those of virgin animals without young. Sham- and nonoperated dams received suckling stimulation from young and consumed about 100% more food than thelectomized or virgin females (Experiment 1). Pregnancy concurrent with lactation does not increase further the hyperphagic response of female mice. Nipple presence is the principle regulator of postpartum hyperphagia in lactating and simultaneously pregnant-lactating mouse dams (Experiment 2).

Animals↗
PubMed2005

Serum leptin and lactational amenorrhea in well-nourished and undernourished lactating women.

OBJECTIVE: To ascertain the possible role of leptin in the resumption of postpartum menstruation in lactating women with differing nutritional statuses. DESIGN: Analysis of data and blood samples collected during a previous prospective study. SETTING: Healthy volunteers in an academic research environment. PATIENT(S): Undernourished (body mass index [BMI]< or =19 kg/m(2)) and well-nourished (BMI> or =26 kg/m(2)) lactating women who resumed regular menstruation before 24 weeks and at or after 24 weeks postpartum. INTERVENTION(S): Venous blood samples at four-weekly intervals and other clinical data collected until resumption of regular menstruation. MAIN OUTCOME MEASURE(S): Serum leptin concentrations. RESULT(S): Leptin concentrations were significantly higher in the well-nourished than in the undernourished women, irrespective of the time of resumption of menstruation. Time of resumption of menstruation did not significantly affect leptin levels within well-nourished and undernourished groups. Leptin significantly correlated with BMI (r = 0.78). The BMI (r = -0.53), but not leptin, was significantly and negatively correlated with the duration of lactational amenorrhea. CONCLUSION(S): Leptin is unlikely to be a major determinant of early resumption of regular menstruation in well-nourished women.

Adult↗