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At least 19 recordsLinked to original sources
PubMed2004

[Effects of lactation, lactation-cessation and lactation-cessation-lactation paradigms on hypothalamic orexin-A immunoreactive neurons in rats].

Orexin-A is a novel neuropeptide produced by neurons mainly located in lateral hypothalamic area that potently facilitates appetite and food intake. The purpose of this study was to investigate the possible change in orexin-A immunoreactivity in suckling-induced hyperphagia. By using immunohistochemistry and image analysis techniques we examined orexin-A-like immunoreactivity in a series of rat brain sections corresponding to the hypothalamus in groups of non-lactating, lactating, lactating with overnight cessation of suckling, lactating and cessation followed by resumed short-term sucklings. Long-term lactation significantly increased daily food intake on day 3 (81%) and day 11 (180%) postpartum compared to that in non-lactating postpartum rats, whereas daily food intake was significantly decreased by overnight cessation of suckling on day 11 postpartum in long-term lactating rats (45%). Moreover, long-term lactating rats on day 12 postpartum exhibited significantly greater number and higher mean staining intensity of orexin-A immunoreactive neurons than those of non-suckling postpartum rats (P<0.001 and P<0.05, respectively). Overnight cessation of lactation in rats on day 12 postpartum significantly decreased both the number and mean staining intensity of orexin-A immunoreactive neurons compared to those in long-term lactating group of rats (P<0.001 and P<0.05, respectively), similar to the levels in the non-lactating postpartum rats. Resumed lactation for 2 and 5 h after overnight cessation of lactation significantly increased the number (P<0.001 and P<0.05, respectively) and mean staining intensity (P<0.05) of orexin-A immunoreactive neurons compared to those in the rats without resumed lactation. Both long-term lactation and short-term resumed suckling enhanced orexin-A immunoreactivity in the hypothalamus in rats, and overnight cessation of lactation down-regulated the increased orexin-A immunoreactivity induced by long-term lactation. Suckling may regulate orexin-A expression in the hypothalamus and the increased orexin-A may be involved in hyperphagia in lactating rats, suggesting the possibility of the existence of some neural-humoral links between suckling and hypothalamic orexin-A-immunoreactive neurons.

Animals↗
PubMed2000

Changes in blood lactate and pyruvate concentrations and the lactate-to-pyruvate ratio during the lactate minimum speed test.

The aim of this study was to assess the responses of blood lactate and pyruvate during the lactate minimum speed test. Ten participants (5 males, 5 females; mean +/- s: age 27.1+/-6.7 years, VO2max 52.0+/-7.9 ml x kg(-1) x min(-1)) completed: (1) the lactate minimum speed test, which involved supramaximal sprint exercise to invoke a metabolic acidosis before the completion of an incremental treadmill test (this results in a 'U-shaped' blood lactate profile with the lactate minimum speed being defined as the minimum point on the curve); (2) a standard incremental exercise test without prior sprint exercise for determination of the lactate threshold; and (3) the sprint exercise followed by a passive recovery. The lactate minimum speed (12.0+/-1.4 km x h(-1)) was significantly slower than running speed at the lactate threshold (12.4+/-1.7 km x h(-1)) (P < 0.05), but there were no significant differences in VO2, heart rate or blood lactate concentration between the lactate minimum speed and running speed at the lactate threshold. During the standard incremental test, blood lactate and the lactate-to-pyruvate ratio increased above baseline values at the same time, with pyruvate increasing above baseline at a higher running speed. The rate of lactate, but not pyruvate, disappearance was increased during exercising recovery (early stages of the lactate minimum speed incremental test) compared with passive recovery. This caused the lactate-to-pyruvate ratio to fall during the early stages of the lactate minimum speed test, to reach a minimum point at a running speed that coincided with the lactate minimum speed and that was similar to the point at which the lactate-to-pyruvate ratio increased above baseline in the standard incremental test. Although these results suggest that the mechanism for blood lactate accumulation at the lactate minimum speed and the lactate threshold may be the same, disruption to normal submaximal exercise metabolism as a result of the preceding sprint exercise, including a three- to five-fold elevation of plasma pyruvate concentration, makes it difficult to interpret the blood lactate response to the lactate minimum speed test. Caution should be exercised in the use of this test for the assessment of endurance capacity.

Adaptation, Physiological↗
PubMed2003

Effect of measuring blood lactate concentrations using different automated lactate analysers on blood lactate transition thresholds.

This study investigated the effect of using three automated blood lactate analysers (Accusport, Lactate Pro, YSI 1500 Sport) on blood lactate transition thresholds (BLTT). Blood lactate concentrations were measured using the three analysers in rowers (n = 17) and kayakers (n = 6) during incremental exercise. The BLTT determined were: 1) ADAPT lactate threshold (data point preceding lactate increase of > or = 0.4 mmol x l(-1)), 2) log-log lactate threshold (point of lactate increase when log lactate plotted against log of relevant exercise parameter), 3) DMAX anaerobic threshold, 4) ADAPT anaerobic threshold (modified DMAX method), 5) Onset of blood lactate accumulation (OBLA, fixed blood lactate concentration of 4 mmol x l(-1)). Measurements of blood lactate concentration differed between analysers (p < 0.0001), resulting in BLTT differing between analysers when expressed as a blood lactate concentration (p < 0.0001), or when the BLTT was defined as a fixed blood lactate concentration (e.g. OBLA) (p < 0.0001). When expressed as a power output or heart rate using BLTT based on relative changes in lactate concentration (log-log, ADAPT and DMAX thresholds) the values were similar between analysers (p > 0.05), except the Accusport provided higher values for the log-log lactate threshold (p < 0.0001). We concluded that, despite providing significantly different lactate concentrations, unless the Accusport was used to determine the log-log lactate threshold, or values were expressed as a blood lactate concentration, the use of different analysers had little effect on the BLTT.

Adult↗
PubMed1999

Role of mitochondrial lactate dehydrogenase and lactate oxidation in the intracellular lactate shuttle.

To evaluate the potential role of mitochondrial lactate dehydrogenase (LDH) in tissue lactate clearance and oxidation in vivo, isolated rat liver, cardiac, and skeletal muscle mitochondria were incubated with lactate, pyruvate, glutamate, and succinate. As well, alpha-cyano-4-hydroxycinnamate (CINN), a known monocarboxylate transport inhibitor, and oxamate, a known LDH inhibitor were used. Mitochondria readily oxidized pyruvate and lactate, with similar state 3 and 4 respiratory rates, respiratory control (state 3/state 4), and ADP/O ratios. With lactate or pyruvate as substrates, alpha-cyano-4-hydroxycinnamate blocked the respiratory response to added ADP, but the block was bypassed by addition of glutamate (complex I-linked) and succinate (complex II-linked) substrates. Oxamate increased pyruvate (approximately 10-40%), but blocked lactate oxidation. Gel electrophoresis and electron microscopy indicated LDH isoenzyme distribution patterns to display tissue specificity, but the LDH isoenzyme patterns in isolated mitochondria were distinct from those in surrounding cell compartments. In heart, LDH-1 (H4) was concentrated in mitochondria whereas LDH-5 (M4) was present in both mitochondria and surrounding cytosol and organelles. LDH-5 predominated in liver but was more abundant in mitochondria than elsewhere. Because lactate exceeds cytosolic pyruvate concentration by an order of magnitude, we conclude that lactate is the predominant monocarboxylate oxidized by mitochondria in vivo. Mammalian liver and striated muscle mitochondria can oxidize exogenous lactate because of an internal LDH pool that facilitates lactate oxidation.

Animals↗
PubMed1988

Studies in human lactation: milk volumes in lactating women during the onset of lactation and full lactation.

After validation of test-weighing procedures milk volumes produced by 13 multiparous Caucasian women were followed longitudinally through the first year of lactation. All practiced exclusive breast-feeding for at least 5 mo. Milk transfer to the infant was low on days 1 and 2 and increased rapidly to 498 +/- 129 g/d (means +/- SD) on day 5 and then more slowly to 753 +/- 89 g/d during months 3-5. There was a characteristic milk volume for each mother-infant pair that was significantly related neither to milk yield on days 4-6 nor to birth weight. It was, however, strongly related to infant weight at 1 mo, suggesting that infant and/or maternal factors coming into play during the first month of life are strong determinants of subsequent milk transfer to the infant.

Adult↗
PubMed1993

Presence of lactate dehydrogenase and lactate racemase in Megasphaera elsdenii grown on glucose or lactate.

Activity of D-lactate dehydrogenase (D-LDH) was shown not only in cell extracts from Megasphaera elsdenii grown on DL-lactate, but also in cell extracts from glucose-grown cells, although glucose-grown cells contained approximately half as much D-LDH as DL-lactate-grown cells. This indicates that the D-LDH of M. elsdenii is a constitutive enzyme. However, lactate racemase (LR) activity was present in DL-lactate-grown cells, but was not detected in glucose-grown cells, suggesting that LR is induced by lactate. Acetate, propionate, and butyrate were produced similarly from both D- and L-lactate, indicating that LR can be induced by both D- and L-lactate. These results suggest that the primary reason for the inability of M. elsdenii to produce propionate from glucose is that cells fermenting glucose do not synthesize LR, which is induced by lactate.

Acetates↗
PubMed1993

Oxidation of D-lactate and L-lactate by Neisseria meningitidis: purification and cloning of meningococcal D-lactate dehydrogenase.

Neisseria meningitidis was found to contain at least two lactate-oxidizing enzymes. One of these was purified 460-fold from spheroplast membranes and found to be specific primarily for D-lactate, with low-affinity activity for L-lactate. The gene for this enzyme (dld) was cloned, and a dld mutant was constructed by insertional inactivation of the gene. The mutant was unable to grow on D-lactate but retained the ability to grow on L-lactate, providing evidence for a second lactate-oxidizing enzyme with specificity for L-lactate. High-affinity L-lactate-oxidizing activity was detected in intact bacteria of both the dld+ and dld mutant strains. This L-lactate-oxidizing activity was also seen in sonicated bacteria but was reduced substantially on detergent solubilization or on preparation of spheroplast membranes.

Amino Acid Sequence↗
PubMed1991

Energy cost of lactation, and energy balances of well-nourished Dutch lactating women: reappraisal of the extra energy requirements of lactation.

At 9 wk postpartum the difference in energy intake of 40 lactating (2440 +/- 430 kcal/d) and 16 nonlactating women (1680 +/- 400 kcal/d) was 760 kcal/d but decreased to 550 kcal/d when adjusted for habitual intakes and body weight. Energy cost of lactation amounted to 650 kcal/d (breast-milk production, 745 +/- 130 g/d). When compared with nonlactating counterparts, the lactating women mainly achieved energy balance by eating more. Sixteen of the 40 lactating women were also studied at 56 wk. Their cost of lactation at 5-13 wk was 630 kcal/d (breast-milk production, 720 +/- 124 g/d); these women met their energy cost of lactation by eating more (415 kcal/d); by tissue mobilization (35 kcal/d), and by reducing energy expenditure (180 kcal/d). The present study helps in the understanding of how well-nourished women with an adequate lactational performance may cope in everyday life with the energy stress of lactation, and suggests that current recommendations of energy needs during lactation are too high.

Adipose Tissue↗
PubMed1995

[Lactate-guanidinium and lactate-lactate weak interactions in aqueous solutions].

Spectropolarimetry was used to quantify the guanidinium-lactate and lactate-lactate equilibrium reactions. Association constants for the guanidinium-lactate and lactate-lactate formations are 6.11 and 1.12, respectively, in aqueous solution. The value 6.11 is certainly high among electrostatic interactions in water. This stability, however, can not account for the extremely strong lactate-protein binding, observed by NMR spectroscopy. The molar rotation coefficients for both the heteroassociation and homoassociation complexes are also calculated. The homoassociative lactate-lactate binding is the first such interaction, whose constant has been determined by spectropolarimetry in aqueous solution.

Guanidine↗
PubMed1986

Inhibition of lactate removal by ketone bodies in rat liver. Evidence for a quantitatively important role of the plasma membrane lactate transporter in lactate metabolism.

We studied the effect of DL-3-hydroxybutyrate and acetoacetate on lactate transport into isolated hepatocytes and on lactate removal in the isolated perfused rat liver. Ketone bodies inhibited lactate transport into isolated hepatocytes (maximum, 35% at concentrations of 10-20 mM). Lactate removal and glucose production by perfused livers were examined before and after the introduction of a constant infusion of hydroxybutyrate, acetoacetate, or appropriate control into the portal venous limb. Lactate removal was significantly inhibited within 10 s of the appearance of increasing concentrations of ketone bodies in the effluent. Corresponding decreases in glucose production were observed. The dependence of inhibition on D-3-hydroxybutyrate concentration was documented in isolated perfused livers (maximum inhibition of lactate removal, 58% at 14 mM). This phenomenon could be a factor in the development of lactic acidosis accompanying ketoacidosis, and indicates that plasma membrane lactate transport may determine the rate of hepatic lactate removal.

3-Hydroxybutyric Acid↗
PubMed1989

[Characterization of the pathology of lactating cows based on the level of lactation. Principal factors in the variation and typing of pathologic profiles of lactation].

The health disturbances investigated were observed during a long-term trial (six years) conducted at an experimental station located at 1,100 m elevation. The study dealt with 487 lactations involving 190 cows of the Montbéliarde and French Friesian breeds, which produced on average 4,200 kg milk per lactation. The disturbances concerned 59% of monitored lactations, with a mean incidence of 2.1 disturbances per lactation. Lameness and mastitis accounted respectively for 52 and 24% of the clinical affections. Pathology was significantly influenced by breed, basic diet (hay or grass silage), concentrate quantities, lactation rank and year. The authors describe a method permitting an independent analysis of the effects of lactation stage and of season on mastitis and lameness frequency, by limiting the biases due to grouping of calvings and to culling. The study of lactations affected by several pathological disturbances shows that the different types of affections recorded are mutually independent but that successive occurrences of the same affection are not. On the basis of these results, the authors have proposed to globally characterize the "pathological profiles" of lactations.

Animals↗
PubMed2006

Lactate production yield from engineered yeasts is dependent from the host background, the lactate dehydrogenase source and the lactate export.

BACKGROUND: Metabolic pathway manipulation for improving the properties and the productivity of microorganisms is becoming a well established concept. For the production of important metabolites, but also for a better understanding of the fundamentals of cell biology, detailed studies are required. In this work we analysed the lactate production from metabolic engineered Saccharomyces cerevisiae cells expressing a heterologous lactate dehydrogenase (LDH) gene. The LDH gene expression in a budding yeast cell introduces a novel and alternative pathway for the NAD+ regeneration, allowing a direct reduction of the intracellular pyruvate to lactate, leading to a simultaneous accumulation of lactate and ethanol. RESULTS: Four different S. cerevisiae strains were transformed with six different wild type and one mutagenised LDH genes, in combination or not with the over-expression of a lactate transporter. The resulting yield values (grams of lactate produced per grams of glucose consumed) varied from as low as 0,0008 to as high as 0.52 g g-1. In this respect, and to the best of our knowledge, higher redirections of the glycolysis flux have never been obtained before without any disruption and/or limitation of the competing biochemical pathways. CONCLUSION: In the present work it is shown that the redirection of the pathway towards the lactate production can be strongly modulated by the genetic background of the host cell, by the source of the heterologous Ldh enzyme, by improving its biochemical properties as well as by modulating the export of lactate in the culture media.

Journal Article↗
PubMed1981

In-vitro uptake and metabolism of [3H] corticosterone by mammary glands from pregnant, lactating, and post-lactational rats and by parametrial adipose tissue from lactating rats.

The study was designed to determine the influence of the physiological state on the in-vitro uptake and metabolism of glucocorticoid hormone by the mammary gland. [3H] Corticosterone was accordingly incubated with minced mammary glands from pregnant, lactating and post-lactational rats. The total uptake of [3H] corticosteroid was obtained from the concentration of radioactivity by the tissue and the specific activity of the steroid substrate. The extent of 21-acylation was determined as the percentage of the radioactivity in the chromatographed tissue extracts attributable to 21-acyl-[3H] corticosterone. The results indicated that the uptake of [3H] corticosteroid increased with advancing pregnancy, attained a high plateau level during lactation, and steadily declined during the post-lactational period. The extent of 21-acylation of [3H] corticosterone varied from 10 to 40%, fluctuating widely in all physiological states, particularly during the post-lactational period. It was inferred that the stromal elements, presumably the adipocytes, of the mammary gland can also acylate the corticosteroid hormone, a view which gained experimental support from similar studies with minced parametrial adipose tissue from lactating rats.

Acylation↗
PubMed1979

Lactate-to-pyruvate or pyruvate-to-lactate assay for lactate dehydrogenase: a re-examination.

The pyruvate-to-lactate assay for determining lactate dehydrogenase (EC 1.1.1.27) can now yield linearity equal to or better than that obtained by the lactate-to-pyruvate assay. In addition, there are significant advantages to the pyruvate-to-lactate reaction: (a) a greater change in absorbance per unit time, which allows more accurate spectrophotometric readout; (b) lower reactant concentrations are required, which substantially reduces the cost per assay; (c) solid reagents are used to prepare the assay solution; and (d) reagent solutions are more stable. However, impurities present in commercial NADH preparations may substantially affect measured lactated dehydrogenase activities; therefore, a Standard Reference Material for NADH is being developed for issuance by the National Bureau of Standards.

L-Lactate Dehydrogenase↗
PubMed1978

Optimal conditions and comparison of lactate dehydrogenase catalysis of the lactate-to-pyruvate and pyruvate-to-lactate reactions in human serum at 25, 30, and 37 degrees C.

We report optimal conditions for assaying highly purified human lactate dehydrogenase isoenzymes with the lactate-to-pyruvate and pyruvate-to-lactate reactions, as they apply to human serum. Interconversion of results between reactions is not practicable. Measurements of lactate dehydrogenase in either reaction direction at 25, 30, or 37 degrees C can be equally reliable if the volume fraction and the resulting deltaA/min is small. However, for interinstrument and interlaboratory comparisons, results from the lactate-to-pyruvate reaction are more reliable.

Buffers↗
PubMed1977

Optimal conditions for assaying human lactate dehydrogenase by the lactate-to-pyruvate reaction: Arrhenium relationships for lactate dehydrogenase isoenzymes 1 and 5.

Optimal reaction conditions to sassay human lactate dehydrogenase (lactate-to-pyruvate) were established for isoenzymes 1 and 5 at 25, 30, and 37 degrees C in diethanolamine and 2-amino-2-methyl-1,3-propanediol. Different substrate concentrations are required at each temperature. The conditions permit measurement of lactate dehydrogenase 1 and 5 with the lowest substrate concentrations that allow for the highest equal sustainable efficiency in measuring both isoenzymes. About 95% of each isoenzyme activity is measured if the assay is performed within the first minute after the reaction is initiated even for activities as high as triple the upper limit of normal. The Arrhenius relationship is different for each isoenzyme, but results obtained for each at one temperature can be compared with results at another temperature by use of simple conversion equations. Assays at 25 and 30 degrees C are more economical and less variable than assays at 37 degrees C.

Buffers↗
PubMed1993

[The energy and nitrogen metabolism of pregnant and lactating sows and suckling piglets. 1. Experimental plan and results concerning the live weight development of pregnant, non-pregnant and lactating sows and the reproductive performance during gestation and lactation].

The aim of the experiments was to work out new results for a factorial derivation of energy and protein requirement. The experiments were carried out according to a 3 x 3 factorial experimental plan with 3 variants of litter number (1, 2 and 4, age of sows) and 3 variants of energy supply (120, 100 and 80% of the norm of pregnancy, continued in lactation with 80, 100 and 120%). Methods of the indirect calorimetry and the slaughtering technique were used. The mean cumulative live weight changes of the sows for the 9 experimental variants amounted from 13.1 to 63.2 kg for the 115 days of pregnancy and from -17.0 to 6.8 kg for the first 26 days of lactation. The chosen variation of energy supply of pregnant and lactating sows had no relevant effect on the reproductive performances, measured by litter size, weight of conception products, litter weight at birth and the quantity of milk per sow and day respectively. In comparison with the sows of litter number 1 the sows of litter number 2 and 4 had higher litter weights at birth and higher milk quantities.

Amino Acids↗
PubMed1996

[O2 sensitive L-lactate biosensors with enzyme membranes based on L-lactate-2-monooxygenase and L-lactate-oxidase with electroanalytic comparison].

O2-sensitive biosensors using oxidase membranes have acquired considerable electro-analytical importance. Since some of these O2-converting enzymes also produce H2O2, the use of additive reagents for the O2-free breakdown of the H2O2 in the second reaction has repeatedly been reported. In contrast to L-lactate oxidase, L-lactate-2-monooxygenase converts its substrate without producing H2O2. Employing reference sera, tests with L-lactate showed that bioelectrochemical membrane electrodes with H2O2-producing enzymes of high purity, require no additive reagents to ensure reliable analysis. Continuous measurements with citrated blood using the principle of intermediate carrier analysis are demonstrated.

Biosensing Techniques↗