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PubMed1988

Intracellular pH recovery and lactate efflux in mouse soleus muscles stimulated in vitro: the involvement of sodium/proton exchange and a lactate carrier.

The intracellular pH recovery after stimulation of mouse soleus muscles in vitro was studied by means of intracellular pH-sensitive microelectrodes. The lactate efflux and the total lactate content were measured by means of an enzymic method. During electrical stimulation for 2 min in a CO2/HCO3- -buffered Ringer's solution, pHi decreased by 0.5 units. The rate of pHi-recovery was independent of external bicarbonate, but dependent on the buffer concentration. The rate of intracellular pH recovery was reduced by the lactate transport inhibitors PCMBS and cinnamate, whereas the inhibitors of inorganic anion-exchange SITS and DIDS had no effect. The Na+/H+ exchange inhibitor amiloride reduced the rate of pHi recovery. The pHi recovery was faster than the lactate efflux, which could be accounted for by an Na+/H+ exchange. A number of inhibitor compounds were used in order to discriminate between the three possible lactate efflux pathways: the monocarboxylate carrier mechanism, the inorganic anion exchange, and the molecular (non-ionic) diffusion of lactic acid. The lactate efflux was partly inhibited by cinnamate, PCMBS and phloretin, but was unaffected by DIDS and tetrathionate. These experiments demonstrate the existence of a lactate carrier in mammalian skeletal muscles. The lactate carrier is responsible for more than half of the lactate efflux after muscle activity. Both the pHi recovery studies and the lactate efflux measurements showed that, under the given conditions, the inorganic anion-exchange mechanism is not essentially involved in the recovery processes after muscle activity.

Amiloride↗
PubMed1983

Endurance training affects lactate clearance, not lactate production.

Primed-continuous infusion of [2-3H]- and [U-14C]lactate was used to study the effects of endurance training (running 2 h/day at 29.4 m/min up a 15% gradient) on lactate metabolism in rats. Measurements were made under three metabolic conditions: rest (Re), easy exercise (EE, 13.4 m/min, 1% gradient) and hard exercise (HE, 26.8 m/min, 1% gradient). Blood lactate levels in trained animals increased from 1.0 +/- 0.09 mM in Re to 1.64 +/- 0.21 in EE and 2.66 +/- 0.38 in HE. Control animals also demonstrated an increase in blood lactate with increasing work rate, but values were 1.93 +/- 0.21 and 4.62 +/- 0.57 mM at EE and HE, respectively. Lactate turnover rates (RtLA) measured with [U-14C]lactate increased from 214.0 +/- 17.0 mumol.kg-1.min-1 in Re to 390.3 +/- 31.6 in EE and 518.1 +/- 56.4 in HE. No significant differences in RtLA were observed between controls and trained animals under any condition. Identical relationships between RtLA and exercise or training were obtained with [2-3H]lactate; however, the values obtained were consistently 90% higher than those observed with [U-14C]lactate. Metabolic clearance rate (MCR) for 14C was not significantly different in Re between controls and trained animals (180.6 +/- 27.7 ml.kg-1.min-1). Metabolic clearance of lactate in trained animals was 37 and 107% greater than in controls during EE and HE, respectively. Results indicate that the effect of endurance training is not on production of lactate but on its clearance from the blood.

Animals↗
PubMed1981

Myocardial lactate metabolism: evidence of lactate release during net chemical extraction in man.

Myocardial blood flow has been recognized to be heterogeneous in patients with coronary artery disease. Traditional arterial-coronary sinus sampling methods cannot demonstrate comparable heterogeneity of myocardial metabolism. In this study we used a tracer technique to investigate possible heterogeneity of myocardial lactate metabolism. Twenty-one patients with symptoms of ischemic heart disease were studied. We injected 14C-1-lactate intravenously as a constant infusion after a priming dose. Coronary sinus and arterial samples were obtained for chemical and radioisotopic analyses. At rest, myocardial lactate extraction by chemical analysis was 24.6 +/- 8.5% (mean +/- SD). By radioisotopic analysis, the lactate extraction was 41.0 +/- 10.2% (p less than 0.001). Thus, certain areas of the myocardium were releasing lactate despite global net extraction of lactate. In the 12 patients with significant left main or both left anterior descending (LAD) and left circumflex (LCX) lesions, the calculated amount of lactate released at rest was 0.136 +/- 0.045 mumol/ml of blood (mean +/- SD). In contrast, the amount released in the six patients with a significant lesion in only the LAD or LCX was 0.076 +/- 0.019 mumol/ml, and in the three patients without left coronary arterial lesions it was 0.039 +/- 0.004 mumol/ml. Using a tracer method, myocardial lactate metabolism was demonstrated to be heterogeneous at rest in patients with ischemic heart disease. A significant amount of lactate can be released by the myocardium at a time when chemical arterial-coronary sinus analysis indicates global myocardial extraction. The amount of lactate released appears to be related to the severity of the coronary artery disease.

Adult↗
PubMed1992

Effects of sodium lactate infusion on cisternal lactate and carbon dioxide levels in nonhuman primates.

OBJECTIVE: To further the understanding of lactate-induced panic in patients with panic disorder, the authors examined cisternal lactate and carbon dioxide levels in nonhuman primates after infusions of sodium lactate comparable to those used in studies of human beings. METHOD: CSF and venous blood lactate, pH, PCO2, PO2, and bicarbonate were measured in five ketamine-anesthetized nonhuman primates, without mechanical ventilation, before and after they underwent infusions of sodium lactate. In addition, the same measurements were made for three of the five subjects who were given saline infusions. RESULTS: Despite the development of the characteristic peripheral biochemical effects of infused sodium lactate--increased lactate and bicarbonate levels and metabolic alkalosis--no increases in central lactate or carbon dioxide levels were observed. Saline infusions produced no biochemical effects on venous and cisternal measures. CONCLUSIONS: The results of this study are in keeping with previous findings of nonpermeability of the blood-brain barrier to anionic compounds such as lactate. They therefore support theories of lactate panic based on cognitive and/or brainstem misevaluation of peripheral somatic sensations.

Animals↗
PubMed1986

Effects of lactation and season on plasma prolactin concentrations and response to bromocriptine during lactation in the Bennett's wallaby (Macropus rufogriseus rufogriseus).

Prolactin concentration was measured in plasma collected each week for 13 months from lactating and non-lactating Bennett's wallabies (Macropus rufogriseus rufogriseus). In non-lactating animals, prolactin concentrations decreased towards the end of the study but such changes did not appear to fit a seasonal pattern. Prolactin concentrations were low during early lactation and at a similar level to non-lactating animals, increased significantly during late pouch life (February-May), and then returned to non-lactating levels at a time coincident with permanent exit of the joey from the pouch. Temporary removal of joeys from their mothers in April was followed by a rapid decline in prolactin concentrations which remained low for 24 h until the joey was returned to its mother, whereupon prolactin concentrations increased significantly within 2 h. The effect of a single injection of bromocriptine (5 mg/kg) on lactation, embryonic diapause and plasma prolactin concentrations was examined at two stages of lactation. In November (lactational diapause), bromocriptine had no effect on prolactin concentrations but two out of four suckling joeys died on days 13 and 14 after treatment, and three out of four females gave birth on days 27, 27 and 28. Bromocriptine treatment in April (seasonal diapause) was followed by a significant reduction in prolactin concentrations and reduced growth rate of joeys belonging to treated females. New births were not observed. In view of the effect of bromocriptine on plasma prolactin concentrations in late lactation and the demonstration that domperidone (a dopamine antagonist) significantly increases plasma prolactin concentrations, it would seem that dopamine can act as a prolactin inhibitory hormone in this as in other mammalian species.

Animals↗
PubMed2002

Ovarian structures and circulating steroids in heifers and lactating cows in summer and lactating and dry cows in winter.

Two experiments compared follicular and luteal development and circulating steroid concentrations from induced luteolysis to ovulation in lactating Holstein cows (n = 27; 40.0 +/- 1.5 kg milk/day) vs. nulliparous heifers (n = 28; 11 to 17 mo-old) during summer (Experiment 1), and in lactating (n = 27; 45.9 +/- 1.4 kg milk/d) vs. dry cows (n = 26) during winter (experiment 2). All females received PGF2,, 6 d after ovulation and were monitored until next ovulation by daily ultrasound and assay of serum progesterone (P4) and estradiol (E2). Every female was used two or three times. In Experiment 1, lactating cows had high incidence of multiple ovulation (63.5%) compared with heifers (1.3%). Among single ovulators, there was no difference in maximal size of ovulatory follicles between lactating cows and heifers (15.8 vs. 16.5 mm, respectively). However, lactating cows had lower peak serum E2 (8.6 vs. 12.1 pg/ml), took longer to ovulate after luteolysis (4.6 vs. 3.8 d), developed more luteal tissue volume (7,293.6 vs. 5,515.2 mm3), and had lower serum P4 on d 6 after ovulation (2.0 vs. 3.0 ng/ml) than heifers (data included multiple ovulators). In experiment 2, multiple ovulations were similar between lactating and dry cows (17.9 vs. 17.2%, respectively). Peak serum E2 was also similar between lactating and dry cows (7.6 vs. 8.5 pg/ml) although lactating cows had larger ovulatory follicles (18.6 vs. 16.2 +/- 0.4 mm). Lactating cows took longer to ovulate (4.8 vs. 4.2 d), developed more luteal tissue (7,599 vs. 5,139 +/- 468 mm3), but had similar serum P4 (2.2 vs. 1.9 ng/ ml) compared with dry cows. Therefore, lactating cows had similar or lower circulating steroid concentrations than dry cows or heifers, respectively, despite having larger ovarian structures.

Animals↗
PubMed1985

Three or two times daily milking of older cows and first lactation cows for entire lactations.

Thirty-eight older (second and greater lactation) and 15 Holstein cows in first lactation were in a full lactation (44 wk) study to evaluate the effect of either twice or three times daily milking on yield of milk and milk components, milk composition, feed intake, and body weight change. All cows were managed alike and were fed diets of high, medium, and low energy concentration as lactation progressed from calving to 44 wk. First lactation cows were switched from diets of high energy to lower energy at the same milk production as lactation advanced. Dietary changes for older cows milked twice and three times (A) were at similar production, whereas three times (B) cows were switched to lower energy at higher milk production. Older cows milked three times daily (A and B) produced 17 and 13% more milk over the entire lactation than cows milked twice daily. Dry matter and energy intakes were not affected by three times milking, but gain of body weight was reduced. Cows milked three times daily during their first lactation produced 6% more milk than their twice counterparts, although this increase was not significant. Dry matter and energy intakes were not affected by three times daily milking, but three times milking of first lactation cows reduced weight gain over the lactation. Reproductive performance of cows milked three times daily was not significantly different from cows milked twice daily. Herds milking three times will require high management of nutrition and reproduction.

Animals↗
PubMed1997

Relationship of yield during early lactation and days open during current lactation with 305-day yield.

To measure and to partition the effect of pregnancy on yield, the relationships among milk, fat, and protein yields during early lactation, current days open, and 305-d yields were investigated using sample day records of 247,310 Holstein cows. The model included fixed effects of calving herd-year-season, calving age, and days open; the continuous variable of early cumulative yield to 80, 100, 120, or 140 d; and a random residual effect. As days open during first lactation increased from 30 to 100 d, 305-d milk yield increased by 876 kg; as days open increased from 100 to 200 d, milk yield increased by only 172 kg. The impact of current days open was greater on second lactation than on first; the difference in 305-d milk yield between cows open 40 and 290 d was 1199 kg for first lactation and 1613 kg for second lactation. If early yield to 120 d was included in the model, the corresponding difference was reduced to 860 kg for first lactation and 1001 kg for second lactation. Inclusion of early yield in the model reduced regression coefficients for days open during first lactation by 22% for 80-d yield, 24% for 100-d yield, 27% for 120-d yield, and 30% for 140-d yield and by 31, 35, 38, and 41%, respectively, for second lactation. Statistical models to derive adjustment factors should account for early lactation yield so that those factors can remove effects of pregnancy but not correlations between yield and fertility caused by early yield.

Animals↗
PubMed1981

Cyclic AMP regulation of lactate dehydrogenase. Quantitation of lactate dehydrogenase M-subunit messenger RNA in isoproterenol-and N6,O2'-dibutyryl cyclic AMP-stimulated rat C6 glioma cells by hybridization analysis using a cloned cDNA probe.

We have cloned DNA complementary to mRNA coding for rat C6 glioma cell lactate dehydrogenase M-subunit. Double-stranded DNA complementary to a portion of lactate dehydrogenase mRNA was inserted into the Pst I site of plasmid pBR322 by the dC.dG tailing technique and amplified in Escherichia coli HB101. A recombinant plasmid containing lactate dehydrogenase cDNA was identified by colony hybridization to a cDNA prepared from partially purified lactate dehydrogenase mRNA and by hybridization-selected translation. The recombinant plasmid (pRLD42) contains a 680 nucleotide insert of lactate dehydrogenase mRNA. Hybridization of nick-translation pRLD42 to glioma cell poly(A)+RNA separated on agarose gel and transferred to nitrocellulose exhibited Mr = 5.9 X 10(5) for lactate dehydrogenase mRNA. Furthermore, Northern blot analysis of RNA from unstimulated and isoproterenol-stimulated glioma cells indicated a 2-fold increase of lactate dehydrogenase mRNA molecules in stimulated cells. The 2-fold increase of lactate dehydrogenase mRNA was confirmed by RNA-excess kinetic hybridization using pRLD42 DNA and poly(A)+RNA from unstimulated, isoproterenol-, and dibutyryl cAMP-stimulated glioma cells. These data demonstrate that isoproterenol and dibutyryl cAMP cause an increase of the number of lactate dehydrogenase M-subunit mRNA molecules in glioma cells which, in part, determines the extent of synthesis of the lactate dehydrogenase M-subunit.

Animals↗
PubMed1997

Effects of antimicrobial treatment at the end of lactation on milk yield, somatic cell count, and incidence of clinical mastitis during the subsequent lactation in a dairy herd with a low prevalence of contagious mastitis.

OBJECTIVE: To determine whether treating cows with antimicrobials at the end of lactation would lower the incidence of clinical mastitis, improve milk production, and decrease somatic cell count (SCC) in the subsequent lactation. DESIGN: Randomized blind field trial. ANIMALS: 233 Holstein cows from a single herd. All cows were in lactation 2 or greater. PROCEDURE: Cows were randomly assigned to treatment groups. Treated cows were given procaine penicillin G and novobiocin by intramammary infusion. Control cows were not treated. Farm personnel recorded cases of clinical mastitis. Milk yield and SCC were recorded during the subsequent lactation. RESULTS: Treatment did not significantly reduce the incidence of clinical mastitis when data for all cows were grouped or when data were stratified by lactation groups (lactation 2 vs lactation > or = 3) or by last SCC (< or = 500,000 cells/ml vs > 500,000 cells/ml). Somatic cell counts (first, mean of first 5, maximum of first 5) for treated and control cows were similar, and proportions of treated and control cows with SCC > 500,000 cells/ml at least once were not significantly different. Treated cows produced 179 kg (394 lb) more milk during the first 17 weeks of lactation than did control cows. CLINICAL IMPLICATIONS: Treating cows with antimicrobials at the end of lactation increased 17-week milk production during the subsequent lactation and, at current milk prices, was financially preferable to not treating them.

Analysis of Variance↗
PubMed1996

Lactate metabolism and regional lactate exchange after cardiac surgery.

Tissue perfusion is at risk during cardiac surgery and in the immediate postoperative period. The association of low blood flow with metabolic acidosis and accumulation of lactate perioperatively has been well established. With the improvements in cardiopulmonary bypass and overall hemodynamic management, severe peri- and postoperative hypoperfusion has become rare. Despite the rarity of severe postoperative complications, several lines of evidence suggest that episodes of less severe hypoperfusion and borderline tissue oxygenation are relatively common, although generally well tolerated. Measurement of blood lactate levels is widely used to assess the adequacy of tissue perfusion. The interpretation of elevated blood lactate levels is limited by several confounding variables. Acute changes in acid-base balance, interorgan substrate flux, peripheral and visceral tissue perfusion, and hepatic lactate uptake will all influence blood lactate levels and may occur during and after cardiac surgery. Peri- and postoperative hyperlactatemia are rare occurrences and their presence may indicate inadequate tissue perfusion. Based on regional blood flow and lactate exchange measurements, we suggest that hyperlactatemia after cardiac surgery is a sign of inadequate or marginal tissue perfusion of the hepatosplanchnic region, as well as other tissues. In this article we briefly review: a) the normal physiology of lactate metabolism and the various causes of hyperlactatemia; b) studies on lactate levels during and after cardiac surgery; c) the evidence of insufficient or marginal tissue perfusion peri- and postoperatively; and d) the pathophysiology of postoperative increases in blood lactate based on regional lactate kinetics.

Blood Circulation↗
PubMed1991

D-lactate dehydrogenase is a member of the D-isomer-specific 2-hydroxyacid dehydrogenase family. Cloning, sequencing, and expression in Escherichia coli of the D-lactate dehydrogenase gene of Lactobacillus plantarum.

The gene encoding D-lactate dehydrogenase (D-lactate: NAD+ oxidoreductase, EC 1.1.1.28) of Lactobacillus plantarum has been sequenced, and expressed in Escherichia coli cells with an inducible expression plasmid, in which the 5'-noncoding region of the gene was replaced with the tac promoter. Comparison of the sequence of D-lactate dehydrogenase with L-lactate dehydrogenases, including the L. plantarum L-lactate dehydrogenase, showed no significant homology. In contrast, the D-lactate dehydrogenase is homologous to E. coli D-3-phosphoglycerate dehydrogenase and Lactobacillus casei D-2-hydroxyisocaproate dehydrogenase. This indicates that D-lactate dehydrogenase is a member of a new family of 2-hydroxyacid dehydrogenases recently proposed, being distinct from L-lactate dehydrogenase and L-malate dehydrogenase, and strongly suggests that the new family consists of D-isomer-stereospecific enzymes. In the reductive reaction, the enzyme showed a broad substrate specificity, although pyruvate was the most favorable of all 2-ketocarboxylic acids tested. In particular, hydroxypyruvate is effectively reduced by the enzyme, the reaction rate, and Km value being comparable to those in the case of pyruvate, indicating that the enzyme has not only D-lactate dehydrogenase activity but also D-glycerate dehydrogenase activity. The conserved residues in this family appear to be the residues involved in the substrate binding and the catalytic reaction, and thus to be targets for site-directed mutagenesis.

Alcohol Oxidoreductases↗
PubMed1989

Metabolism of D lactate in patients receiving hypertonic sodium lactate solution.

The use of hypertonic saline solutions for resuscitation of patients with a decreased extracellular fluid volume is generating more clinical interest. One of the solutions, hypertonic lactated Ringer's solution (HLS), contains lactate in both the D(-) and L(+) forms. Because humans lack D lactate dehydrogenase, the metabolism of D lactate in patients receiving large amounts of lactate in a clinical setting was examined. Three patients undergoing extensive aortic surgical procedures and receiving HLS for replacement of perioperative fluid loss were studied. These patients were given an average of 27 grams of D lactate in a 24 hour period and excreted 8 per cent of the total dose in the urine. The average maximum elevation of D lactate in the serum of 3.53 millimoles per liter. Pharmacokinetic analysis revealed a half-life of D lactate in the serum of 36.4 minutes. The volume of distribution was 20 per cent of the body weight. These results demonstrate that D lactate is metabolized rapidly even when given in large amounts to humans during the perioperative period. Whether or not this metabolism occurs during hypoperfusion is not known.

Aorta↗
PubMedDate not supplied

[Lactate level in the tissues of animals with a tumor administered oxythiamine and the properties of lactate dehydrogenase].

Content of lactate in blood, liver and kidney tissues, skeletal muscle and in tumor tissue as well as some properties of lactate dehydrogenase (LDH), isolated from liver tissue, were studied in three groups of rats - intact rats, the tumor-bearing animals with sarcoma S-45 and the tumor-bearing rats treated with hydroxythiamin within 22 days. In skeletal muscle on the side of the tumor localization content of lactate was decreased as compared with the opposite side of the body. As shown by analysis of correlation between the content of lactate and the tumor weight and the lactate concentration in the tumor-bearing rat tissues studied, the tumor appears to be responsible for consumption but not for production of lactate. Hydroxythiamin altered distinctly the ratio of lactate content in various tissues and normalized the liver tissue LDH isoenzyme spectrum in tumor-bearing rats; the vitamin decreased 9- and 15-fold the enzyme specific activity in oxidation of lactate in presence of NAD+ and NADP, respectively. After the hydroxythiamin treatment the apparent KM value of the enzyme, isolated from the tumor-bearing rat liver tissue, was increased with pyruvate and decreased with lactate as substrate.

Animals↗
PubMed1987

Influence of lactation and pregnancy + lactation on mechanical properties and mineral content of the rat femur.

The quality of bone was assessed from femurs of rats both during lactation and after pregnancy + lactation. Mechanical properties of stiffness, strength, toughness, and ductility were measured, along with standard measurements of dry weight, ash weight, and total bone mineral. No changes occurred during the first week of lactation. During the second and third weeks of lactation all bone parameters except ductility decreased significantly. These data are consistent with bone losing mineral in order to supplement the dietary calcium intake necessary for milk production. In other experiments, femurs were collected from nulliparous rats and from rats that had previously undergone 1-3 pregnancy + lactations. The largest changes in bone mineral and mechanical properties occurred after a single pregnancy + lactation period, although significant further decreases in stiffness and strength occurred after the second pregnancy + lactation. No additional losses occurred following the third pregnancy + lactation. Even 5 months after only one pregnancy + lactation period, the bone quality was still impaired as all bone properties were lower than in nulliparous controls. Because the changes, especially stiffness and strength, were relatively larger than the changes in dry and ash weights of bone, measurements of these mechanical properties provide a more sensitive method to evaluate the quality of bone.

Animals↗
PubMed1987

Increase in serum parathyroid hormone concentration in the lactating rat: effects of dietary calcium and lactational intensity.

The change in circulating levels of immunoreactive parathyroid hormone (iPTH), measured with an N-terminal specific radioimmunoassay, was examined during lactation in rats. In lactating rats consuming a diet containing 0.4% Ca (basic diet), serum iPTH was a) increased by an average of 53% between days 10 and 18 compared to the level of age-matched nonlactating rats (24.7 +/- 2.1 pg/ml vs 16.1 +/- 0.8 pg/ml, mean +/- SE, p less than 0.01) and b) significantly higher in dams suckling large litters (10-15 pups) than in dams suckling small litters (3 pups) over the period 3-13 days of lactation. Lactating rats consuming a low calcium diet (0.04% Ca), had serum iPTH levels on days 16-18 of lactation approximately twice those of nonlactating rats fed the same diet and 73% higher than those of lactating rats fed the basic diet. Serum Ca concentrations were 22% and 10% lower in dams consuming the 0.04 and 0.4% Ca diets, respectively, than in the nonlactating controls fed the same diets. Regression analysis showed a significant (p less than 0.001) negative correlation between iPTH and total serum calcium. Compared with nonmated controls, net mineral loss from femurs of dams consuming the 0.4% Ca diet was a) insignificant at day 6, b) 27% at day 15, and c) 34% at day 21 of lactation. Our data demonstrate that lactation in the rat is characterized by hyperparathyroidism that appears to be related to lactational intensity and that is accentuated when dietary calcium intake is restricted.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The influence of blood sampling site on lactate concentration during submaximal exercise at 4 mmol.l-1 lactate level.

This study examined lactate concentration during incremental and submaximal treadmill exercise at work rates corresponding to 4 mmol.l-1 lactate concentration, determined by fingertip (OBLA1) and venous blood (OBLA2). Initially, eight subjects performed a 4-min incremental exercise test until exhaustion. On two other occasions, seven of the subjects undertook submaximal exercise tests (30 min) at work rates corresponding to OBLA1 and OBLA2. Blood was simultaneously obtained from both sites at rest and at the end of each exercise stage during the incremental exercise, and at 5, 10, 20 and 30 min during the submaximal exercise and 5 min into recovery. Fingertip blood lactate concentrations were significantly higher (P < 0.05) than venous blood at rest, throughout the incremental exercise, consistently during exercise at OBLA1 and OBLA2, and into recovery. Data also revealed an exercise intensity-dependent lactate difference between the two sampling sites during both exercise protocols. Exercise at OBLA1 did not result in a progressive increase in lactate level nor exhaustion, and the lactate value at the end of 30 min corresponded to the predetermined value. However, exercise at OBLA2 resulted in a significantly higher (P < 0.05) lactate level than OBLA1, the lactate concentration at the end of 30 min was substantially higher than the predetermined value (P < 0.05) and exhaustion was evident. It is concluded that the lactate concentration value during incremental and submaximal exercise (at 4 mmol.l-1 OBLA) is dependent on the blood sampling site. This finding should be considered in studies concerned with the determination of OBLA.

Adult↗
PubMedDate not supplied

L-lactate enzyme electrode obtained with immobilized respiratory chain from Escherichia coli and oxygen probe for specific determination of L-lactate in yogurt, wine and blood.

An enzyme electrode for L-lactate measurements in various biological media was prepared with an immobilized bacterial respiratory chain fixed to a Clark electrode. The enzymatic film, which was easy to prepare, contained bacteria immobilized in gelatin, tanned with glutaraldehyde. This electrode was sensitive to 0.1 mM L-lactate and could be utilized to 10 mM. The apparent K50 was 5 mM. Less than 8% of the respiration rate with L-lactate was measured with D-lactate and succinate. The competitive inhibitors D-lactate and pyruvate had a K50 of 50 mM. They could be quantitatively measured by inhibition in a range between 5 and 50 mM. It was also possible to discriminate between L-lactate and various metabolites of the respiratory chain: L-malate, succinate, 3-glycero-phosphate or NAD(P)H. Growing E. coli on 1% D-L-lactate as the sole carbon source in minimal medium induced L-lactate respiration tenfold. All other respiratory activities remained below 10% of the activity with L-lactate. A computerized instrument allowed successive measurements every 3 min for more than 10 h with the same enzymatic film. Most of the measured samples required dilution but no clarification or purification. This enzyme electrode may have many applications in basic research (metabolism, enzymology) and applied research (blood, yogurt, juices, wine).

Biotechnology↗