Hyperoxia decreases muscle glycogenolysis, lactate production, and lactate efflux during steady-state exercise

The aim of this study was to determine whether the decreased muscle and blood lactate during exercise with hyperoxia (60% inspired O2) vs. room air is due to decreased muscle glycogenolysis, leading to decreased pyruvate and lactate production and efflux. We measured pyruvate oxidation via PDH, muscle pyruvate and lactate accumulation, and lactate and pyruvate efflux to estimate total pyruvate and lactate production during exercise. We hypothesized that 60% O2 would decrease muscle glycogenolysis, resulting in decreased pyruvate and lactate contents, leading to decreased muscle pyruvate and lactate release with no change in PDH activity. Seven active male subjects cycled for 40 min at 70% VO2 peak on two occasions when breathing 21 or 60% O2. Arterial and femoral venous blood samples and blood flow measurements were obtained throughout exercise, and muscle biopsies were taken at rest and after 10, 20, and 40 min of exercise. Hyperoxia had no effect on leg O2 delivery, O2 uptake, or RQ during exercise. Muscle glycogenolysis was reduced by 16% with hyperoxia (267 +/- 19 vs. 317 +/- 21 mmol/kg dry wt), translating into a significant, 15% reduction in total pyruvate production over the 40-min exercise period. Decreased pyruvate production during hyperoxia had no effect on PDH activity (pyruvate oxidation) but significantly decreased lactate accumulation (60%: 22.6 +/- 6.4 vs. 21%: 31.3 +/- 8.7 mmol/kg dry wt), lactate efflux, and total lactate production over 40 min of cycling. Decreased glycogenolysis in hyperoxia was related to an approximately 44% lower epinephrine concentration and an attenuated accumulation of potent phosphorylase activators ADPf and AMPf during exercise. Greater phosphorylation potential during hyperoxia was related to a significantly diminished rate of PCr utilization. The tighter metabolic match between pyruvate production and oxidation resulted in a decrease in total lactate production and efflux over 40 min of exercise during hyperoxia.     

The movement of pyruvate, lactate and lactate dehydrogenase into rabbit oviductal fluid.

Pyruvate, lactate and lactate dehydrogenase appeared linearly in 2 ml 0.9% NaCl recirculated through the rabbit oviduct for 4 h in vivo. In oviducts from rabbits injected 3 days previously with 100 i.u. hCG, the rate of appearance of all three constituents was considerably reduced. It is considered unlikely that the lactate dehydrogenase secreted brings about the interconversion of pyruvate and lactate in the oviduct lumen.     

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.     

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

After 4 days in an atmosphere of N₂, aleurone layers of barley (Hordeum vulgare L. cv Himalaya) remained viable as judged by their ability to produce near normal amounts of α-amylases when incubated with gibberellic acid (GA₃) in air. However, layers did not produce α-amylase when GA₃ was supplied under N₂, apparently because α-amylase mRNA failed to accumulate.     

Interstitial lactate,lactate/pyruvate and glucose in rat muscle before,during and in the recovery from global hypoxia

Background

Hypoxia results in an imbalance between oxygen supply and oxygen consumption. This study utilized microdialysis to monitor changes in the energy-related metabolites lactate, pyruvate and glucose in rat muscle before, during and after 30 minutes of transient global hypoxia. Hypoxia was induced in anaesthetised rats by reducing inspired oxygen to 6% O₂ in nitrogen.

Results

Basal values for lactate, the lactate/pyruvate ratio and glucose were 0.72 ± 0.04 mmol/l, 10.03 ± 1.16 and 3.55 ± 0.19 mmol/l (n = 10), respectively. Significant increases in lactate and the lactate/pyruvate ratio were found in the muscle after the induction of hypoxia. Maximum values of 2.26 ± 0.37 mmol/l for lactate were reached during early reperfusion, while the lactate/pyruvate ratio reached maximum values of 35.84 ± 7.81 at the end of hypoxia. Following recovery to ventilation with air, extracellular lactate levels and the lactate/pyruvate ratio returned to control levels within 30-40 minutes. Extracellular glucose levels showed no significant difference between hypoxia and control experiments.

Conclusions

In our study, the complete post-hypoxic recovery of metabolite levels suggests that metabolic enzymes of the skeletal muscle and their related cellular components may be able to tolerate severe hypoxic periods without prolonged damage. The consumption of glucose in the muscle in relation to its delivery seems to be unaffected.

     

Epinephrine, glucose, and lactate infusion in exercising adrenodemedullated rats

The purpose of this study was to determine the metabolic function of the marked increase in plasma epinephrine which occurs in fasted rats during treadmill exercise. Fasted adrenodemedullated (ADM) and sham-operated (SHAM) rats were run on a rodent treadmill (21 m/min, 15% grade) for 30 min or until exhaustion. ADM rats were infused with saline, epinephrine, glucose, or lactate during the exercise bouts. ADM saline-infused rats showed markedly reduced endurance, hypoglycemia, elevated plasma insulin, reduced blood lactate, and reduced muscle glycogenolysis compared with exercising SHAM's. Epinephrine infusion corrected all deficiencies. Glucose infusion restored endurance run times and blood glucose to normal without correcting the deficiencies in blood lactate and muscle glycogenolysis. Infusion of lactate partially corrected the hypoglycemia at 30 min of exercise, but endurance was not restored to normal and rats were hypoglycemic at exhaustion. We conclude that in the fasted exercising rat, actions of epinephrine in addition to provision of gluconeogenic substrate are essential for preventing hypoglycemia and allowing the rat to run for long periods of time.     

Citrate, pyruvate, and lactate contaminants of commercial serum albumin

Commercial serum albumin was found to contain lactate, pyruvate, and especially citrate in addition to fatty acids. Glucose, aspartate, and alpha-ketoglutarate were also present but at lower concentrations. Charcoal treatment followed by prolonged dialysis was effective in removing most of these contaminants.     

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.     

Motility, heat, and lactate production in ejaculated bovine sperm

Effects of various inhibitors on motility, heat, and lactate production of ejaculated bovine sperm were determined in the presence of antimycin A and rotenone. erythro-9-[3-(2-Hydroxynonyl)]adenine (EHNA) and polyvinylpyrrolidone (PVP-360) stopped motility and reduced heat or lactate production by 30-50%. Carbodiimides resulted in loss of motility and a reduction of metabolism by 60-75%. Quercetin treatment, which enhanced rather than inhibited motility, depressed heat and lactate production by 50-60%. Since mechanical immobilization reduced heat production by only 30%, the question arises as to what other cellular processes are major contributors to the energy budget. Inhibitors of ion flux had little-to-no effect on heat or lactate production, suggesting that neither mitochondrial nor Na+/K+ ATPases were major ATP-requiring processes. Calcium flux at the plasma membrane also was minimal and previous reports eliminated glycolytic substrate cycling as major consuming processes for ATP. Although quercetin inhibited lactate production in intact cells, no effect of quercetin on cell-free glycolysis and the ATPase activities of isolated dynein was detected. Quercetin did, however, inhibit ATPase activity of plasma membrane, suggesting that this unidentified ATPase may contribute to the formation of ADP and Pi required for lactate production by the intact cell. We propose (a) that the bioenergetic costs of motility are divided between regulatory events and dynein-microtubule interaction (dynein ATPase), (b) that some of the membrane-related processes may be "inefficient," and (c) that quercetin may render these steps more "efficient," in a manner analogous to its action on the Na+/K+ pump of Ehrlich ascites tumor cells.     

Aerobic training effects on maximum oxygen consumption, lactate threshold and lactate disappearance during exercise recovery of dogs

1. Dogs were submitted to an aerobic training schedule and its maximum oxygen consumption, lactate threshold and lactate concentration during recovery were compared among the following conditions: not trained (UT), after 1 month of training (T1), after 2 months of training (T2) and after detraining (DT). 2. Maximum oxygen consumption increased significantly in relation to UT condition only at T2 condition. The detraining reversed this alteration. 3. Lactate threshold when expressed as Vo2 or absolute work load increased significantly after aerobic training (T2) but did not present any alteration when it was expressed as % of Vo2 max. 4. The lactate decreasing during recovery did not differ between the four experimental conditions (after 10 min). 5. The latency time for the lactate concentration to reach the top values was reduced by aerobic training (T2).     

Specific changes in lactate levels, lactate dehydrogenase patterns and cytochrome b559 in Dictyostelium discoideum caused by queuine

Higher eukaryotes contain tRNA transglycosylases that incorporate the guanine derivative queuine from the nutritional environment into specific tRNAs by exchange with guanine at position 34. Alterations in the queuosine content of specific tRNAs are suggested to be involved in regulatory mechanisms of major routes of metabolism during differentiation. Dictyostelium discoideum has been applied as a model to investigate the function of queuine or queuine-containing tRNAs. Axenic strains are supplied with queuine by peptone, but they grow equally well in a defined queuine-free medium. Queuine-lacking amoebae, starved in suspension culture for 24 h, lose their ability to differentiate into stalk cells and spores, whereas amoebae sufficiently supplied with queuine will overcome this metabolic stress and undergo further development when plated on agar. The results presented here show that D(-)-lactate occurs in the slime mould in millimolar amounts and that its level is remarkably decreased in queuine-lacking cells after 24 h of starvation in suspension culture. On isoelectric-focusing polyacrylamide gels, nine different forms of NAD-dependent D(-)-lactate dehydrogenase can be separated from extracts of vegetative cells, and six forms from extracts of the starved cells. Under queuine limitation, one form is missing in the starved cells. Low amounts of L(+)-lactate are usually found in vegetative amoebae but significantly less in queuine-lacking cells. Five forms of NAD-dependent L(+)-lactate dehydrogenase are detectable in extracts from vegetative, queuine-treated cells, and slight alterations occur in queuine-deficient amoebae. In the starved cells only one form of L(+)-lactate dehydrogenase is found, irrespective of the supply of queuine to the cells. A cytochrome of type b with an absorption maximum at 559 nm accumulates during starvation only in queuine-lacking cells; it might be a component of an NAD-independent lactic acid oxidoreductase as is cytochrome b 557 in yeast and be responsible for the reduced level of lactate in cells lacking queuine in tRNA.     

Anaerobiosis, lactate, and gas exchange during exercise: the issues

The lactate increase during exercise is a critically important biochemical and physiological event that leads to decreasing cell pH, an accelerated rate of glycogen depletion in the muscle, and important changes in ventilatory and gas exchange dynamics. Lactate increases only slightly at low work rates, and this increase is proportional to pyruvate increase (i.e. compatible with accelerated glycolysis without a change in redox state). At high work rates lactate increases disproportionately to pyruvate, the increased rate of lactate accumulation and lactate/pyruvate ratio appearing to occur at a threshold O2 consumption for a given individual. This symposium addresses the biochemical origin and physiological consequences of the increased lactate production during exercise.     

Transpulmonary lactate shuttle

The shuttling of intermediary metabolites such as lactate through the vasculature contributes to the dynamic energy and biosynthetic needs of tissues. Tracer kinetic studies offer a powerful tool to measure the metabolism of substrates like lactate that are simultaneously taken up from and released into the circulation by organs, but in each circulatory passage, the entire cardiac output traverses the pulmonary parenchyma. To determine whether transpulmonary lactate shuttling affects whole-body lactate kinetics in vivo, we examined the effects of a lactate load (via lactate clamp, LC) and epinephrine (Epi) stimulation on transpulmonary lactate kinetics in an anesthetized rat model using a primed-continuous infusion of [U-(13)C]lactate. Under all conditions studied, control 1.2 (SD 0.7) (Con), LC 1.9 (SD 2.5), and Epi 1.9 (SD 3.5) mg/min net transpulmonary lactate uptake occurred. Compared with Con, a lactate load via LC significantly increased mixed central venous ([v]) [1.9 mM (SD 0.5) vs. 4.7 (SD 0.4)] and arterial ([a]) [1.6 mM (SD 0.4) vs. 4.1 (SD 0.6)] lactate concentrations (P < 0.05). Transpulmonary lactate gradient ([v] - [a]) was highest during the lactate clamp condition [0.6 mM (SD 0.7)] and lowest during Epi [0.2 mM (SD 0.5)] stimulation (P < 0.05). Tracer measured lactate fractional extractions were similar for control, 16.6% (SD 15.3), and lactate clamp, 8.2% (SD 15.3) conditions, but negative during Epi stimulation, -25.3% (SD 45.5) when there occurred a transpulmonary production, the conversion of mixed central venous pyruvate to arterial lactate. Further, isotopic equilibration between L and P occurred following tracer lactate infusion, but depending on compartment (v or a) and physiological stimulus, [L]/[P] concentration and isotopic enrichment ratios ranged widely. We conclude that pulmonary arterial-vein concentration difference measurements across the lungs provide an incomplete, and perhaps misleading picture of parenchymal lactate metabolism, especially during epinephrine stimulation.     

Needle-type lactate biosensor

A needle-type lactate biosensor has been developed for continuous intravascular lactate monitoring. The sensor employs poly(1,3-phenylenediamine) as the inner layer on the platinum electrode in order to eliminate the interference from oxidizable physiological substances. Cross-linking with glutaraldehyde was used for enzyme immobilization. Dithiothreitol was used as the stabilizer of lactate oxidase. PVC (polyvinyl chloride) was chosen as the external diffusion control membrane. Sensor performance was evaluated in vitro and the sensor shows a sensitivity of 10-15 nA/mM, and a linear range from 1 mM to at least 15 mM lactate. Evaluation of the sensor response in blood plasma showed similar sensitivity and linear range as indicated by the calibration curves obtained in buffer solution. The sensor has a short response time of approximately 1 minute. The sensors were operated continuously for 7 days in phosphate buffer containing solution with a concentration at the physiological lactate level. No significant change in sensor sensitivity and its linear range has been observed. Sensors show a minimum change in its performance when stored in buffer at 4 degrees C for at least 9 months.     

Characterization of rabbit lactate dehydrogenase-M and lactate dehydrogenase-H cDNAs. Control of lactate dehydrogenase expression in rabbit muscle

Two cDNA clones were isolated, one corresponding to the mRNA coding for lactate dehydrogenase-M (LDH-M), the other to the mRNA coding for lactate dehydrogenase-H (LDH-H). The cDNA inserts consist of the entire open reading frame for LDH-M and a partial sequence, from amino acid 117 to 332, for LDH-H. Using these two clones as probes we demonstrate that: (a) the abundance of mRNA is muscle-type dependent; (b) the ratio M/H subunit for protein and mRNA is well related in the muscles studied; and (c) the M + H mRNA level is not relative to the total LDH activity.