Net Lactate Production Research Articles

Physiological and Energetic Demands During Still-Rings Routines of Elite Artistic Gymnasts.

The aim of the study was to analyze physiological and energetic demands of elite gymnasts during still-rings routines (SRRs). Eleven male gymnasts (mean [SD] 23.6 [3.9]y, 65.9 [5.6]kg, 171.1 [6.7]cm) performed a maximal graded exercise test and an individual SRR, during which respiratory gas and heart rate (HR) were measured using a mobile spiroergometer and a paired HR sensor. Metabolic energy and the energy contribution in terms of aerobic, anaerobic lactic, and anaerobic alactic were determined by oxygen uptake (VO2) during exercise, net lactate production, and the fast component of postexercise VO2 kinetics. Mean routine duration of the SRRs was 48.3 (4.5)seconds. VO2 and HR during SRRs were shown to be 86.9% (5.9%) and 91.0% (3.3%), respectively, of the maximal values measured during the graded exercise test. The anaerobic alactic, aerobic, and anaerobic lactic systems provided 50.9% (6.6%), 28.6% (4.8%), and 20.5% (5.2%), respectively, of the total energy required during SRRs. The energy contribution of the anaerobic lactic system correlated negatively with individual anaerobic threshold (r = -.715) and maximal VO2 (r = -.682). The anaerobic alactic system is the predominant energy source for ATP resynthesis during SRRs. The high relative VO2 and HR values reached during SRRs showthat these routines strongly stress the cardiovascular system.

The Contribution of Energy Systems in Repeated-Sprint Protocols: The Effect of Distance, Rest, and Repetition

ABSTRACT Purpose: This study aims to investigate the effects of rest intervals, sprint distance, and number of repetitions on performance variables, physiological responses, and energy system contributions in repeated-sprint protocols when total distance variable was the controlled (300 m). Method: Sixteen male soccer players participated in this study. The four protocols, each totaling a distance of 300 m, consisted of the combination of 15 and 30 m sprints with 30 s rest intervals (15meters30sec and 30meters30sec, respectively) and 1:5 work–rest ratios (15meters12sec and 30meters22sec, respectively). Aerobic, glycolytic, and phosphagen energy systems’ contributions were calculated from the oxygen consumption (VO2) during the exercise, net lactate production, and the recovery VO2 kinetics using mono-exponential models. Repeated measures ANOVA with the Bonferroni correction was applied to examine the hypothesized differences. Results: The findings indicated that total sprint duration (F3:45=281.14; p<0.001), percentage of performance decline (F3:45=16.58; p<0.001), delta lactate (F3:45=39.72, p<0.001), rating of perceived exertion (F3:45=28.64; p<0.001), energy demand (F3:45=101.6; p<0.001), VO2 during the rest intervals (F3:45=42.72; p<0.001), and the absolute contribution of glycolytic (F3:45=119.6; p<0.001) and phosphagen energy systems (F3:45=72.9; p<0.001) were lowest in the 15meters30sec compared to other protocols. However, the relative contribution of aerobic system was greatest in the 15meters30sec compared to other protocols (F3:45=28.1, p<0.001). Both absolute (F3:45=119.6; p<0.001) and relative contribution of glycolytic system (F3:45=88.5, p<0.001) were greatest in the 30meters22sec compared to other protocols. Conclusion: This study showed that increasing sprint distance when rest interval is equal and decreasing rest interval when sprint distance is equal can increase the glycolytic system contribution.

Physiological Responses And Energetic Of Two Sprint Interval Exercise Protocols Based On Rope-skipping And Cycling

High-intensity interval training could improve performance effectively. However, the acute physiological response and energy expenditure of a low-volume, high-intensity rope-skipping based protocol have not been determined. PURPOSE: To compare the physiological response and energy resource in repeated bouts of sprint interval cycling (SIC) and high-intensity intermittent double-under rope skipping (HIT-RS). METHOD: Fifteen college students (age=20.2±0.8yrs, body mass=67.7±4.8kg, BMI=22.4±1.2kg.m-2, VO2peak=51.90±7.83ml.kg-1.min-1) volunteered for this study. Participants completed two protocols (4⊆30s with 4min active recovery) on separate days with 1 week between trials. VO2 and heart rate were monitored at rest, during test and continue to 1 hour after test. Blood lactate was measured 3 minutes after each bout, and minute by minute after the last bout. Lactic (WBla) and alactic anaerobic (WPCr) energy outputs were calculated from net lactate production and the fast component of EPOC. Aerobic metabolism (Waer) was determined from VO2 during exercise. RESULT: Mean values for %VO2peak and %HRpeak for SIC (78.79±15.35% and 85.33±4.69%) and HIT-RS (74.93±16.21% and 83.17±5.37%) were not significantly different (p>0.05). The overall energy cost for SIC (102.75±13.15 kJ) was significantly higher (p<0.001) compared to HIT-RS (70.86±10.25 kJ). Waer, WBla and WPCr for SIC (17.39±3.08, 59.50±8.10 and 25.86±5.40 kJ) and HIT-RS (13.05±2.01, 27.97±6.77 and 29.84±6.28 kJ) were significantly different (p<0.01). Fractions of Waer, WBla and WPCr for SIC (16.92±1.77%, 57.99±4.70% and 25.09±3.65%) and HIT-RS (18.80±3.13%, 38.84±6.09% and 42.36±5.98%) were significantly different (p<0.001). Both protocols were anaerobic-dominated with similar fraction (SIC:83.08±3.01% vs HIT-RS: 81.20±4.52%). Compared to SIC, HIT-RS was more PCr dominant (42.36±5.98% vs 25.09±3.65%, p<0.01) with lower anaerobic lactic contribution (38.84±6.09% vs 57.99±4.70%, p<0.001). CONCLUSION: High-intensity interval protocol of rope skipping elicits vigorous cardiorespiratory responses and may confer physiological adaptations and performance improvements resembling as SIC.

Energy Resource Of Four Styles Of 30s All-out Rope Skipping

Rope jumping has been popular and a major tool for training and entertainment. When skipping rate per jump increments from single under to quad under, flight time prolonged and increased swinging frequency, the proportion of aerobic and anaerobic energy supply may be different. PURPOSE: To compare 30-s all-out rope skipping energy resource between four styles. METHOD: 10 elite rope-skipper from Shanghai University of Sport(height=169.3±4.7cm;body mass=65.5±9.2kg; age=23.2±2.1yrs, years of training=3.8±1.3yrs)volunteered for this study. Participants conducted 30-second rope skipping test at 1 skip per jump (single under, SU), 2 skip per jump (double under, DU), 3 skip per jump (triple under, TU) and 4 skip per jump (quad under, QU), and completed as many repetitions as possible with 24 hours between trials. VO2 were monitored at rest, during test and up to 1 hour after test. Blood lactate was measured immediately, minute by minute after test. Lactic (WBla) and alactic anaerobic (WPCr) energy outputs were calculated from net lactate production and the fast component of EPOC. Aerobic metabolism (Waer) was determined from VO2 during exercise. Net energy expenditure (Wtot) was calculated as summary of WPCr,WBla and Waer. RESULT: SU exhibited significantly lower Wtot value (49.9±12.70 kJ) than in DU (69.2±11.05), TU (72.0±13.59) and QU (81.0±16.25) (p<0.01). WPCr (kJ) was significantly different between SU (23.4±6.9), TU (33.7±12.8) and QU (40.0±10.5) (p<0.05), and DU (29.1±8.0) and QU (p<0.05). Wbla (kJ) in SU and QU were significantly different (16.5±6.8 v.s 27.2±12.4, p<0.05). SU (10.0±2.2) had significantly lower Waer (kJ) value than the other styles (DU 12.3±3.1, TU 14.8±2.4, QU 13.7±3.7, p<0.05). WPCr and Wbla accounted for 45.6%~50.2% and 32.2%~35.3% of total energy in four styles with no difference between styles (p>0.05). Aerobic provided 16.8~22.1% of total energy in all styles, with significant difference between SU and QU (20.6±4.8% v.s 16.8 ±2.5%, p<0.05), TU (22.1±8.6%) and QU (p<0.05). CONCLUSION: Four styles of 30s all-out rope skipping are all anaerobic-dominated with similar fractions, PCr and anaerobic lactic account for 45.6%~50.2% and 32.2%~35.3% of total energy. Keywords: rope skipping, metabolism, energy resource

Determinants Of Metabolic Cost During Four Styles Of 30-second Sprint Rope Skipping

Rope jumping has been a major training tool for many sports. However, no study has been conducted as yet to determine energy expenditure with incremental skipping rate per jump (difficulty) from single under to quad under. PURPOSE: To determine and compare 30-seconds all-out effort energy expenditure between four incremental rope skipping difficulties. METHOD: Ten skilled rope-jumpers (height=169.3±4.7cm, body mass=65.5±9.2kg, age=23.2±2.1yrs, years of training=3.8±1.3yrs) volunteered to participate this study. Participants conducted rope skipping as many repetitions as possible at 1 skip.jump-1 (single under, SU), 2 skips.jump-1 (double under, DU), 3 skips.jump-1 (triple under, TU) and 4 skips.jump-1 (quad under, QU) during 30-second test with 24 hours between trials. Kinematic and kinetic data were collected to calculate flight time (FT) and vertical center of mass displacement (vCOM). Each style was assessed in three trials and then averaged. Net energy expenditure (Wtot) was calculated from VO2 during exercise, the fast component of the EPOC above resting and net blood lactate production. RESULT: SU exhibited significantly lower VO2peak (28.01±4.62 ml.kg-1.min-1, p<0.05) compared to TU (34.96±3.45) and QU (36.12±6.38). Wtot (J.jump-1) in QU (7975.1±3265.66 J.jump-1) was significantly higher than these values of the other three styles (SU 474.9±108.80, DU 1086.4±183.17, TU 1769.3±540.46, p<0.05). FT (ms) and vCOM (cm) increased significantly with increase in difficulty (SU: 125.0±19.6 and 1.95±0.66, DU: 276.6±36.1 and 9.53±2.24, TU: 473.6±32.1 and 27.64±3.76, QU: 544.4±60.5 and 36.76±8.15, p<0.01). 30s skip repetitions in QU (46.0±19.34) was significantly lower than the other styles (SU 105.2±12.08, DU 128.2±15.12, TU 126.9±20.39, p<0.01). Standard Wtot (J.kg-1.jump-1) was exponentially related to skipping difficulty from 1 skip.jump-1 to 4 skips.jump-1 (R2=0.89, p<0.001). CONCLUSION: Skipping difficulty (skip per jump) is one of the main determinants of metabolic cost, whereas skip repetition does not significantly contribute to metabolic cost during 30 seconds all-out rope skipping.

Changes in energy system contributions to the Wingate anaerobic test in climbers after a high altitude expedition.

The Wingate anaerobic test measures the maximum anaerobic capacity of the lower limbs. The energy sources of Wingate test are dominated by anaerobic metabolism (~ 80%). Chronic high altitude exposure induces adaptations on skeletal muscle function and metabolism. Therefore, the study aim was to investigate possible changes in the energy system contribution to Wingate test before and after a high-altitude sojourn. Seven male climbers performed a Wingate test before and after a 43-day expedition in the Himalaya (23days above 5.000m). Mechanical parameters included: peak power (PP), average power (AP), minimum power (MP) and fatigue index (FI). The metabolic equivalents were calculated as aerobic contribution from O2 uptake during the 30-s exercise phase (WVO2), lactic and alactic anaerobic energy sources were determined from net lactate production (WLa) and the fast component of the kinetics of post-exercise oxygen uptake (WPCr), respectively. The total metabolic work (WTOT) was calculated as the sum of the three energy sources. PP and AP decreased from 7.3 ± 1.1 to 6.7 ± 1.1W/kg and from 5.9 ± 0.7 to 5.4 ± 0.8W/kg, respectively, while FI was unchanged. WTOT declined from 103.9 ± 28.7 to 83.8 ± 17.8kJ. Relative aerobic contribution remained unchanged (19.9 ± 4.8% vs 18.3 ± 2.3%), while anaerobic lactic and alactic contributions decreased from 48.3 ± 11.7 to 43.1 ± 8.9% and increased from 31.8 ± 14.5 to 38.6 ± 7.4%, respectively. Chronic high altitude exposure induced a reduction in both mechanical and metabolic parameters of Wingate test. The anaerobic alactic relative contribution increased while the anaerobic lactic decreased, leaving unaffected the overall relative anaerobic contribution to Wingate test.

Kinetics of Hepatic Volume Evolution and Architectural Changes after Major Resection in a Porcine Model

Background: The hepatic volume gain following resection is essential for clinical recovery. Previous studies have focused on cellular regeneration. This study aims to explore the rate of hepatic regeneration of the porcine liver following major resection, highlighting estimates of the early microarchitectural changes that occur during the cellular regeneration. Methods: Nineteen large white pigs had 75% resection with serial measurements of the hepatic volume, density, blood flow, and architectural changes. Results: The growth rate initially was 45% per day, then rapidly decreased and was accompanied by a similar pattern of hepatic fat deposition. The architectural changes showed a significant increase in the Ki67 expression (p < 0.0001) in the days following resection with a peak on the 2nd day and nearly normalized on day 7. The expression of CD31 increased significantly on the 2nd and 3rd days compared to the pre-resection samples (p = 0.03). Hepatic artery flow per liver volume remained at baseline ranges during regeneration. Portal flow per liver volume increased after liver resection (p < 0.001), was still elevated on the 1st postoperative day, then decreased. Correlations were significantly negative between the hepatic volume increase on day 3 and the hepatic oxygen consumption and the net lactate production at the end of the procedure (r = –0.82, p = 0.01, and r = –0.70, p = 0.03). Conclusion: The volume increase in the first days – a fast process – is not explained by cellular proliferation alone. The liver/body weight ratio is back to 50% of the preoperative value after 3 days to close to 100% volume regain on days 10–15.

Energetic Profile of the Basketball Exercise Simulation Test in Junior Elite Players.

To analyze the energetic profile of the Basketball Exercise Simulation Test (BEST). Ten male elite junior basketball players (age 15.5 [0.6]y, height 180 [9]cm, and body mass 66.1 [11.2]kg) performed a modified BEST (20 circuits consisting of jumping, sprinting, jogging, shuffling, and short breaks) simulating professional basketball game play. Circuit time, sprint time, sprint decrement, oxygen uptake (VO2), heart rate, and blood lactate concentration (blc) were obtained. Metabolic energy and metabolic power above rest (Wtot and Ptot), as well as energy share in terms of aerobic (Waer), glycolytic (Wblc), and high-energy phosphates (WPCr), were calculated from VO2 during exercise, net lactate production, and the fast component of postexercise VO2 kinetics, respectively. Waer, Wblc, and WPCr reflect 89% (2%), 5% (1%), and 6% (1%) of total energy needed, respectively. Assuming an aerobic replenishment of PCr energy stores during short breaks, the adjusted energy share yielded Waer 66% (4%), Wblc 5% (1%), and WPCr 29% (1%). Waer and WPCr were negatively correlated (-0.72 and -0.59) with sprint time, which was not the case for Wblc. Consistent with general findings on energy system interaction during repeated high-intensity exercise bouts, the intermittent profile of the BEST relies primarily on aerobic energy combined with repetitive supplementation by anaerobic utilization of high-energy phosphates.

The reference values for hepatic oxygen consumption and net lactate production, blood gasses, hemogram, major electrolytes, and kidney and liver profiles in anesthetized large white swine model

Aim: Pigs are extensively used as experimental models to study the human physiology and pathophysiological conditions. Knowledge of the normal values of the commonly used parameters is indispensable to the correct interpretation of the test results. This study reports on the normal hemogram, blood gas, major electrolytes, kidney and liver profiles, hepatic oxygen consumption, and net lactate production in a large white pig model. Methods: Twenty-five female large white pigs were included in this study. Blood gas samples were collected from the portal and hepatic veins as well as the carotid artery. Results: The mean hemoglobin level was 97.7 ± 15.8 g/L. white blood cells were 13.5 ± 3.3 10 [3] /mm [3] , and platelet count was 279 ± 104.6 10 [3] /mm [3] . The mean aspartate aminotransferase, alanine aminotransferase, gamma-glutamyltransferase, alkaline phosphatase, total bilirubin, and direct bilirubin were 83.8 ± 73.9 IU/L, 43.7 ± 5.9 IU/L, 33.6 ± 8.6 IU/L, 296.5 ± 39.7 IU/L, 5.6 ± 3.2 mmol/L, and 1.6 ± 0.73 mmol/L. The mean albumin level was 29 ± 3.9 g/L. The mean ammonia and arterial lactate levels were 49.1 ± 45.67 mmol/L and 1.5 ± 0.46 mmol/L. Kidney profile parameters were comparable to human values. Hepatic oxygen consumption was 17.3 ± 9.7 mL/100 g liver tissue/min and net hepatic lactate production was 0.017 ± 0.03 mmol/L. Conclusion: Knowledge of the normal parameters is mandatory for accurate interpretation of the experimental results that involves large white animals.

Lactate transport and signaling in the brain: potential therapeutic targets and roles in body-brain interaction.

Lactate acts as a 'buffer' between glycolysis and oxidative metabolism. In addition to being exchanged as a fuel by the monocarboxylate transporters (MCTs) between cells and tissues with different glycolytic and oxidative rates, lactate may be a 'volume transmitter' of brain signals. According to some, lactate is a preferred fuel for brain metabolism. Immediately after brain activation, the rate of glycolysis exceeds oxidation, leading to net production of lactate. At physical rest, there is a net efflux of lactate from the brain into the blood stream. But when blood lactate levels rise, such as in physical exercise, there is net influx of lactate from blood to brain, where the lactate is used for energy production and myelin formation. Lactate binds to the lactate receptor GPR81 aka hydroxycarboxylic acid receptor (HCAR1) on brain cells and cerebral blood vessels, and regulates the levels of cAMP. The localization and function of HCAR1 and the three MCTs (MCT1, MCT2, and MCT4) expressed in brain constitute the focus of this review. They are possible targets for new therapeutic drugs and interventions. The author proposes that lactate actions in the brain through MCTs and the lactate receptor underlie part of the favorable effects on the brain resulting from physical exercise.

Effects of copper on CHO cells: Insights from gene expression analyses

Copper concentration can impact lactate metabolism in Chinese Hamster ovary (CHO) cells. In our previous study, a 20-fold increase in initial copper concentration enabled CHO cultures to shift from net lactate production to net lactate consumption, and achieve higher cell growth and productivity. In this follow-up study, we used transcriptomics to investigate the mechanism of action (MOA) of copper that mediates this beneficial metabolism shift. From microarray profiling (days 0-7), the number of differentially expressed genes increased considerably after the lactate shift (>day 3). To uncouple the effects of copper at early time points (days 0-3) from that of lactate per se (>day 3), and to validate microarray hits, we analyzed samples before the lactate shift by RNA-Seq. Out of 6,398 overlapping genes analyzed by both transcriptomic methods, only the early growth response 1 gene-coding for a transcription factor that activates signaling pathways in response to environmental stimuli-satisfied the differential expression criteria (fold change ≥ 1.5; P < 0.05). Gene expression correlation and biological pathway analyses further confirmed that copper differences exerted minimal transcriptional impact on the CHO cultures before the lactate shift. By contrast, genes associated with hypoxia network and oxidative stress response were upregulated after the lactate shift. These upregulations should boost cell proliferation and survival, but do not account for the preceding shift in lactate metabolism. The findings here indicate that the primary MOA of copper that enabled the shift in lactate metabolism is not at the transcriptional level.

Blood Lactate Diagnostics in Exercise Testing and Training

A link between lactate and muscular exercise was seen already more than 200 years ago. The blood lactate concentration (BLC) is sensitive to changes in exercise intensity and duration. Multiple BLC threshold concepts define different points on the BLC power curve during various tests with increasing power (INCP). The INCP test results are affected by the increase in power over time. The maximal lactate steady state (MLSS) is measured during a series of prolonged constant power (CP) tests. It detects the highest aerobic power without metabolic energy from continuing net lactate production, which is usually sustainable for 30 to 60 min. BLC threshold and MLSS power are highly correlated with the maximum aerobic power and athletic endurance performance. The idea that training at threshold intensity is particularly effective has no evidence. Three BLC-orientated intensity domains have been established: (1) training up to an intensity at which the BLC clearly exceeds resting BLC, light- and moderate-intensity training focusing on active regeneration or high-volume endurance training (Intensity < Threshold); (2) heavy endurance training at work rates up to MLSS intensity (Threshold ≤ Intensity ≤ MLSS); and (3) severe exercise intensity training between MLSS and maximum oxygen uptake intensity mostly organized as interval and tempo work (Intensity > MLSS). High-performance endurance athletes combining very high training volume with high aerobic power dedicate 70 to 90% of their training to intensity domain 1 (Intensity < Threshold) in order to keep glycogen homeostasis within sustainable limits.

Ischemic Preconditioning Attenuates Lactate Release by the Liver During Hepatectomies Under Vascular Control: A Case–Control Study

BackgroundWe have previously demonstrated lactate release by the liver itself in hepatectomies performed under selective hepatic vascular exclusion. We hypothesized that ischemic preconditioning applied in this setting might lead to a reduction of hepatic lactate production. MethodsTwenty-one patients underwent hepatectomy under inflow and outflow occlusion combined with ischemic preconditioning (IP group, n = 21). These patients were matched 1:1 with patients subjected to the same technique of hepatectomy under vascular occlusion without ischemic preconditioning (control group, n = 21). The transhepatic lactate gradient (hepatic vein–portal vein) was calculated before liver dissection and 60 min post-reperfusion. ResultsIn the control group, the transhepatic lactate gradient before liver resection was negative indicating consumption by the liver. After 60 min post-reperfusion, this gradient became positive, indicating net lactate production by the liver (0.2±0.3 vs. −0.3±0.2 mmol/L, P < 0.001). In the IP group, the liver consumed lactate both before resection and 60 min post-reperfusion (gradients −0.2±1.1 and −0.1±0.6 mmol/L, respectively). The magnitude of lactate release by the liver correlated with systemic hyperlactatemia post-reperfusion and 24 h postoperatively (r2 = 0.54, P < 0.001 and r2 = 0.67, P < 0.001, respectively). Significant correlations between the transhepatic lactate gradient post-reperfusion and peak postoperative AST as well as the apoptotic response of the liver remnant were also demonstrated (r2 = 0.72, P < 0.001 and r2 = 0.66, P < 0.001, respectively). ConclusionThe microcirculatory derangement and cellular aerobic metabolism breakdown elicited by ischemia–reperfusion insults can be prevented with hepatoprotective measures such as ischemic preconditioning. The transhepatic lactate gradient could act as a monitoring and prognostic tool of the efficacy of ischemic preconditioning.

The brain does not take up lactate during exercise in hypoxia

Cerebral function depends on continuous oxygen delivery, but whether the brain has a potential for anaerobic metabolism is not known. The brain has a small net lactate production at rest while during exercise it takes up lactate in proportion to the arterial concentration. This study evaluated whether cerebral oxygen availability affects the brains lactate metabolism as arterio-venous lactate differences (a-v diff) in 16 subjects during 3 cycling trials: 20 min of submaximal exercise at a normal inspired oxygen fraction (FIO2 0.21); at a FIO2 of 0.10; and 3) during exercise to exhaustion (FIO2 0.21). Blood was sampled from the brachial artery and a catheter placed at the jugular bulb, while cerebral blood flow was appreciated with transcranial ultrasound Doppler. At rest and during submaximal exercise at FIO2 0.21, the mean cerebral a-v diff was −0.1 ± 0.1 (SD) mM. Maximal exercise increased arterial lactate to 10.5 ± 2.1 mM with a lactate a-v diff of 0.7 ± 0.4 mM. However, exercise at a FIO2 of 0.10 reduced oxygen availability from 476 ± 80 to 350 ± 41 μmol 100 g−1 min−1 and the arterial lactate concentration increased to 10.1 ± 4.0 mM, but no a-v diff for lactate was observed. While net cerebral carbohydrate [glucose + ½lactate] turn-over was preserved, the cerebral oxygen metabolic rate for oxygen decreased by 15 ± 10 %. This indicates that exercise in hypoxia provokes the brain to provide energy by anaerobic metabolism.

Transhepatic lactate gradient in relation to liver ischemia/reperfusion injury during major hepatectomies

Hepatectomies performed under selective hepatic vascular exclusion are associated with a series of events culminating in ischemia/reperfusion injury, a state that shares common characteristics with situations known to result in global or regional hyperlactatemia. Accordingly, we sought to determine whether lactate is released by the liver during hepatic resections performed under blood flow deprivation and what relation this has to a possible systemic hyperlactatemic state. After ethical approval, 14 consecutive patients with resectable liver tumors subjected to hepatectomy under inflow and outflow occlusion of the liver were studied. Lactate concentrations were assessed in simultaneously drawn arterial, portal venous, and hepatic venous blood before liver dissection and 50 minutes postreperfusion. Moreover, the transhepatic lactate gradient (hepatic vein - portal vein) was calculated to see if there was net production or consumption of lactate. Before hepatic dissection, the transhepatic lactate gradient was negative, suggesting consumption by the liver. Fifty minutes after reperfusion, this gradient became significantly positive, demonstrating release of lactate by the liver (0.12 +/- 0.31 vs. -0.38 +/- 0.30 mmol/L, P < 0.05). The magnitude of lactate release correlated with systemic arterial lactate levels at the same time point (r(2) = 0.63, P < 0.001). A weaker but significant correlation was demonstrated between the transhepatic lactate gradient postreperfusion and systemic arterial lactate levels 24 hours postoperatively (r(2) = 0.41, P = 0.013). A strong correlation between the transhepatic lactate gradient postreperfusion and peak postoperative aspartate aminotransferase values was also demonstrated (r(2) = 0.73, P < 0.001). The liver becomes a net producer of lactate in hepatectomies performed under blood flow deprivation. This lactate release can explain some of the systemic hyperlactatemia seen in this context and relates to the extent of ischemia/reperfusion injury.

Relevance of the NOS3 T–786C and G894T variants for cholinergic and adrenergic coronary vasomotor responses in man

We investigated the impact of the -786C allele at the promoter and the 894T allele in exon 7 of the gene encoding the endothelial nitric oxide synthase (NOS3) on coronary vasomotor responses to exogenous and endogenous stimuli. In 47 individuals undergoing coronary angiography for chest pain, but without significant stenosis in the left anterior descending artery (LAD), nitroglycerine and acetylcholine were infused intracoronarily, and a cold pressor test (CPT) was performed. Coronary blood flow (CBF) in the LAD was calculated from quantitative coronary angiography and intracoronary Doppler measurements. Aortic and coronary sinus lactate levels were determined in 18 individuals. To analyze the impact of NOS3 genotypes, a logistic regression model was used. In response to acetylcholine (p = 0.002) and CPT (p = 0.015) CBF reduction was associated with homocygosity for the -786C allele. Myocardial lactate uptake was reversed into net lactate production in CC homocygotes. No independent effects of the G894T polymorphism were observed in the present study. Haplotype analysis revealed a significant linkage disequilibrium between both polymorphisms (p < 0.001). Our findings suggest a pathophysiologically relevant role for the T-786C polymorphism in human coronary vasomotion. The observed linkage disequilibrium between both NOS3 genotypes deserves further research in future studies.

Physiological Responses during a Submaximal Cycle Test in Chronic Fatigue Syndrome

Numerous studies have assessed physical function in individuals suffering from chronic fatigue syndrome (CFS) but neglected to match control subjects according to current activity levels, consequently casting doubt on reported results. The purpose of this study was to include current activity levels as one criterion for matching CFS subjects with healthy control subjects in order to more accurately assess physical function in these subjects. Thirty-one healthy control subjects were matched to CFS subjects according to age, gender, body mass, height, and current activity levels. Physiological function was assessed weekly over a 4-wk period using a submaximal cycle test. Comparison of absolute physiological results recorded at the end of each incremental work level of the exercise test showed that ratings of perceived effort (RPE) was the only variable that was significantly different between the two groups. Scores for RPE were significantly higher in CFS subjects for each incremental work level assessed. Conversely, results recorded on completion of the exercise test showed that the control group was capable of a greater power output than the CFS group as reflected by significantly higher scores for watts per kilogram (P < 0.0005), net lactate production (P = 0.003), oxygen uptake (mL x kg(-1) x min(-1); P < 0.0005), respiratory exchange ratio (P = 0.021), and HR values as a percentage of age predicted HR(max) (P = 0.001). End-point RPE scores were again significantly higher in the CFS group (P < 0.0005). It is proposed that the reduced exercise tolerance in CFS is due to impairment in the mechanisms that constitute effort sense and/or to avoidance behaviors that result in a reluctance by these subject to exercise to full capacity.

Cultured retinal neuronal cells and M�ller cells both show net production of lactate

Glucose has long been considered the substrate for energy metabolism in the retina. Recently, an alternative hypothesis (metabolic coupling) suggested that mitochondria in retinal neurons utilize preferentially the lactate produced specifically by Müller cells, the principal glial cell in the retina. These two views of retinal metabolism were examined using confluent cultures of photoreceptor cells, Müller cells, ganglion cells, and retinal pigment epithelial cells incubated in modified Dulbecco’s minimal essential medium containing glucose or glucose and lactate. The photoreceptor and ganglion cells represented neural elements, and the Müller and pigment epithelial cells represented non-neural cells. The purpose of the present experiments was two-fold: (1) to determine whether lactate is a metabolic product or substrate in retinal cells, and (2) to examine the evidence that supports the two views of retinal energy metabolism. Measurements were made of lactic acid production, cellular ATP levels, and cellular morphology over 4 h. Results showed that all cell types incubated with 5 mM glucose produced lactate aerobically and anaerobically at linear rates, the anaerobic rate being 2–3-fold higher (Pasteur effect). Cells incubated with both 5 mM glucose and 10 mM lactate produced lactate aerobically and anaerobically at rates similar to those found when cells were incubated with glucose alone. Anaerobic ATP content in the cells was maintained at greater than 50% of the control, aerobic value, and cellular morphology was well preserved under all conditions. The results show that the cultured retinal cells produce lactate, even in the presence of a high starting ambient concentration of lactate. Thus, the net direction of the lactic dehydrogenase reaction is toward lactate formation rather than lactate utilization. It is concluded that retinal cells use glucose, and not glial derived lactate, as their major substrate.

Assessment of Critical Velocity and Blood Lactate in Pre-Pubertal Swimmers

0824 Critical velocity (CV) in swimming represents the speed that can be theoretically maintained indefinitely without exhaustion and has been suggested as a marker of endurance ability. Previous investigations have found high correlations between CV and the anaerobic threshold but also differences between the corresponding velocities. PURPOSE: The aims of the study were 1) to investigate different performance models for the determination of CV and 2) to test the hypothesis that CV identifies an exercise intensity without net lactate production in pre-pubertal male swimmers. METHODS: Data were collected from 7 boys (mean ± SD age 10.5 ± 1.1yr; height 1.41 ± 0.08m and weight 32.6 ± 6.8kg) during 4 maximal front crawl time trials (54.8m, 109.7m, 219.4m and 438.7m) with blood lactate measurements pre and post each trial. CV was determined for each subject by regression analysis using the distance-time model [Distance = ASC + (CV × Time)] and velocity-1/time model [Velocity = CV + (ASC × 1/Time)], where ASC is the Anaerobic Swimming Capacity. The velocity with zero net lactate accumulation was determined based on the interrelationship between swimming velocity and lactate appearance rate (lactate/velocity model). RESULTS: A within subject ANOVA analysis revealed no significant differences between the CV and the goodness of fit (R2) for the distance-time model, (CV = 0.67 ± 0.08 m.s−1, R2 = 1.00 ± 0.001), the velocity-1/time model (CV = 0.68 ± 0.06 m.s−1, R2 = 0.94 ± 0.10), and the lactate/velocity model (CV = 0.70 ± 0.07, r2 0.94 ± 0.08). CONCLUSION: The results demonstrate that 1) the application of the tested models did not generate differences in CV and 2) identified an intensity domain without net lactate appearance. Assessment of critical velocity provides a practical, inexpensive and non-invasive method for determining endurance ability in male pre-pubertal swimmers.

Assessment of Critical Velocity and Blood Lactate in Pre-Pubertal Swimmers

0824 Critical velocity (CV) in swimming represents the speed that can be theoretically maintained indefinitely without exhaustion and has been suggested as a marker of endurance ability. Previous investigations have found high correlations between CV and the anaerobic threshold but also differences between the corresponding velocities. PURPOSE: The aims of the study were 1) to investigate different performance models for the determination of CV and 2) to test the hypothesis that CV identifies an exercise intensity without net lactate production in pre-pubertal male swimmers. METHODS: Data were collected from 7 boys (mean ± SD age 10.5 ± 1.1yr; height 1.41 ± 0.08m and weight 32.6 ± 6.8kg) during 4 maximal front crawl time trials (54.8m, 109.7m, 219.4m and 438.7m) with blood lactate measurements pre and post each trial. CV was determined for each subject by regression analysis using the distance-time model [Distance = ASC + (CV × Time)] and velocity-1/time model [Velocity = CV + (ASC × 1/Time)], where ASC is the Anaerobic Swimming Capacity. The velocity with zero net lactate accumulation was determined based on the interrelationship between swimming velocity and lactate appearance rate (lactate/velocity model). RESULTS: A within subject ANOVA analysis revealed no significant differences between the CV and the goodness of fit (R2) for the distance-time model, (CV = 0.67 ± 0.08 m.s−1, R2 = 1.00 ± 0.001), the velocity-1/time model (CV = 0.68 ± 0.06 m.s−1, R2 = 0.94 ± 0.10), and the lactate/velocity model (CV = 0.70 ± 0.07, r2 0.94 ± 0.08). CONCLUSION: The results demonstrate that 1) the application of the tested models did not generate differences in CV and 2) identified an intensity domain without net lactate appearance. Assessment of critical velocity provides a practical, inexpensive and non-invasive method for determining endurance ability in male pre-pubertal swimmers.