Examination of the metabolism of oedematous brain tissue

Summary Oedema were induced in rabbit brains by the application of cold metal to defined areas of intact dura for constant times. Trephine openings were made over the right cerebral hemispheres. 24 hours later the animals were killed, and identical pieces of occipital cortex from both hemispheres were removed. In all specimens we determined the water content, the water uptake of the sliced brain in vitro, and the glucose metabolism of the brain slices. Respiration, carbon dioxide production in the presence of bicarbonate, consumption of glucose, and production of lactate and pyruvate were measured. The incubations were made in physiological saline (with K⁺, Ca²⁺, Mg²⁺ and PO₄ ³- additions) in the presence of gas mixtures with different contents of oxygen.The mean difference of the water contents in vivo was 1.3%. The lowest water content after in vitro incubations was found in the presence of 95% O₂ and 5% CO₂.The oedematous tissue had a slightly stimulated respiration, and its aerobic glycolysis was markedly increased. These metabolic differences were observed only in the presence of 12% O₂ and 5% CO₂ and higher oxygen concentrations. In the presence of 4% O₂ and 5% CO₂ neither respiratory nor glycolytic differences existed between normal and oedematous tissue.A pronounced Pasteur effect was seen in all the experiments. Increase in glycolysis is a more sensitive indicator of oxygen lack than is decrease in respiration.During 150 min of incubation respiration and carbon dioxide production become slower. The decrease in total and glycolytic CO₂ production is greater in slices of control hemispheres than in slices of oedematous hemispheres.The best correlation between metabolic activities determined by manometry and metabolic activities determined by glucose, lactate and pyruvate determinations was found in experiments in the presence of 4% O₂ and 5% CO₂. It is concluded that unsliced brain in the presence of air, at room temperature and below, has nearly the same respiration and glycolysis within the whole glucose degradation process as have brain slices at 38 °C in the presence of 4% O₂ and 5% CO₂.The conclusion is made that in vitro the best metabolic situation for brain slices, normal and oedematous, is between 20% and 95% of oxygen.Supported by the Deutsche Forschungsgemeinschaft: He 573/3.With technical assistance from E. Seifert and H. Verfürth.     

Sodium nitroprusside (NPS) stimulates the lactate formation and causes intracellular electrolyte shifts in brain slices

Summary Nitroprusside sodium (NPS) was added to slices from grey and white rabbit brain matter. The respiration, consumption of glucose, formation of lactate and pyruvate, water content, size of the extracellular space, and total and intracellular sodium and potassium concentrations were determined and calculated.0.5 and 1 mM NPS stimulated the glycolytic glucose breakdown, and inhibited the respiration of grey and white slices. The respiration of white matter slices was stimulated by 0.05 and 0.01 mM NPS.The total and intracellular potassium concentrations in slices from grey and white matter were lowered markedly by 1 mM NPS. The total and the intracellular sodium concentrations in grey brain matter slices became higher in the presence of 1 mM NPS. A warning is given against uncritical clinical use of higher concentrations of NPS.Part of the Dissertation, Med. Fakultät Homburg/Saar, 1979.     

Gut exchange of glucose and lactate in basal state and after oral glucose ingestion in postoperative patients

Glucose uptake by the intestine and its conversion into 3-carbon compounds in the human intestine in the basal state and after an oral glucose load are not understood. Consequently, we studied the arterial and portal venous concentration differences (A-PV) for glucose and glucogenic substrates in the basal state and 3 h after the ingestion of a 100-g glucose load with the catheter technique. Five patients were studied 3-11 days after surgery for gallbladder disease or cancer of the colon or liver. A-PV for glucose in the basal state was 0.12 +/- 0.02 mM (P less than 0.01), indicating net glucose uptake by extrahepatic splanchnic tissues. No net exchange of lactate or pyruvate was detected, but there was release of alanine and uptake of glutamine. After glucose ingestion, glucose was released by the gut, reflecting absorption of the load (mean A-PV for glucose -2.10 +/- 0.04 mM, P less than 0.01). The arterial glucose concentration rose gradually from 4.6 +/- 0.1 mM before glucose ingestion to a plateau at 9.5 +/- 0.7 mM from 90 to 180 min. Glucose ingestion was accompanied by net lactate and alanine release (A-PV -0.16 +/- 0.06 mM and -48 +/- 7 microM, respectively), whereas A-PV for pyruvate did not change. We conclude that, in postoperative patients, there is a significant net glucose uptake by the gastrointestinal tract in the basal state. Glucose ingestion is accompanied by a small release of lactate and alanine from the intestine. However, the estimated net gut formation of lactate and alanine can play only a minor role in the disposal of an oral glucose load.     

Use of a sealed mini-chamber to investigate human sperm motility in real time under aerobic and anaerobic conditions.

To study the correlation between metabolism and motility, ejaculated human spermatozoa were washed in media containing glucose, pyruvate, and deoxyglucose in various combinations. Spermatozoa suspended in these media were incubated in sealed mini-chambers and subjected to aerobic or anaerobic conditions at 37 degrees C. The effect on the patterns of sperm motility was investigated in real time by direct observation and objective determination with the multiple exposure photography (MEP) method. The motility of spermatozoa incubated in media containing excess of glucose showed similar changes of motility quality with time, whether exposed to aerobic or anaerobic conditions, and in both cases motility lasted about 13 h. Motility of sperm incubated with pyruvate only was of a much lower quality, especially under anaerobic conditions, and in both circumstances lasted about 7 h. When glycolysis of fructose remnants was totally inhibited by deoxyglucose and sperm were incubated with pyruvate only, motility lasted for 2 h under aerobic conditions and only for about 1 h under anaerobic conditions. It is concluded that the main metabolic process that supplies energy for sperm motility is glycolysis, under both aerobic and anaerobic conditions. Oxidative respiration was less efficient as a source of energy for sperm motility. When glycolysis was inhibited and oxidative respiration was eliminated under anaerobic conditions, sperm motility lasted only for about 1 h, probably by using intracellular energy reserves.     

Examination of the metabolism of oedematous brain tissue

Summary A circumscribed brain oedema was caused by the localized application of cold in the rabbit's brain. The metabolism of oedematous brain slices and analogous areas from the non-lesioned hemisphere were examined with the new 2-vessel method ofWarburg. In comparison with the uninjured brain, aerobic and anaerobic glycolyses were strongly increased in oedematous tissue, the respiration was slightly increased. These findings may be interpreted as the expression of an elimination of a previously existing energy deficit.The work was supported by D.F.G. (German Res. Community) H. 573/1.     

Evidence for aerobic glycolysis in lambda-carrageenan-wounded skeletal muscle

Classically, increased lactate production in wounded tissue is ascribed to anaerobic glycolysis although its oxygen consumption has been found to be similar to normal tissue. This apparent inconsistency was studied in a standardized isolated perfused wound model. Male Sprague-Dawley rats were wounded (group W) with intramuscular injections of lambda-carrageenan and fed ad lib.; not wounded and pair fed to the decreased food intake of the wounded animals (group PFC); or not wounded and fed ad lib. (group ALC). After 5 days, the hindlimbs of animals from each group were either perfused using a standard perfusate with added [U-14C]glucose or [1-14C]pyruvate or assayed for the tissue content of lactate and pyruvate. In addition, the effect of a 30% hemorrhage on the tissue lactate and pyruvate concentration was examined. Wounding increased glucose uptake and lactate production by 100 and 96%, respectively, above that seen in ALC animals. Oxygen consumption was unchanged by wounding (5.74, 5.14, and 5.83 mumole/min/100 g in W, PFC, and ALC, respectively). Glucose and pyruvate oxidation were also unaltered among the groups. Hemorrhage resulted in a comparable increase in lactate and pyruvate in tissue from wounded and pair-fed control animals (above those concentrations found in tissue harvested without preexisting hemorrhage). As a consequence, the same relationship in L/P ratio was maintained after hemorrhage. Taken together, these results confirm the presence of aerobic glycolysis in wounded tissue (unchanged oxygen consumption, glucose, and pyruvate oxidation). In addition, pyruvate dehydrogenase activity in the wound was apparently the same as that found in muscle from pair-fed control animals.     

Effect of extended cold ischemia time on glucose metabolism in liver grafts: experimental study in pigs

Background/Purpose Recovery of normal carbohydrate metabolism in the liver after transplantation is highly important. The aim of the present study was to evaluate how short and long cold ischemia (CI) time followed by warm ischemia (WI) impact intrahepatic glucose metabolism in a pig liver transplantation model. Methods Twenty-six animals were divided into two transplantation groups: group I with a liver ischemia time of 5 h (n = 6), and group II with 15 h of liver ischemia (n = 7). Intrahepatic microdialysis samples were collected throughout the experiment at 20-min intervals, during the donor operation, cold preservation, liver implantation, and liver reperfusion in the recipient. Glucose, lactate, and pyruvate concentrations were analyzed and the lactate/pyruvate ratio (L/Pr) was calculated. Result There were no changes in glucose levels during CI. However, during WI, glucose and lactate increased and the increase was significantly higher in the group with longer CI (P < 0.01). The L/Pr increased at the beginning of CI but accelerated to increase during WI in both groups, with significantly prolonged and higher levels in the group with longer CI (P < 0.01). Conclusions Extended CI results in increased intrahepatic glycogenolysis, delayed restoration of aerobic glycolysis, and prolonged anaerobic glycolysis shortly after reperfusion. Improvements in glycogen protection and faster restoration of aerobic metabolism during preservation and reperfusion time seem to be necessary in order to improve liver preservation protocols per se.     

Content of CoA-esters in perifused rat islets stimulated by glucose and other fuels

Fluorometry and high-performance liquid chromatography were used to measure the content of free CoA and the esters of acetate, malonate, succinate, and long-chain fatty acids in isolated perifused rat pancreatic islets exposed to 25 mM glucose or a mixture of fuels (25 mM glucose plus 10 mM glutamine, 10 mM lactate, and 1 mM pyruvate) to assess the role of intermediates of lipid metabolism as candidate metabolic coupling factors in the mechanism of fuel-induced insulin secretion. Insulin secretion was stimulated in a biphasic manner with the fuel mixture, showing twice the potency compared with high glucose alone. Islets perifused for 3 min with high glucose alone or the fuel mixture compared with 2.5 mM glucose showed a significant increase in malonyl-CoA and succinyl-CoA and a decrease in acetyl-CoA. Free CoA and long-chain acyl-CoA levels were unaltered. Perifused islets stimulated with 25 mM glucose for 30 min showed a significant increase in succinyl-CoA and long-chain acyl-CoA and decrease in acetyl-CoA, whereas malonyl-CoA was not affected. However, when islets were stimulated by the fuel mixture for 30 min, malonyl-CoA was maintained at a high level, and the change in succinyl-CoA and long-chain acyl-CoA was similar to that observed in islets stimulated with 25 mM glucose alone. The acetyl-CoA concentration in the islets stimulated with the fuel mixture decreased slightly. These results confirm the viability of the hypothesis that malonyl-CoA and long-chain acyl-CoA serve as metabolic coupling factors in signal transduction when islets are stimulated by high glucose or glucose combined with other fuels.     

Relationship between lactate and glutamine metabolism in vitro by the kidney: differences between dog and rat and importance of alanine synthesis in the dog

Interaction between lactate (1 or 5 mM) and glutamine (1 or 5 mM) metabolism was studied with renal cortical slices incubated at a pH of 7.0 and obtained from acidotic (ammonium chloride) dogs and rats. The effect of aminooxyacetate (0.2 mM), dichloroacetate (3 mM), and fluoroacetate (0.05 mM) was also studied. Significant differences were observed between dog and rat. In the dog, lactate had no effect on glutamine uptake and vice versa, but gluconeogenesis increased. Ammonia production, however, decreased by 13 to 21%, whereas a significant increase in alanine production was noted. In the rat, glutamine extraction and ammonia production dropped by 33% with 5 mM lactate. In contrast to the observation in the dog, no production of alanine was noted, but significant accumulation of glutamate took place. Amino-oxyacetate inhibited alanine production in the dog and reestablished ammoniagenesis, and it led to a marked decrement in the uptake of lactate and glucose production in both species. Dichloroacetate in the dog resulted in a reduction in pyruvate, alanine, glucose, and ammonia production while glutamate accumulation was observed. In both species, fluoroacetate stimulated glutamine uptake and ammonia production. With lactate alone, fluoroacetate decreased lactate uptake and glucose production. With both lactate and glutamine in the medium, fluoroacetate prevented any effect of lactate on ammoniagenesis. The present study demonstrates that lactate has a modest depressing effect on renal ammonia production by dog slices through increased synthesis of alanine and redistribution of nitrogen from glutamine. In the rat, the depressing effect of lactate on ammonia production in the alanine amino-transferase deficient kidney occurs through accumulation of glutamate. The data also reveal that oxidation of lactate to carbon dioxide is greater in the dog than it is in the rat, but that gluconeogenesis from lactate is more important in the rat.     

Leberstoffwechsel während kalter ischämischer Inkubation in UW-Lösung am Rattenmodell

Simple cold storage of livers for transplantation activates glycolysis due to lack of oxygen. Energy derived from glycolysis may be critical for cell survival and liver cell death may occur once glycolysis is inhibited in the liver due to accumulation of end products or lack of substrates (glycogen). The relationship between cell death (lactate dehydrogenase, LDH release), anaerobic glycolysis (lactate production), and glycogen content of liver tissue was studied during cold incubation of liver slices in UW solution. Rat livers slices from male Sprague Dawley rats were incubated at 4°C in UW solution, with continuous gentle shaking, under conditions of chemical hypoxia (KCN, 5 mM). The rate of lactate production, LDH release, ATP and glycogen content were measured spectrophotometrically and by HPLC. Lactate increased nearly linearly for the first 48 h of incubation; total lactate which had accumulated after 48 h was 33.9±0.81 µmol/g and at 96 h nearly the same, 31.3±1.2 µmol/g. Glycolysis stopped, apparently, because of the depletion of liver slice glycogen which was initially 228.8±1.7 µmol/g wet wt. It decreased to 34.7±2.7 µmol/g at 48 h and to 18.7±1.1 µmol/g at 72 h and remained at this level for the next 24 h. An increased leakage of LDH occurred once glycogen metabolism (and accumulation) ceased. LDH release could be stimulated after only a few hours of cold incubation of liver tissue slices by adding glycolysis inhibitor (iodoacetic acid) to the medium. After 24 h, LDH release was 24.4±1.8% and increased to 52.8±5.2% (P<0.05, Student'st-test) with iodoacetic acid. Adding a glycolytic substrate (fructose, 10 mM) to the medium maintained lactate production for 96 h. The stimulation of glycolysis by fructose also reduced cell death: LDH release was significantly lower at 72- and 96-h incubation (P<0.001, two-way ANOVA). The ATP content was significantly higher with fructose (P<0.001). Adding glucose (20 mM) and fructose (10 mM) in combination resulted in prolonged cell survival, significantly delayed glycogen depletion and significantly higher ATP content at 48 and 72 h (two-way ANOVA). Livers from rats who had fasted for 24 h demonstrated the same LDH release at 48 h when incubated with glucose (20 mM) and fructose (10 mM). In conclusion, LDH leakage from hypoxic cold-stored liver slices is related to anaerobic glycolysis. Anaerobic glycolysis appears to continue slowly under hypothermia and provides sufficient energy for maintenance of cell viability. A stimulation of glycolysis in the cold is possible by fructose and results in prolonged cell survival under hypothermic conditions. Glycogen depletion can be slowed down by combining glucose and fructose.     

The relationship between glycolysis, mitochondrial respiration, protein-carboxyl methylation and motility in hamster epididymal spermatozoa

Endogenous protein-carboxyl methylase activity can be measured in intact motile spermatozoa by using [³H]methionine as a precursor of the methyl donor, S-adenosylmethionine (SAM). Since the conversion of methionine to SAM requires ATP, the relationship between the energy metabolism of spermatozoa and methylation was investigated using inhibitors of glycolysis and mitochondrial respiration. When hamster spermatozoa from cauda epididymides were incubated in 12.2 mM glucose, glycolysis was progressively inhibited as concentrations of 2-deoxyglucose (2-DOG) increased. On the other hand, endogenous protein-carboxyl methylation showed a biphasic response being stimulated at low concentrations of 2-DOG and inhibited at higher concentrations. Sperm movement was also altered by 2-DOG. Increasing concentrations of 2-DOG in the incubation medium resulted in an increase in beat amplitude and a corresponding decrease in beat frequency. When the glucose concentration of the medium was reduced to 5 mM, protein methylation was inhibited at all concentrations of 2-DOG. The biphasic effect of 2-DOG on methylation at 12.2 mM and its monophasic effect at 5 mM suggested that this reaction was related to the effective glucose concentration. To investigate this possibility, endogenous protein-carboxyl methylation was measured after incubation of sperm in glucose concentrations ranging from 0–48.8 mM. Low glucose concentrations stimulated protein methylation (up to 6.1 mM for maximal effect), but further increases in the glucose concentration***     

Prostate epithelial cells utilize glucose and aspartate as the carbon sources for net citrate production

The prostate gland (human, rat ventral prostate) has the major function of accumulating and secreting extremely high levels of citrate. This function requires unique and specialized metabolic pathways associated with prostate secretory epithelial cells by which exogenous substrates must be utilized as the six-carbon sources of citrate. Recent studies demonstrated that aspartate can serve as the four-carbon source of oxalacetate for citrate synthesis. Identification of the two-carbon source of acetyl CoA (AcCoA) had not been established. The present study investigated the probability that exogenous glucose, via pyruvate oxidation, is a physiological source of AcCoA for net citrate production by isolated epithelial cells from rat ventral prostate. Under adequate oxygenation, 5 mM glucose in the presence of aspartate plus glutamate markedly stimulated citrate production. Exogenous and endogenous pyruvate also stimulated net citrate production. We propose that glucose via aerobic glycolysis and pyruvate oxidation provides AcCoA, which condenses with oxalacetate obtained from aspartate transamination for citrate synthesis. Prostate epithelial cells do not readily oxidize citrate, which permits accumulation and secretion of the synthesized citrate.     

Diabetes-induced glomerular dysfunction: links to a more reduced cytosolic ratio of NADH/NAD+.

These studies were undertaken to examine effects of elevated glucose levels on glycolysis, sorbitol pathway activity, and the cytosolic redox state of NADH/NAD+ in isolated glomeruli. Blood-free glomeruli were isolated from kidneys of male, Sprague-Dawley rats using standard sieving techniques, then incubated for one hour at 37 degrees C, pH 7.4, pO2 approximately 500 torr, in Krebs bicarbonate/Hepes buffer containing 5 or 30 mM glucose. Elevated glucose levels increased glucose 6-phosphate, fructose 6-phosphate, total triose phosphates, lactate, the lactate/pyruvate ratio, sorbitol, and fructose, but did not affect sn-glycerol 3-phosphate, pyruvate, or myo-inositol levels. The more reduced glomerular cytosolic redox state (manifested by the tissue lactate/pyruvate ratio) induced by 30 mM glucose was completely abrogated by aldose reductase inhibitors added to the diet two to seven days prior to glomerular isolation. These observations, coupled with evidence linking glucose- and diabetes-induced glomerular dysfunction to increased sorbitol pathway metabolism, support the hypothesis that metabolic imbalances associated with a more reduced ratio of cytosolic NADH/NAD+ (resulting from increased glucose metabolism via the sorbitol pathway) play an important role in mediating glucose- and diabetes-induced glomerular dysfunction.     

Influence of Abdominal Surgical Trauma on Substrate Utilization by the Human Brain

In 10 patients undergoing cholecystectomy, measurements of jugular venous blood flow (one side) and arterio-jugular vein differences of oxygen, glucose, lactate, pyruvate, glycerol, 3-hydroxybutyrate and alanine were made. The arterial concentration of 3-hydroxybutyrate was raised during surgery, but this substrate only covered a minute part of the total energy demand. The need for substrates of oxidative metabolism in the brain was met by glucose. During the operation the stoichiometrically calculated oxygen uptake was lower than that of glucose, indicating an increase in the brain glucose content.     

Isotopic evaluation of the metabolism of pyruvate and related substrates in normal adult volunteers and severely burned children: effect of dichloroacetate and glucose infusion

In this study we have assessed the hypothesis that there is a postreceptor defect in glucose metabolism that makes the severely burned patient unable to oxidize glucose efficiently as an energy source. The intracellular pyruvate pool was labeled by the infusion of 3-13C-lactate, and expired CO2 production and isotopic enrichment of both pyruvate and CO2 were determined to calculate the rate of pyruvate production and oxidation. 6,6-d2-Glucose and 15N-alanine were infused simultaneously to relate pyruvate kinetics and oxidation to glucose and alanine kinetics. Five normal volunteers and 10 severely burned patients (mean of 80% +/- 5% body surface burned) were studied in the basal state and during continuous (unlabeled) glucose infusion. Also, the effect of dichloroacetate, which normally stimulates pyruvate dehydrogenase activity, was assessed in both volunteers and patients. The burned patients had many of the classic metabolic responses to severe injury, including significant increases in resting energy expenditure, glucose production, and alanine release from protein breakdown. However, rather than being inhibited, the rate of pyruvate oxidation was increased approximately 300% in burned patients. Although the patients had an elevated mean concentration of lactate, stemming from increased lactate production, no deficit in pyruvate dehydrogenase activity was evident. Rather, the high rate of lactate production was apparently a consequence of the high rate of glycolysis. On the other hand, the direct pathway for synthesis of glycogen from infused glucose appeared to be impaired in burned patients. In both volunteers and patients, dichloroacetate stimulated the percent of pyruvate directed to oxidation, thereby reducing the conversion of pyruvate to other fates, including lactate. However, because there was no deficit in pyruvate dehydrogenase activity in the patients compared with normal volunteers before dichloroacetate treatment, no unique effect of dichloroacetate on glucose or protein kinetics was observed in burned patients. From these results we conclude that if there is a postreceptor defect in glucose metabolism in burned patients, it involves the pathway of direct glycogen synthesis and not the pathway of oxidation.     

Hypothalamic glucose sensor: similarities to and differences from pancreatic beta-cell mechanisms.

Glucose-responsive neurons in the ventromedial hypothalamus (VMH) are stimulated when glucose increases from 5 to 20 mmol/l and are thought to play an essential role in regulating metabolism. The present studies examined the role of glucose metabolism in the mechanism by which glucose-responsive neurons sense glucose. The pancreatic, but not hepatic, form of glucokinase was expressed in the VMH, but not cerebral cortex, of adult rats. In brain slice preparations, the transition from 5 to 20 mmol/l glucose stimulated approximately 17% of the neurons (as determined by single-cell extracellular recording) from VMH but none in cortex. In contrast, most cells in both VMH and cortex were silent below 1 mmol/l and active at 5 mmol/l glucose. Glucosamine, 2-deoxyglucose, phloridzin, and iodoacetic acid blocked the activation of glucose-responsive neurons by the transition from 5 to 20 mmol/l glucose. Adding 15 mmol/l mannose, galactose, glyceraldehyde, glycerol, and lactate to 5 mmol/l glucose stimulated glucose-responsive neurons. In contrast, adding 15 mmol/l pyruvate to 5 mmol/l glucose failed to activate glucose-responsive neurons, although pyruvate added to 0 mmol/l glucose permitted neurons to maintain activity. Tolbutamide activated glucose-responsive neurons; however, diazoxide only blocked the effect of glucose in a minority of neurons. These data suggest that glucose-responsive neurons sense glucose through glycolysis using a mechanism similar to the mechanism of pancreatic beta-cells, except that glucose-responsive neurons are stimulated by glycerol and lactate, and diazoxide does not generally block the effect of glucose.     

Experimental transplantation gliomas in the adult cat brain

Experimental brain tumours were produced in adult cats by stereotactic xenotransplantation of the rat glioma clone F98. Regional ATP, glucose and lactate were measured after 2-4 weeks on coronal cryostat sections by substrate-induced bioluminescence, potassium content was imaged by the histochemical sodium cobaltinitrite method, and regional pH by incubating cryostat sections with the fluorescent pH-indicator umbelliferone. The regional biochemical alterations were correlated with magnetic resonance imaging and tissue water content. Biochemical changes were heterogeneous in tumours but exhibited a rather uniform pattern in peritumoural oedema. ATP was consistently reduced, glucose and lactate were increased and pH was more alkaline than in normal white matter. The decrease of ATP matched the increase of water, indicating that ATP decline represents fractional dilution in the oedematous tissue rather than break-down of energy metabolism. The increased lactate levels, therefore, may originate from the tumour and not from a metabolic disturbance in the peritumoural oedematous tissue. The implications of this interpretation for the pathogenesis of peritumoural oedema are discussed.     

Influence of glucose kinetics on plasma lactate concentration and energy expenditure in severely burned patients

BACKGROUND: In critically ill patients, elevation in the plasma lactate concentration has traditionally been interpreted as indicating a deficiency in oxygen availability and is often an impetus to increase oxygen delivery clinically. However, another possible basis for increased lactate concentrations may be simply a mass effect from increased pyruvate availability (i.e., accelerated glycolysis). METHODS: In six hypermetabolic burned patients, the rates of glucose production and oxidation were quantified using a tracer infusion of 6,6 d2 glucose combined with indirect calorimetry. Measurements were obtained after a 9-hour fast and after a 3-hour infusion of unlabeled glucose at 30 micromol/kg/min. No patient was overtly septic, hypoxic, or hypovolemic. RESULTS: The infusion of glucose significantly increased the arterial glucose concentration and rate of glucose oxidation, with a corresponding increase in the arterial plasma concentration of lactate and pyruvate. Resting energy expenditure and oxygen consumption were not affected by the infusion of glucose. CONCLUSIONS: These findings show that elevations in plasma lactate in severely injured patients may, in part, be related to increases in glucose flux and not entirely a reflection of any deficit in oxygen availability. Such findings highlight a potential pitfall for interpreting plasma lactate concentrations as an index of tissue oxygen availability in hypermetabolic patients.     

Adrenergic blockade reduces skeletal muscle glycolysis and Na(+), K(+)-ATPase activity during hemorrhage

BACKGROUND: Recent evidence suggests that hyperlactatemia in shock may reflect accelerated aerobic glycolysis linked to activity of the Na(+), K(+)-ATPase rather than hypoxia. Epinephrine stimulates glycolysis in resting muscle largely by stimulating Na(+), K(+)-ATPase activity. This study evaluates the effects of hemorrhagic shock, with and without combined alpha- and beta-adrenergic receptor blockade, on lactate production, glycogenolysis, Na(+)-K(+) pump activity, and high-energy phosphates in rat skeletal muscle. METHODS: Male Sprague-Dawley rats in four treatment groups were studied: unhemorrhaged control not receiving blockers (CN), controls receiving blockers (CB), shocked animals not receiving blockers (SN), and shocked rats receiving blockers (SB). Shocked rats (SN and SB) were bled to a MAP of 40 mm Hg, maintained for 60 min. Blocker groups (CB and SB) received propranolol and phenoxybenzamine. Arterial blood was drawn for plasma lactate, epinephrine, norepinephrine, and gas analysis. Lactate, glycogen, glucose 6-phosphate, ATP, phosphocreatine, and intracellular Na(+) and K(+) were determined in extensor digitorum longus and soleus muscles. For comparison, muscles were exposed to epinephrine and/or ouabain in vitro. RESULTS: With the exception of P(a)CO(2), HCO(3), and base excess in the SN group, no significant differences in arterial blood gas parameters were noted. Adrenergic blockade significantly reduced plasma lactate concentration. In shocked rats, adrenergic blockade significantly reduced muscle lactate and glucose 6-phosphate accumulation. Intracellular Na(+):K(+) ratio was decreased in SN rats, implying increased Na(+)-K(+) pump activity. Adrenergic blockade raised the intracellular Na(+):K(+) ratio in shocked animals, implying decreased pump activity. Epinephrine exposure in vitro stimulated muscle lactate production, raised glucose 6-phosphate content, and significantly reduced soleus phosphocreatine stores. CONCLUSIONS: Neither hypoxia nor defective oxidative metabolism appeared responsible for increased glycolysis during hemorrhagic shock. Adrenergic blockade concurrently reduced plasma lactate, muscle levels of lactate and glucose 6-phosphate, and muscle Na(+)-K(+) pump activity during shock. Rapid skeletal muscle aerobic glycolysis in response to increased plasma epinephrine levels may be an important contributor to increased glycolysis in muscle and increased plasma lactate during hemorrhagic shock.     

Lgr4 promotes aerobic glycolysis and differentiation in osteoblasts via the canonical Wnt/β-catenin pathway

Lgr4, a G-protein-coupled receptor, is associated with various physiological and pathological processes including oncogenesis, energy metabolism, and bone remodeling. However, whether Lgr4 is involved in osteoblasts' metabolism is not clear. Here we uncover that in preosteoblast cell line, lacking Lgr4 results in decreased osteogenic function along with reduced glucose consumption, glucose uptake, and lactate production in the presence of abundant oxygen, which is referred to as aerobic glycolysis. Activating canonical Wnt/β-catenin signaling rescued the glycolytic dysfunction. Lgr4 promotes the expression of pyruvate dehydrogenase kinase 1 (pdk1) and is abolished by interfering canonical Wnt/β-catenin signaling. Mice lacking Lgr4 specifically in osteoblasts (Lgr4^osb−/−) exhibit decreased bone mass and strength due to reduced bone formation. Additionally, glycolysis of osteoblasts is impaired in Lgr4^osb−/− mice. Our study reveals a novel function of Lgr4 in regulating the cellular metabolism of osteoblasts. © 2021 American Society for Bone and Mineral Research (ASBMR).