The impact of hypoxia on in vivo glucose uptake in a hypoglycemic fish, Myoxocephalus scorpius

The mechanisms controlling carbohydrate utilization in teleost fish are poorly understood, particularly in the heart. Tissue glucose uptake and cardiovascular characteristics were measured in the short-horned sculpin, Myoxocephalus scorpius, a species exhibiting low blood glucose levels, during normoxia and hypoxia to assess the role of adenosine receptors in the control of glucose uptake and anaerobic metabolism. As expected, hypoxia exposure (300 min at 2 mg/l dissolved oxygen) resulted in a bradycardia and plasma lactate accumulation, but glucose uptake rates did not change in heart, brain, gill, spleen, and white muscle. Plasma glucose-to-intracellular glucose ratios indicated that glucose uptake was the rate-limiting step in glucose utilization. The majority of intracellular glucose was unphosphorylated, however, suggesting that hexokinase is also important in controlling the tissue glucose gradient. During hypoxia, the cholinergic blocker atropine resulted in tachycardia but did not significantly change tissue glucose uptake rates or heart and brain adenosine levels. In contrast, the combined treatment of atropine and an adenosine receptor blocker [8-(p-sulfophenyl)theophylline] during hypoxia increased heart glucose uptake to levels fivefold higher than normoxic fish, with no additive effects on cardiovascular parameters. Significant tissue lactate accumulation was observed in this group of fish, signifying that adenosine receptors may depress anaerobic metabolism, even though tissue adenosine accumulation was absent during hypoxia. White muscle accumulated glucose during normoxia, suggesting the presence of gluconeogenic pathways or active uptake mechanisms not previously described in this tissue.     

Effects of adenosine, exercise, and moderate acute hypoxia on energy substrate utilization of human skeletal muscle

Glucose metabolism increases in hypoxia and can be influenced by endogenous adenosine, but the role of adenosine for regulating glucose metabolism at rest or during exercise in hypoxia has not been elucidated in humans. We studied the effects of exogenous adenosine on human skeletal muscle glucose uptake and other blood energy substrates [free fatty acid (FFA) and lactate] by infusing adenosine into the femoral artery in nine healthy young men. The role of endogenous adenosine was studied by intra-arterial adenosine receptor inhibition (aminophylline) during dynamic one-leg knee extension exercise in normoxia and acute hypoxia corresponding to ～3,400 m of altitude. Extraction and release of energy substrates were studied by arterial-to-venous (A-V) blood samples, and total uptake or release was determined by the product of A-V differences and muscle nutritive perfusion measured by positron emission tomography. The results showed that glucose uptake increased from a baseline value of 0.2 ± 0.2 to 2.0 ± 2.2 μmol·100 g(-1)·min(-1) during adenosine infusion (P < 0.05) at rest. Although acute hypoxia enhanced arterial FFA levels, it did not affect muscle substrate utilization at rest. During exercise, glucose uptake was higher (195%) during acute hypoxia compared with normoxia (P = 0.058), and aminophylline had no effect on energy substrate utilization during exercise, despite that arterial FFA levels were increased. In conclusion, exogenous adenosine at rest and acute moderate hypoxia during low-intensity knee-extension exercise increases skeletal muscle glucose uptake, but the increase in hypoxia appears not to be mediated by adenosine.     

Regulation of glycogen phosphorylase and PDH during exercise in human skeletal muscle during hypoxia

The present study examined the acute effects of hypoxia on the regulation of skeletal muscle metabolism at rest and during 15 min of submaximal exercise. Subjects exercised on two occasions for 15 min at 55% of their normoxic maximal oxygen uptake while breathing 11% O(2) (hypoxia) or room air (normoxia). Muscle biopsies were taken at rest and after 1 and 15 min of exercise. At rest, no effects on muscle metabolism were observed in response to hypoxia. In the 1st min of exercise, glycogenolysis was significantly greater in hypoxia compared with normoxia. This small difference in glycogenolysis was associated with a tendency toward a greater concentration of substrate, free P(i), in hypoxia compared with normoxia. Pyruvate dehydrogenase activity (PDH(a)) was lower in hypoxia at 1 min compared with normoxia, resulting in a reduced rate of pyruvate oxidation and a greater lactate accumulation. During the last 14 min of exercise, glycogenolysis was greater in hypoxia despite a lower mole fraction of phosphorylase a. The greater glycogenolytic rate was maintained posttransformationally through significantly higher free [AMP] and [P(i)]. At the end of exercise, PDH(a) was greater in hypoxia compared with normoxia, contributing to a greater rate of pyruvate oxidation. Because of the higher glycogenolytic rate in hypoxia, the rate of pyruvate production continued to exceed the rate of pyruvate oxidation, resulting in significant lactate accumulation in hypoxia compared with no further lactate accumulation in normoxia. Hence, the elevated lactate production associated with hypoxia at the same absolute workload could in part be explained by the effects of hypoxia on the activities of the rate-limiting enzymes, phosphorylase and PDH, which regulate the rates of pyruvate production and pyruvate oxidation, respectively.     

Differences in response to hypoxia in the three‐spined stickleback from lotic and lentic localities: dominance and an anaerobic metabolite

Dominance hierarchies of the three‐spined stickleback Gasterosteus aculeatus from river and pond populations were subjected to hypoxia (20%, range ± 1%). Under hypoxia, the hierarchies were less stable in terms of rank position and tissue L‐lactate was higher in river fish than pond fish under normoxia and hypoxia. Dominant fish gained mass under normoxia but lost mass under hypoxic conditions possibly due to them maintaining high levels of aggression.     

Differential metabolic adaptation to acute and long-term hypoxia in rat primary cortical astrocytes

Brain astrocytes provide structural and metabolic support to surrounding cells during ischemia. Glucose and oxygen are critical to brain function, and glucose uptake and metabolism by astrocytes are essential to their metabolic coupling to neurons. To examine astrocyte metabolic response to hypoxia, cell survival and metabolic parameters were assessed in rat primary cortical astrocytes cultured for 3 weeks in either normoxia or in either 1 day or 3 weeks sustained hypoxia (5% O2). Although cell survival and proliferation were not affected by the mildly hypoxic environment, substantial differences in glucose consumption and lactate release after either acute or prolonged hypoxia suggest that astrocyte metabolism may contribute to their adaptation. Hypoxia over a period of 1 day increased glucose uptake, lactate release, and glucose transporter 1 (GLUT1) and monocarboxylate transporter 1 (MCT1) expression, whereas hypoxia over a period of 3 weeks resulted in a decrease of all parameters. Furthermore, increased glucose uptake at 1 day of hypoxia was not inhibited by cytochalasin B suggesting the involvement of additional glucose transporters. We uncovered hypoxia-regulated expression of sodium-dependent glucose transporters (SGLT1) in astrocytes indicating a novel adaptive strategy involving both SGLT1 and GLUT1 to regulate glucose intake in response to hypoxia. Overall, these findings suggest that although increased metabolic response is required for the onset of astrocyte adaptation to hypoxia, prolonged hypoxia requires a shift to an energy conservation mode. These findings may contribute to the understanding of the relative tolerance of astrocytes to hypoxia compared with neurons and provide novel therapeutic strategies aimed at maintaining brain function in cerebral pathologies involving hypoxia.     

1H-NMR study of the metabolome of a moderately hypoxia-tolerant fish, the common carp (Cyprinus carpio)

All 20.000 different fish species vary greatly in their ability to tolerate and survive fluctuating oxygen concentrations in the water. Especially fish of the genus Carassius, e.g. the crucian carp and the goldfish, exhibit a remarkable tolerance to limited/absent oxygen concentrations. The metabolic changes of anoxia-tolerant crucian carp were recently studied and published. Contrary to crucian carp, the hypoxia-tolerant common carp cannot survive a complete lack of oxygen (anoxia). Therefore, we studied the ¹H-NMR-based metabolomics of brain, heart, liver and white muscle extracts of common carp, subjected to anoxia (0 mg O₂ l^?1) and hypoxia (0.9 mg O₂ l^?1) at 5 °C. Specifically, fish were exposed to normoxia (i.e. 9 mg O₂ l^?1; controls 24 h, 1 week and 2 weeks), acute hypoxia (24 h), chronic hypoxia (1 week) and chronic hypoxia (1 week) with normoxic reoxygenation (1 week). Additionally, we also investigated the metabolic responses of fish to anoxia for 2 h. Both anoxia and hypoxia significantly changed the tissue levels of standard energy metabolites as lactate, glycogen, ATP/ADP and phosphocreatine. Remarkably, anoxia induced increased lactate levels in all tissues except for the heart whereas hypoxia resulted in decreased lactate concentrations in all tissues except for brains. Furthermore, hypoxia and anoxia influenced amino acids (alanine, valine/(iso)leucine) and neurotransmitters levels (GABA, glutamate). Lastly, we also detected ‘other’ i.e. previously not reported compounds to play a role in the present context. Scyllo-inositol levels changed significantly in heart, liver and muscle, providing novel insights into the anoxia/hypoxic responses of the common carp.     

Metabolic adjustments of an air-breathing teleost, Channa maculata, to acute and prolonged exposure to hypoxic water

Plasma and tissue metabolite levels were measured in the air-breathing Channa maculata during acute and prolonged exposure to normoxic and hypoxic water. Exposure of the fish to hypoxic water (water oxygen partial pressure, PwO ₂= 50 mmHg) for 1 h caused increases in plasma glucose and lactate, liver and brain lactate, liver a-amino acid, heart and brain alanine and brain succinate levels. The metabolic changes in heart, brain and muscle could only be detected when Pw O₂ was 30 or 10 mmHg. Heart glycogen and liver lipid decreased during acute exposure. Prolonged exposure to hypoxic water ( Pw O₂= 30 mmHg) for 3 days caused an increase in plasma glycerol and liver lactate dehydrogenase activity, and a depletion of glycogen store in all tissues investigated. However, metabolite levels which had been elevated during acute hypoxic exposure were observed to return to their normoxic values after prolonged exposure. It was concluded that anaerobic metabolism was triggered by acute exposure to hypoxic water. Prolonged exposure to hypoxic water induced a metabolic readjustment involving mobilisation of lipid and glycogen stores, which is probably a reflection of the high metabolic load of aerial respiration imposed on the fish during exposure to hypoxic water.     

Tissue-Specific Induction of Hsp90 mRNA and Plasma Cortisol Response in Chinook Salmon following Heat Shock, Seawater Challenge, and Handling Challenge

In studying the whole-body response of chinook salmon (Oncorhynchus tshawytscha) to various stressors, we found that 5-hour exposure to elevated temperature (mean 21.6°C; + 10.6°C over ambient) induced a marked increase in Hsp90 messenger RNA accumulation in heart, brain, gill, muscle, liver, kidney, and tail fin tissues. The most vital tissues (heart, brain, gill, and muscle) showed the greatest Hsp90-mRNA response, with heart tissue increasing approximately 35-fold. Heat shock induced no increase in plasma cortisol. In contrast, a standard handling challenge induced high plasma cortisol levels, but no elevation in Hsp90 mRNA in any tissue, clearly separating the physiological and cellular stress responses. We saw no increase either in tissue Hsp90 mRNA levels or in plasma cortisol concentrations after exposing the fish to seawater overnight. Received October 1, 1999; accepted January 21, 2000     

Effects of acute hypobaric hypoxia on the appearance of ingested deuterium from a deuterium oxide-labelled carbohydrate beverage in body fluids of humans during prolonged cycling exercise

To determine whether or not acute hypobaric hypoxia alters the rate of water absorption from a carbohydrate beverage ingested during exercise, six men cycled for 80 min on three randomly assigned different occasions. In one trial, exercise was performed in hypoxia (barometric pressure, P(B) = 594 hPa, altitude 4,400 m) at an exercise intensity selected to elicit 75% of the individual's maximal oxygen uptake (VO2max) previously determined in such conditions. In the two other experiments, the subjects cycled in normoxia (P(B) = 992 hPa) at the same absolute and the same relative intensities as in hypoxia, which corresponded to 55% and 75%, respectively, of their VO2max determined in normoxia. The subjects consumed 400 ml of a 12.5% glucose beverage just prior to exercise, and 250 ml of the same drink at 20, 40 and 60 min from the beginning of exercise. The first drink contained 20 ml of deuterium oxide to serve as a tracer for the entry of water into body fluids. The heart rate (HR) during exercise was higher in hypoxia than in normoxia at the same absolute exercise intensity, whereas it was similar to HR measured in normoxia at the same relative exercise intensity. Both in normoxia and hypoxia, plasma noradrenaline concentrations were related to the relative exercise intensity up to 40 min of exercise. Beyond that duration, when exercise was performed at the highest absolute power in normoxia, the noradrenaline response was higher than in hypoxia at the same relative exercise intensity. No significant differences were observed among experimental conditions, either in temporal profiles of plasma D accumulation or in elimination of water ingested in sweat. Conversely, elimination in urine of the water ingested appeared to be related to the severity of exercise, either high absolute power or the same relative power combined with hypoxia. We concluded that water absorption into blood after drinking a 12.5% glucose beverage is not altered during cycling exercise in acute hypobaric hypoxia. It is suggested that the elimination of water ingested in sweat and urine may be dependent on local circulatory adjustments during exercise.     

Lactate metabolism in the muscle of the crab Chasmagnathus granulatus during hypoxia and post-hypoxia recovery

The present study showed that the lactate/glucose ratio in the hemolymph of Chasmagnathus granulatus maintained in normoxia (controls) was 4.9, suggesting that lactate is an important substrate for this crab. Periods of hypoxia are part of the biological cycle of this crab, and lactate is the main end product of anaerobiosis in this crab. Our hypothesis was that this lactate would be, therefore, used by gluconeogenic pathway or can be oxidized or excreted to the aquatic medium during hypoxia and post-hypoxia periods in C. granulatus. The concentrations of hemolymphatic lactate in animals in normoxia are high, and are used as an energy substrate. In hypoxia, muscle gluconeogenesis and excretion of lactate to the aquatic medium would contribute significantly in regulating the concentration of circulating lactate. Utilization of these pathways would serve the objective of maintaining the acid-base equilibrium of the organism. Muscle gluconeogenesis participates, during the recovery process, in metabolizing the lactate produced during the period of hypoxia. Lactate excretion to the external medium, was one of the strategies used to decrease the higher hemolymphatic lactate levels. However, oxidation of lactate in the muscle is not a main strategy used by this crab to metabolize lactate in the recovery periods.     

Effects of adenosine perfusion on the metabolism and contractile activity of Rana ridibunda heart

The effects of adenosine were examined on the isolated perfused heart of the frog Rana ridibunda. Adenosine produced negative chronotropic and inotropic effects on frog ventricle in a concentration-dependent manner. The effects of adenosine on cardiac metabolism were also investigated by measuring the tissue content of adenine nucleotides, lactate, pyruvate, adenosine and inorganic phosphate, during adenosine perfusion. Adenosine had no effect on the tissue content of metabolites. No net synthesis of adenine nucleotides was observed during perfusion with increasing concentrations of adenosine. Lactate output from the heart decreased significantly with adenosine perfusion. Correlation of adenosine effects on cardiac muscle with the effects of hypoxia are discussed.     

Effects of exogenous growth hormone on milk production and nutrient uptake by muscle and mammary tissues of dairy cows in mid-lactation

Responses to exogenous growth hormone were measured in lactating dairy cows surgically prepared to allow measurement of nutrient exchanges across mammary and hind-limb muscle tissues. Cows were injected daily with either saline or growth hormone, at a dose of 0.1 mg/kg liveweight, over periods of 6 days. During administration of growth hormone milk yield, milk fat content and yields of milk fat protein and lactose increased. Arterial plasma concentrations of glucose and non-esterified fatty acids were increased, uptake of glucose by leg muscle tissue decreased, lactate release from leg muscle tended to increase, mammary uptake of non-esterified fatty acids increased, blood flow to leg muscle tended to increase and blood flow to mammary tissue increased during injection of growth hormone. The results show that growth hormone affects supply to and utilization of key nutrients by tissues, resulting in the supply to the mammary gland of additional precursors for milk synthesis.     

Effect of hypoxia on carbohydrate metabolism in scorpion tissues

The levels of glycogen, glucose, lactate, as well the activities of ten enzymes of carbohydrates metabolism in brain, liver and white muscle of sea scorpion have been investigated. Metabolite concentrations didn't change in brain and the levels of glycogen and lactate were constant in the rest tissues investigated. Glucose concentration decreased in the liver and increased in muscle. In brain hypoxia decreased the activity of hexokinase and increased one of pyruvate kinase, phosphoglucoisomerase and fructoso-1,6-bisphosphatase. In liver most of the enzymes showed the tendency to decrease of their activities. In muscle the activities of phosphofructokinase and phosphoglucoisomerase decreased. Mechanisms of carbohydrates metabolism regulation under hypoxia are discussed.     

Strategies adopted by the mudskipper Boleophthalmus boddaerti to survive sulfide exposure in normoxia or hypoxia

The effects of sulfide on the energy metabolism of Boleophthalmus boddaerti in normoxia and hypoxia were examined. The 24-, 48-, and 96-h LC50 values of sulfide for B. boddaerti with body weight ranging from 11.6 to 14.2 g were 0.786, 0.567, and 0.467 mM, respectively. The tolerance of B. boddaerti to sulfide was not due to the presence of a sulfide-insensitive cytochrome c oxidase. There was no accumulation of lactate in the muscle and liver of specimens exposed to sulfide in normoxia. In addition, the levels of ATP, AMP, and energy charge in both the muscle and the liver were unaffected. These results indicate that B. boddaerti was able to sustain the energy supply required for its metabolic needs via mainly aerobic respiration when exposed to sulfide (up to 0.4 mM) in normoxia. Exposure of B. boddaerti simultaneously to hypoxia and 0.2 mM sulfide for 48 h resulted in decreases in the ATP levels in the muscle and liver. However, the energy charge in both tissues remained unchanged, and the level of lactate accumulated in the muscle was too low to have any major contribution to the energy budget of the fish. Our results reveal that B. boddaerti possesses inducible mechanisms to detoxify sulfide in an ample supply or a lack of O2. In normoxia, it detoxified sulfide to sulfate, sulfite, and thiosulfate. There were significant increases in the activities of sulfide oxidase in the muscle and liver of specimens exposed to sulfide, with that in the liver being >13-fold higher than that in the muscle. However, in hypoxia, sulfide oxidase activity in the liver was suppressed in response to environmental sulfide. In such conditions, there were significant increases in the activities of sulfane sulfur-forming enzyme(s) in the muscle and liver that were not observed in specimens exposed to sulfide in normoxia. Correspondingly, there were no changes in the levels of sulfate or sulfite in the muscle or liver. Instead, B. boddaerti detoxified sulfide mainly to sulfane sulfur in hypoxia. In conclusion, B. boddaerti was able to activate different mechanisms to detoxify sulfide, producing different types of detoxification products in normoxia and hypoxia.     

Tissue glycogen and lactate handling by the developing domestic fowl

The levels of glycogen and lactate in liver, intestine, yolk sac membrane and leg and breast muscle of domestic fowl from day 10 of "in ovo" development to day 5 after hatching compared with adults have been measured and compared with the circulating concentrations in blood of glucose and lactate. Glycogen stores in most tissues increased before hatching to attain a minimum around the eclosion and then increased to adult values in muscle and liver. Lactate maintained its plasma concentrations with higher effectiveness than plasma glucose, which increased steadily up to adult levels from hatching. The study of tissue vs plasma lactate concentration ratios suggests a general activation of lactate metabolism from hatching, coinciding with the ingestion of carbohydrate-based food. Both muscles studied, as well as intestine, seem to be net lactate producers; blood cells can speculatively be considered as lactate users and liver maintains its concentration of lactate very close to that of plasma, suggesting a fast utilization of this material as well as liver being the main site for control of circulating lactate.     

Rates and tissue sites of noninsulin- and insulin-mediated glucose uptake in diabetic rats.

The purpose of the present study was to determine whether streptozotocin-induced diabetes alters the rates and tissue distribution of insulin-mediated glucose uptake (IMGU) and noninsulin-mediated glucose uptake (NIMGU). In vivo glucose disposal was assessed using the tracer [U-14C]-2-deoxyglucose technique in chronically catheterized conscious rats. For nondiabetic animals, rates of NIMGU were determined during severe insulinopenia (less than 5 microU/ml), induced by the infusion of somatostatin, under both euglycemic (6 mM) and hyperglycemic (17 mM) conditions. In diabetic rats, in which a severe insulin deficiency already existed, NIMGU was determined under basal hyperglycemic conditions and during euglycemic conditions produced by inhibiting hepatic glucose output. IMGU was determined in both groups using the euglycemichyperinsulinemic clamp technique. Glucose uptake was consistently higher (50-280%) in all tissues removed from diabetic rats under basal conditions, compared with tissues from control animals in the basal state. When control animals were rendered insulinopenic, glucose uptake by the skeletal muscle, heart, and diaphragm was reduced 30-60%, indicating that the uptake by these tissues occurred by both insulin- and noninsulin-mediated mechanisms. Glucose disposal by the other tissues sampled was entirely due to NIMGU under basal conditions. When blood glucose levels were elevated from 6 to 17 mM in control animals, NIMGU increased in all tissues (60-280%) except the brain. Rates of NIMGU were essentially identical between control and diabetic animals, under either euglycemic or hyperglycemic conditions, when glucose uptake was determined under the same steady-state plasma glucose levels. In contrast to the normal rate of NIMGU by muscle, IMGU by the skeletal muscle and heart from diabetic rats were reduced under mild hyperinsulinemic conditions (100 microU/ml), compared with control animals. Furthermore, in response to a maximal, stimulating dose of insulin (500 microU/ml), IMGU was impaired in the diaphragm, liver, lung, spleen, skin, and kidney removed from diabetic animals. These results indicate that the majority of glucose disposal under basal postabsorptive conditions occurs by NIMGU in both control and diabetic rats. Furthermore, while IMGU was selectively impaired in this model of insulin-dependent diabetes, the rates and tissue distribution of NIMGU were unaltered when glucose uptake was determined under similar plasma glucose levels.     

Tissue glycogen and lactate handling by the developing domestic fowl

The levels of glycogen and lactate in liver, intestine, yolk sac membrane and leg and breast muscle of domestic fowl from day 10 of "in ovo" development to day 5 after hatching compared with adults have been measured and compared with the circulating concentrations in blood of glucose and lactate. Glycogen stores in most tissues increased before hatching to attain a minimum around the eclosion and then increased to adult values in muscle and liver. Lactate maintained its plasma concentrations with higher effectiveness than plasma glucose, which increased steadily up to adult levels from hatching. The study of tissue vs plasma lactate concentration ratios suggests a general activation of lactate metabolism from hatching, coinciding with the ingestion of carbohydrate-based food. Both muscles studied, as well as intestine, seem to be net lactate producers; blood cells can speculatively be considered as lactate users and liver maintains its concentration of lactate very close to that plasma, suggesting a fast utilization of this material as well as liver being the main site for control of circulating lactate.     

Accumulation of intra-arterially administered [3H]adrenaline and [3H]noradrenaline in various tissues of the Atlantic cod, Gadus morhua

The accumulation of intra-arterially administered radiolabelled adrenaline and noradrenaline was studied in various tissues of the Atlantic cod, Gadus morhua. The largest uptake was seen in the posterior cardinal vein (chromaffin tissue), head kidney, kidney, heart and gill filaments. All these tissues, except the heart, also accumulated noradrenaline to a greater extent than adrenaline. The heart, spleen, gas gland and muscularis mucosae of the swimbladder instead favoured adrenaline accumulation. Small amounts of the injected label (both adrenaline and noradrenaline) were also recovered in the intestine, liver and hypothalamus. The lowest detectable amine accumulation was seen in the rest of the brain and in the skeletal muscle. It is suggested that innervation density, blood flow to the tissue and the concentration of circulating and endogenously stored amine, as well as the affinity of the amine for the degrading enzymes and a possible stereospecificity of the uptake mechanisms, determine the rate and preference of accumulation between the amines.     

Lactate Formation in Primary and Metastatic Colon Cancer Cells at Hypoxia and Normoxia

High glucose consumption and lactate synthesis in aerobic glycolysis are a hallmark of cancer cells. They can form lactate also in glutaminolysis, but it is not clear how oxygen availability affects this process. We studied lactate synthesis at various oxygen levels in human primary (SW480) and metastatic (SW620) colon cancer cells cultured with L‐Ser and/or L‐Asp. Glucose and lactate levels were determined colorimetrically, amino acids by HPLC, expression of AST1‐mRNA and AST2‐mRNA by RT‐PCR. In both lines glucose consumption and lactate synthesis were higher at 10% than at 1% oxygen, and lactate/glucose ratio was increased above 2.0 by L‐Asp. AST1‐mRNA expression was independent on oxygen and cell line, but AST2‐mRNA was lower at hypoxia in SW480. We conclude that, in both cell lines at 1% hypoxia, lactate is formed mainly from glucose but at 10% normoxia also from L‐Asp. At 10% normoxia, lactate synthesis is more pronounced in primary than metastatic colon cancer cells.