Inhibition Of Lactate Production Research Articles

Stimulation by hexose esters of lactate production by rat erythrocytes: insensitivity to 3-O-methyl-D-glucose and inhibition by 2-deoxy-D-glucose and its tetraacetic ester.

Selected esters of D-glucose were recently proposed as tools to provide the sugar to cells, whilst bypassing the carrier system for hexose transport across the plasma membrane. In the present study, alpha-D-glucose pentaacetate, beta-D-glucose pentaacetate, alpha-D-mannose pentaacetate and, to a lesser extent, 6-O-acetyl-D-glucose, all tested at a 1.7 mM concentration, were found to increase lactate production above basal value in rat erythrocytes. Over 90 min incubation, the increment in lactate production ranged from about 1.2 (alpha-D-glucose pentaacetate) to 0.6 (6-O-acetyl-D-glucose) micromol/microl of erythrocytes. Little or no change in lactate production was observed in cells exposed to beta-L-glucose pentaacetate, alpha-D-glucose pentaethylsuccinate, alpha-D-galactose pentaacetate or beta-D-galactose pentaacetate. The metabolic response to alpha-D-glucose pentaacetate was resistant to 3-O-methyl-D-glucose (10-80 mM) which suppressed, however, that evoked by D-glucose. D-mannoheptulose (10 mM) virtually failed to affect the response to D-glucose and its pentaacetate ester. On the contrary, 2-deoxy-D-glucose (10.6 mM) inhibited to the same relative extent (55% decrease) lactate production in erythrocytes exposed to either unesterified D-glucose or alpha-D-glucose pentaacetate. The tetraacetic ester of 2-deoxy-D-glucose was more efficient than unesterified 2-deoxy-D-glucose in inhibiting lactate production from alpha-D-glucose pentaacetate. It is proposed that selected esters of saccharides represent useful tools to bypass defects in hexose transport, and to increase their nutritional or therapeutic efficiency.

The Protective Action of Tetrodotoxin and (±)-Kavain on Anaerobic Glycolysis, ATP Content and Intracellular Na+ and Ca2+ of Anoxic Brain Vesicles

Because recent reports point to Na+ channel blockers as protective agents directed against anoxia-induced neuronal damage including protection of anaerobic glycolysis, the influences of tetrodotoxin (TTX) and (±)-kavain on anoxic rat brain vesicles were investigated with respect to lactate synthesis, vesicular ATP content and cytosolic free Na+ and Ca2+ ([Na+]i, [Ca2+]i), both of the latter determined fluorometrically employing SBFI and FURA-2, respectively. After anoxia, basal lactate production was increased from 2.9 to 9.8 nmol lactate/min/mg protein. Although lactate synthesis seemed to be stable for at least 45 min of anoxia, as deduced from the linearity of lactate production, the ATP content declined continuously with a half life (τ12) af 14.5 min, indicating that anaerobic glycolysis was insufficient to cover the energy demand of anoxic vesicles. Correspondingly, [Na+]i and [Ca2+]i increased persistently after anoxia by 22.1 mmol/l Na+ and 274.9 nmol/l Ca2+, determined 6.3 min after onset. An additional stimulation of vesicles with veratridine accelerated the drop of ATP (τ12 = 5.1 min) and provoked a massive Na+ overload, which levelled off to 119 mmol/l Na+ within a few minutes. Concomitantly, [Ca2+]i increased linearly with a rate of 355 nmol Ca2+/l/min. Despite the massive perturbation of ion homeostasis, lactate production was unaffected during the first 8 min of veratridine stimulation. However, complete inhibition of lactate synthesis took place 30 min after veratridine was added. The Na+ channel blockers TTX and (±)-kavain, if applied before anoxia, preserved vesicular ATP content, diminished anoxia-induced increases in [Na+]i and [Ca2+]i and prevented both the veratridine-induced increases of [Na+]i and [Ca2+]i and the inhibition of lactate production. The data indicate a considerable Na+ influx via voltage-dependent Na+ channels during anoxia, which speeds up the decline in ATP and provokes an increase in [Ca2+]i. A massive Na+ and Ca2+ overload induced by veratridine failed to influence lactate synthesis directly, but initiated its inhibition. © 1997 Elsevier Science Ltd. All rights reserved.

Fatty acid, tricarboxylic acid cycle metabolites, and energy metabolism in vascular smooth muscle.

The influence of octanoate on O2 consumption, tricarboxylic acid (TCA) cycle intermediates, and high-energy phosphates was examined in intact resting porcine carotid artery to investigate the role of fatty acid in energy metabolism and its integration with glucose metabolism in vascular smooth muscle. Incubation of resting arteries with octanoate (0.5 mM), which was previously shown to inhibit aerobic glycolysis (6), inhibited lactate production by 64% and increased O2 consumption by 30%. The increase in O2 consumption with octanoate was approximately equal to that calculated to account for the ATP production lost by inhibition of aerobic lactate production by octanoate. In glucose-free medium, the level of high-energy phosphate was reduced but was restored when octanoate was included in the incubation medium. This was associated with an increase in O2 consumption. These results suggest that the energy requirements of resting carotid artery can be largely met by the oxidative metabolism of fatty acid. Octanoate induced anaplerosis of the TCA cycle, as indicated by a 70% increase in the level of citrate. Extracellular glucose was necessary for octanoate-induced anaplerosis, probably by providing the extra carbon via pyruvate carboxylation, whereas a coupled transamination involving aspartate was a less important anaplerotic mechanism.

Regulation of fos and jun immediate-early genes by redox or metabolic stress in cardiac myocytes.

We have previously demonstrated coordinate inductions of c-fos, c-jun, jun B, and jun D in cardiac myocytes exposed to hypoxia for 2 to 4 hours. Induction of these transcripts occurred before any significant loss of intracellular ATP. In the present study, the origin of the signal(s) that regulates immediate-early gene induction was investigated by comparing the effects of hypoxia with those of the metabolic inhibitors cyanide, deoxyglucose and cyanide combined, and iodoacetic acid. Cyanide, an inhibitor of oxidative metabolism, closely mimicked the metabolic effects of hypoxia, with elimination of oxygen consumption, increased lactate production, and minimal decline in ATP levels under both conditions. Compared with hypoxia, cyanide mediated small transient inductions of fos and jun transcripts that followed a different time course. The combination of cyanide and deoxyglucose resulted in inhibition of lactate production as well as respiration, and ATP dropped rapidly to 20% of control levels. The loss of intracellular ATP was followed by fourfold inductions of c-fos and c-jun with minor changes in jun B and jun D transcript levels. Similarly, iodoacetic acid caused a major (90%) loss of ATP and irreversible cell damage as measured by leakage of creatine phosphokinase enzyme and loss of membrane arachidonic acid; ATP loss was followed by fivefold to sevenfold inductions of c-fos, c-jun and jun B transcripts.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasmodium falciparum: In Vitro Studies of the Pharmacodynamic Properties of Drugs Used for the Treatment of Severe Malaria

The speed and stage specificity of antimalarial drug action on the metabolic activities of cultured Plasmodium falciparum were studied for chloroquine (CQ), quinine (QN), artemisinin (AR), and sodium artelinate (SA). CQ had the most rapid onset of action on [3H]hypoxanthine and [3H]isoleucine uptake, reaching 50% of its maximum effect in 1.8 hr compared with 3.5–7.4 hr for the other three drugs. In contrast there was a lag time of 1–4 hr before AR and SA had a measurable inhibitory effect, although after this delay antimalarial action was very rapid. Parasite glycolysis was relatively drug resistant; the inhibition of lactate production was <60% of that for [3H]hypoxanthine and [3H]isoleucine uptake. The susceptibility of P. falciparum changed markedly as the parasite matured. Maximum drug effects occurred at the late ring and early trophozoite stage, which corresponds to the time at which the most rapid increases in synthetic and glycolytic activities occur. Mature schizonts and young rings were relatively unaffected by the antimalarial drugs. Young rings were particularly resistant to QN. Schizonts multiplied successfully in the presence of relatively high concentrations of all four drugs. The two artemisinin compounds had the broadest time window of action and may be particularly suitable for the treatment of severe malaria.

A submucosal mechanism of action for prostaglandin E2 on hexose absorption and metabolism in mouse intestine.

1. The involvement of prostaglandin E2 (PGE2) in hexose absorption and metabolism was studied in mouse small intestinal villus cells. 2. Phlorizin-sensitive, Na(+)-dependent alpha-methyl-D-glucoside (alpha-MG) uptake (0.8 mM) during 2 min cell incubations (37 degrees C) was 74 +/- 4 nmol (mg protein)-1. Maximal uptake was 110 +/- 8 nmol (mg protein)-1, representing an accumulation of 50-fold. Metabolism of D-glucose (5 mM) to L-lactate was 38 nmol min-1 (mg protein)-1. 3. Incubation of isolated cells with indomethacin or PGE2 did not affect alpha-MG uptake or D-glucose metabolism. By including indomethacin during cell isolation from whole intestine, alpha-MG uptake was inhibited dose dependently (50-250 microM) by up to 70% (P < 0.001). PGE2 present during both isolation and incubation inhibited by 85% (P < 0.001) at 1 microM and by 27% (P < 0.05) at 0.1 microM, with no effect at lower concentrations. alpha-MG uptake was reduced to 38% (P < 0.01) when 1 microM-PGE2 and 250 microM-indomethacin were presented in combination. When present during cell isolation and incubation, 1 microM-PGE2 inhibited lactate production by 24% (P < 0.05), except when present in combination with 250 microM-indomethacin. Indomethacin, itself, had no effect on lactate production. 4. A submucosal mechanism is proposed to account for the observed inhibitory effects of PGE2 on brush-border uptake of alpha-MG and cellular lactate production. Indomethacin appears to exert not only an effect of its own, possibly via PG-independent actions within the submucosa, but at high concentrations also disrupts the effects of exogenously applied PGE2.

Vasopressin stimulates pyruvate utilization through a Ca 2+-dependent mechanism and lactate formation by a protein kinase C-dependent mechanism in isolated rat hepatocytes

Vasopressin stimulates lactate production by hepatocytes from fed rats, an effect which has been attributed exclusively to Ca 2+ activation of glycogenolysis. We provide evidence here for two further actions of vasopressin which affect lactate formation by rat hepatocytes. In the presence of 50 mM glucose, vasopressin inhibited lactate production by hepatocytes. The inhibition was relieved by the presence of α-cyano-4-hydroxycinnamate (α-CHC), which blocks mitochondrial pyruvate transport. This suggests that vasopressin stimulates pyruvate utilization in the presence of a high concentration of glucose. Epidermal growth factor (EGF), which also increases lactate formation by hepatocytes, did not similarly decrease lactate accumulation in the presence of high glucose, suggesting no stimulation of lactate and pyruvate utilization by this hormone. In cells depleted of Ca 2+, vasopressin also stimulated lactate formation. Although vasopressin did not cause the apparent translocation of protein kinase C between cell spaces, phospholipase C treatment of hepatocytes did duplicate vasopressin stimulation of lactate formation, provided fatty acid oxidation was suppressed by the simultaneous presence of the inhibitor palmixorate. We conclude that three actions of vasopressin affect lactate and pyruvate formation; the calcium-linked activations of glycogenolysis and mitochondrial pyruvate utilization, and a stimulation of glycolysis likely mediated by protein kinase C.

The effect of salivary clearance of sucrose and fluoride on human dental plaque acidogenicity

Ten subjects rinsed with a 20% (0.58 M) sucrose solution with or without 0.2% NaF (905 parts/10 6 F −) added in two separate experiments. Saliva and plaque were collected before rinsing and after 2, 5, 10 and 30 min. Sucrose and fluoride concentrations in saliva and acid anion and fluoride concentrations in plaque were analysed. There was a statistically significant and positive correlation between the concentration of sucrose in the saliva 2 min after the rinse and the subsequent concentrations of lactate in plaque at 10 and 30 min after the rinse with sucrose alone but not in the presence of fluoride. Salivary fluoride concentrations during 2–30 min after the sucrose rinse were significantly correlated with plaque fluoride concentrations during the same time. The addition of fluoride to the sucrose rinse significantly inhibited lactate production.

A Na-K-Cl cotransporter in isolated rat papillary collecting duct cells

Lactate production and ion fluxes were measured in isolated rat papillary collecting duct cells (PCD) to gain further insight into the transport properties of the papillary collecting duct. Lactate production was found to be inhibited by bumetanide in a dose-dependent manner, a maximum inhibition of 22% was obtained at 10(-4) M bumetanide and an apparent Ki of 10(-8) M was determined. Bumetanide inhibition of lactate production was dependent on the presence of sodium and chloride. Chloride removal inhibited lactate production also by 20%. Bumetanide (10(-4) M) inhibited by 35% sodium uptake into PCD cells exposed to 10 mM ouabain and chloride uptake into ion depleted PCD cells by 40%. In addition, this bumetanide-sensitive chloride uptake was dependent on the presence of sodium and potassium in the incubation medium. Furthermore, 86Rb uptake into these cells was significantly reduced in the presence of 10(-4) M bumetanide. These data provide evidence for the operation of a Na-K-Cl cotransport system in rat papillary collecting duct cells. This transport system might be involved in active chloride transport in the papillary collecting duct and/or volume regulation of the PCD cells.

Motility, heat, and lactate production in ejaculated bovine sperm

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

Activation of the human neutrophil respiratory burst by an anion channel blocker.

We found that 4,4'-diisothiocyano-2,2'-disulfonic acid (DIDS), an anion channel blocker in erythrocytes, caused a concentration-related stimulation of oxygen radicals in human neutrophils, as measured by luminol- and lucigenin-amplified chemiluminescence. The DIDS-elicited oxygen radical burst followed the kinetic pattern of other stimuli with a lag period of 20 seconds, reaching a maximum after 12 to 15 minutes. Washing neutrophils that had been pretreated with DIDS did not reverse neutrophil activation. DIDS was found to strongly stimulate lactate production and did not block the efflux of this anion. Cytochalasin B completely abolished the chemiluminescence responses when added before DIDS stimulation. It also inhibited lactate production, however, only in a glucose-containing medium. Modulation of oxygen radical production by DIDS may reveal an additional transductional pathway for neutrophil activation.

Inhibition of lactate production in rat brain extracts and synaptosomes by 3-[4-(reduced 3-pyridine aldehyde-adenine dinucleotide)]-pyruvate.

In basic solutions, pyruvate enolizes and reacts (through its 3-carbon) with the 4-carbon of the nicotinamide ring of NAD+, yielding an NAD-pyruvate adduct in which the nicotinamide ring is in the reduced form. This adduct is a strong inhibitor of lactate dehydrogenase, presumably because it binds simultaneously to the NADH and pyruvate sites. The potency of the inhibition, however, is muted by the adduct's tendency to cyclize to a lactam. We prepared solutions of the pyruvate adduct of NAD+ and of NAD+ analogues in which the -C(O)NH2 of NAD+ was replaced with -C(S)NH2, -C(O)CH3, and -C(O)H. Of the four, only the last analogue, 3-[4-(reduced 3-pyridine aldehyde-adenine dinucleotide)]-pyruvate (RAP) cannot cyclize and it was found to be the most potent inhibitor of beef heart and rat brain lactate dehydrogenases. The inhibitor binds very tightly to the NADH site (Ki approximately 1 nM for the A form). Even at high concentrations (20 microM), RAP had little or no effect on rat brain glyceraldehyde-3-phosphate, pyruvate, alpha-ketoglutarate, isocitrate, soluble and mitochondrial malate, and glutamate dehydrogenases. The glycolytic enzymes, hexokinase and phosphofructokinase, were similarly unaffected. RAP strongly inhibited lactate production from glucose in rat brain extracts but was less effective in inhibiting lactate production from glucose in synaptosomes.

Glucose metabolism by human cataracts in culture

Metabolism in human senile cataracts has been studied using uniformly labeled [14C]glucose. Intracapsularly extracted lenses were cultured in TC-199 media with a glucose concentration of 5.5 mM. Results show that lactate production accounts for 97% of the glucose metabolized. Under these standard incubation conditions there is negligible accumulation of alpha-glycerol phosphate, glucose-6-phosphate, and sorbitol. The rate of lactate production was found to be relatively uniform over a range of cataract severities which were determined from the CCRG classification. The effects of several perturbants in the medium were measured. An ATP concentration of 3 mM was found to inhibit lactate production. Labeled glucose-6-phosphate in the medium was found to produce lactate at a rate approximately one half that of glucose. Elevated glucose concentration resulted in a slight decrease in lactate production and, in some lenses, production of a small amount of sorbitol. Overall, the glycolytic pathway appears to be functioning normally and without regard for cortical and nuclear opacification.

Neurotoxic effects of copper: inhibition of glycolysis and glycolytic enzymes.

The effects of Cu2+ on glycolysis and several glycolytic enzymes were studied in rat brain extracts in vitro. At concentrations reportedly found in Wilson's disease, Cu2+ significantly inhibited lactate production from glucose or glucose-6-phosphate in rat brain postnuclear supernatant with an IC50 of about 3 microM. Cu2+ also inhibited several glycolytic enzymes. Amongst the latter, Cu2+ was most effective in inhibiting hexokinase (IC50 for Cu2+ = 7 microM), moderately effective in inhibiting pyruvate kinase (IC50 for Cu2+ = 56 microM), but least effective in inhibiting lactate dehydrogenase (IC50 for Cu2+ = 300 microM). These results suggest that inhibition of brain glycolysis may have pathophysiological importance in copper poisoning and in Wilson's disease.

Effect of 5-thio-D-glucose on hexose transport and metabolism in the mouse small intestine.

5-Thio-D-glucose ( 5TG ) elicits a time-dependent effect on net D-glucose transport and metabolism in the mouse small intestine. When incubation periods were less than 45 min, 5TG inhibited net D-glucose transport. As incubation periods were lengthened to 60 min or greater, net D-glucose transport was potentiated by 5TG , with a concomitant inhibition of lactate production from exogenous D-glucose. Furthermore, D-glucose inhibited 5TG transport at every time point studied. Initial velocity profiles done with 5TG and D-glucose, respectively, resulted in a KT of 6.3 mM and a Tmax of 18.5 mumole/g/30 min for 5TG ; while for D-glucose the KT was 11.7 mM and the Tmax was 43.4 mumole/g/30 min. Competitive inhibition between 5TG and D-glucose was demonstrated. The apparent KI's for 5TG and D-glucose were 3.0 mM and 9.3 mM, respectively. These findings indicated that 5TG has a lower affinity for the hexose-transport carrier than D-glucose. 5TG was also found to inhibit 3-O-methyl-D-glucose (3MG) and D-galactose transport in a dose-dependent manner. Basal levels of lactate production were not affected by 5TG nor did 5TG affect lactate levels in the presence of 3MG. These results suggest that 5TG decreases intestinal utilization of D-glucose via glycolysis to partially account for the observed increase in net transmural transport of D-glucose.

Hyperthermia, Na+K+ATPase and lactic acid production in some human tumour cells.

When HeLa cells are exposed to brief heat shock at 45 degrees C there is a reduction in the cellular level of Na+K+ATPase. Return of the cells to the normal growth temperature of 37 degrees C leads to a partial restoration of enzyme activity. The pattern of this recovery of activity suggests that it may be associated with the induction of heat shock proteins. Indeed other means of heat shock protein induction such as continuous heat treatment at 42 degrees C, or treatment of cells at 37 degrees C with sodium arsenite, leads to elevated levels of Na+K+ATPase activity and alterations in the kinetic properties of the enzyme. Continuous hyperthermia at 42 degrees C led to increased lactate production which could be blocked with ouabain suggesting that effects on Na+K+ATPase activity could partly influence glycolysis. A number of other human and hamster cells also showed increased lactate production at 42 degrees C and also an inhibition of lactate production by ouabain. Whilst incubation of HeLa cells with cyanide had little effect on glycolysis at 37 degrees C elevation of the temperature to 42 degrees C (or 45 degrees C), in the presence of cyanide, impaired glycolysis. The possible role in this phenomenon, of an unusual oxygen-sensitive isoenzyme of lactate dehydrogenase, expressed in human cancers, is discussed.

Transaminase inhibitors block glycolysis and G1 to S phase progression in chick embryo fibroblasts: reversal by alpha-keto acids.

Two transaminase inhibitors, aminooxyacetate and cycloserine, inhibited the initiation of insulin-stimulated DNA synthesis in chick embryo fibroblasts. This inhibition was overcome when pyruvate (4 mM), oxaloacetate (4 mM), or alpha-ketobutyrate (10 mM) was included in the culture medium with hormone and inhibitor. Aminooxyacetate also inhibited lactate production in insulin-treated cultures in the absence of added alpha-keto acid.

Inhibition of brain glycolysis by aluminum.

Aluminum inhibited both the cytosolic and mitochondrial hexokinase activities in rat brain. The IC50 values were between 4 and 9 microM. Aluminum was effective at mildly acidic (pH 6.8) or slightly alkaline (pH 7.2-7.5) pH, in the presence of a physiological level of magnesium (0.5 mM). However, saturating (8 mM) magnesium antagonized the effect of aluminum on both forms of hexokinase activity. Other enzymes examined were considerably less sensitive to inhibition by aluminum. The IC50 of aluminum for phosphofructokinase was 1.8 mM and for lactate dehydrogenase 0.4 mM. At 10-600 microM, aluminum actually stimulated pyruvate kinase. Aluminum also inhibited lactate production by rat brain extracts: this effect was much more marked with glucose as substrate than with glucose-6-phosphate. However, the IC50 for inhibiting lactate production using glucose as substrate was 280 microM, higher than that required to inhibit hexokinase. This concentration of aluminum is comparable to those reportedly found in the brains of patients who had died with dialysis dementia and in the brains of some of the patients who had died with Alzheimer disease. Inhibition of carbohydrate utilization may be one of the mechanisms by which aluminum can act as a neurotoxin.

The Effect of Nitroimidazoles on Glucose Utilization and Lactate Accumulation in Mouse Brain

The radiation sensitizers misonidazole (MISO) and desmethylmisonidazole (DMM) can produce central and peripheral neuropathy in patients and laboratory animals. Behavioral and pathological investigations have indicated that in the central nervous system this primarily involves the cochlear and vestibular systems. Nitroimidazoles can also interfere with glycolysis in vitro under aerobic and anaerobic conditions. In the present work we have studied the effect of MISO or DMM on lactate production and glucose utilization in mouse brain. It is observed that these compounds result in a 25% inhibition of lactate production in brain slices relative to the control at a 10 mM level. Additionally, MISO (1.0 mg/g/day) or DMM (1.4 mg/g/day) were administered daily (oral) for 1, 4, 7, or 14 days to examine the effect of these two drugs on the regional glucose utilization in C3Hf mouse brain. Five microcuries of 2-deoxy[14C]glucose was given following the last drug dose and autoradiographs of serial brain sections were made and analyzed by a densitometer. Following a single dose of either MISO or DMM, no significant differences in glucose uptake were observed when compared with controls. However, following 4, 7, and 14 doses the rate of glucose utilization was significantly reduced in the intoxicated animals. Larger reductions were measured in specific regions including the posterior colliculus, cochlear nuclei, vestibular nuclei, and pons with increasing effects observed at later stages. These results share a degree of correspondence with the regional brain pathology produced by these nitroimidazoles.

Inhibition of glycolysis potentiates hypoxic vasoconstriction in rat lungs.

The purpose of this study was to test whether inhibition of glycolysis would potentiate hypoxic vasoconstriction in isolated rat lungs, and, if so, to evaluate whether potentiation was due to decreased aerobic production of the mitochondrial substrate, pyruvate, or to inhibition of anaerobic synthesis of ATP. In blood-perfused lungs, both iodoacetate and 2-deoxyglucose inhibited lactate production and increased pressor responses to ventilation with gases containing from 15 to 3% O2. In lungs perfused with physiological salt solution, both 2-deoxyglucose and glucose-free perfusion inhibited lactate and pyruvate production and potentiated the dose-response curve to hypoxia. Dose responses to angiotensin II and KCl were not increased by glucose-free perfusion. Lungs perfused with glucose-free salt solution containing increased levels of lactate and pyruvate did not show an increased dose response to hypoxia. In contrast, lungs perfused with the inhibitor of citric acid cycle, malonate, in addition to the increased lactate and pyruvate, did show an increased dose response to hypoxia. These results indicate that potentiation of hypoxic vasoconstriction by inhibition of glucose metabolism is due to decreased production of pyruvate, rather than to decreased glycolytic generation of ATP. The potentiation might be directly related to either limitation of mitochondrial oxidative phosphorylation in an oxygen-sensing cell or to a decreased level of some intra- or intercellular modulating peptide, fatty acid, or lipid.