The stimulation of hepatic gluconeogenesis by acetoacetate precursors. A role for the monocarboxylate translocator

The regulation of the gluconeogenic pathway from the 3-carbon precursors pyruvate, lactate, and alanine was investigated in the isolated perfused rat liver. Using pyruvate (less than 1 mM), lactate, or alanine as the gluconeogenic precursor, infusion of the acetoacetate precursors oleate, acetate, or beta-hydroxybutyrate stimulated the rate of glucose production and, in the case of pyruvate (less than 1 mM), the rate of pyruvate decarboxylation. alpha-Cyanocinnamate, an inhibitor of the monocarboxylate transporter, prevented the stimulation of pyruvate decarboxylation and glucose production due to acetate infusion. With lactate as the gluconeogenic precursor, acetate infusion in the presence of L-carnitine stimulated the rate of gluconeogenesis (100%) and ketogenesis (60%) without altering the tissue acetyl-CoA level usually considered a requisite for the stimulation of gluconeogenesis by fatty acids. Hence, our studies suggest that gluconeogenesis from pyruvate or other substrates which are converted to pyruvate prior to glucose synthesis may be limited or controlled by the rate of entry of pyruvate into the mitochondrial compartment on the monocarboxylate translocator.     

Phototrophic Fe(II) oxidation by Rhodopseudomonas palustris TIE-1 in organic and Fe(II)-rich conditions

Rhodopseudomonas palustris TIE-1 grows photoautotrophically with Fe(II) as an electron donor and photoheterotrophically with a variety of organic substrates. However, it is unclear whether R. palustris TIE-1 conducts Fe(II) oxidation in conditions where organic substrates and Fe(II) are available simultaneously. In addition, the effect of organic co-substrates on Fe(II) oxidation rates or the identity of Fe(III) minerals formed is unknown. We incubated R. palustris TIE-1 with 2 mM Fe(II), amended with 0.6 mM organic co-substrate, and in the presence/absence of CO₂. We found that in the absence of CO₂, only the organic co-substrates acetate, lactate and pyruvate, but not Fe(II), were consumed. When CO₂ was present, Fe(II) and all organic substrates were consumed. Acetate, butyrate and pyruvate were consumed before Fe(II) oxidation commenced, whereas lactate and glucose were consumed at the same time as Fe(II) oxidation proceeded. Lactate, pyruvate and glucose increased the Fe(II) oxidation rate significantly (by up to threefold in the case of lactate). ⁵⁷Fe Mössbauer spectroscopy revealed that short-range ordered Fe(III) oxyhydroxides were formed under all conditions. This study demonstrates phototrophic Fe(II) oxidation proceeds even in the presence of organic compounds, and that the simultaneous oxidation of organic substrates can stimulate Fe(II) oxidation.     

Effects of dichloroacetate on the metabolism of glucose, pyruvate, acetate, 3-hydroxybutyrate and palmitate in rat diaphragm and heart muscle in vitro and on extraction of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo

1. The extractions of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo were calculated from measurements of their arterial and coronary sinus blood concentration. Elevation of plasma free fatty acid concentrations by infusion of intralipid and heparin resulted in increased extraction of free fatty acids and diminished extractions of glucose, lactate and pyruvate by the heart. It is suggested that metabolism of free fatty acids by the heart in vivo, as in vitro, may impair utilization of these substrates. These effects of elevated plasma free fatty acid concentrations on extractions by the heart in vivo were reversed by injection of dichloroacetate, which also improved extraction of lactate and pyruvate by the heart in vivo in alloxan diabetes. 2. Sodium dichloroacetate increased glucose oxidation and pyruvate oxidation in hearts from fed normal or alloxan-diabetic rats perfused with glucose and insulin. Dichloroacetate inhibited oxidation of acetate and 3-hydroxybutyrate and partially reversed inhibitory effects of these substrates on the oxidation of glucose. In rat diaphragm muscle dichloroacetate inhibited oxidation of acetate, 3-hydroxybutyrate and palmitate and increased glucose oxidation and pyruvate oxidation in diaphragms from alloxan-diabetic rats. Dichloroacetate increased the rate of glycolysis in hearts perfused with glucose, insulin and acetate and evidence is given that this results from a lowering of the citrate concentration within the cell, with a consequent activation of phosphofructokinase. 3. In hearts from normal rats perfused with glucose and insulin, dichloroacetate increased cell concentrations of acetyl-CoA, acetylcarnitine and glutamate and lowered those of aspartate and malate. In perfusions with glucose, insulin and acetate, dichloroacetate lowered the cell citrate concentration without lowering the acetyl-CoA or acetylcarnitine concentrations. Measurements of specific radioactivities of acetyl-CoA, acetylcarnitine and citrate in perfusions with [1-(14)C]acetate indicated that dichloroacetate lowered the specific radio-activity of these substrates in the perfused heart. Evidence is given that dichloroacetate may not be metabolized by the heart to dichloroacetyl-CoA or dichloroacetylcarnitine or citrate or CO(2). 4. We suggest that dichloroacetate may activate pyruvate dehydrogenase, thus increasing the oxidation of pyruvate to acetyl-CoA and acetylcarnitine and the conversion of acetyl-CoA into glutamate, with consumption of aspartate and malate. Possible mechanisms for the changes in cell citrate concentration and for inhibitory effects of dichloroacetate on the oxidation of acetate, 3-hydroxybutyrate and palmitate are discussed.     

Quantitative analysis of growth and volatile fatty acid production by the anaerobic ruminal bacterium Megasphaera elsdenii T81

Megasphaera elsdenii T81 grew on either dl-lactate or d-glucose at similar rates (0.85 h^?1) but displayed major differences in the fermentation of these substrates. Lactate was fermented at up to 210-mM concentration to yield acetic, propionic, butyric, and valeric acids. The bacterium was able to grow at much higher concentrations of d-glucose (500 mM), but never removed more than 80 mM of glucose from the medium, and nearly 60 % the glucose removed was sequestered as intracellular glycogen, with low yields of even-carbon acids (acetate, butyrate, caproate). In the presence of both substrates, glucose was not used until lactate was nearly exhausted, even by cells pregrown on glucose. Glucose-grown cultures maintained only low extracellular concentrations of acetate, and addition of exogenous acetate increased yields of butyrate, but not caproate. By contrast, exogenous acetate had little effect on lactate fermentation. At pH 6.6, growth rate was halved by exogenous addition of 60 mM propionate, 69 mM butyrate, 44 mM valerate, or 33 mM caproate; at pH 5.9, these values were reduced to 49, 49, 18, and 22 mM, respectively. The results are consistent with this species’ role as an effective ruminal lactate consumer and suggest that this organism may be useful for industrial production of volatile fatty acids from lactate if product tolerance could be improved. The poor fermentation of glucose and sensitivity to caproate suggests that this strain is not practical for industrial caproate production.     

Glucose inhibits development of hamster 8-cell embryos in vitro

Relative preferences of energy substrates (glucose, pyruvate, and lactate) for in vitro development of hamster 8-cell embryos were investigated. Using protein-free modified Tyrode's medium (TLP-PVA) containing 10 mM lactate (L), 0.1 mM pyruvate (P), and amino acids (Phe, Ile, Met and Gln), we found that development of hamster 8-cell embryos to blastocysts was supported better in the absence of glucose than in medium containing (standard) 5 mM glucose (88.1% and 50%, respectively). Addition of even 0.25 mM glucose to the medium significantly inhibited blastocyst formation (54.1%). Medium T-PVA, containing 5 mM glucose as sole energy substrate (without pyruvate, lactate, and amino acids), very poorly supported embryo development (less than or equal to 7.9% blastocysts), but addition of 0.1 mM pyruvate enhanced blastocyst formation (52%). Elimination of pyruvate in TL-PVA medium containing 5 mM glucose and amino acids markedly reduced blastocyst formation by 4-fold (13.5%); the optimal pyruvate concentration was 0.2 mM. However, if the same medium was devoid of glucose, blastocyst formation was high both in the absence (71.1%) and presence (83.3%) of 0.1 mM pyruvate. Similarly, in glucose-free T-PVA medium, addition of either 10 mM lactate or amino acids supported 8-cell embryo development to blastocysts (61.7% and 60.5%, respectively) as opposed to 18.8% and 30.6%, respectively, in the presence of 5 mM glucose. This augmented development in the absence of glucose is suggested to the due to the efficient conversion of lactate to pyruvate and of amino acids to amphibolic intermediates and hence their utilization via the Krebs cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lactate oxidation byTreponema pallidum

Whole cells ofTreponema pallidum consumed O₂ with lactate in a glucose-depleted medium.d(–) Lactate caused marked stimulation of O₂ uptake at a rate similar to that with glucose, whereasl(+) lactate resulted in no increase over the reduced rate observed upon glucose depletion. Lactate oxidation was specific for -hydroxy straight-chain acids of 3,4, and 5 carbons. O₂ uptake during lactate oxidation proceeded independently of pyruvate oxidation and required NAD. The product of lactate oxidation was pyruvate.d(–) Lactate-stimulate O₂ uptake was sensitive to chlorpromazine and resistant to amytal and cyanide. Glucose did not inhibit the oxidation of lactate as shown by the additive effect of both substrates on O₂ uptake. Oxidation of glucose, but not lactate, provided energy necesary for motilibty or maintenance of virulence. A mixture of lactate isomers was formed from glucose with thel(+) isomer concentration remaining constant and thed(–) isomer concentration varying inversely with dissolved O₂ concentration. The function of lactate as an oxidizable substrate is apparently quite distinct from that of glucose.     

Support of Xenopus laevis spermatogenesis in vitro by different energy substrates

The support of Xenopus laevis spermatogenesis in vitro by different energy-yielding substrates has been investigated. Isolated spermatogenic cells maintained their levels of adenosine-triphosphate for 24 h in serum-free medium containing only amino acids as energy substrates. DL-Aminocarnitine, an inhibitor of carnitine palmitoyltransferase, reduced cell viability 87% during a 15-h culture in the same medium, indicating that beta oxidation of endogenous fatty acids is a significant source of energy when exogenous substrates are unavailable. Isolated spermatocytes developed into spermatids for 7 days in medium supplemented with either pyruvate, oxaloacetate, or lactate, with maximal survival and development at 0.5 mM pyruvate, 2.0 mM oxaloacetate, and 4.0 mM lactate. Few spermatocytes survived more than 3 days in serum-free medium supplemented with only glucose and amino acids as energy substrates. In contrast, glucose-supplemented medium supported spermatocyte differentiation for 14 days in testis fragment culture and 7 days in spermatocyte-Sertoli cell cocultures due to the excretion of lactate and pyruvate by Xenopus Sertoli cells during culture in glucose-supplemented medium. Glucose also enhanced spermatocyte development in medium containing dialyzed, heat-inactivated fetal calf serum. Spermatogenic cells oxidized glucose to CO2 with C1 oxidized 6- to 7-fold more than C6, suggesting that glucose may be metabolized in the hexose monophosphate shunt. The results are discussed in comparison to energy metabolism in mammalian testes and spermatogenic cells.     

Tricarboxylic acid cycle inhibition by Li+ in the human neuroblastoma SH-SY5Y cell line: a 13C NMR isotopomer analysis

Li+ effects on glucose metabolism and on the competitive metabolism of glucose and lactate were investigated in the human neuroblastoma SH-SY5Y cell line using 13C NMR spectroscopy. The metabolic model proposed for glucose and lactate metabolism in these cells, based on tcaCALC best fitting solutions, for both control and Li+ conditions, was consistent with: (i) a single pyruvate pool; (ii) anaplerotic flux from endogenous unlabelled substrates; (iii) no cycling between pyruvate and oxaloacetate. Li+ was shown to induce a 38 and 53% decrease, for 1 and 15 mM Li+, respectively, in the rate of glucose conversion into pyruvate, when [U-13C]glucose was present, while no effects on lactate production were observed. Pyruvate oxidation by the tricarboxylic acid cycle and citrate synthase flux were shown to be significantly reduced by 64 and 84% in the presence of 1 and 15 mM Li+, respectively, suggesting a direct inhibitory effect of Li+ on tricarboxylic acid cycle flux. This work also showed that when both glucose and lactate are present as energetic substrates, SH-SY5Y cells preferentially consumed exogenous lactate over glucose, as 62% of the acetyl-CoA was derived from [3-13C]lactate while only 26% was derived from [U-13C]glucose. Li+ did not significantly affect the relative utilisation of these two substrates by the cells or the residual contribution of unlabelled endogenous sources for the acetyl-CoA pool.     

Inhibition of lactate glucogneogenesis in rat kidney by dichloroacetate.

1. Sodium dichloroacetate (1mM) inhibited glucose production from L-lactate in kidney-cortex slices from fed, starved or alloxan-diabetic rates. In general gluconeogenesis from other substrates was no inhibited. 2. Sodium dichloracetate inhibited glucose production from L-lactate but no from pyruvate in perfused isolated kidneys from normal or alloxan-diabetic rats. 3. Sodium dichloroacetate is an inhibitor of the pyruvate dehydrogenase kinase reaction and it effected conversion of pyruvate dehydrogenase into its its active (dephosphorylated) form in kidney in vivo. In general, pyruvate dehydrogenase was mainly in the active form in kidneys perfused or incubated with L-lactate and the inhibitory effect of dichloroacetate on glucose production was not dependent on activation of pyruvate dehydrogenase. 4. Balance data from kidney slices showed that dichloroacetate inhibits lactate uptake, glucose and pyruvate production from lactate, but no oxidation of lactate. 5. The mechanism of this effect of dichloroactetate on glucose production from lactate has not been fully defined, but evidence suggests that it may involve a fall in tissue pyruvate concentration and inhibition of pyruvate carboxylation.     

Inhibitory effect of gentamicin on gluconeogenesis from pyruvate, propionate, and lactate in isolated rabbit kidney-cortex tubules

The effect of gentamicin on glucose production in isolated rabbit renal tubules was studied with lactate, propionate, malate, 2-oxoglutarate, and succinate as substrates. This antibiotic at 5 mM concentration inhibited gluconeogenesis from lactate by about 60% and that from either pyruvate or propionate by about 30%. In contrast, it did not alter the rate of glucose formation from other substrates studied. The rate of gluconeogenesis was higher at 1 mM propionate than at increasing concentrations of this substrate and was stimulated in the presence of 1 mM carnitine. However, the addition of carnitine did not affect the degree of inhibition of glucose formation by gentamicin. Since the mitochondrial free coenzyme A level was significantly lower in the presence of 10 than 1 mM propionate and increased on the addition of carnitine to the reaction medium, the inhibitory effect of propionate concentrations above 1 mM on gluconeogenesis in rabbit renal tubules may be due to a depletion of the free mitochondrial coenzyme A level, resulting in an inhibition of the mitochondrial coenzyme A-dependent reactions. In intact rabbit kidney cortex mitochondria incubated in State 4 as well as in Triton X-100-treated mitochondria, 5 mM gentamicin inhibited by about 30-40% the incorporation of 14CO2 into both pyruvate and propionate. The results indicate that the inhibitory effect of gentamicin on glucose formation in isolated kidney tubules incubated with lactate, pyruvate, or propionate is likely due to a decrease of the rate of carboxylation reactions.     

Metabolism, protein content, and in vitro embryonic development of goat cumulus-oocyte complexes matured with physiological concentrations of glucose and L-lactate

No information is available concerning how the maturation environment controls the metabolism of goat oocytes. The objectives of this experiment were to: (1) Determine the concentrations of glucose, lactate, and pyruvate in caprine follicular fluid; and (2) Investigate the effects of physiological concentrations of glucose and lactate in the in vitro maturation (IVM) medium on the metabolism (glycolysis and pyruvate oxidation), protein content, and developmental competence of caprine oocytes and cumulus-oocyte complexes (COCs). Abattoir-derived COCs were matured for 18-20 hr in a defined, SOF-based medium containing 0.75, 1.5 (follicular fluid = 1.4 mM), or 3.0 mM glucose, and 3.0, 6.0 (follicular fluid = 7.1 mM), or 12.0 mM L-lactate. The protein content of oocytes and COCs was not affected (P > 0.05) by the concentration of glucose and lactate in the maturation medium. Increasing glucose and lactate decreased (P < or = 0.05) glycolytic activity of oocytes, without affecting (P > 0.05) pyruvate oxidation. In COCs, increasing glucose concentrations tended (P = 0.07) to decrease glycolysis. When metabolic activity was corrected for protein content (pmol/microg protein/3 hr), increasing glucose or lactate concentrations in the medium decreased (P < or = 0.05) pyruvate oxidation in oocytes, but increased (P < or = 0.05) pyruvate oxidation in COCs. Embryonic development (cleavage and blastocyst development, hatching, and cell number) was not affected (P > 0.05) by the glucose and lactate concentrations tested. These results indicate that concentrations of glucose and lactate in the medium have cell type-specific effects on metabolism of oocytes and COCs, but do not affect developmental competence within the range of concentrations tested.     

Effect of exogenous carbohydrates in a serum-free culture medium on the development of in vitro matured and fertilized porcine embryos

This study was conducted to examine the effect of energy substrates in a serum-free culture medium on in vitro development of porcine embryos. Presumptive zygotes derived from in vitro fertilization were cultured in glucose-free North Carolina State University (NCSU)-23 medium with glucose, pyruvate, fructose and lactate added to the culture medium singly or in various combinations. In experiment 1, a higher percentage of embryos cleaved (53-63% vs 10-13%) and developed to the blastocyst stage (18-27% vs 0) after the single addition of glucose (5.6 mM), pyruvate (0.5 mM) or lactate (10 mM) than with no energy substrate addition or the addition only of fructose (5.6 mM). In experiment 2, the addition of pyruvate and lactate resulted in higher blastocyst formation (25%) than other combinations (6-22%), while the addition of glucose and pyruvate significantly inhibited blastocyst formation. Increasing lactate concentration, as a single energy supplement, from 5 to 20 mM significantly improved blastocyst formation (7% vs 14-18%), while no benefit was achieved from increasing pyruvate concentration up to 2 mM (experiment 3). Glucose-free NCSU-23 medium supplemented with 0.5 mM pyruvate and 5 mM lactate significantly improved blastocyst formation (28% vs 17%) compared with NCSU-23 medium supplemented with 5.6 mM glucose (experiment 4). In conclusion, pyruvate and lactate are preferable energy substrates to support in vitro development of porcine embryos cultured in a serum-free NCSU-23 medium.     

Pyruvate kinase and alanine synthesis in skeletal muscle

L-Phenylalanine is an allosteric inhibitor of M₁-type pyruvate kinase. Accordingly, the effects were studied of 20 mM phenylalanine on the metabolism of 5 mM [U-¹⁴C]glucose and 3 mM L-[U-¹⁴C]glutamate by isolated hemidiaphragms from starved rats. Phenylalanine inhibited lactate and¹⁴CO₂ production from both substrates and stimulated alanine release. It is concluded that pyruvate kinase may have a dual role in intermediary metabolism in skeletal muscle: the enzyme is a component of the lower glycolytic pathway and is implicated in a pathway of amino acid oxidation and alanine synthesis.     

Enhanced glycolysis after maturation of bovine oocytes in vitro is associated with increased developmental competence

The effect of maturation in vitro on metabolism of individual bovine oocytes was examined. Three maturation media were used: standard, consisting of tissue culture medium 199 supplemented with serum and pyruvate, and a chemically defined medium supplemented with either amino acids or lactate. Development to blastocyst was significantly higher (P < 0.05) after maturation in standard medium (47%) than in defined medium with lactate (17%) but was not different than maturation in defined medium with amino acids (29%). Glucose metabolism through the Krebs cycle was not different after maturation in standard or defined medium with amino acids or lactate (0.48, 0.43, 0.38 pmol/oocyte/3 hr, respectively) but was affected by the removal of unlabeled pyruvate from the metabolic measurement medium (0.16, 0.21, 0.27 pmol/oocyte/3 hr, respectively). When physiological concentrations of glucose (0.52 mM) and pyruvate (0.5 mM) were used, oxidation of pyruvate was not different after maturation in standard or defined medium with amino acids or lactate (1.38, 1.13, 1.13 pmol/ oocyte/3 hr, respectively); however, glycolysis was significantly increased (P < 0.05) in treatments that supported higher blastocyst development (standard medium, 1.77 pmol/oocyte/3 hr; defined medium with amino acids, 1.58 pmol/oocyte/3 hr; defined medium with lactate, 1.32 pmol/oocyte/3 hr). Metabolism of glucose through the Krebs cycle was low in all media. In contrast, oxidation of pyruvate readily occurred after maturation in vitro. Metabolism of glucose through the Embden-Meyerhof pathway is important during oocyte maturation in vitro, and higher glycolytic rates in in vitro matured oocytes may reflect increased developmental competence.     

Interrelation of aerobic glycolysis and lipogenesis in isolated perfused liver of well-fed rats

The rates of glycolysis and lipogenesis in isolated perfused liver of well-fed rats were studied. When liver was allowed to synthesize [14C]glycogen prior to perfusion, no more than 9% of the degraded [14C]glycogen was recovered in lactate and 6% in lipid. Addition of glucose, fructose and sorbitol enhanced concomitantly the formation of lactate and pyruvate and the rate of release of triglyceride and free fatty acid. Glucose was less efficient than fructose or sorbitol. The incorporation of 14C from these 14C-labelled substrates into lactate, pyruvate and lipids confirmed their role as carbon sources. Incorporation of 14C into the glycerol moiety of neutral lipid exceeded that found in the fatty acids, suggesting that these substrates contributed largely to the esterification of fatty acids. The total rate of de novo fatty acid synthesis was correlated with the formation of lactate and pyruvate. It is concluded that increased rates of aerobic glycolysis are related to increased rates of lipogenesis.     

Metabolism of low molecular weight organic compounds by sulfate-reducing bacteria in a Delaware salt marsh

Oxidation of acetate, lactate, pyruvate, and ethanol to CO₂ in anaerobic salt marsh sediments was rapid, with the oxidation rate being significantly inhibited (60–90% decrease) in the presence of 2 mM sodium molybdate, an inhibitor of sulfate-reducing bacteria (SRB). 2-Bromoethanesulfonic acid (BES), an inhibitor of methanogenic bacteria, generally had no effect on the oxidation rate. Acetate was the only intermediate product detected in the oxidation of lactate and ethanol. Competition studies with lactate, acetate, and ethanol indicated that the preferred order of substrate utilization was lactate, then acetate, then ethanol. The turnover times of these three compounds in salt marsh sediments via the combined CO₂ plus acetate pool was rapid (10–13 hours) with a two- to threefold increase in the turnover time in the presence of molybdate. These results strongly suggest that SRB play a major role in the terminal metabolism of low molecular weight organic compounds in anaerobic salt marsh sediment.     

Differential modulation of glucose,lactate, and pyruvate oxidation by insulin and dichloroacetate in the rat heart

Despite the fact that lactate and pyruvate are potential substrates for energy production in vivo, our understanding of the control and regulation of carbohydrate metabolism is based principally on studies where glucose is the only available carbohydrate. Therefore, the purpose of this study was to determine the contributions of lactate, pyruvate, and glucose to energy production in the isolated, perfused rat heart over a range of insulin concentrations and after activation of pyruvate dehydrogenase with dichloroacetate (DCA). Hearts were perfused with physiological concentrations of [1-13C]glucose, [U-13C]lactate, [2-13C]pyruvate, and unlabeled palmitate for 45 min. Hearts were freeze clamped, and 13C NMR glutamate isotopomer analysis was performed on tissue extracts. Glucose, lactate, and pyruvate all contributed significantly to myocardial energy production; however, in the absence of insulin, glucose contributed only 25-30% of total pyruvate oxidation. Even under conditions where carbohydrates represented >95% of substrate entering the tricarboxylic acid (TCA) cycle, we found that glucose contributed at most 50-60% of total carbohydrate oxidation. Despite being present at only 0.1 mM, pyruvate contributed between approximately 10% and 30% of total acetyl-CoA entry into the TCA cycle. We also found that insulin and DCA not only increased glucose oxidation but also exogenous pyruvate oxidation; however, lactate oxidation was not increased. The differential effects of insulin and DCA on pyruvate and lactate oxidation provide further evidence for compartmentation of cardiac carbohydrate metabolism. These results may have important implications for understanding the mechanisms underlying the beneficial effects of increasing cardiac carbohydrate metabolism.     

Interaction of lipogenic substrates in porcine adipose tissue in vitro

• 1.1. Porcine adipose tissue was incubated with radiolabeled glucose, acetate or lactate. Saturation curves indicated that lactate > glucose > acetate in providing two-carbon units for fatty-acid synthesis.
• 2.2. Competition between individual substrates indicated that lactate was the best lipogenic substrate.
• 3.3. Incubation of all three substrates at concentrations observable in serum indicated that at 5.56mM, glucose was the preferred lipogenic substrate in the presence of 0.1 mM acetate and 1.0 mM lactate.
• 4.4. At elevated concentrations (18.52mM glucose, 1.0 mM acetate and 10.0 mM lactate), acetate and lactate were preferred to glucose as lipogenic substrates.

     

Energy substrate requirement for in vitro maturation of oocytes from unstimulated adult rhesus monkeys

The energy substrates lactate, pyruvate, and glucose were evaluated for supporting in vitro cytoplasmic maturation of rhesus monkey oocytes. A total of 321 cumulus-oocyte complexes (COCs) aspirated from > or = 1000 microm diameter follicles of unstimulated adult monkeys were matured in one of six media with various individual or combinations of energy substrates: (1) mCMRL-1066 (control); (2) HECM-10 (containing 4.5 mM lactate); (3) HECM-10+0.2 mM pyruvate; (4) HECM-10 + 5.0 mM glucose; (5) HECM-10+ 0.2 mM pyruvate + 5.0 mM glucose; and (6) HECM-10 minus lactate + 5.0 mM glucose. All media contained gonadotropins, oestradiol, and progesterone. Following maturation, all mature oocytes were subjected to the same in vitro fertilization and embryo culture procedures. Oocytes matured in control medium or in treatment groups 4 and 6 had the best morulae+ blastocysts developmental responses (35, 36, and 32%, respectively, P < 0.05). HECM-10 + 0.2 mM pyruvate + 5.0 mM glucose for COC maturation supported intermediate embryonic development (16% morulae + blastocysts). The lowest (P < 0.05) morula + blastocyst developmental responses were obtained after maturation of COCs in HECM-t10 and HECM-10 + 0.2 mM pyruvate (4 and 6%, respectively). The COCs matured in glucose-containing medium showed greater levels of cumulus expansion than those in glucose-free medium. These results indicate that (a) glucose is both necessary and sufficient as the energy substrate for supporting optimal cytoplasmic maturation in vitro of oocytes from unstimulated rhesus monkeys; (b) pyruvate suppresses the stimulatory effect of glucose on oocyte maturation; (c) glucose is involved in cumulus expansion; (d) cumulus expansion is not a reliable indicator of primate oocyte competence.     

Regulation of glucose formation from lactate and pyruvate in isolated tubules of chicken kidney.

1. Isolated kidney tubules from chicken have been used to study the actions of ethanol, ouabain and aminooxyacetate on glucose formation from lactate and pyruvate. 2. In kidney tubules from well-fed chickens the rate of glucose production from lactate was higher than from pyruvate. Ethanol (10 mM) and ouabain (0.1 mM) were found to increase glucose formation from pyruvate but not from lactate. 3. It is concluded that in the presence of ethanol the fluxes of pyruvate through pyruvate dehydrogenase are in favour of the pyruvate carboxylase reaction restricted. 4. Glucose formation from lactate is decreased by aminooxyacetate (0.1 mM) and ouabain (0.1 mM). 5. Aminooxyacetate inhibited glucose formation from lactate, although chicken phosphoenolpyruvate carboxykinase is located intramitochondrially. 6. The results indicate that the effect of aminooxyacetate like that of ouabain is caused by the restricted formation of pyruvate.