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PubMed2000

Cellular uptake of valine by lactating porcine mammary tissue.

The cellular uptake of branched-chain amino acids in mammary tissue is important for understanding their role in milk synthesis in the sow. This study characterized the kinetic properties and substrate specificity of the valine uptake system in the porcine mammary gland. Mammary tissue was collected from lactating sows at slaughter and tissue explants were incubated in media containing isosmotic salt and amino acids of interest, plus [3H]valine tracer. Valine uptake was time-dependent and was dependent on the presence of sodium, as indicated by a reduction in uptake when sodium in the medium was replaced by choline. The valine transport system in porcine mammary tissue had a Km of 0.64 mM, a Vmax of 1.84 mmol-kg cell water(-1) 30 min(-l), and a Kd (diffusion constant) of 1.16 L x kg cell water(-1) x 30 min(-1). Valine uptake was inhibited by leucine and alpha-aminoisobutyric acid and by high concentrations of L-alanine, L-lysine, cycloleucine, L-glutamine, and L-methionine, but not by 2-(methyl-amino)-isobutyric acid. This transport system is the primary system responsible for uptake of valine, and probably other branched-chain amino acids, in lactating sow mammary tissue. Physiological concentrations of valine in the blood are below the Km of the specific valine transport system and well below the diffusion uptake capabilities. The kinetic parameters of this valine transport system should not be limiting to valine uptake for milk protein synthesis. However, competition of valine uptake with branched-chain amino acids, as well as with other amino acids, may affect valine uptake in lactating tissue.

Amino Acids, Branched-Chain↗
PubMed1983

Valine requirement for reproduction in swine.

Five levels of L-valine [3.3 (basal), 5.5, 7.8, 10.1 and 12.4 g/d] were fed to gilts from one estrus before mating through two pregnancies and for 30 d of a third pregnancy. Five litter-mate outcome groups of five animals each were allocated randomly to the diet treatments. Animals were individually fed 1.82 kg/d premating and during pregnancy. A common diet was fed to all animals during lactation at levels of 4.0 and 4.75 kg/d for first and second farrowings, respectively. Animals fed 3.3 g/d L-valine retained less N (P less than .10) at d 45 and 90 for two pregnancies than did animals fed higher valine levels. Plasma valine concentrations determined after a 24-h fast and 2 h postfeeding increased sharply (P less than .01) among animals fed more than 5.5 g/d L-valine. There was a treatment X bleeding time interaction (P less than .01) for plasma valine, explained by a postfeeding depression compared with a higher fasting concentration for animals fed 3.3 g/d L-valine. At all other levels of valine, the fasting and postfeeding plasma valine concentrations were equal or increased after feeding. Sow weight gain during the experiment increased (linear, P less than .05) as dietary L-valine increased. Estimated milk yield was greatest for animals fed 5.5 g/d, but average pig gain was maximized at 7.8 g/d L-valine. We conclude that 5.5 g/d L-valine met the requirement for pregnancy in this experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1976

Leucine, isoleucine and valine interactions in turkey poults.

In four experiments, the interactions of leucine, isoleucine and valine in turkey poults were studied. The additon of 1.50% excess leucine to a 22% protein starter diet, marginal in isoleucine and valine, depressed growth. This growth depression was corrected by the addition of valine and isoleucine. The addition of the excess leucine caused a decrease in plasma valine and isileucine concentrations in experiments 3 and 4, and plasma valine concentration in experiment 1. The addition of valine caused a marked linear increase in plasma valine with little or no effect on plasma isoleucine. The addition of isoleucine to the diet caused an increase in plasma isoleucine. Plasma valine, however, was decreased by the addition of isoleucine to a high-leucine diet. It is concluded that interactions exist in turkey poults between leucine-valine, leucine-isoleucine and isoleucine-valine and that the growth reduction caused by added leucine can be partly alleviated by addition of valine or by valine plus isoleucine, but not be isoleucine alone.

Animal Feed↗
PubMed1984

Effects of D-valine on pulmonary artery endothelial cell morphology and function in cell culture.

The effects of D-valine on the cell culture of bovine pulmonary artery endothelial cells were studied using D-valine-modified Minimal Essential Medium (MEM). D-Valine-treated cultures (46-920 mg/l) were compared with replicate cells grown in L-valine (46 mg/l)-MEM. All media were supplemented with 15% fetal bovine serum (FBS). Endothelial cells were grown for 14 passages with split ratios varying from 1:3 to 1:6. Unlike cells grown in L-valine MEM, cells grown in D-valine MEM did not become contaminated by the growth fibroblasts in primary cultures. D-Valine-treated cells were found to grow in cobblestone array, exhibit contact inhibition and strongly express factor-VIII antigen (F-VIII). D-Valine-grown cells produced PGI2 in greater proportion to PGE2, both constitutively and when stimulated by bradykinin, on comparison with cells grown in L-valine. In addition, cells grown in L-valine, although able to express factor VIII, were not comparable to D-valine cells with respect to other parameters assayed (morphology and growth as a monolayer).

Animals↗
PubMed1994

Epimerization of the D-valine portion in the biosynthesis of actinomycin D.

In the biosynthesis of actinomycin, the multifunctional actinomycin synthetase II (ACMS II) assembles 4-methyl-3-hydroxyanthranilic acid (4-MHA), L-threonine and D-valine, the first three residues of the 4-MHA peptide lactone chain. ACMS II activates L-threonine and L-valine but not D-valine as thioesters via their adenylates, and there is no epimerization of the covalently bound L-valine. When L-threonine and L-valine are presented to the enzyme together with the 4-MHA analogue p-toluic acid and the 4-MHA-activating enzyme ACMS I, ACMS II forms the two diastereomers p-toluyl-L-Thr-L-Val and p-toluyl-L-Thr-D-Val in equal amounts along with p-toluyl-L-Thr in a cofactor-independent manner. Studies with [2,3-3H2]valine revealed that p-toluyl-L-Thr-D-Val contained approximately 50% of the tritium label found in the LL-diastereomer. Concomitantly, radioactive water was formed due to enzyme-catalyzed hydrogen exchange with the solvent during epimerization. In the absence of threonine (or MgATP), however, the amount of radioactive water formed from [3H]valine was significantly less, which suggests that the peptide bond between L-threonine and L-valine is formed prior to the epimerization at C-2 of valine. The facts that both LL- and LD-acyldipeptides are equally present on the enzyme's surface--as revealed by using 14C-labeled threonine or valine as precursors--and that the L-valine in the LL-diastereomer apparently has not lost hydrogen strongly suggests that the LL-diastereomer is an obligatory intermediate in the formation of the LD-dipeptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1984

Regulation of valine metabolism in man: a stable isotope study.

Valine and leucine kinetics were studied in four young healthy men in the postabsorptive state with a 4-h primed infusion of either L-[1-13C,15N] valine or L-[1-13C,15N]-leucine. For 1 wk before each infusion study each subject consumed a diet that provided an adequate amount of energy and 1.6 kg/day of protein. During infusion of tracer, plasma valine or leucine, and expired 13CO2 reached isotopic steady state by 2 h. The valine and leucine carbon fluxes (mean +/- SE) were 80.3 +/- 1.2 and 86.6 +/- 2.0 mumol kg-1h-1, respectively, consistent with the lesser content of valine compared with leucine in body protein. Valine and leucine oxidation rates were 11.8 +/- 0.6 and 15.9 +/- 1.1 mumol kg-1h-1, respectively. From these values and values for valine and leucine nitrogen flux, the rates of valine and leucine transamination were calculated. Valine and leucine deamination were 84.0 +/- 3.5 and 103.0 +/- 6.5 mumol kg-1h-1, and values for reamination were 72.2 +/- 3.3 and 87.1 +/- 7.5 mumol kg-1h-1, respectively. Thus, the patterns of valine and leucine catabolism are similar. However, when the plasma substrate levels are used to estimate transamination rate constants, we estimate that the transamination equilibrium favors leucine transamination over valine by 5-fold.

Adult↗
PubMed1995

Leucine affects the metabolism of valine by isolated perfused rat hearts: relation to branched-chain amino acid antagonism.

This study was conducted to determine the effects of different concentrations of leucine on the transport, transamination and oxidation of valine and on incorporation of valine into heart proteins in the isolated perfused rat heart. Valine metabolism was studied in rat hearts perfused with medium containing glucose and graded levels of L-leucine. In transport studies L-phenylalanine was also tested. Uptake of L-[1-14C]valine (0.2 mmol/L) was significantly reduced (-50%) by inclusion of 0.2 mmol/L phenylalanine or leucine, and by -70% by inclusion of 1.0 mmol/L phenylalanine or leucine in the perfusate. Transamination of valine decreased by 37 and 48%, and oxidation of valine by 53 and 71%, respectively, when 0.2 or 1.0 mmol/L leucine was included in the perfusate. Tissue concentrations of valine decreased by 43, 48 and 62% in the presence of 0.2, 0.5 and 1.0 mmol/L leucine, respectively; tissue concentrations of leucine, glutamate and alanine increased approximately 11-fold, 1.2-fold and 0.5-fold, respectively, when 1.0 mmol/L leucine was present in the perfusate. Addition of 0.2-1.0 mmol/L leucine did not affect incorporation of valine into heart proteins. We conclude that 1) competition among large neutral amino acids for transport into heart occurs at physiological concentrations of these amino acids in plasma; 2) inhibition of valine uptake by leucine can limit the rate of valine catabolism in heart; and 3) depletion of tissue valine concentration by an excess of leucine did not affect the rate of protein synthesis.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1995

Valine requirement of the finishing pig.

Pigs weighing approximately 70 kg were used in two experiments to determine the valine requirement during the finishing period. In the first experiment, 10 gilts were allotted in two 5 x 5 Latin square designs to five semipurified diets that ranged in valine concentration from .35 to .55%. Urinary urea excretion was measured during each of the 3-d periods of the Latin square. Urea N excretion in relation to N intake and to creatinine N excretion was minimized (quadratic effect, P < .10) at valine concentrations of .45 to .50%. In Exp. 2, 36 barrows and 36 gilts were fed one of six diets containing .35 to .60% valine. The highest weight gains (not significant) and feed efficiencies (quadratic effect, P < .05) were achieved by the pigs that consumed .45% valine. Plasma urea concentration at the end of the experiment was lowest (quadratic effect, P < .05) in pigs that consumed .50% valine. Estimates of the valine requirement based on breakpoint and quadratic equation analyses ranged from .40 to .50% total valine (.33 to .43% ileal digestible valine). Pigs in Exp. 2 consumed approximately 2.5 kg/d (8,850 kcal/d of ME). Thus, the estimate of the valine requirement is approximately 11 g/d. These estimates of the valine requirements of finishing pigs are slightly higher than the National Research Council requirements when expressed as a percentage of the diet but are similar when expressed on a grams per day basis.

Animal Feed↗
PubMedDate not supplied

D-valine medium maintains prolactin production in primary culture.

Prolactin secretion by bovine pituitary cells in L-valine-containing medium decreases approximately 96% from day 3 to day 11 of culture. We hypothesized that this decrease was caused by overgrowth of these cultures by fibroblasts. Our present objective was to maintain the synthesis and secretion of PRL by bovine pituitary cells in culture. We attempted this by growing pituitary cells in D-valine-containing medium to achieve selective suppression of fibroblast growth. Substitution of D-valine for L-valine in Earle's or Swim's medium resulted in undiminished PRL synthesis and release over a 30-day culture period. In contrast, comparable measures for cells maintained in medium with L-valine decreased more than 90% from day 5 to day 20 of culture and remained low thereafter. Cells cultured in medium containing D-valine retained their ability to release PRL in response to thyrotropin-releasing hormone throughout the 30-day culture period, although there was a decrease in magnitude of response with time. Similarly, estradiol increased PRL release by pituitary cells maintained in D-valine, but this stimulatory effect was no longer demonstrable by day 20 of culture. The amount of growth hormone (GH) and luteinzing hormone (LH) released into the medium decreased with time and this decrease was independent of the valine isomer contained in the medium. We conclude that substituting D-valine for L-valine in culture medium allows PRL synthesis and release to persist undiminished for at least 30 days in culture.

Animals↗
PubMed1997

Amniotic fluid glycine-valine ratio and neonatal morbidity in fetal growth restriction.

OBJECTIVE: To test the hypothesis that an elevated amniotic fluid glycine-valine ratio predicts neonatal morbidity in growth-restricted newborns. METHODS: Amniotic fluid (AF) was collected from 122 third-trimester pregnancies (range 31-39 weeks), 49 of which were complicated by fetal growth restriction. Amino acid analysis was performed by high-pressure liquid chromatography. Glycine-valine ratios were compared between normal and growth-restricted fetuses. Neonatal morbidity within the group of growth-restricted fetuses was characterized by evaluation of neonatal hypoglycemia, arterial cord blood gas analysis, and birth weight percentile. We also examined the correlation of AF glycine-valine ratio to the umbilical artery resistance index. The median interval between AF sampling and delivery was 1 day (range 0-8 days). Analyses were performed by Student t test, chi 2 with Yates correction, or simple correlation when appropriate. P < .05 was considered significant. RESULTS: Growth-restricted fetuses have a significantly elevated AF glycine-valine ratio compared with control subjects (3.31 +/- 1.06 versus 2.61 +/- 0.77, respectively, P < .001). There was no association of the glycine-valine ratio with gestational age for either group. An elevated glycine-valine ratio was not associated with neonatal hypoglycemia within the growth-restricted group (hypoglycemia: [n = 16] 3.19 +/- 1.07; no hypoglycemia: (n = 30) 3.44 +/- 1.09). There were no significant correlations of glycine-valine ratio with arterial cord blood pH (r = -0.10), oxygen pressure (r = 0.04), or base deficit (r = 0.12). There were no significant correlations of glycine-valine ratio and birth weight percentile (r = -.24) or umbilical artery resistance index (r = -.14). CONCLUSION: Amniotic fluid glycine-valine ratio is elevated in growth-restricted fetuses compared with control fetuses. However, the level of glycine-valine elevation is not associated with neonatal morbidity related to hypoglycemia, arterial cord blood gas abnormalities, or birth weight percentile.

Adult↗
PubMed2000

Nephrotic proteinuria has No net effect on total body protein synthesis: measurements with (13)C valine.

In nephrotic syndrome, significant amounts of plasma proteins, mostly of hepatic origin, are lost in urine. Total hepatic protein synthesis increases, suggesting that other protein pools must be conserved to maintain steady state. This can be accomplished either by decreased amino acid oxidation or decreased protein synthesis in other organs to replace lost liver-derived proteins. To determine the effect of nephrotic syndrome on total-body protein metabolism, we compared whole-body valine use in seven nephrotic patients and five controls using a primed continuous infusion of [1-(13)C]-valine, with additional priming of NaH(13)CO(3). Plasma [(13)C]-valine, (13)C alpha ketoisovaleric acid, and the expired (13)CO(2) enrichments were used to assess whole-body valine flux, valine oxidation, and nonoxidative valine disposal (NOVD). The valine flux into the blood compartment (97.7 +/- 3.0 versus 95.3 +/- 3.3 micromol/kg/h), oxidation of valine (19.4 +/- 1.9 versus 21.2 +/- 2. 8 micromol/kg/h), and NOVD (78.3 +/- 2.5 versus 74.2 +/- 2.7 micromol/kg/h) were not statistically different in patients compared with controls. Valine oxidation correlated positively with urinary urea excretion (r = 0.70; P = 0.01) in all subjects. Compared with control subjects who have similar urinary urea excretion, nephrotic subjects do not compensate for urinary loss of protein by decreased amino acid oxidation or decreased nonoxidative valine disposal. Previous studies have shown that synthesis of several hepatic proteins increases when subjects are fed the same dietary regime, whereas the present study shows that total-body protein synthesis does not increase. This would imply reduced synthesis of nonhepatic protein pools.

Adult↗
PubMed1998

Effect of valine-depleted total parenteral nutrition on fatty liver development in tumor-bearing rats.

Valine-depleted amino acid imbalance, while having a suppressive effect on tumor growth, may induce fatty liver. We administered valine-depleted total parenteral nutrition (TPN) solution to rats subcutaneously transplanted with ascites containing hepatoma AH-109A and examined the time course of the development of fatty liver. An accumulation of fatty vacuoles was observed in hepatocytes on day 4. To prevent the development of fatty liver in tumor-bearing rats, we administered a small amount of valine in addition to the valine-depleted imbalance solution via the central vein. Such treatment, however, resulted in neither the prevention of fatty liver development nor the suppression of tumor growth. To supply valine to the liver, we administered a low concentration of valine via the portal vein simultaneously with central venous administration of valine-depleted TPN solution. As a result, the peripheral blood valine level of these rats was < 0.5 that of the control group, but the valine in the liver was maintained at the same level as that of the control group, and accumulation of triacylglycerols in the liver was slight. However, the suppressive effect on tumor growth was maintained, as the tumor weight was suppressed to almost the same degree as that of rats administered only the valine-depleted solution.

Amino Acids↗
PubMed1974

Regulation of the pool size of valine in Escherichia coli K-12.

Three mutations (ilvH611, ilvH612, and ilvH613) are described which make Escherichia coli K-12 resistant to valine inhibition and are located near leu. The expression of the ilv genes appears to be normal in these mutants since the isoleucine-valine biosynthetic enzymes are not derepressed relative to the wild type. The intracellular concentration of valine is, however, higher in the mutants than in the isogenic ilvH(+) strain. These mutants also excrete valine, probably because of the high intracellular concentration of this amino acid. The pool size of valine is regulated independently from that of isoleucine and leucine. The increased intracellular concentration of valine is due to a decreased feedback inhibition that valine exerts on its own biosynthetic pathway. In fact, acetolactate synthase activity assayed in extracts of ilvH612 and ilvH613 mutants is more resistant to valine inhibition than the activity assayed in the ilvH(+) isogenic strain. Two forms of acetolactate synthase activity can be separated from these extracts by adsorption and elution on hydroxylapatite. One of them is as sensitive to valine inhibition as that of the wild type, the other is more resistant to valine inhibition.

Cell-Free System↗
PubMed1975

Studies on the valine sensitivity in non-ketotic hyperglycinemia.

An oral loading test with L-valine (100 mg/kg body weight) in 3 patients with non-ketotic hyperglycinemia was accompanied by drowsiness and hyperreflexia of the patients. Metabolic studies revealed a slightly lower rate of disappearance of valine from blood in 2 of the patients. In a third patient, the curve was not different from controls. Gas chromatographic analysis for short-chain fatty acids in serum carried out during the valine loading test did not show increased concentrations. Urine collected during the valine loading test did not show excretion of N-acylglycine derivatives. As neither of the branched chain amino acid transaminases proved to be inhibited by glycine, inhibition by glycine of the uptake of valine by the tissues became likely. This uptake has been measured in rat liver slices. Glycine was found to be a competitive inhibitor of valine uptake, with a Ki of 4.9 mM. It is concluded that the tendency to a decreased rate of valine disappearance from blood in non-ketotic hyperglycinemia could be due to an inhibition of valine uptake by the high plasma glycine concentration. The relationship of the inhibited valine uptake in liver slices of rats with the clinical symptoms in non-ketotic hyperglycinemia patients after a valine load remains to be established.

Animals↗
PubMed1988

Transamination and oxidation of leucine and valine in rat adipose tissue.

Leucine was oxidized by rat adipose tissue at a rate which was not limited by the activity of branched chain amino acid transaminase since high concentrations (10 mM) of [1-14C]leucine and its transamination product, alpha-keto[1-14C]isocaproate, were oxidized at similar rates. Despite the apparent abundance of transaminase activity, however, [1-14C]valine was oxidized at only 10 to 25% of the rate of its transamination product, alpha-keto[1-14C]isovalerate. The net rate at which [1-14C] valine was transaminated by intact tissues was estimated as the sum of the rates of 14CO2 production and alpha-ketoiso[1-14C]valerate release into the medium. Transamination did not limit the rate of valine oxidation since valine was transaminated 3 times as fast as it was oxidized. The rate of valine transamination increased 18-fold when its concentration was raised 100-fold, but the fraction of [1-14C]valine oxidized to 14CO2 remained constant over the range of incubation conditions studied. The oxidation/transamination ratio for leucine was also constant and exceeded the oxidation/transamination ratio for valine unless valine oxidation was stimulated, either by the addition of glucose or leucine. Stimulation of valine oxidation did not increase its transamination but reduced the rate at which alpha-ketoisovalerate was released from the tissue. The faster oxidation of alpha-ketoisocaproate than of alpha-ketoisovalerate may be due to the activation of branched chain alpha-keto acid dehydrogenase by alpha-ketoisocaproate, but the alpha-keto acid oxidation rates do not fully account for the faster transamination of leucine than of valine.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1981

Short-term and long-term ethanol administration inhibits the placental uptake and transport of valine in rats.

Ethanol ingestion during pregnancy causes a pattern of fetal/neonatal dysfunction called the FAS. The effects of short- and long-term ethanol ingestion on the placental uptake and maternal-fetal transfer of valine were studied in rats. The in vivo placental uptake and fetal uptake were estimated after injection of 0.04 micromol of 14C-valine intravenously on day 20 of gestation in Sprague-Dawley rats. Short-term ethanol ingestion (4 gm/kg) caused a significant reduction in the placental uptake of 14C-valine by 33%, 60%, and 30%, and 31% at 2.5, 5, 10, and 15 min after valine administration, respectively (p less than 0.01), and a similar significant reduction occurred in the fetal uptake of 14C-valine (p less than 0.01). Long-term ethanol ingestion prior to and throughout gestation resulted in a 47% reduction in placental valine uptake (p less than 0.01) and a 46% reduction in fetal valine uptake (p less than 0.01). Long-term ethanol feeding from day 4 to day 20 of gestation caused a 32% reduction in placental valine uptake (p less than 0.01) and a 26% reduction in fetal valine uptake (p less than 0.01). We conclude that both short- and long-term ingestion of ethanol inhibit the placental uptake and maternal-fetal transfer of an essential amino acid--valine. An alteration of placental function may contribute to the pathogenesis of the FAS.

Animals↗
PubMed1992

Incorporation of [h]leucine and [h]valine into protein of freshwater bacteria: field applications.

Incorporation of leucine and valine into proteins of freshwater bacteria as a measure of bacterial production was tested in two eutrophic Danish lakes and was related to bacterial production measured by thymidine incorporation. In a depth profile (0 to 8 m) in Frederiksborg Castle Lake, incorporation of 100 nM leucine and valine gave similar rates of protein production. In terms of carbon, this production was about 50% lower than incorporation of 10 nM thymidine. In another depth profile in the same lake, incorporations of 10 nM valine and 100 nM leucine were identical, but differed from incorporations of 10 nM leucine and 100 nM valine. Bacterial carbon production calculated from incorporations of 10 nM thymidine and 10 nM leucine was similar, whereas 10 nM valine and 100 nM leucine and valine indicated an up to 2.4-fold-higher rate of carbon production. In a diel study in Lake Bagsvaerd, incorporation of 100 nM leucine and valine indicated a similar protein production, but the calculated carbon production was about 1.9-fold higher than the production based on uptake of 10 nM thymidine. Different diel changes in incorporation of the two amino acids and in incorporation of thymidine were observed. In both lakes, concentrations of naturally occurring leucine and valine were <5 nM in most samples. This means that the specific activity of a H isotope added at a concentration of 100 nM usually was diluted a maximum of 5%. Net assimilation of natural free amino acids in the lakes sustained 8 to 69% of the net bacterial carbon requirement, estimated from incorporation of leucine, valine, or thymidine. The present results indicate that incorporation of leucine and valine permits realistic measurements of bacterial production in freshwater environments.

Journal Article↗
PubMed1993

Valine oxidation in the rat medullary thick ascending limb.

In the kidney, a branched-chain amino acid transferase (BCAAT) activity has been localized mainly in the medullary thick ascending limb (MTAL) of the rat nephron. BCAAT is the first enzyme involved in the metabolic pathway of the three branched-chain amino acids (BCAA): leucine, isoleucine and valine. The present work has been designed to study valine catabolism. Valine and leucine oxidation in MTAL were compared by measuring the rate of 14CO2 produced when these substrates were incubated as sole substrates at a final concentration of 1 mM. Since glucose is also metabolized in MTAL, valine and leucine oxidation were quantified also in the presence of glucose (1 mM). The results show that: (1) valine oxidation was greater than that of leucine (63.0 +/- 4.7 vs 39.7 +/- 5.2 pmol.h-1 x micrograms-1 protein, respectively; P < 0.001). As previously shown, leucine oxidation was found to be increased in the presence of glucose whereas glucose oxidation decreased. In contrast, the presence of glucose strongly diminished valine oxidation (19.2 +/- 1.9 vs 63.1 +/- 4.7 pmol.h-1 x micrograms-1 protein; P < 0.001) whereas glucose oxidation was increased in the presence of valine (268.2 +/- 14.9 vs 229.6 +/- 16.2 pmol.h-1 x micrograms-1 protein; P < 0.05). We conclude that in rat MTAL, under near physiological conditions (in the presence of glucose, as in vivo), leucine is a preferential respiratory fuel as compared to valine. However, valine supports energetic salt transport and facilitates glucose oxidation.

Animals↗