Biomedical subjects

C D Hardin

Publications and source records attributed to C D Hardin.

At least 19 recordsLinked to original sources

PubMed2006

Vascular metabolic dysfunction and lipotoxicity.

The purpose of this study was to determine the role of lipotoxicity in vascular smooth muscle (VSM). C(1)-BODIPY 500/510 C(12) used to assess the ability of VSM A7r5 cells to transport long-chain fatty acids showed that lipid transport did not appear to limit metabolism. Thin layer chromatography revealed that storage of transported fatty acid occurred primarily as mono- and diglycerides and fatty acids but not as triglycerides. We used lipid-induced apoptosis as a measure of lipotoxicity and found that 1.5 mM palmitate (6.8:1) bound to albumin resulted in a 15-fold increase in the number of apoptotic cells compared to the control at 24 hours. This apoptosis did not seem to be due to an increase in reactive oxygen species (ROS) since VSM cells incubated in palmitate showed less ROS production than cells incubated in albumin only. Similar exposure to oleate did not significantly increase the number of apoptotic cells compared to the control. Oleate actually significantly attenuated the apoptosis induced by palmitate, suggesting that unsaturated fatty acids have a protective effect on cells undergoing palmitate-induced apoptosis. These results suggest that vascular smooth muscle is vulnerable to lipotoxicity and that this lipotoxicity may play a role in the development of atherosclerosis.

Albumins↗

PubMed2001

Caveolae and the organization of carbohydrate metabolism in vascular smooth muscle.

We have previously found that glycolysis and gluconeogenesis occur in separate "compartments" of the VSM cell. These compartments may result from spatial separation of glycolytic and gluconeogenic enzymes (Lloyd and Hardin [1999] Am J Physiol Cell Physiol. 277:C1250-C1262). We have also found that an intact plasma membrane is essential for compartmentation to exist (Lloyd and Hardin [2000] Am J Physiol Cell Physiol. 278:C803-C811), suggesting that glycolysis and gluconeogenesis may be associated with distinct plasma membrane microdomains. Caveolae are one such microdomain, in which proteins of related function colocalize. Thus, we hypothesized that membrane-associated glycolysis occurs in association with caveolae, while gluconeogenesis is localized to non-caveolae domains. To test this hypothesis, we disrupted caveolae in vascular smooth muscle (VSM) of pig cerebral microvessels (PCMV) with beta methyl-cyclodextrin (CD) and examined the metabolism of [2-(13)C]glucose (a glycolytic substrate) and [1-(13)C]fructose 1,6-bisphosphate (FBP, a gluconeogenic substrate in PCMV) using (13)C nuclear magnetic resonance spectroscopy. Caveolar disruption reduced flux of [2-(13)C]glucose to [2-(13)C]lactate, suggesting that caveolar disruption partially disrupted the glycolytic pathway. Caveolae disruption may also have resulted in a breakdown of compartmentation, since conversion of [1-(13)C]FBP to [3-(13)C]lactate was increased by CD treatment. Alternatively, the increased [3-(13)C]lactate production may reflect changes in FBP uptake, since conversion of [1-(13)C]FBP to [3-(13)C]glucose was also elevated in CD-treated cells. Thus, a link between caveolar organization and metabolic organization may exist.

Animals↗

PubMed2001

Alterations in the oxidative metabolic profile in vascular smooth muscle from hyperlipidemic and diabetic swine.

High cholesterol, especially LDL cholesterol, has been associated with the development of atherosclerotic plaques in arteries. To investigate the changes in cellular substrate metabolism early in the atherogenic process, Sinclair miniature swine were treated for 12 weeks with either a control diet, a high fat diet, or a high fat diet with the addition of alloxan to induce diabetes. The fractional entry into the TCA cycle of 1,2-(13)C-acetate (5 mM), 1-(13)C-glucose (5 mM), and unlabeled, endogenous lipids was determined in control, hyperlipidemic, and diabetic/hyperlipidemic pigs using 13C-isotopomer analysis of glutamate. The diabetic state of the pigs was validated by plasma glucose measurements made after 10 weeks of alloxan treatment for control (65 +/- 6 mg/dL), hyperlipidemic (63 +/- 5 mg/dL), and diabetic/hyperlipidemic (333 +/- 52 mg/dL) pigs. Plasma glucose values did not correlate with the percentage of glucose entry into the TCA cycle (R2 = 0.0819, n = 10). Alterations in the pattern of substrate oxidation were better correlated with changes in plasma lipids (cholesterol and triglycerides) than with changes in plasma glucose. Plasma total cholesterol and total triglyceride levels significantly correlated with changes in acetate metabolism (R2 = 0.7768 and R2 = 0.4787, respectively) and with changes in glucose metabolism (R2 = 0.6067 and R2 = 0.4506, respectively). We conclude that alterations in lipid profile, especially those that were observed in the diabetic milieu, are associated with early changes in vascular smooth muscle oxidative metabolism. These changes in oxidative metabolism may precede alterations in smooth muscle phenotype and, therefore, may play an important role in the early pathogenesis of atherosclerosis.

Acetates↗

PubMed2001

Social influence effects on automatic racial prejudice.

Although most research on the control of automatic prejudice has focused on the efficacy of deliberate attempts to suppress or correct for stereotyping, the reported experiments tested the hypothesis that automatic racial prejudice is subject to common social influence. In experiments involving actual interethnic contact, both tacit and expressed social influence reduced the expression of automatic prejudice, as assessed by two different measures of automatic attitudes. Moreover, the automatic social tuning effect depended on participant ethnicity. European Americans (but not Asian Americans) exhibited less automatic prejudice in the presence of a Black experimenter than a White experimenter (Experiments 2 and 4), although both groups exhibited reduced automatic prejudice when instructed to avoid prejudice (Experiment 3). Results are consistent with shared reality theory, which postulates that social regulation is central to social cognition.

Automatism↗

PubMed2001

Myocardial metabolism of exogenous FDP is consistent with transport by a dicarboxylate transporter.

The extent to and the mechanism by which fructose-1,6-bisphosphate (FDP) crosses cell membranes are unknown. We hypothesized that its transport is either via band 3 or a dicarboxylate transporter. The question was addressed in isolated Langendorff rat hearts perfused under normoxic conditions. Groups of hearts received the following metabolic substrates (in mM): 5 FDP; 5 FDP + either 5, 10, or 20 fumarate; 10 FDP and either 5, 10, or 20 fumarate; or 5 FDP + 2 4,4'-dinitrostilbene-2,2'-disulfonate (DNDS), a band 3 inhibitor. FDP uptake and metabolism were measured as production of [(13)C]lactate from [(13)C]FDP or (14)CO(2) and [(14)C]lactate from uniformly labeled [(14)C]FDP in sample perfusates. During 30 min of perfusion, FDP metabolism was 12.4 +/- 2.6 and 31.2 +/- 3.0 micromol for 5 and 10 mM FDP, respectively. Addition of 20 mM fumarate reduced FDP metabolism over a 30-min perfusion period to 3.1 +/- 0.6 and 6.3 +/- 0.5 micromol for 5 and 10 mM FDP groups, respectively. DNDS did not affect FDP utilization. These data are consistent with transport of FDP by a dicarboxylate transport system.

Animals↗

PubMed2000

Sorting of metabolic pathway flux by the plasma membrane in cerebrovascular smooth muscle cells.

We used beta-escin-permeabilized pig cerebral microvessels (PCMV) to study the organization of carbohydrate metabolism in the cytoplasm of vascular smooth muscle (VSM) cells. We have previously demonstrated (Lloyd PG and Hardin CD. Am J Physiol Cell Physiol 277: C1250-C1262, 1999) that intact PCMV metabolize the glycolytic intermediate [1-(13)C]fructose 1,6-bisphosphate (FBP) to [1-(13)C]glucose with negligible production of [3-(13)C]lactate, while simultaneously metabolizing [2-(13)C]glucose to [2-(13)C]lactate. Thus gluconeogenic and glycolytic intermediates do not mix freely in intact VSM cells (compartmentation). Permeabilized PCMV retained the ability to metabolize [2-(13)C]glucose to [2-(13)C]lactate and to metabolize [1-(13)C]FBP to [1-(13)C]glucose. The continued existence of glycolytic and gluconeogenic activity in permeabilized cells suggests that the intermediates of these pathways are channeled (directly transferred) between enzymes. Both glycolytic and gluconeogenic flux in permeabilized PCMV were sensitive to the presence of exogenous ATP and NAD. It was most interesting that a major product of [1-(13)C]FBP metabolism in permeabilized PCMV was [3-(13)C]lactate, in direct contrast to our previous findings in intact PCMV. Thus disruption of the plasma membrane altered the distribution of substrates between the glycolytic and gluconeogenic pathways. These data suggest that organization of the plasma membrane into distinct microdomains plays an important role in sorting intermediates between the glycolytic and gluconeogenic pathways in intact cells.

Adenosine Triphosphate↗

PubMed2000

Influence of glycogen storage on vascular smooth muscle metabolism.

The role of glycogen as an oxidative substrate for vascular smooth muscle (VSM) remains controversial. To elucidate the importance of glycogen as an oxidative substrate and the influence of glycogen flux on VSM substrate selection, we systematically altered glycogen levels and measured metabolism of glucose, acetate, and glycogen. Hog carotid arteries with glycogen contents ranging from 1 to 11 micromol/g were isometrically contracted in physiological salt solution containing 5 mM [1-(13)C]glucose and 1 mM [1, 2-(13)C]acetate at 37 degrees C for 6 h. [1-(13)C]glucose, [1, 2-(13)C]acetate, and glycogen oxidation were simultaneously measured with the use of a (13)C-labeled isotopomer analysis of glutamate. Although oxidation of glycogen increased with the glycogen content of the tissue, glycogen oxidation contributed only approximately 10% of the substrate oxidized by VSM. Whereas [1-(13)C]glucose flux, [3-(13)C]lactate production from [1-(13)C]glucose, and [1, 2-(13)C]acetate oxidation were not regulated by glycogen content, [1-(13)C]glucose oxidation was significantly affected by the glycogen content of VSM. However, [1-(13)C]glucose remained the primary ( approximately 40-50%) contributor to substrate oxidation. Therefore, we conclude that glucose is the predominate substrate oxidized by VSM, and glycogen oxidation contributes minimally to substrate oxidation.

Acetates↗

PubMed1999

Transport and metabolism of exogenous fumarate and 3-phosphoglycerate in vascular smooth muscle.

The keto (linear) form of exogenous fructose 1,6-bisphosphate, a highly charged glycolytic intermediate, may utilize a dicarboxylate transporter to cross the cell membrane, support glycolysis, and produce ATP anaerobically. We tested the hypothesis that fumarate, a dicarboxylate, and 3-phosphoglycerate (3-PG), an intermediate structurally similar to a dicarboxylate, can support contraction in vascular smooth muscle during hypoxia. To assess ATP production during hypoxia we measured isometric force maintenance in hog carotid arteries during hypoxia in the presence or absence of 20 mM fumarate or 3-PG. 3-PG improved maintenance of force (p < 0.05) during the 30-80 min period of hypoxia. Fumarate decreased peak isometric force development by 9.5% (p = 0.008) but modestly improved maintenance of force (p < 0.05) throughout the first 80 min of hypoxia. 13C-NMR on tissue extracts and superfusates revealed 1,2,3,4-(13)C-fumarate (5 mM) metabolism to 1,2,3,4-(13)C-malate under oxygenated and hypoxic conditions suggesting uptake and metabolism of fumarate. In conclusion, exogenous fumarate and 3-PG readily enter vascular smooth muscle cells, presumably by a dicarboxylate transporter, and support energetically important pathways.

Animals↗

PubMed1999

Role of microtubules in the regulation of metabolism in isolated cerebral microvessels.

We used (13)C-labeled substrates and nuclear magnetic resonance spectroscopy to examine carbohydrate metabolism in vascular smooth muscle of freshly isolated pig cerebral microvessels (PCMV). PCMV utilized [2-(13)C]glucose mainly for glycolysis, producing [2-(13)C]lactate. Simultaneously, PCMV utilized the glycolytic intermediate [1-(13)C]fructose 1,6-bisphosphate (FBP) mainly for gluconeogenesis, producing [1-(13)C]glucose with only minor [3-(13)C]lactate production. The dissimilarity in metabolism of [2-(13)C]FBP derived from [2-(13)C]glucose breakdown and metabolism of exogenous [1-(13)C]FBP demonstrates that carbohydrate metabolism is compartmented in PCMV. Because glycolytic enzymes interact with microtubules, we disrupted microtubules with vinblastine. Vinblastine treatment significantly decreased [2-(13)C]lactate peak intensity (87.8 +/- 3.7% of control). The microtubule-stabilizing agent taxol also reduced [2-(13)C]lactate peak intensity (90.0 +/- 2. 4% of control). Treatment with both agents further decreased [2-(13)C]lactate production (73.3 +/- 4.0% of control). Neither vinblastine, taxol, or the combined drugs affected [1-(13)C]glucose peak intensity (gluconeogenesis) or disrupted the compartmentation of carbohydrate metabolism. The similar effects of taxol and vinblastine, drugs that have opposite effects on microtubule assembly, suggest that they produce their effects on glycolytic rate by competing with glycolytic enzymes for binding, not by affecting the overall assembly state of the microtubule network. Glycolysis, but not gluconeogenesis, may be regulated in part by glycolytic enzyme-microtubule interactions.

Animals↗

PubMed1999

Examining glucose transport in single vascular smooth muscle cells with a fluorescent glucose analog.

Changes in vascular smooth muscle glucose transport are thought to contribute to the pathogenesis of vascular disease in conditions such as diabetes, yet no single-cell assay for glucose uptake by VSM exists. Therefore, we examined the uptake of the fluorescent glucose analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) in isolated pig vascular smooth muscle cells (VSMC) using digital imaging microscopy. Uptake of 2-NBDG by VSMC was inhibited by D-glucose but not by L-glucose, suggesting that 2-NBDG enters VSMC via glucose transporters. Uptake of 2-NBDG was linear in the presence of 10 mM D-glucose (n=6, R2=0.9408) but not in its absence (n=4, R2=0.9993), indicating that 2-NBDG is not metabolized and accumulates within the cells. 2-NBDG fluorescence in VSMC was often non-uniform and appeared to represent binding of 2-NBDG to some cytoplasmic component. The present study demonstrates that 2-NBDG is a useful tool for examining vascular smooth muscle glucose uptake at the single cell level.

4-Chloro-7-nitrobenzofurazan↗

PubMed1998

Glycolytic flux in permeabilized freshly isolated vascular smooth muscle cells.

To determine whether channeling of glycolytic intermediates can occur in vascular smooth muscle (VSM), we permeabilized freshly isolated VSM cells from hog carotid arteries with dextran sulfate. The dextran sulfate-treated cells did not exclude trypan blue, a dye with molecular weight of approximately 1,000. If glycolytic intermediates freely diffuse, plasmalemmal permeabilization would allow intermediates to exit the cell and glycolytic flux should cease. We incubated permeabilized and nonpermeabilized cells with 5 mM [1-13C]glucose at 37 degrees C for 3 h. 13C nuclear magnetic resonance (NMR) was used to determine relative [3-13C]lactate production and to identify any 13C-labeled glycolytic intermediates that exited from the permeabilized cells. [3-13C]lactate production from [1-13C]glucose was decreased by an average of 32% (n = 6) in permeabilized cells compared with intact cells. No 13C-labeled glycolytic intermediates were observed in the bathing solution of permeabilized cells. We conclude that channeling of glycolytic intermediates can occur in VSM cells.

Animals↗

PubMed1998

Pattern of substrate utilization in vascular smooth muscle using 13C isotopomer analysis of glutamate.

Although vascular smooth muscle (VSM) derives the majority of its energy from oxidative phosphorylation, controversy exists concerning which substrates are utilized by the tricarboxylic acid (TCA) cycle. We used 13C isotopomer analysis of glutamate to directly measure the entry of exogenous [13C]glucose and acetate and unlabeled endogenous sources into the TCA cycle via acetyl-CoA. Hog carotid artery segments denuded of endothelium were superfused with 5 mM [1-13C]glucose and 0-5 mM [1,2-13C]acetate at 37 degreesC for 3-12 h. We found that both resting and contracting VSM preferentially utilize [1,2-13C]acetate compared with [1-13C]glucose and unlabeled substrates. The entry of glucose into the TCA cycle (30-60% of total entry via acetyl-CoA) exhibited little change despite alterations in contractile state or acetate concentrations ranging from 0 to 5 mM. We conclude that glucose and nonglucose substrates are important oxidative substrates for resting and contracting VSM. These are the first direct measurements of relative substrate entry into the TCA cycle of VSM during activation and may provide a useful method to measure alterations in VSM metabolism under physiological and pathophysiological conditions.

Acetates↗

PubMed1997

Regulation of glycogen utilization, but not glucose utilization, by precontraction glycogen levels in vascular smooth muscle.

These experiments were designed to determine whether glycogenolysis was influenced by the glycogen concentration of vascular smooth muscle. Segments of hog carotid artery smooth muscle were allowed to synthesize variable amounts of 1-[13C]glucosyl units of glycogen. Artery segments were then isometrically contracted in the presence of 2-[13C]glucose. Prior to and after isometric contraction, measurements were made of tissue glycogen content and superfusate glucose and lactate concentrations. 2-[13C]Lactate and 3-[13C]lactate peak intensities in the superfusate were measured using 13C-NMR spectroscopy. The tissue glycogen content decreased exponentially during the 4.5 h of isometric contraction (R2 = 0.990), despite more than a 3-fold range of glycogen concentration prior to contraction. The extent of glycogen utilization during a 3 h isometric contraction varied linearly with the precontraction glycogen concentration (R2 = 0.727). Lactate production specifically from glycogen breakdown increased with an increase in precontraction glycogen concentration (R2 = 0.620). During a 3 h isometric contraction neither the glucose utilization (R2 = 0.007) nor lactate production specifically produced from glucose (R2 = 0.00002) varied with the precontraction glycogen concentration. It is concluded that the rate of glycogenolysis is determined by the content of glycogen during prolonged contractions. In addition, precontraction glycogen levels influence the pathway for glycogen utilization but not the pathway for glucose utilization. Therefore, glycolysis and glycogenolysis behave independently in vascular smooth muscle.

Animals↗

PubMed1997

Differential regulation of glucose and glycogen metabolism in vascular smooth muscle by exogenous substrates.

The aim of this study was to determine whether the pathways of glycolysis and glycogenolysis can be independently modulated by the provision of acetate or pyruvate as exogenous substrates. Hog carotid artery segments were allowed to replete glycogen stores to over 6 micromol/g of new 13C-labeled glycogen by incubation at 37 degrees C with 5 mM [1-13C]glucose for 6-16 h and then were isometrically contracted for 3 h with 80 mM KCl in the presence of 5 mM [2-13C]glucose and either 2 mM sodium acetate or 5 mM sodium pyruvate. Measurements were made of total lactate production, glucose utilization, glycogen utilization, isometric force, [2-13C]lactate and [3-13C]lactate production. Compared to experiments with glucose as the sole exogenous substrate, provision of pyruvate significantly decreased glucose utilization (by 28%) but insignificantly decreased glycogen utilization. In contrast, provision of acetate resulted in a statistically insignificant decrease in glucose utilization (by 23%) and an increase in glycogen utilization (by 20%). The fraction of [3-13C]pyruvate derived from glycogen that was converted to [3-13C]lactate was significantly decreased in the presence of acetate despite the enhanced glycogen utilization. Despite these alterations in cellular energy balance, isometric force generation and maintenance was similar for all experimental groups. This differential regulation of glycolysis and glycogenolysis may either reflect the compartmentation of these pathways or suggest a novel regulation of carbohydrate metabolism in vivo.

Acetates↗

PubMed1997

Acetate or octanoate increases glycogenolysis in smooth muscle as determined by 13C-NMR.

Vascular smooth muscle is considered a model system for the study of the compartmentation of carbohydrate metabolism. Since vascular smooth muscle is capable of synthesizing substantial glycogen stores and utilizing a variety of metabolic substrates, we sought to determine the effects of utilization of either acetate or octanoate on 2-13C-glucose metabolism and on 1-13C-glycogen metabolism in contracting hog carotid arteries having high levels of 13C-labeled glycogen. In carotid arteries that have been allowed to synthesize substantial amounts of glycogen (to a total content of 7.84 +/- 0.31 mumol/gm wet wt glucosyl units), provision of either 5 mM 2-13C-glucose and 2 mM sodium acetate or 5 mM 2-13C-glucose and 0.5 mM octanoic acid during a 3 hr. contraction resulted in a 74% and 71% increase in glycogen utilization compared to that in the presence of glucose as the sole exogenous substrate. The fraction of the 3-13C-lactate from 1-13C-glycogen was substantially reduced in the presence of either acetate or octanoate. We speculate that AMP production by thiokinases with localized access of AMP to phosphorylase may be the common mechanism of glycogenolytic modulation by acetate and octanoate in contracting vascular smooth muscle with high glycogen content. We conclude that utilization of exogenous fatty acids can regulate glycogenolysis independent of glycolysis in contracting vascular smooth muscle with high glycogen content.

Acetates↗

PubMed1996

Fructose-1,6-bisphosphate as a metabolic substrate in hog ileum smooth muscle during hypoxia.

Exogenously applied fructose-1,6-bisphosphate has been reported to be effective in preventing some damage to the small intestine during ischemia. To determine whether exogenously applied fructose-1,6-bisphosphate protects ileum smooth muscle from damage from hypoxia and from reoxygenation, we examined the effect of fructose-1,6-bisphosphate on the ability of hog ileum smooth muscle to maintain isometric force during hypoxia and to generate isometric force after reoxygenation in the presence of 5 mM glucose. After 180 min of hypoxia, tissues incubated with 20 mM fructose-1,6-bisphosphate maintained significantly greater levels of isometric force than tissues incubated in the absence of exogenous substrate (23% of pre-hypoxia force compared to 16%). During the first contraction following reoxygenation there was a significantly greater force generation in tissues incubated with 20 mM fructose-1,6-bisphosphate during the hypoxia period compared to tissues with no exogenous substrate included during the hypoxia period (29% of pre-hypoxia force compared to 19%). However, glucose always was a better metabolic substrate compared to fructose-1,6-bisphosphate under all experimental conditions. The presence of fructose-1,6-bisphosphate during hypoxia likely improved tissue function by fructose-1,6-bisphosphate entering the cells and acting as a glycolytic intermediate, since during a 120 min period of hypoxia, unmounted ileum smooth muscle metabolized 1,6-13C-fructose-1,6-bisphosphate to 3-13C-lactate. This conversion of 1,6-13C-fructose-1,6-bisphosphate to 3-13C-lactate was inhibited by the addition of 1 mM iodoacetic acid, a glycolytic inhibitor. We conclude that exogenously provided fructose-1,6-bisphosphate does provide modest protection of ileum smooth muscle from hypoxic damage by functioning as a glycolytic intermediate and improving the cellular energy state.

Animals↗

PubMed1996

Preservation of phosphagen kinase function during transient hypoxia via enzyme abundance or resistance to oxidative inactivation.

Mammalian lactate dehydrogenase and phosphofructokinase are more susceptible in vitro to superoxide (O2) and hydroxyl (.OH) radicals than pyruvate kinase and glucose-6-phosphate dehydrogenase, suggesting that differential inactivation of regulatory enzymes contributes to the metabolic disintegration in stenoxic tissues during transient hypoxia. Likewise, creatine kinase in smooth muscle from porcine ileum is significantly reduced by hypoxia-reoxygenation ex vivo from 300 (+/- 18.2 SE, n = 8) to 196 U.g wet wt-1 (+/- 16.7, P < 0.001, ANOVA). Conversely, arginine kinase, from the myocardium of Limulus polyphemus, a species that tolerates anoxia for days was 2.9-fold less susceptible to oxidative inactivation. To examine whether preservation of kinase function is related to euryoxic capacity, a combination of non-invasive 31P-NMR spectroscopy and enzyme-linked assays was used to follow ATP and phosphagen status during hypoxia-reoxygenation in porcine ileum smooth muscle, L. polyphemus myocardium, and the myocardium of Argopecten irradians, a scallop species tolerant of hypoxia for only 24 h. Despite wide differences in phylogeny, euryoxic capacity and oxidative vulnerability of the phosphagen kinases, in all three tissues, the phosphagen pool recovered concomitant with ATP during reoxygenation, thereby revealing competent kinase function. In the mammalian tissue, such preservation of kinase function is facilitated by a 2400-fold excess of enzyme activity.

Animals↗

PubMed1995

Compartmentation of glucose and fructose 1,6-bisphosphate metabolism in vascular smooth muscle.

We examined the metabolism of exogenously added 13C-labeled fructose 1,6-bisphosphate (either labeled at the first and sixth carbons or labeled at the first carbon only) and of [2-13C]glucose in well-oxygenated and well-superfused hog carotid artery segments. Exogenously added fructose 1,6-bisphosphate was utilized by hog carotid artery and primarily participated in gluconeogenesis while the production of [3-13C]lactate was not significantly different from zero. When [1,6-13C]fructose 1,6-bisphosphate or [1-13C]fructose 1,6-bisphosphate was utilized individually, gluconeogenic flux occurred without metabolism through aldolase and triosephosphate isomerase resulting in formation of [1,6-13C]-glucose and [1-13C]glucose respectively. When [2-13C]glucose was the sole exogenous substrate, it was utilized and exclusively participated in glycolytic flux with production of [3-13C]lactate and no gluconeogenic flux from the trioses to [5-13C]glucose. When both glucose and fructose 1,6-bisphosphate were provided together as exogenous substrates, glucose still participated exclusively in glycolytic flux with no trioses participating in gluconeogenesis while fructose 1,6-bisphosphate participated in glycolytic flux with [3-13C]lactate production approximately being approximately half of the [1,6-13C]glucose production from [1,6-13C]fructose 1,6-bisphosphate. In the presence of glucose, [1-13C]fructose 1,6-bisphosphate also participated in glycolytic flux and gluconeogenic flux simultaneously. However in the presence of [2-13C]glucose, [1-13C]fructose 1,6-bisphosphate underwent isomerization through the trioses prior to gluconeogenesis since [6-13C]glucose was produced.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗