1
|
Xiang Y, Shen J. In vivo detection of intermediate metabolic products of [1-(13) C]ethanol in the brain using (13) C MRS. NMR IN BIOMEDICINE 2011; 24:1054-62. [PMID: 21312308 PMCID: PMC3400341 DOI: 10.1002/nbm.1653] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 09/29/2010] [Accepted: 11/07/2010] [Indexed: 05/30/2023]
Abstract
In this study, in vivo (13) C MRS was used to investigate the labeling of brain metabolites after intravenous administration of [1-(13) C]ethanol. After [1-(13) C]ethanol had been administered systemically to rats, (13) C labels were detected in glutamate, glutamine and aspartate in the carboxylic and amide carbon spectral region. (13) C-labeled bicarbonate HCO 3- (161.0 ppm) was also detected. Saturating acetaldehyde C1 at 207.0 ppm was found to have no effect on the ethanol C1 (57.7 ppm) signal intensity after extensive signal averaging, providing direct in vivo evidence that direct metabolism of alcohol by brain tissue is minimal. To compare the labeling of brain metabolites by ethanol with labeling by glucose, in vivo time course data were acquired during intravenous co-infusion of [1-(13) C]ethanol and [(13) C(6) ]-D-glucose. In contrast with labeling by [(13) C(6) ]-D-glucose, which produced doublets of carboxylic/amide carbons with a J coupling constant of 51 Hz, the simultaneously detected glutamate and glutamine singlets were labeled by [1-(13) C]ethanol. As (13) C labels originating from ethanol enter the brain after being converted into [1-(13) C]acetate in the liver, and the direct metabolism of ethanol by brain tissue is negligible, it is suggested that orally or intragastrically administered (13) C-labeled ethanol may be used to study brain metabolism and glutamatergic neurotransmission in investigations involving alcohol administration. In vivo (13) C MRS of rat brain following intragastric administration of (13) C-labeled ethanol is demonstrated.
Collapse
Affiliation(s)
- Yun Xiang
- Molecular Imaging Branch, National Institute of Mental Health Intramural Research Program, National Institutes of Health, Bethesda, MD, United States
| | - Jun Shen
- Molecular Imaging Branch, National Institute of Mental Health Intramural Research Program, National Institutes of Health, Bethesda, MD, United States
| |
Collapse
|
2
|
Lieber CS. Alcohol and the liver: metabolism of ethanol, metabolic effects and pathogenesis of injury. ACTA MEDICA SCANDINAVICA. SUPPLEMENTUM 2009; 703:11-55. [PMID: 2418640 DOI: 10.1111/j.0954-6820.1985.tb08903.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
|
3
|
Comparison of deuterium incorporation and mass isotopomer distribution analysis for measurement of human cholesterol biosynthesis. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)33464-7] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
|
4
|
Hellerstein MK. Synthesis of fat in response to alterations in diet: insights from new stable isotope methodologies. Lipids 1996; 31 Suppl:S117-25. [PMID: 8729105 DOI: 10.1007/bf02637062] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Synthesis of fatty acids, or de novo lipogenesis (DNL), is an intensively researched metabolic pathway whose functional significance and metabolic role have nevertheless remained uncertain. Methodologic problems that limited previous investigations of DNL in vivo and recent methodologic advances that address these problems are discussed here. In particular, deuterated water incorporation and mass isotopomer distribution analysis techniques are described. Recent experimental results in humans based on these techniques are reviewed, emphasizing dietary and hormonal factors that modulate DNL and quantitative significance of DNL under various conditions, including carbohydrate overfeeding. The somewhat surprising finding that DNL appears not to be a quantitatively major pathway even under conditions of surplus carbohydrate energy intake, at least in normal adults on typical Western diets, is discussed in depth. Nutritional and metabolic implications of these results are also noted, and some speculations on possible functional roles of DNL in normal physiology and disease states are presented in this context. In summary, methodologic advances have added to our understanding of DNL and its regulation, but many questions concerning quantitation and function remain unanswered.
Collapse
Affiliation(s)
- M K Hellerstein
- Department of Nutritional Sciences, University of California, Berkeley 94720-3104, USA
| |
Collapse
|
5
|
Jones PJ, Leitch CA, Li ZC, Connor WE. Human cholesterol synthesis measurement using deuterated water. Theoretical and procedural considerations. ARTERIOSCLEROSIS AND THROMBOSIS : A JOURNAL OF VASCULAR BIOLOGY 1993; 13:247-53. [PMID: 8381301 DOI: 10.1161/01.atv.13.2.247] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Human cholesterogenesis is measurable as the rate of incorporation of deuterium derived from deuterium oxide (D2O) within the body water pool into plasma or erythrocyte cholesterol pools. Oral D2O equilibrates across body water, thus enabling extracellular sampling of pools (such as urine) to serve as accurate indicators of intracellular deuterium enrichments at the point of synthesis. Required doses of D2O fall below the threshold associated with negative side effects. Deuterium/carbon incorporation ratios into cholesterol during biosynthesis have been established that are applicable in humans. Models using unconstrained and constrained curve fitting permit improved flexibility in interpretation of deuterium-uptake kinetics. However, sample-size restrictions presently limit the ability of the technique to examine the kinetics within individual lipoprotein species. Correction of enrichment data for proton exchange during combustion and reduction phases of sample preparation is an additional important procedural concern. In summary, the deuterated-water procedure is a useful tool in studies of human cholesterol synthesis that offers the advantages of short measurement interval, relative noninvasiveness, and provision of a direct index of synthesis in comparison with other available techniques.
Collapse
Affiliation(s)
- P J Jones
- Division of Human Nutrition, University of British Columbia, Vancouver, Canada
| | | | | | | |
Collapse
|
6
|
Neese RA, Faix D, Kletke C, Wu K, Wang AC, Shackleton CH, Hellerstein MK. Measurement of endogenous synthesis of plasma cholesterol in rats and humans using MIDA. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 264:E136-47. [PMID: 8430782 DOI: 10.1152/ajpendo.1993.264.1.e136] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We used the mass isotopomer distribution analysis (MIDA) technique to measure endogenous synthesis of plasma cholesterol in vivo in rats and normal human subjects. Sodium [1-13C]- or [2-13C]acetate was infused, and plasma free cholesterol was analyzed by gas chromatography-mass spectrometry. Frequencies of mass isotopomers M0-M4 (mass-to-charge ratio 368-372) were quantified. The enrichment of the true precursor for cholesterol synthesis (acetyl-coenzyme A in contributing tissues) was determined using the MIDA method. This technique remains mathematically valid even if more than one tissue contributes to circulating free cholesterol. The fractional contribution (f) from endogenous synthesis to free cholesterol in normal women (n = 5) was 2.48 +/- 0.39% after 7 h in the postabsorptive state and 1.27 +/- 0.41% after 8 h of refeeding. In ad libitum-fed rats (n = 12), f was 2.89 +/- 0.44% after 12 h, whereas administration of recombinant tumor necrosis factor increased this value fourfold. Next, the rate constant (k) for removal of labeled free cholesterol from plasma was calculated. Higher masses (M2-M4) were followed to avoid the problem of persistent label incorporation. During the 60 h after cessation of [13C]acetate infusions, k was 0.02490 +/- 0.00298/h in humans. Using these values of k and f, absolute cholesterogenesis was 568 +/- 55 mg/day in normal women (follicular menstrual phase), similar to prior estimates based on whole body sterol balances. Women also exhibited a diurnal variation for endogenous cholesterol synthesis (34.6 +/- 5.4 mg/h nighttime vs. 15.9 +/- 5.2 mg/h daytime) consistent with current knowledge about rhythms in cholesterogenesis. Checks on the model were internally consistent (e.g., comparisons among different isotopomers for calculating precursor enrichment). We conclude that fractional and absolute endogenous cholesterol synthesis can be measured using stable isotopes in vivo by the MIDA technique.
Collapse
Affiliation(s)
- R A Neese
- Department of Nutritional Sciences, University of California, Berkeley 94720
| | | | | | | | | | | | | |
Collapse
|
7
|
Abstract
Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.
Collapse
Affiliation(s)
- C S Lieber
- Alcohol Research and Treatment Center, Bronx VA Medical Center, New York
| |
Collapse
|
8
|
Takahashi H, Geoffrion Y, Butler KW, French SW. In vivo hepatic energy metabolism during the progression of alcoholic liver disease: a noninvasive 31P nuclear magnetic resonance study in rats. Hepatology 1990; 11:65-73. [PMID: 2295473 DOI: 10.1002/hep.1840110113] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
We investigated serially in vivo the ratios of phosphorylated metabolites and the intracellular pH in the livers of rats fed ethanol chronically to evaluate the relation between changes in energy metabolism and the progression of alcoholic liver disease with 31P nuclear magnetic resonance spectroscopy. 31P nuclear magnetic resonance spectra of the liver were acquired noninvasively from rats pair-fed a nutritionally adequate liquid diet containing ethanol or an isocaloric amount of dextrose with an implanted intragastric cannula for up to 24 wk. A high blood alcohol level was constantly maintained. The spectra were obtained using a surface coil combined with a ferrite screen to eliminate nuclear magnetic resonance signals derived from the superficial muscles. Contaminating 31P nuclear magnetic resonance signals arising from abdominal tissues other than the liver were eliminated from the spectra by digital subtraction. Throughout the study the inorganic phosphate/beta-ATP peak area ratio observed in alcohol-fed rats was found to be consistently elevated in comparison with the control rats (at 3 to 5 wk alcohol-fed rats = 1.20 +/- 0.10, control rats = 0.78 +/- 0.04, p less than 0.05.; at 22 to 24 wk alcohol-fed rats = 1.23 +/- 0.10, control rats = 0.81 +/- 0.06, p less than 0.05.; mean +/- S.E.). The phosphomonoesters/beta-ATP ratio tended to be higher in alcohol-fed rats when compared with control rats. The intracellular pH measured by the chemical shift of the inorganic phosphate peak showed no significant differences between alcohol-fed rats and control rats.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- H Takahashi
- Department of Pathology, Faculty of Health Sciences, University of Ottawa, Ontario, Canada
| | | | | | | |
Collapse
|
9
|
Teschke R, Gellert J. Hepatic microsomal ethanol-oxidizing system (MEOS): metabolic aspects and clinical implications. Alcohol Clin Exp Res 1986; 10:20S-32S. [PMID: 3544926 DOI: 10.1111/j.1530-0277.1986.tb05176.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
|
10
|
Quistorff B, Dich J, Grunnet N. Periportal and perivenous hepatocytes retain their zonal characteristics in primary culture. Biochem Biophys Res Commun 1986; 139:1055-61. [PMID: 3021146 DOI: 10.1016/s0006-291x(86)80284-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Periportal and perivenous hepatocytes from rat liver were isolated by combined digitonin-collagenase perfusion, and gluconeogenesis, urea synthesis and fatty acid synthesis was measured both in freshly isolated cells and in primary culture. A periportal zonation of gluconeogenesis and urea synthesis of about 3 and 1.5 fold, respectively, was observed. This zonation persisted unchanged for 23 hours in culture under identical conditions of incubation for periportal and perivenous cells. Fatty acid synthesis was not zonated.
Collapse
|
11
|
Vind C, Grunnet N. Contribution of non-ADH pathways to ethanol oxidation in hepatocytes from fed and hyperthyroid rats. Effect of fructose and xylitol. Biochem Pharmacol 1985; 34:655-61. [PMID: 3156600 DOI: 10.1016/0006-2952(85)90260-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The metabolism of (1R)[1-3H]ethanol, [2-3H]lactate or [2-3H]xylitol was studied in hepatocytes from fed or T3-treated rats in the presence or absence of fructose or xylitol. The yields of tritium in ethanol, lactate, water, glycerol and glucose were determined. A simple model, describing the metabolic fate of tritium from these substrates is presented. The model allows estimation of the ethanol oxidation rate by the non-alcohol dehydrogenase pathways from the relative yield of tritium in water and glucose. The calculations are based on a comparison of the fate of the 1-proR-hydrogen of ethanol and the hydrogen bound to carbon 2 of lactate (or xylitol) under identical condition. In our calculations we have taken into account that the reactions catalyzed by lactate dehydrogenase and alcohol dehydrogenase are reversible and that lactate or ethanol labelled during the metabolism of the other tritiated substrates will contribute to the tritium found in water. The contribution of non-ADH pathways to ethanol oxidation varied from 10 to 50% and was correlated to changes in the lactate/pyruvate ratio from 80 to 500. In T3-treated rats the activity of non-ADH pathways were greater than in fed rats for the same lactate/pyruvate ratio.
Collapse
|
12
|
Abstract
The interaction of ethanol with lipid metabolism is complex. When ethanol is present, it becomes a preferred fuel for the liver and displaces fat as a source of energy. This favors fat accumulation. In addition, the altered redox state secondary to the oxidation of ethanol promotes lipogenesis, for instance, through enhanced formation of acylglycerols. The depressed oxidative capacity of the mitochondria injured by chronic alcohol feeding also contributes to the development of the fatty liver. Accumulation of fat acts as a stimulus for the secretion of lipoproteins and the development of hyperlipemia. Hyperlipemia may also be facilitated by the proliferation of the endoplasmic reticulum after chronic ethanol consumption and the associated increase of enzymes involved in the production of triglycerides and lipoproteins. The propensity to enhance lipoprotein secretion is offset, at least in part, by a decrease in microtubules and an impairment of the secretory capacity of the liver. The level of blood lipids depends on the balance between these two opposite changes: At the early stage of alcohol abuse, when liver damage is still small, hyperlipemia will prevail, whereas the opposite occurs with severe liver injury. When hyperlipemia occurs, it involves all lipoprotein classes, including high density lipoprotein (HDL). The latter have been suggested to be responsible for the lower incidence of coronary complications of moderate drinkers compared to teetotalers, but in fact, the subtype of HDL involved (HDL3) differs from the HDL2 subtype associated with protection.
Collapse
|
13
|
Dich J, Bro B, Grunnet N, Jensen F, Kondrup J. Accumulation of triacylglycerol in cultured rat hepatocytes is increased by ethanol and by insulin and dexamethasone. Biochem J 1983; 212:617-23. [PMID: 6349622 PMCID: PMC1153135 DOI: 10.1042/bj2120617] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Isolated hepatocytes from female rats were cultured in HI-WO/BA medium for 6 days. To the medium was added oleate, ethanol, dexamethasone and insulin. With oleate To alone, triacylglycerol accumulated; ethanol augmented the accumulation by 90%. To the best of our knowledge, this is the first demonstration that ethanol in vitro increases the content of triacylglycerol in liver cells. Further addition of dexamethasone or insulin did not alter the accumulation of triacylglycerol, indicating that these hormones did not play permissive roles for the effect of ethanol in the present system. Dexamethasone and insulin, in the absence of ethanol, increased the accumulation of triacylglycerol by 30% and 50% respectively. The concentration of glycerol 3-phosphate was increased in the presence of ethanol; however, with time the concentration of glycerol 3-phosphate declined almost to control values, while the accumulation of triacylglycerol continued linearly; this suggests that the effect of ethanol was not mediated via fluctuations in the concentration of glycerol 3-phosphate. These results are discussed in relation to earlier investigations in vivo and in vitro.
Collapse
|
14
|
Damgaard SE. The D(V/K) isotope effect of the cytochrome P-450-mediated oxidation of ethanol and its biological applications. EUROPEAN JOURNAL OF BIOCHEMISTRY 1982; 125:593-603. [PMID: 7117257 DOI: 10.1111/j.1432-1033.1982.tb06724.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
|
15
|
Zahlten RN, Nejtek ME, Jacobsen JC. Ethanol metabolism in guinea pig: ethanol oxidation and its effect on NAD/NADH ratios, oxygen consumption, and ketogenesis in isolated hepatocytes of fed and fasted animals. Arch Biochem Biophys 1982; 213:200-31. [PMID: 7036906 DOI: 10.1016/0003-9861(82)90456-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
|
16
|
Zahlten RN, Nejtek ME, Jacobson JC. Ethanol metabolism in guinea pig: in vivo ethanol elimination, alcohol dehydrogenase distribution, and subcellular localization of acetaldehyde dehydrogenase in liver. Arch Biochem Biophys 1981; 207:371-9. [PMID: 7018402 DOI: 10.1016/0003-9861(81)90044-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
|
17
|
Berry MN, Fanning DC, Grivell AR, Wallace PG. Ethanol oxidation by isolated hepatocytes from fed and starved rats and from rats exposed to ethanol, phenobarbitone or 3-amino-trizazole. No evidence for a physiological role of a microsomal ethanol oxidation system. Biochem Pharmacol 1980; 29:2161-8. [PMID: 7426022 DOI: 10.1016/0006-2952(80)90193-8] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
|
18
|
Mørland J, Bessesen A, Svendsen L. The role of alcohol metabolism in the effect of ethanol on protein synthesis in isolated rat hepatocytes. Alcohol Clin Exp Res 1980; 4:313-21. [PMID: 6996518 DOI: 10.1111/j.1530-0277.1980.tb04821.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
|
19
|
Sjöblom M, Mørland J. Metabolism of ethanol and acetaldehyde in parenchymal and non-parenchymal rat liver cells. Biochem Pharmacol 1979; 28:3417-23. [PMID: 533548 DOI: 10.1016/0006-2952(79)90081-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
|
20
|
Wood CK, Lamb RG. The effect of ethanol on glycerolipid biosynthesis by primary monolayer cultures of adult rat hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 572:121-31. [PMID: 760795 DOI: 10.1016/0005-2760(79)90206-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
This study evaluates the effects of ethanol exposure on glycerolipid production and release by hepatocyte monolayers. Glycerolipid formation from [1,3-14C]glycerol was increased in monolayers exposed to ethanol (1--50 mM) for 6 h. Monolayers exposed to 1 mM ethanol for 24 h also exhibited a rise in glycerolipid formation from either [1,3-14C]glycerol or [1-14C]palmitate; however, higher ethanol concentrations produced a dose dependent decrease in glycerolipid formation. Glycerolipids released into the medium by monolayers declined after all periods of ethanol exposure. The effects of ethanol on the enzymatic reactions involved in glycerolipid biosynthesis were determined in homogenates prepared from monolayers exposed to ethanol. Two enzymes, phosphatidate phosphohydrolase and glycerol kinase, exhibited ethanol-induced alterations in enzyme activity; however, only glycerol kinase activity correlated well with monolayer glycerolipid formation. These ethanol-induced alterations in enzyme activities and glycerolipid biosynthesis were reduced by simultaneously exposing monolayers to pyrazole or cycloheximide.
Collapse
|
21
|
|
22
|
Walli RA. Interrelation of aerobic glycolysis and lipogenesis in isolated perfused liver of well-fed rats. BIOCHIMICA ET BIOPHYSICA ACTA 1978; 539:62-80. [PMID: 623794 DOI: 10.1016/0304-4165(78)90122-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
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.
Collapse
|