scholarly journals Lactate-stimulated ethanol oxidation in isolated hepatocytes

1978 ◽  
Vol 172 (1) ◽  
pp. 29-36 ◽  
Author(s):  
Kathryn E. Crow ◽  
Neal W. Cornell ◽  
Richard L. Veech
Keyword(s):  
Ethanol Oxidation ◽  
Lactate Concentration ◽  
Isolated Hepatocytes ◽  
Cell Preparation ◽  
O2 Uptake ◽  
Glucose Synthesis ◽  
The Relationship ◽  
Pyruvate Ratio ◽  
Stimulation Of

1. Hepatocytes isolated from starved rats and incubated without other substrates oxidized ethanol at a rate of 0.8–0.9μmol/min per g wet wt. of cells. Addition of 10mm-lactate increased this rate 2-fold. 2. Quinolinate (5mm) or tryptophan (1mm) decreased the rate of gluconeogenesis with 10mm-lactate and 8mm-ethanol from 0.39 to 0.04–0.08μmol/min per g wet wt. of cells, but rates of ethanol oxidation were not decreased. From these results it appears that acceleration of ethanol oxidation by lactate is not dependent upon the stimulation of gluconeogenesis and the consequent increased demand for ATP. 3. As another test of the relationship between ethanol oxidation and gluconeogenesis, the initial lactate concentration was varied from 0.5mm to 10mm and pyruvate was added to give an initial [lactate]/[pyruvate] ratio of 10. This substrate combination gave a large stimulation of ethanol oxidation (from 0.8 to 2.6μmol/min per g wet wt. of cells) at low lactate concentrations (0.5–2.0mm), but rates remained nearly constant (2.6–3.0μmol/min per g wet wt. of cells) at higher lactate concentrations (2.0–10mm). 4. In contrast, owing to the presence of ethanol, the rate of glucose synthesis was only slightly increased (from 0.08 to 0.12μmol/min per g wet wt. of cells) between 0.5mm- and 2.0mm-lactate and continued to increase (from 0.12 to 0.65μmol/min per g wet wt. of cells) with lactate concentrations between 2 and 10mm. 5. In the presence of ethanol, O2 uptake increased with increasing substrate concentration over the entire range. 6. Changes in concentrations of glutamate and 2-oxoglutarate closely paralleled changes in the rate of ethanol oxidation. 7. In isolated hepatocytes, rates of ethanol oxidation are lower than those in vivo apparently because of depletion of malate–aspartate shuttle intermediates during cell preparation. Rates are returned to those observed in vivo by substrates that increase the intracellular concentration of shuttle metabolites.

scholarly journals Regulation of mitochondrial pyruvate carboxylation in isolated hepatocytes by acute insulin treatment

1983 ◽  
Vol 214 (2) ◽  
pp. 451-458 ◽  
Author(s):  
A B Chisholm ◽  
E H Allan ◽  
M A Titheradge
Keyword(s):  
Insulin Treatment ◽  
Second Messengers ◽  
Isolated Hepatocytes ◽  
Carboxylase Activity ◽  
Effector Molecules ◽  
Pyruvate Carboxylation ◽  
Isolated Mitochondria ◽  
Glucose Synthesis ◽  
Important Site ◽  
Stimulation Of

The effect of acute insulin treatment of hepatocytes on pyruvate carboxylation in both isolated mitochondria and cells rendered permeable by filipin was examined. Challenging the cells with insulin alone had no effect on either the basal rate of pyruvate carboxylation or gluconeogenesis, although it did suppress the responses to both glucagon and catecholamines. Insulin treatment was unable to antagonize the enhanced rate of pyruvate carboxylation caused by stimulation of the cells with either angiotensin or vasopressin. Neither insulin nor the gluconeogenic hormones altered the total extractable pyruvate carboxylase activity in the isolated mitochondria, suggesting that the effect of hormones at the level of the isolated intact organelle was mediated via alterations in the intramitochondrial concentrations of effector molecules, notably ATP and the [ATP]/[ADP] ratio and substrate availability. The alterations in pyruvate carboxylation correlate well with glucose synthesis in terms of sensitivity to effector molecules, putative second messengers and time of onset of the response, indicating that alterations in the flux through this enzyme are compatible with it being an important site in the control of gluconeogenesis from C3 precursors.

scholarly journals Metabolic effects of platelet-activating factor in rats in vivo. Stimulation of hepatic glycogenolysis and lipogenesis

1990 ◽  
Vol 269 (1) ◽  
pp. 269-272 ◽  
Author(s):  
R D Evans ◽  
V Ilic ◽  
D H Williamson
Keyword(s):  
Platelet Activating Factor ◽  
Hepatic Metabolism ◽  
Isolated Hepatocytes ◽  
Metabolic Effects ◽  
Hepatic Glycogen ◽  
Dose Dependent Fashion ◽  
Paf Receptor ◽  
High Doses ◽  
Stimulation Of

1. The effects of platelet-activating factor (1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphocholine; PAF) on hepatic metabolism in vivo in rats were studied. 2. PAF stimulated synthesis of hepatic lipid (saponified and non-saponified) in a dose-dependent fashion and caused hypertriglyceridaemia. There was no effect of PAF on lipogenesis in isolated hepatocytes. 3. High doses of PAF also decreased hepatic glycogen. 4. All doses of PAF decreased plasma insulin, and this was accompanied by hyperglycaemia, except at the lowest dose. 5. The selective PAF-receptor antagonist L659.989 prevented the stimulation of lipogenesis, but indomethacin did not.

scholarly journals Effect of treatment of rats with dexamethasone in vivo on gluconeogenesis and metabolite compartmentation in subsequently isolated hepatocytes

1984 ◽  
Vol 219 (1) ◽  
pp. 117-123 ◽  
Author(s):  
E H Allan ◽  
M A Titheradge
Keyword(s):  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Intact Cell ◽  
Isolated Hepatocytes ◽  
Dexamethasone Treatment ◽  
Acetyl Coa ◽  
General Activation ◽  
Effect Of Treatment ◽  
Stimulation Of

Hepatocytes prepared from rats treated with dexamethasone for 2 or 3h and maintained in the presence of 10 microM-dexamethasone in the preparation and incubation buffers showed significantly elevated rates of gluconeogenesis compared with those prepared from control animals. Dexamethasone treatment also increased the sensitivity of the cells to glucagon and the catecholamines. Analysis of the concentrations of metabolites in the gluconeogenic pathway indicated that dexamethasone decreased the intracellular concentration of pyruvate and increased those of phosphoenolpyruvate, acetyl-CoA and citrate, suggesting a stimulation of the reaction(s) converting pyruvate into phosphoenolpyruvate. This was substantiated by analysis of the pattern of metabolites found in the mitochondrial compartment after digitonin fractionation of the cells. Inclusion of 3-mercaptopicolinate in the incubation enhanced the effect of the hormone on the distribution of metabolites. Thus, in the absence of an effect of the steroid at the level of phosphoenolpyruvate carboxykinase or pyruvate kinase, dexamethasone treatment still increased the formation of malate, aspartate and citrate from pyruvate, indicating a stimulation in the intact cell of pyruvate carboxylase. It is suggested that the stimulation of pyruvate carboxylase is a result of a general activation of mitochondrial function, with an increase in the intramitochondrial concentrations of acetyl-CoA and ATP, a decrease in glutamate and an enhanced intramitochondrial [ATP]/[ADP] ratio.

scholarly journals An in Vitro Model of Post-Exercise Hepatic Gluconeogenesis in the Gulf Toadfish Opsanus Beta

1989 ◽  
Vol 147 (1) ◽  
pp. 393-406 ◽  
Author(s):  
PATRICK J. WALSH
Keyword(s):  
Isolated Hepatocytes ◽  
Blood Parameters ◽  
Strenuous Exercise ◽  
Hepatic Gluconeogenesis ◽  
Post Exercise ◽  
Opsanus Beta ◽  
Stimulation Of ◽  
Gulf Toadfish

During strenuous exercise, fish develop substantial proton and lactate loads. Although acidosis is usually rapidly corrected during recovery (1–2 h), lactate levels often remain elevated for up to 8–12 h. The quantitative role of the liver in clearance of the lactate load during recovery from exercise in fish has received little direct examination. The purposes of this study were (1) to attempt to quantify hepatic contribution to lactate clearance, and (2) to identify factors that regulate hepatic gluconeogenesis during recovery from exercise in fish. Both in vivo and in vitro (isolated hepatocytes) approaches were used. Important blood parameters (pHe, Ccoco2, [lactate], [glucose], [epinephrine] and [norepinephrine]) were measured in the gulf toadfish (Opsanus beta Goode and Bean) during recovery from strenuous exercise, and they conformed to the general patterns for sluggish benthic species noted in earlier studies. When toadfish hepatocytes wereexposed to simulated post-exercise conditions in vitro, gluconeogenesis from lactate was stimulated by over 2.5-fold in ‘0–1 h-’ and ‘l-2h-post-exercise periods’. Variation of the extracellular parameters in controlled combinations indicated that exercise-induced changes in [glucose], [epinephrine], [norepinephrine], Pcoco2 and [HCO3−] had no significant effects on rates of gluconeogenesis.The observed stimulation of gluconeogenesis could be induced independently byeither decreased pH (which lowered Km for lactate) or increased [lactate] (bysimple hyperbolic kinetic effects), but the effects were not additive. Despite thispotentially adaptive stimulation of gluconeogenesis, I estimate, based on observedin vitro rates and in vivo estimates of lactate load, that hepatic gluconeogenesisaccounts for less than 2% of the lactate load clearance in toadfish.

Mechanism responsible for aminooxyacetate and glycolate stimulation of ethanol oxidation by isolated hepatocytes

1982 ◽  
Vol 213 (2) ◽  
pp. 414-425 ◽  
Author(s):  
Robert A. Harris ◽  
Neal W. Cornell ◽  
Christopher Straight ◽  
Richard L. Veech
Keyword(s):  
Ethanol Oxidation ◽  
Isolated Hepatocytes ◽  
Stimulation Of

Stimulation of flux through hepatic pyruvate dehydrogenase by 3-mercaptopicolinate

1984 ◽  
Vol 4 (5) ◽  
pp. 441-450 ◽  
Author(s):  
David D. Myles ◽  
Peter Strong ◽  
Garry D. Stratton ◽  
Ian F. Skidmore ◽  
Mary C. Sugden
Keyword(s):  
Pyruvate Dehydrogenase ◽  
Blood Glucose Concentration ◽  
Tricarboxylic Acid Cycle ◽  
Pyruvate Dehydrogenase Complex ◽  
Isolated Hepatocytes ◽  
Blood Concentrations ◽  
Decrease Blood Glucose ◽  
Hypoglycaemic Agent ◽  
Stimulation Of

Isolated hepatocytes from 24-h-starved rats were used to assess the possible effect of Ahe hypoglycaemic agent 3-mercaptopicolinate on flux through the hepatic pyruvate dehydrogenase complex. Increasing the extraceIIular pyruvate concentration from 1 mM to 2 mM or 5 mM resulted in an increase in flux through pyruvate dehydrogenase and the tricarboxylic acid cycle as measured by14CO2 evolution from [1-14C]pyruvate and [3-14C]pyruvate. Gluconeogenesis was inhibited by 3-mercaptopicolinate from both 1 mM and 2 mM pyruvate, but significant increases in malate and citrate concentrations only occurred in cells incubated with 1 mM pyruvate. Flux through pyruvate dehydrogenase was stimulated by 3-mercaptopicolinate with 1 mM pyruvate but was unaltered with 2 mM pyruvate. Dichloroacetate stimulated flux through pyruvate dehydrogenase with no effect on gluconeogenesis in the presence of I mM pyruvate. There was no effect of 3-mercaptopicolinate, administered in vivo, to 24-h-starved rats on the activity of pyruvate dehydrogenase in freeze-clamped heart or liver tissue, although the drug did decrease blood glucose concentration and increase the blood concentrations of lactate and alanine. Dichloroacetate, administered in vivo to 24-h-starved rats, increased the activity of pyruvate dehydrogenase in freeze-clamped heart and liver, and caused decreases in the blood concentrations of glucose, lactate, and alanine. The results suggest that 3-mercaptopicolinate increases flux through hepatocyte pyruvate dehydrogenase by an indirect mechanism.

scholarly journals Effect of ornithine and lactate on urea synthesis in isolated hepatocytes

1976 ◽  
Vol 160 (2) ◽  
pp. 205-209 ◽  
Author(s):  
S Briggs ◽  
R A Freedland
Keyword(s):  
Lactate Concentration ◽  
Isolated Hepatocytes ◽  
Liver Cells ◽  
Urea Synthesis ◽  
Isolated Liver Cells ◽  
Urea Production ◽  
Relationship Of ◽  
The Relationship ◽  
Isolated Liver

1. In hepatocytes isolated from 24 h-starved rats, urea production from ammonia was stimulated by addition of lactate, in both the presence and the absence of ornithine. The relationship of lactate concentration to the rate of urea synthesis was hyperbolic. 2. Other glucose precursors also stimulated urea production to varying degrees, but none more than lactate. Added oleate and butyrate did not stimulate urea synthesis. 3. Citrulline accumulation was largely dependent on ornithine concentration. As ornithine was increased from 0 to 40 mM, the rate of citrulline accumulation increased hyperbolically, and was half-maximal when ornithine was 8-12 mM. 4. The rate of citrulline accumulation was independent of the presence of lactate, but with pyruvate the rate increased. 5. The rate of urea production continued to increase as ornithine was varied from 0 to 40 mM. 6. It was concluded that intermediates provided by both ornithine and lactate are limiting for urea production from ammonia in isolated liver cells. It was suggested that the stimulatory effect of lactate lies in increased availability of cytosolic aspartate for condensation with citrulline.

scholarly journals Effect of calcium ions on ethanol oxidation and drug glucuronidation in isolated hepatocytes

1979 ◽  
Vol 184 (3) ◽  
pp. 709-711 ◽  
Author(s):  
B Andersson ◽  
D P Jones ◽  
S Orrenius
Keyword(s):  
Drug Metabolism ◽  
Calcium Ions ◽  
Ethanol Oxidation ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Physiological Concentration ◽  
Isolated Rat Hepatocytes ◽  
Similar Dependence ◽  
Isolated Rat ◽  
Stimulation Of

The effect of extracellular Ca2+ concentration on ethanol oxidation and drug metabolism was studied in isolated rat hepatocytes. Both ethanol oxidation and drug glucuronidation showed similar dependence upon Ca2+, which was a stimulation of activity as Ca2+ was increased to physiological concentration, and inhibition at higher concentration.

scholarly journals The effect of acute ethanol treatment on rates of oxygen uptake, ethanol oxidation and gluconeogenesis in isolated rat hepatocytes

1985 ◽  
Vol 230 (3) ◽  
pp. 595-602 ◽  
Author(s):  
K M Stowell ◽  
K E Crow
Keyword(s):  
Ethanol Oxidation ◽  
Physiological State ◽  
Rat Hepatocytes ◽  
O2 Uptake ◽  
Isolated Rat Hepatocytes ◽  
Liver Preparation ◽  
Acute Ethanol ◽  
Ethanol Pretreatment ◽  
In Cells

In hepatocytes isolated from fed rats, acute ethanol pretreatment (at a dose of 5.0 g/kg body wt.) did not change rates of O2 uptake. In cells from starved animals, acute ethanol pretreatment increased O2 uptake by 17-29%. The increased O2 uptake in hepatocytes from starved rats was not accompanied by increased rates of ethanol oxidation, but was accompanied by increased rates of gluconeogenesis under some conditions. The provision of ethanol (10 mM) as a substrate to cells from fed or starved rats decreased O2 uptake in the absence of other substrates or in the presence of lactate, and increased it in the presence of pyruvate or lactate and pyruvate. The results of this study show that the acute effects of ethanol on liver O2 uptake are dependent on the physiological state of the liver. Previously reported large (2-fold) increases in O2 uptake after acute ethanol pretreatment may have been an artefact owing to low control uptake rates (approximately 1.8 micromol/min per g wet wt. of cells) in the liver preparation used. The ATP contents (2.4-2.6 micromol/g wet wt. of cells) and rates of O2 uptake (2.5-5.0 micromol/min per g wet wt. of cells) of cells used in the present study were the same as values reported under conditions close to those in vivo. Therefore the increase in O2 uptake in cells from starved rats after acute ethanol pretreatment is likely to be of physiological significance.

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