scholarly journals Fuel utilization in colonocytes of the rat

1985 ◽  
Vol 231 (3) ◽  
pp. 713-719 ◽  
Author(s):  
M S M Ardawi ◽  
E A Newsholme
Keyword(s):  
Colonic Mucosa ◽  
Ketone Bodies ◽  
Adenine Nucleotides ◽  
Maximum Activity ◽  
Glutamine Metabolism ◽  
O2 Consumption ◽  
Fructose Bisphosphatase ◽  
Fuel Utilization ◽  
Donor Animal ◽  
End Products

In incubated colonocytes isolated from rat colons, the rates of utilization O2, glucose or glutamine were linear with respect to time for over 30 min, and the concentrations of adenine nucleotides plus the ATP/ADP or ATP/AMP concentration ratios remained approximately constant for 30 min. Glutamine, n-butyrate or ketone bodies were the only substrates that caused increases in O2 consumption by isolated incubated colonocytes. The maximum activity of hexokinase in colonic mucosa is similar to that of 6-phosphofructokinase. Starvation of the donor animal decreased the activities of hexokinase and 6-phosphofructokinase, whereas it increased those of glucose-6-phosphatase and fructose-bisphosphatase. Isolated incubated colonocytes utilized glucose at about 6.8 mumol/min per g dry wt., with lactate accounting for 83% of glucose removed. These rates were not affected by the addition of glutamine, acetoacetate or n-butyrate, and starvation of the donor animal. Isolated incubated colonocytes utilized glutamine at about 5.5 mumol/min per g dry wt., which is about 21% of the maximum activity of glutaminase. The major end-products of glutamine metabolism were glutamate, aspartate, alanine and ammonia. Starvation of the donor animal decreased the rate of glutamine utilization by colonocytes, which is accompanied by a decrease in glutamate formation and in the maximum activity of glutaminase. Isolated incubated colonocytes utilized acetoacetate at about 3.5 mumol/min per g dry wt. This rate was not markedly affected by addition of glucose or by starvation of the donor animal. When colonocytes were incubated with n-butyrate, both acetoacetate and 3-hydroxybutyrate were formed, with the latter accounting for only about 19% of total ketones produced.

scholarly journals Glutamine metabolism in lymphocytes of the rat

1983 ◽  
Vol 212 (3) ◽  
pp. 835-842 ◽  
Author(s):  
M S M Ardawi ◽  
E A Newsholme
Keyword(s):  
Amino Acids ◽  
Concanavalin A ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Thymidine Incorporation ◽  
Adenine Nucleotides ◽  
Glutamine Metabolism ◽  
Mesenteric Lymph Nodes ◽  
Mesenteric Lymph ◽  
End Products ◽  
Stimulation Of

The metabolism of glutamine in resting and concanavalin-A-stimulated lymphocytes was investigated. In incubated lymphocytes isolated from rat mesenteric lymph nodes, the rates of oxygen and glutamine utilization and that of aspartate production were approximately linear with respect to time for 60 min, and the concentrations of adenine nucleotides plus the ATP/ADP or ATP/AMP concentration ratios remained approximately constant for 90 min. The major end products of glutamine metabolism were glutamate, aspartate and ammonia: the carbon from glutamine may contribute about 30% to respiration. When both glucose and glutamine were presented to the cells, the rates of utilization of both substances increased. Evidence was obtained that the stimulation of glycolysis by glutamine could be due, in part, to an activation of 6-phosphofructokinase. Starvation of the donor animal increased the rate of glutamine utilization. The phosphoenolpyruvate carboxykinase inhibitor mercaptopicolinate decreased the rate of glutamine utilization by 28%; the rates of accumulation of glutamate and ammonia were decreased, whereas those of lactate, aspartate and malate were increased. The mitogen concanavalin A increased the rate of glutamine utilization (by about 51%). The rate of [3H]thymidine incorporation into DNA caused by concanavalin A in cultured lymphocytes was very low in the absence of glutamine; it was increased about 4-fold at 1 microM-glutamine and was maximal at 0.3 mM-glutamine; neither other amino acids nor ammonia could replace glutamine.

scholarly journals Effect of adenosine on the adenine nucleotide content and metabolism of hepatocytes

1975 ◽  
Vol 152 (3) ◽  
pp. 593-599 ◽  
Author(s):  
P Lund ◽  
N W Cornell ◽  
H A Krebs
Keyword(s):  
Time Course ◽  
Ketone Bodies ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Adenosine Kinase ◽  
Urea Synthesis ◽  
O2 Consumption ◽  
Nucleotide Content ◽  
Adenosine Concentration ◽  
Glucose Formation

ADENOSINE (0.5 MM) added to hepatocyte suspensions increased the intracellular concentration of ATP and total adenine nucleotides within 60 min up to three-fold. 2. Adenosine at 0.5 mM inhibited gluconeogenesis from lactate by about 50%. At higher adenosine concentrations the inhibition was less. There was no strict parallelism between the time-course of the increase of the adenine nucleotide content and the time-course of the inhibition of gluconeogenesis from lactate. 3. Adenosine abolished the accelerating effects of oleate and dibutyryl cyclic AMP on gluconeogenesis from lactate. 4. Gluconeogenesis was no significant effect of adenosine with fructose, dihydroxyacetone or glycerol. With asparagine, adenosine caused anacceleration of glucose formation. 5. Adenosine incorporation into adenine nucleotides accounted for about 20% of the adenosine removal. 6. Inosine, hypoxanthine or adenine compared with adenosine gave relatively slight increases of adenine nucleotides. 7. Urea synthesis from NH4Cl under optimum conditions i.e. in the presence of ornithine, lactate and oleate, was also inhibited by adenosine. The inhibition increased with the adenosine concentration and was 65% at 4 mM-adenosine. Again there was no correlation between the degree of inhibition of urea synthesis and the increase in the adenine nucleotide content. 8. The basal O2 consumption, the increased O2 consumption on the addition of oleate and the rate of formation of ketone bodies were not affected by the addition of adenosine. The [β-hydroxybutyrate]/[acetoacetate] ratio was increased by adenosine, provided that lactate was present. 9. The increase of the adenine nucleotide content of the hepatocytes on the addition of adenosine may be explained on the assumption that adenosine kinase is not regulated by feedback but by substrate supply.

scholarly journals Glutamine and ketone-body metabolism in the gut of streptozotocin-diabetic rats

1988 ◽  
Vol 249 (2) ◽  
pp. 565-572 ◽  
Author(s):  
M S M Ardawi
Keyword(s):  
Small Intestine ◽  
Ketone Body ◽  
Ketone Bodies ◽  
Diabetic Rats ◽  
Glutamine Metabolism ◽  
Gut Mucosa ◽  
Streptozotocin Induced Diabetes ◽  
Streptozotocin Diabetic Rats ◽  
Short And Long Term

1. In short- and long-term diabetic rats there is a marked increase in size of both the small intestine and colon, which was accompanied by marked decreases (P less than 0.001) and increases (P less than 0.001) in the arterial concentrations of glutamine and ketone bodies respectively. 2. Portal-drained viscera blood flow increased by approx. 14-37% when expressed as ml/100 g body wt., but was approximately unchanged when expressed as ml/g of small intestine of diabetic rats. 3. Arteriovenous-difference measurements for ketone bodies across the gut were markedly increased in diabetic rats, and the gut extracted ketone bodies at approx. 7 and 60 nmol/min per g of small intestine in control and 42-day-diabetic rats respectively. 4. Glutamine was extracted by the gut of control rats at a rate of 49 nmol/min per g of small intestine, which was diminished by 45, 76 and 86% in 7-, 21- and 42-day-diabetic rats respectively. 5. Colonocytes isolated from 7- or 42-day-diabetic rats showed increased and decreased rates of ketone-body and glutamine metabolism respectively, whereas enterocytes of the same animals showed no apparent differences in the rates of acetoacetate utilization as compared with control animals. 6. Prolonged diabetes had no effects on the maximal activities of either glutaminase or ketone-body-utilizing enzymes of colonic tissue preparations. 7. It is concluded that, although the epithelial cells of the small intestine and the colon during streptozotocin-induced diabetes exhibit decreased rates of metabolism of glutamine, such decreases were partially compensated for by enhanced ketone-body utilization by the gut mucosa of diabetic rats.

Amino Acid Metabolism and Water Transport Across the Seawater Eel Intestine

1988 ◽  
Vol 138 (1) ◽  
pp. 93-106 ◽  
Author(s):  
MASAAKI ANDO
Keyword(s):  
Water Transport ◽  
Water Flux ◽  
Glutamine Metabolism ◽  
Metabolic Inhibitors ◽  
O2 Consumption ◽  
Glutamine Concentration ◽  
Net Water Flux ◽  
Concentration Response Curve ◽  
Glutamine Uptake

To elucidate how intracellular L-alanine enhances water transport across the seawater eel intestine, effects of various metabolic inhibitors were examined. The L-alanine-induced water flux was inhibited by amino-oxyacetate, an inhibitor of aminotransferase. After blocking the synthesis of pyruvate from L-alanine with this drug, water transport was stimulated with pyruvate, whose effects were inhibited by oxythiamine, an inhibitor of pyruvate dehydrogenase. 2,4-Dinitrophenol (DNP) also inhibited the effects of L-alanine. Furthermore, L-alanine enhanced ouabain-sensitive O2 consumption in this tissue, and the enhancement in O2 consumption preceded that in the transepithelial potential difference (PD) and the net water flux. These results indicate that L-alanine is metabolized through the citric acid cycle to produce ATP, and that a metabolic product stimulates ion and water transport. L-Glutamine also seems to be metabolized just like L-alanine because: L-glutamine acted from inside the enterocyte; DNP inhibited the effects of L-glutamine; neither of the effects of L-glutamine and L-alanine were additive but they were mutually complementary; L-glutamine also enhanced ouabainsensitive O2 consumption; and the increment in O2 consumption preceded that in the PD and the net water flux. The effects of L-glutamine on the PD and the net water flux depended on glutamine concentration and the concentration-response curve was of the Michaelis-Menten type, indicating that the rate of L-glutamine uptake into the enterocyte limits the overall rate of L-glutamine metabolism. A regulatory role of amino acids for ion and water transport is discussed.

scholarly journals Impaired sensitivity to insulin of rat livers perfused with blood of diminished haematocrit

1980 ◽  
Vol 192 (1) ◽  
pp. 219-222 ◽  
Author(s):  
G B Storer ◽  
R P Trimble ◽  
D L Topping
Keyword(s):  
Amino Acids ◽  
Whole Blood ◽  
Bile Flow ◽  
Ketone Bodies ◽  
O2 Consumption ◽  
Rat Livers

1. In livers from fed rats perfused with homologous whole blood of a haematocrit value of 37%, insulin decreased the perfusate concentrations of glucose and amino acids, production of ketone bodies (3-hydroxybutyrate + acetoacetate) and increased bile flow. 2. Perfusion with blood diluted with buffer to a haematocrit value of 17% decreased hepatic O2 consumption by 40-50%. Perfusate concentrations of glucose and lactate, the rate of ketogenesis and the ratios [lactate]/[pyruvate] and [3-hydroxybutyrate]/[acetoacetate] were all increased. 3. In livers perfused with blood of diminished haematocrit, effects of insulin on perfusate glucose an amino acids, ketogenesis and bile flow were abolished.

scholarly journals Maximum activities of some enzymes of glycolysis, the tricarboxylic acid cycle and ketone-body and glutamine utilization pathways in lymphocytes of the rat

1982 ◽  
Vol 208 (3) ◽  
pp. 743-748 ◽  
Author(s):  
M. Salleh M. Ardawi ◽  
Eric A. Newsholme
Keyword(s):  
Ketone Body ◽  
Citrate Synthase ◽  
Ketone Bodies ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Maximum Activity ◽  
Graft Versus Host Reaction ◽  
Acid Cycle ◽  
Oxoglutarate Dehydrogenase

1. The maximum activity of hexokinase in lymphocytes is similar to that of 6-phosphofructokinase, but considerably greater than that of phosphorylase, suggesting that glucose rather than glycogen is the major carbohydrate fuel for these cells. Starvation increased slightly the activities of some of the glycolytic enzymes. A local immunological challenge in vivo (a graft-versus-host reaction) increased the activities of hexokinase, 6-phosphofructokinase, pyruvate kinase and lactate dehydrogenase, confirming the importance of the glycolytic pathway in cell division. 2. The activities of the ketone-body-utilizing enzymes were lower than those of hexokinase or 6-phosphofructokinase, unlike in muscle and brain, and were not affected by starvation. It is suggested that the ketone bodies will not provide a quantitatively important alternative fuel to glucose in lymphocytes. 3. Of the enzymes of the tricarboxylic acid cycle whose activities were measured, that of oxoglutarate dehydrogenase was the lowest, yet its activity (about 4.0μmol/min per g dry wt. at 37°C) was considerably greater than the flux through the cycle (0.5μmol/min per g calculated from oxygen consumption by incubated lymphocytes). The activity was decreased by starvation, but that of citrate synthase was increased by the local immunological challenge in vivo. It is suggested that the rate of the cycle would increase towards the capacity indicated by oxoglutarate dehydrogenase in proliferating lymphocytes. 4. Enzymes possibly involved in the pathway of glutamine oxidation were measured in lymphocytes, which suggests that an aminotransferase reaction(s) (probably aspartate aminotransferase) is important in the conversion of glutamate into oxoglutarate rather than glutamate dehydrogenase, and that the maximum activity of glutaminase is markedly in excess of the rate of glutamine utilization by incubated lymphocytes. The activity of glutaminase is increased by both starvation and the local immunological challenge in vivo. This last finding suggests that metabolism of glutamine via glutaminase is important in proliferating lymphocytes.

Hepatic fatty acid metabolism in pigs and rats: major differences in endproducts, O2 uptake, and beta-oxidation

1997 ◽  
Vol 272 (5) ◽  
pp. R1641-R1646 ◽  
Author(s):  
S. H. Adams ◽  
X. Lin ◽  
X. X. Yu ◽  
J. Odle ◽  
J. K. Drackley
Keyword(s):  
Lipid Metabolism ◽  
Ketone Bodies ◽  
Carbon Accumulation ◽  
O2 Consumption ◽  
Beta Oxidation ◽  
Hepatic Lipid Metabolism ◽  
Adult Rats ◽  
Hepatic Lipid ◽  
Carbon Reservoir ◽  
Carboxyl Carbon

Models of mammalian hepatic lipid metabolism are based largely on observations made in adult rats, emphasizing ketogenesis as a primary adjunct to mitochondrial beta-oxidation. Studies using piglets have illustrated the divergent nature of intermediary metabolism in this model, wherein ketogenesis and beta-oxidation are small and acetogenesis is an important route of fuel carbon flux. To clarify potential species differences in hepatic lipid metabolism and its control, we compared O2 consumption and metabolic end products in fasted pig and rat liver homogenates treated with 1-[14C]C16:0. Carboxyl carbon accumulation in acid-soluble products (ASP) plus CO2 was threefold greater and O2 consumption was twofold greater in rats (P < 0.05). Unlike rats, pigs showed negligible carboxyl carbon accumulation in ketone bodies (3-7% of ASP), whereas acetate was a carboxyl carbon reservoir in both animals (17-31% of ASP in pigs). Malonate increased (approximately 2-fold) and antimycin/rotenone decreased (40-60%) radiolabel accumulation in acetate. These data concur with the hypotheses that comparatively low hepatic beta-oxidative flux in piglets is partially related to a smaller metabolic rate and that substantial acetogenesis occurs intramitochondrially in both pigs and rats.

scholarly journals Evaluation of the isolated perfused rat hindquarter for the study of muscle metabolism

1971 ◽  
Vol 124 (3) ◽  
pp. 639-651 ◽  
Author(s):  
N. B. Ruderman ◽  
C. R. S. Houghton ◽  
R. Hems
Keyword(s):  
Glucose Uptake ◽  
Nerve Stimulation ◽  
Ketone Bodies ◽  
Synthetic Medium ◽  
Lactate Production ◽  
Muscle Metabolism ◽  
High Rate ◽  
O2 Consumption ◽  
Glycerol Release

1. The metabolic integrity of a new isolated rat hindquarter preparation was studied. The hindquarter was perfused with a semi-synthetic medium containing aged human erythrocytes. More than 95% of the oxidative metabolism of the preparation was due to muscle, the remainder being due to bone, adipose tissue and, where present, skin. 2. Consumption of O2, glucose utilization, glycerol release and lactate production were similar in the presence and in the absence of the skin, indicating that the latter contributed little to the overall metabolism of the preparation. 3. After 40min of perfusion, tissue concentrations of creatine phosphate, ATP and ADP were similar to those found in muscle taken directly from intact animals. The muscle also appeared normal under the electron microscope. 4. The hindquarter did not lose K% to the medium during a 30min perfusion. In the presence of insulin it had a net K% uptake. 5. Insulin caused a sixfold increase in glucose uptake, stimulated O2 consumption by nearly 40% and depressed glycerol release to less than half the control value. 6. Bilateral sciatic-nerve stimulation caused severalfold increases in O2 consumption and lactate production. In the absence of insulin nerve stimulation also enhanced glucose uptake; in the presence of insulin it did not further increase the already high rate of glucose uptake. 7. Rates of lactate production and O2 consumption of the rat hindquarter in vivo and the isolated perfused hindquarter were very similar. 8. Ketone bodies were a major oxidative fuel in vivo of the hindquarter of a rat starved for 2 days. If the acetoacetate and 3-hydroxybutyrate removed by the tissue were completely oxidized, they would have accounted for 77% of the O2 consumption. 9. Acetoacetate accounted for 84% of the ketone bodies removed by the hindquarter in vivo even though its arterial concentration was half that of 3-hydroxybutyrate. 10. Similar rates of acetoacetate and 3-hydroxybutyrate utilization were observed in the perfused hindquarter. 11. Acetoacetate utilization by the perfused hindquarter was not diminished by the addition of either oleate or insulin to the perfusate. 12. Oxidation of glucose to CO2 accounted for less than 4% of the O2 consumed by the perfused hindquarter in both the presence and the absence of insulin. 13. The results indicate that the isolated perfused hindquarter is a useful tool for studying muscle metabolism. They also suggest that ketone bodies, if present in sufficient concentration, are the preferred oxidative fuel of resting muscle.

scholarly journals Effect of ischaemic limb injury on the rates of metabolism of ketone bodies in starved rats

1976 ◽  
Vol 156 (2) ◽  
pp. 233-238 ◽  
Author(s):  
R N Barton
Keyword(s):  
Clearance Rate ◽  
Ketone Body ◽  
Ketone Bodies ◽  
Whole Body ◽  
Metabolic Clearance ◽  
O2 Consumption ◽  
Clearance Rates ◽  
Metabolic Clearance Rate ◽  
Limb Injury ◽  
Blood Ketone Bodies

1. Rats starved for 30h were injected with trace amounts of [3-14C]acetoacetate and β-hydroxy[3-14C]butyrate 1h after ischaemic limb injury in a 20 °C environment, and the concentrations and radioactivities of blood ketone bodies were determined at intervals. 2. Starvation alone raised the rates of production and utilization of β-hydroxybutyrate plus acetoacetate about 3.7-fold, but lowered their metabolic clearance rates by about 50%. In the starved rat ketone-body oxidation could account for up to 30% of whole body O2 consumption. 3. Injury in starved rats lowered the rates of production and utilization of both β-hydroxybutyrate and acetoacetate, the combined fall of about 37% slightly exceeding the concomitant fall in whole-body O2 consumption. The concentration of β-hydroxybutyrate decreased after injury, but its metabolic clearance rate was unaltered; the concentration of acetoacetate rose slightly and its metabolic clearance rate fell.

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