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Carbohydrate synthesis from lactate in pigeon liver homogenate

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... Ghiconeogenesis is an energy consuming process requiring six moles of high energy phosphate for every mole of glucose formed [22]. The addition of gluconeogenie substrates such as lactate to liver or kidney tissue greatly stimulates oxygen consumption as well as gluconeogenesis [23,24,34]. It should be also noted that the increase in oxygen consumption induced by lactate is always in excess of that calculated to be required for the synthesis of ATP necessary for the concomitant gluconeogenesis. ...
Tryptophan and quinolinic acid, inhibitors of gluconeogenesis, were used to block the removal of lactate by the liver in order to investigate the involvement of the Cori cycle in oxygen debt. Five male, mongrel dogs were run on a treadmill at 4 mph with a 20 percent grade for 19 min. The mean exercise [(V)\dot]O2 \dot V_{O_2 } was 80.673.11 ml/kg/min for the control tests while peak arterial lactate values ranged from 3.83 to 4.98 mM/l. When removal of lactate by the liver was blocked, oxygen debt showed a mean reduction of 44 percent. Moreover, oxygen consumption during the last minute of exercise was reduced by 11 percent.Fasting (72 h) was used in 1 dog to prevent the accumulation of lactate during exercise. This procedure reduced oxygen debt to the same level as when the removal of lactate by the liver was blocked with tryptophan and quinolinic acid.The data show that the lactacid as well as the alactacid component is involved in oxygen debt when lactate is being removed by the liver during the recovery period following exercise.
... Such a system, involving the mitochondrial as well as the cytosolic reactions of gluconeogenesis, has so far only been set up for avian cell preparations. On the one hand, Krebs et al. (1964) showed that glucose is formed from lactate at physiological rates in homogenates of pigeon liver, and on the other hand Mendicino & Utter (1962) reported that glucose 6-phosphate is formed from either 3phosphoglycerate or fumarate by combination ofpurified gluconeogenic enzymes with chicken liver mitochondria. However, in mitochondria from pigeon as well as from chicken liver, phosphoenolpyruvate carboxykinase is localized within the mitochondria, whereas in rat liver this enzyme is mainly cytosolic. ...
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A cell-free system prepared from rat liver containing cytosol and mitochondria as well as a number of cofactors and gluconeogenic intermediates at near-physiological concentrations was shown to form hexose 6-phosphates linearly from lactate + pyruvate + glutamate at a rate of 0.82 +/- 0.05 mumol/min per g of liver (mean +/- S.E.M., n = 8, 37 degrees C). The indicated rates were measured between 20 min and 60 min incubation time, when the system was near steady state. Experiments with either [1-14C]lactate or [U-14C]glutamate revealed that the incorporation of radioactive label into hexose 6-phosphates was proportional to the utilization of lactate + pyruvate and of glutamate during incubation and that both served as gluconeogenic substrates at a ratio of about 2:1. When the [ATP]/[ADP] ratio was lowered from 60 to 19 by addition of ATPase, the rate of hexose 6-phosphate formation fell to one-third. This decrease in gluconeogenic flux was mainly due to a decreased flow through the phosphoglycerate kinase step. Hexose 6-phosphate formation could also be decreased by increasing the ratio [NADH]/[NAD+], either by addition of ethanol or by increasing the initial concentration of lactate + pyruvate at a fixed ratio of 10:1. The observed inhibition was linked to a limitation in the availability of oxaloacetate for the phosphoenolpyruvate carboxykinase reaction and to an increased formation of sn-glycerol 3-phosphate. Finally, the rates of hexose 6-phosphate formation in incubations with cytosols from fed rats were only 50% of those observed with cytosols from animals starved for 48 h. One of the limiting steps was found to be the flow through the phosphoenolpyruvate carboxykinase step.
... Free glycerol was measured by enzymic assay (Garland & Randle, 1962). Neutralized HCl04 extracts were used for the determination of glucose (Krebs et al., 1963(Krebs et al., , 1964. ...
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Treatment with dexamethasone enhanced 3H2O incorporation into liver and blood lipid, and also increased plasma glucose, insulin, non-esterified fatty acid and triacylglycerol concentrations during late gestation in the mother rat. An inverse relationship between glycogen and lipid synthesis in foetal liver and lung was observed in control rats. This relationship was also observed in foetal liver, but not in foetal lung, after treatment with dexamethasone.
... Analytical methods Glycogen was determined as glucose after enzymic hydrolysis, as described byKrebs et al. (1963). Blood glucose was assayed by the glucose oxidase method as described byKrebs et al. (1963Krebs et al. ( , 1964). Blood samples were collected in a heparinized tube after cutting the jugular vein. ...
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1. After nicotinic acid treatment, rat liver glycogen is depleted and phosphoenolpyruvate carboxykinase activity increased, to about twice the initial value. 2. The increase in phosphoenolpyruvate carboxykinase activity promoted by nicotinic acid is prevented by cycloheximide or actinomycin D, suggesting that this effect is produced by synthesis of the enzyme de novo. 3. Despite the enhancement of phosphoenolpyruvate carboxykinase activity and glycogen depletion, which occurs 5h after the injection of nicotinic acid, the gluconeogenic capacity of liver is low and considerably less than the values found in rats starved for 48h. 4. When the livers of well-fed rats are perfused in the presence of low concentrations of glucose, the activity of phosphoenolpyruvate carboxykinase significantly increases compared with the control. 5. This increase is not related to the glycogen content, but seems to be also the result of synthesis of the enzyme de novo, since this effect is counteracted by previous treatment with cycloheximide or actinomycin D. 6. Phosphoenolpyruvate carboxykinase activity is not increased in the presence of low concentrations of circulating glucose when 40 mM-imidazole (an activator of phosphodiesterase) is added to the perfusion medium. 7. Addition of dibutyryl cyclic AMP to the perfusion medium results in an increase in phosphoenolpyruvate carboxykinase activity, in spite of the presence of normal concentrations of circulating glucose. On the other hand, the concentration of cyclic AMP in the liver increases when that of glucose in the medium is low. 8. These results suggest that, in the absence of hormonal factors, the regulation of phosphoenolpyruvate carboxykinase can be accomplished by glucose itself, inadequate concentrations of it resulting in the induction of the enzyme. The mediator in this regulation, as in hormonal regulation, seems to be cyclic AMP.
... Fib was determined spectrophotometrically after it had been converted to cyanmethemoglobin (Schalm et al., 1975); total protein and fibrinogen were measured by the refractive index method (Schalm et al., 1975). Glucose was measured by the procedure of Krebs et al. (1964); D(-) and L(+) lactic acids were measured by the methods of Gawehn and Bergmeyer (1974) and Gutmann and Wahlefeld (1974), respectively. The methods for total bacterial count, percentage gram-positive and gram-negative bacteria and assay for endotoxin conccntration in thc cell-free rumen fluid were as described above. ...
Article
SUMMARY Feeding grain to animals not adapted to grain resulted in a marked increase in the ./ . concentration of free endotoxln m the rumen. Endotoxin concentration increased 15 to 18 times within 12 hr after lactic acidosis was induced through grain engorgement. The increase was accompanied by a shift from predominantly gram-negative to gram-positive bacteria. Data from in vitro fermentations showed that the increase in free endotoxin concentration was not accompanied by a decrease in the number of gram-negative bacteria. The absorption of endotoxin from the rumen was not apparent by the actinomycin D assay procedure because no difference was observed in mice lethality of plasma from control and post-engorgement samples. How- ever, the significant granulocytosis that accom- panied acidosis was suggestive of systemic action of rumen bacterial endotoxin.
... Glycogen was determined as glucose after enzymic hydrolysis, as described by Krebs et al. (1963). Glucose was assayed by the glucose oxidase method (Krebs et al., 1963(Krebs et al., , 1964. Lactate was determined as described by Gutmann & Wahlefeld (1974); acetoacetate, by the method of ; 3-hydroxybutyrate, by the method of ; malate, as described by Hohorst (1965); pyruvate, phosphoenolpyruvate, 2-phosphoglycerate and 3-phosphoglycerate, by the method of Czok & Eckert (1965); dihydroxyacetone phosphate, glyceraldehyde-3-phosphate and fructose 1,6-bisphosphate, as described by Bucher (1965); glucose 6-phosphate and fructose 6-phosphate, by the method of Lang & Michal (1974); aspartate, as described by Bergmeyer et al. (1974); citrate, by the method of Dagley (1974). ...
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1. Glucose production from L-lactate was completely inhibited 24h after carbon tetrachloride treatment in liver from 48 h-starved rats. The activities of phosphoenolpyruvate carboxykinase, fructose diphosphatase and glucose 6-phosphatase were decreased by this treatment in fed and starved rats, whereas lactate dehydrogenase activity was only decreased in fed animals. 2. The production of glucose by renal cortical slices from fed rats previously treated with carbon tetrachloride was enhanced when L-lactate, pyruvate and glutamine but not fructose were used as glucose precursors. Renal phosphoenolpyruvate carboxykinase activity was increased in this condition. 3. This increase was counteracted by cycloheximide or actinomycin D, suggesting that the effect was due to the synthesis de novo of the enzyme. 4. The pattern of hepatic gluconeogenic metabolites in treated animals was characterized by an increase in lactate, pyruvate, malate and citrate as well as a decrease in glucose 6-phosphate, suggesting an impairment of liver gluconeogenesis in vivo. 5. In contrast, the profile of renal metabolites suggested that gluconeogenesis was operative in the treated rats, as indicated by the marked increase in the content of phosphoenolpyruvate, 2-phosphoglycerate, 3-phosphoglycerate and glucose 6-phosphate. 6. It is postulated that renal gluconeogenesis could contribute to the maintenance of glycaemia in carbon tetrachloride-treated rats.
... The samples were kept hertactically in syringes on ice until analyzed within 2 hours. Venous blood plasma was analyzed for L(+) lactic acid by the method of Horhorst (1963) and glucose, by the procedure of Krebs et al. (1964). Electrocardiographic measurements (lead II) were made at each sampling. ...
Article
SUMMARY Two rumen fistulated cows, not adapted to urea, were given .5 g urea intraruminally per 1 kg body weight 16 hr after a previous feeding. Ammonia-N concentration 5 min after dosing rose from .t 3 to .71 mg per 100 ml for carotid blood and from. 11 to .43 mg for jugular blood, then to 1.47 mg (carotid) and .95 mg (jugular) at time of toxicity. Toxicity, judged by appear- ance of definite muscle tetany, occurred be- tween 17 and 30 min after dosing. The marked difference in ammonia concentrations in ca- rotid and jugular blood suggests that the brain takes up ammonia rapidly. Other changes ob- served between dosing and toxicity were: ru- men ammonia-N, 6.18 to 51.30 mg per 100 ml; rumen pH, 6.94 to 7.90; arterial blood pH, 7.44 to 7.50; arterial blood pO2,87.1 to 96.1;blood lactic acid, 9.5 to 23.4 mg per 100 ml; blood glucose, 72 to 91.9 mg per 100 ml; and packed cell volume, 24.5 to 28.5%. Plasma protein did not change. Heart beat increased slightly to toxicity (63.8 to 71.8 beats per minute) and more markedly after toxicity. No significant changes in electrocardiographic patterns were observed. Emptying the rumens at toxicity resulted in complete recovery within 1 hour.
... Both metabolites were expressed as mg/g wet weight. Plasma glucose was quantified by the glucose oxidase method (Krebs et al., 1964). Glycogen phosphorylase activity (E.C. 2.4.1.1.; ...
1. A study of the levels of glycogen and glucose, as well as the activities of glycogen phosphorylase (GPase), glycogen synthetase (GSase), fructose 1,6-bisphosphatase (FBPase), phosphofructokinase (PFK), glucose 6-phosphate dehydrogenase (G6PDH), pyruvate kinase (PK) and lactate dehydrogenase (LDH) was carried out in livers of domesticated rainbow trout (Oncorhynchus mykiss) of two different weights [small (80 g) and large (140 g)) after transfer to seawater (28 p.p.t.) for 21 days. 2. The results indicate that metabolic changes during adaptation of rainbow trout to seawater appear to occur in two stages which, in addition, appear to be size-dependent. 3. During the first stage a clear glycogenolysis (associated with an increase in GPase activity and a decrease in GSase activity) and hyperglycemia were observed both in small and large animals, being higher in the small ones. 4. A seeming increase in gluconeogenesis (as indicated by the activation of FBPase activity) was observed only in large animals. 5. The mobilization of energy reserves could be associated with the increase in energetic demand of the osmoregulatory organs. On the other hand, the second stage indicates that a successful adaptation to seawater did not occur, since the animals ceased to feed from day 7 of the experiment onwards.
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The constant-infusion, isotope-dilution method was used to investigate the interrelationships between the glucose and lactate pools of six trained sheep deprived of food overnight. Arterial plasma lactate concentration was a linear function of the net lactate entry rate as was the net production of glucose from lactate, which suggests that the net rate of formation of glucose from lactate is dependent on the availability of lactate. Similarly the arterial plasma glucose concentration was correlated with the net entry rate of glucose as was the net production rate of lactate from glucose, suggesting that the net rate of lactate production from glucose is a function of arterial plasma glucose concentration. The demonstration of these two interrelations between glucose and lactate in normal sheep suggests that, in the absence of external factors producing hormonal or other changes that could cause perturbations of carbohydrate homeostasis, the net rates of conversion of glucose to lactate and of lactate to glucose may be largely determined by the arterial concentrations of glucose and lactate, respectively.
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Hepatocytes were isolated from rats which had been fed 1000 ppm o,p′-DDT for 2 weeks and starved for 48 hr. Hepatocytes were incubated with 10 mm lactate: pyruvate (L : P) plus increasing concentrations of glucagon or dibutyryl cAMP. DDT feeding resulted in decreased sensitivity to both glucagon and dibutyryl cAMP in isolated hepatocytes and a decrease in the absolute rate of gluconeogenesis from L : P in the presence of hormones. These data suggest that the effect of o,p′-DDT may be on the response of the gluconeogenic process to the level of cAMP in the cell and not on the mechanism by which glucagon increases the level of cAMP. Gluconeogenesis from 10 mm lactate was decreased by DDT feeding but gluconeogenesis from 10 mm pyruvate was not affected, suggesting that DDT is inhibiting a step in the gluconeogenic pathway of lactate that is not involved in the pathway of pyruvate gluconeogenesis. The observation that lactate dehydrogenase and aspartate amino transferase are not decreased in hepatocytes from rats fed DDT suggest that the step in gluconeogenesis from lactate that DDT feeding may be inhibiting is aspartate transport out of the mitochondria.
Article
Isolated rat liver cells were found to catalyze the cytochrome P-450 dependent, oxidative metabolism of alprenolol [1-(2-allylphenoxy)-3-isopropylaminopropanol] at a rate similar to that obtained with the isolated microsomal fraction in the presence of a NADPH-generating system. Alprenolol was rapidly taken up into the liver cells and the apparent Michaelis constant was similar to that obtained with liver microsomes. Further, inhibitors of drug metabolism such as SKF 525-A and metyrapone showed similar inhibitory patterns in the cellular and microsomal systems. With liver cells isolated from control rats, NADPH generation from endogenous substrates was sufficient to support optimal alprenolol metabolism, whereas the addition of glucose or lactate stimulated this rate in liver cells isolated from starved, phenobarbital-treated rats. Inhibitors of mitochondrial respiration such as rotenone, antimycin A and KCN and the uncoupler carbonyl cyanide-p-trifluoromethoxy-phenyl hydrazone inhibited cellular alprenolol metabolism, presumably by lowering the ATP/ADP ratio thereby interfering with NADPH generation via the malic enzyme system; this effect was more pronounced in liver cells from starved rats. Furthermore, in analogy with previous findings, the rate of gluconeogenesis from lactate was inhibited during alprenolol metabolism; this effect in turn was most pronounced in liver cells from phenobarbital-treated rats. The findings indicate that under certain conditions, the level of cytoplasmic NADPH may become rate-limiting for drug metabolism linked to cytochrome P-450 and support the previous assumption that in fed rats, generation of cytoplasmic NADPH is mainly via the pentose phosphate shunt whereas the malic enzyme system becomes more important for this purpose during starvation.
Article
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The levels of intermediary metabolites in the perfused liver have been measured to determine the location of the rate-limiting step for gluconeogenesis from lactate and the site at which glucagon, epinephrine, and cyclic AMP exert control. The reaction limiting maximum gluconeogenesis from lactate is situated between pyruvate and phosphopyruvate. Glucagon or epinephrine, acting through cyclic AMP, appears to activate a reaction in this portion of the pathway. At less than saturating levels of lactate, the rate of gluconeogenesis is determined by the activities of the above reaction and also of lactate dehydrogenase. The latter step is not under hormonal control. Gluconeogenesis is not limited by the supply of NAD⁺ or NADH and is virtually independent of the oxidation-reduction potential of the extramitochondrial NAD⁺-NADH couple as reflected by the lactate-pyruvate ratio of the tissue. The liver has potent mechanisms to restore a displaced oxidation-reduction potential to normal. Glucagon does not stimulate gluconeogenesis or inhibit lactate formation from fructose or dihydroxyacetone. It is suggested that a sparing of pyruvate oxidation or inhibition of the pyruvate kinase reaction is not responsible for the gluconeogenic action of glucagon and that effects, if any, of glucagon on reactions at the level of triose phosphate dehydrogenase, fructose diphosphatase, or glucose 6-phosphatase are of no physiological importance.
Chapter
Since the discovery of the process of oxidative phosphorylation, biochemical textbooks have tacitly assumed that most, if not all, of mammalian mitochondrial respiration is tightly coupled to ATP turnover, so that any increase in cellular oxygen uptake (JO) must necessarily indicate an augmented demand for ATP. On the other hand, much evidence has now accrued that the increase in JO observed when hepatocytes are presented with substrates, particularly fatty acids (Berry, 1974a; Williamson et al., 1969; Debeer et al., 1974; Berry et al., 1983a), cannot be wholly or even mainly accounted for by increased utilization of ATP in biosynthetic processes such as gluconeogenesis and urea formation (Berry, 1974a; Berry et al., 1983a; Hems et al., 1966; Krebs et al., 1964). The mechanism by which oxygen consumption is stimulated to a greater extent than predicted from any increased metabolic activity of the cells has not been established unequivocally. Possibilities include uncoupling of the mitochondria (Scholz et al., 1984; Soboll and Stucki, 1985), changes in eficiency of coupling, perhaps by alterations in the H+/e- ratio of mitochondrial proton pumping (Nicholls, 1974; Pietrobon et al., 1981), induction of futile cycles of ATP synthesis and hydrolysis (Debeer et al., 1974; Newsholme and Crabtree, 1976; Katz and Rognstad, 1976; Plomp et al., 1985), or stimulation of some other pathway such as reversed electron flow (Berry et al., 1983a). None of these explanations seems entirely satisfactory.
Chapter
The writer of a chapter on “methods” is beset with difficulties for, ideally, he should be a historian, a sage, a bench worker, a biologist and a crystal gazer. He should be a historian so that he may select from the contributions of the past, not only those which should be recorded because they have established new principles and opened new paths of investigations, not only those which are used today in their original form, but also those which are still valid in principle even though camouflaged by modern gadgetry and techniques. He should be a sage because he must strike a wise balance between principle and detail and because he must decide what is or is not within the scope of his review. He should be a bench worker with at least a passing familiarity with the techniques he is asked to describe so that he may properly discuss their advantages and limitations. He should be a biologist so that he may understand purposes and results placing them in the proper perspective. He should be a crystal gazer so that he may select among the new methods those that are more likely to withstand the test of time. Obviously, this is an impossible task for anyone, but an encyclopedic mind.
Article
Exercise (swimming 2 hr in water at 22°) results in a substantial increase in the activity of the kidney cortex phosphoenolpyruvate carboxykinase (EC 4.1.1.32) measured in the direction of oxaloacetate synthesis as well as in the direction of phosphoenolpyruvate formation. This increase probably is not due to de novo synthesis of the enzyme, since it is not counteracted by treatment with actinomycin d or cycloheximide.Blood lactate concentration sharply increases in the first 15 min of exercise and drops, also very rapidly, to the normal levels in 45 min. Renal phosphoenolpyruvate carboxykinase activity and gluconeogenic ability increase continuously during 2 hr of exercise. When the rats are previously treated with sodium bicarbonate, the increase in blood lactate is of the same order but its fall is considerably less pronounced than in normal exercised animals. In the bicarbonate treated rats, the phosphoenolpyruvate carboxykinase activity reaches only a slight enhancement in 2 hr.When swimming takes place in water at 37°—instead of 22°, as usual—the concentrations of blood lactate are only slightly higher than the normal values. In these conditions, the renal phosphoenolpyruvate carboxykinase activity is much lower, and the renal gluconeogenic capacity remains close to the normal values.The production of glucose and ammonia from glutamine is greater in kidney cortical slices from exercised rats than in the control animals, this increase being substantially overcome by previous treatment with bicarbonate.From these findings, it can be reasonably assumed that the increase in the renal phosphoenolpyruvate carboxykinase activity and gluconeogenic ability which takes place during exercise in our experimental conditions is mediated by the metabolic acidosis caused by overproduction of muscular lactate.
1.1. In rainbow trout (Salmo gairdneri), liver and muscle glycogen concentrations decreased in response to severe physical disturbance, liver glycogen recovered 30 min after the treatment, probably due to an increase in gluconeogenesis.2.2. The activity of glycogen phosphorylase in muscle and liver was increased during disturbance, the former being affected by AMP, the latter not.3.3. Lactate and glucose concentrations in blood increased in the early stages of the treatment. Lactate was probably converted into glucose to be used as the source of energy during the disturbance.
Article
Renal glucose and ammonia production as well as phosphoenolpyruvate carboxykinase and phosphate-dependent glutaminase activities were measured after acute liver intoxication. Gluconeogenesis and phosphoenolpyruvate carboxykinase activity increased, whereas ammonia production and phosphate-dependent glutaminase showed no changes with respect to the controls.The dissociation between gluconeogenesis and ammoniagenesis may be explained by the differential effect on the enzymes in these conditions.
Article
1.1. The presence of d-fructose-1,6-diphosphate 1-phosphohydrolase (E.C.3.1.3.11) activity has been established in the mammary glands of late pregnant Fisher 344 rats and in the R3230AC rat mammary adenocarcinoma.2.2. Homogenates of the R3230AC tumour are capable of synthesizing glucose from fructose-1,6-diphosphate a and other gluconeogenic precursors. The rate of glucose synthesis from fructose-1,6-diphosphate is decreased by high substrate concentrations, estrogen administration to the tumour bearing rats and by the addition of 5′AMP or ATP to the incubation mixture.3.3. Starvation increases glucose formation from fructose-1,6-diphosphate in the estrogen-treated rats but has no effect in the non-treated animals.4.4. Tumour homogenates produced α-glycerophosphate from glucose and other glycolytic precursors. The latter finding points to the presence of the α-glycerophosphate shunt in the R3230AC adenocarcinoma.
Article
The rates of O2 consumption during fatty acid oxidation to acetyl-CoA and to CO2 were determined for isolated liver cells from starved rats on the basis of measured rates of respiration and ketogenesis. About 60% of the endogenous O2 uptake was associated with acetyl-CoA formation. The remainder was assumed to represent total combustion of fatty acid to CO2 and H2O through the Krebs cycle. In the absence of added fatty acid, 1.90 μmol · min⁻¹· g⁻¹ of acetyl-CoA was generated, of which 1.40 μmol · min⁻¹· g⁻¹ gave rise to ketone bodies. O2 consumption was stimulated about 30% by the addition of 2 mM palmitate or 4 mM hexanoate. This increase was entirely due to stimulation of O2 consumption related to oxidation of fatty acid to acetyl-CoA. The extra acetyl-CoA produced was channelled into ketone body formation.
Article
The time courses of liver glycogen, blood glucose, plasma free fatty acids, ketone bodies, immunoreactive insulin, and glucagon and liver cyclic AMP concentrations after treatment with nicotinic acid were investigated. The administration of nicotinic acid caused a rapid glycogen depletion which was followed by a decrease in blood glucose and a rise in plasma free fatty acids and ketone bodies. Supplementation of nicotinic acid with theophylline accelerated the glycogen depletion, the onset of hypoglycemia, and the rise in free fatty acids and ketone bodies. Liver cyclic AMP doubled 15 min after the administration of nicotinic acid and the effect of theophylline was synergistic. The plasma immunoreactive insulin/glucagon ratio decreased after treatment with nicotinic acid. The rise in plasma free fatty acids and ketone bodies which occurred after the administration of nicotinic acid was prevented by the administration of glucose or insulin. These results suggest that the increase in plasma free fatty acids observed after treatment with nicotinic acid is a consequence of the operation of the “glucose-fatty acid cycle” promoted by the decrease in the plasma insulin/glucagon ratio.
1.1. The glyoxylic acid cycle pathway could be regulated through the modulation of the isocitrate dehydrogenase-NADP activity. This enzyme is inhibited by NADPH.2.2. The effect on the glyoxylate cycle flux of variations in the rate of the NADPH-consuming pathways has been studied.3.3. Increase in the rate of NADPH-consuming activity by addition of H2O2 produces inhibition of the glyoxylate cycle and decrease in the NADPH/NADP ratio.4.4. These results suggest that the glyoxylate flux in Tetrahymena could be modulated by regulation of NADP-dependent isocitrate dehydrogenase by the NADPH/NADP ratio.
1.1. The effect of dietary composition (high-protein, high-carbohydrate and high-fat diets) and starvation on in totum gluconeogenesis from l-(U-14C)glutamate was studied in the rainbow trout.2.2. High-fat and high-carbohydrate diets produced a significant hyperglycaemia. Lower blood glucose values were obtained in trout fed on a high-protein diet.3.3. Liver glycogen levels were significantly lower m trout fed on carbohydrate-free diets (high-protein and high-fat diets) and in starved fish.4.4. Gluconeogenesis from l-(U-14C)glutamate was markedly reduced in fish given the high-carbohydrate diet and significantly enhanced in starved fish.5.5. Radioactive liver glycogen was higher in starved fish, although the amount of radioactivity incorporated into glycogen was very low.
1. Assessment of glycogen and glucose content and glycogen phosphorylase, glycogen synthetase, hexokinase and fructose 1,6-bisphosphatase activity in liver and white muscle of domesticated rainbow trout (Oncorhynchus mykiss) transferred to diluted seawater (12 p.p.t.). Plasma glucose levels were also determined. 2. A decline in liver glycogen content was observed throughout the 12-120 hr period in diluted seawater (dSW). Liver free glucose also showed a decrease, though only significant at 120 hr in dSW. 3. The activity of liver glycogen phosphorylase a and a + b was higher in dSW animals, but glycogen synthetase was unchanged. 4. No changes in liver hexokinase and fructose 1,6-bisphosphatase activity were observed. 5. In white muscle and plasma only white muscle glycogen synthetase activity showed a change, in particular a decline in dSW animals. 6. Although domesticated rainbow trout do not naturally migrate to seawater, these data suggest that a depletion of liver reserves occurred in a way similar to that described for other salmonids.
Article
To determine the metabolic changes related to gill (Na+-K+)-ATPase activity, a study of the levels of glycogen, glucose, and protein as well as of the activities of glycogen phosphorylase (GPase), glycogen synthetase (GSase), fructose 1,6-bisphosphatase (FBPase) and hexokinase (HK), was carried out in liver, white muscle and kidney of rainbow trout (Oncorhynchus mykiss) reared in freshwater. Plasma protein, glucose and liver lactate levels were also measured. In liver an increment in the levels of glycogen, glucose and lactate was observed prior to an increase in ATPase activity. A decline in these parameters, associated with a drop in glycemia, was detected when ATPase activity was increased. Variations in the activities of both GPase and GSase were found associated with changes in levels of glycogen. A peak in liver FBPase activity and a decrease in liver HK activity was found when ATPase activity was increased. In white muscle and kidney, only the increase in kidney FBPase activity seems to be related to the rise in ATPase activity. These data suggest that, in contrast to the results obtained in white muscle and kidney, a storage followed by a depletion of liver reserves occurs coincidentally with the increase and subsequent decline in gill (Na+-K+)-ATPase activity.
Article
Glycogen, glucose, protein and glycogen phosphorylase and glycogen synthetase activity in liver, white muscle and kidney were determined in domesticated rainbow trout (Oncorhynchus mykiss) treated with 3,5,3'-triiodo-L-thyronine (T3), thyroxine (T4) and cortisol and combinations of all these hormones for 10 days. Plasma protein and glucose levels were also determined. Declines in liver glycogen and glucose were observed after cortisol treatment as compared to values obtained in controls (controls: 27.54 +/- 1.73 mg glycogen/g and 16.81 +/- 1.50 mg glucose/g) such as 15.94 +/- 2.64 mg glycogen/g and 8.63 +/- 1.22 mg glucose/g. T4 treatment did not produce any effects on the measured parameters. T3 plus T4 treatment caused a fall in hepatic glycogen and glucose levels (11.97 +/- 1.27 mg glycogen/g and 8.98 +/- 2.06 mg/g, respectively). All cortisol and thyroid hormone combinations produced a fall in liver glycogen levels (range between 6.07 +/- 1.19 and 16.38 +/- 1.56 mg glycogen/g) as well as an increase (from 37 to 44%) in glycogen phosphorylase activity. No changes were observed in any of the measured parameters for the different hormone treatments assessed in white muscle and kidney. Under our experimental conditions, cortisol and probably T3 are involved in liver glycogen mobilization and apparently do not elicit a response in white muscle and kidney.
Article
It is generally recognized that the liver is the major gluconeogenic tissue concerned with the regulation of glycemia because of the relative organ size as compared to that of the kidney cortex. In fact, glucose formed by the kidneys should provide only a small fraction of the blood glucose under normal physiological conditions, considering the renal removal of lactate, the main gluconeogenic precursor. However, Owen et al. have reported that renal glucose production after prolonged fasting in obese patients approached that of the liver, which is decreased in these conditions. On the other hand, Niederland et al. showed that kidneys of partially hepatectomized rats synthetized more glucose both in vitro and in vivo than the sham-operated animals and Jones et al. reported a significant increase in net renal glucose production in fasted anesthetized dogs in which liver gluconeogenesis was inhibited by ethanol administration.
Article
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Previous studies have indicated that, in rat liver, gluconeogenesis from pyruvate and lactate involves carboxylation of pyruvate in mitochondria but the oxalacetate formed does not diffuse to the cytosol. Instead it is reduced to malate or transaminated to aspartate. The present study indicates that aspartate and malate may be converted to phosphoenolpyruvate by enzymes in rat liver cytosol almost as rapidly as is oxalacetate. The rates of conversion are sufficient to account for the formation of carbohydrate in livers of normal rats and are greatly elevated in preparations from livers of diabetic rats. The synthesis of phosphoenolpyruvate from pyruvate via the malic enzyme or pyruvate carboxylase in the cytosol was found to be insignificant. Quantitative measurements of enzymes in the cytosol indicate that fumarase is elevated in diabetes and fasting but is not altered by adrenalectomy or administration of hydrocortisone. Malate dehydrogenase is elevated in diabetes and after hydrocortisone. Both glutamate-oxalacetate and glutamate-pyruvate transaminase are elevated in diabetes, in fasting, and after hydrocortisone. In agreement with other workers, citrate cleavage enzyme was depressed in diabetes and fasting, and elevated after insulin administration and refeeding of fasted animals. The enzyme adaptations and the rates of metabolite conversion in rat liver cytosol are thus in keeping with the proposed pathway of carbon in gluconeogenesis.
Article
1. The activities at 15° of three gluconeogenic enzymes, d -fructose-1,6-diphosphate, 1-phosphohydrolase ( EC 3.1.3.11), pyruvate carboxylase ( EC 6.4.1.1) and phosphoenolpyruvate carboxykinase (4.1.1.32), were determined in liver, kidney, gill and muscle of rainbow trout ( Salmo gairdneri ) given a commercial diet. The results indicated that liver and kidney are the main sites of gluconeogenesis. 2. Glucose formation from pyruvate was approximately 6 μmol/h per g wet weight at 15° in liver slices of trout given a commercial diet. 3. Glucose diffusion space in trout was measured by the dilution principle after intravascular injection of a trace dose of [U- ¹⁴ C]glucose. Glucose space was found to be 13.7% of the body-weight. Gluconeogenesis in vivo amounted to approximately 45 μmol/kg body-weight per h. 4. Intraperitoneally injected [U- ¹⁴ C]alanine was quickly converted to glucose. Maximal incorporation of alanine into glucose occurred 6 h after alanine administration. 5. Rainbow trout given a high-protein diet gained in weight significantly during a 4-week period. Those given a high-carbohydrate diet did not make a significant weight gain over the same period. Gluconeogenesis from alanine was markedly reduced in fish given the high-carbohydrate diet. There was no significant difference in gluconeogenesis from alanine in fish given a high-protein diet and fish which were fasted for 21 d. 6. Gluconeogenesis from alanine in trout was suppressed by intravenous injection of insulin. This effect was found both in trout given a high-protein diet and in fasted trout.
Article
Infection with Hymenolepis microstoma significantly affected the lipid metabolism of young male Balb/C mice. Infection increased the rates of hepatic fatty acid and cholesterol synthesis and cholesterol synthesis by the gut. Decreases were recorded in testicular fatty acid synthesis and in the weights of testes and white epididymal adipose tissue. Plasma glucose decreased rapidly during infection. The observed changes in lipogenesis could not be attributed to changes in food intake or body temperature. The changes are discussed in relation to nutritional interactions between host and parasite and the possible effects on host hormone levels. The presence of newly synthesized fatty acid in H. microstoma is also reported.
Article
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I am using the term gluconeogenesis in this lecture to denote any new formation of carbohydrate from non-carbohydrates. These non-carbohydrates include amino acids, as well as the lactate continuously produced in the body, e.g. in blood cells and in the exercised muscles. When lactate is the precursor of carbohydrate the formation of glucose from it constitutes a re-formation rather than a new formation as the lactate has been derived from glucose. But as the enzymic mechanisms of glucose formation from lactate and from amino acids are essentially the same, it is reasonable to treat them jointly. Gluconeogenesis is a biosynthetic process of major importance. I intend to review first some aspects of the physiological role of gluconeogenesis. This will lead to the fact that the amounts of carbohydrate which are synthesized vary within very wide limits—between almost nil and perhaps 200 g per day in the case of the human adult—and this will bring me to the main subject: the question of how the rate of gluconeogenesis is regulated and adjusted to changing needs.
Article
A multi-enzyme system consisting of purified lactic dehydrogenase and mitochondria reduces DPN in the presence of lactate. The mitochondria greatly alter the external DPNH-DPN ratio by oxidizing pyruvate which is formed from lactate concomitantly with DPNH. The rate-limiting step in the overall reaction is the oxidation of pyruvate and the rate of formation of DPNH is dependent on the ability of mitochondria to maintain low levels of pyruvate. Some of the kinetic and thermodynamic properties of this reconstructed system are described as well as its possible relationship to reductive biosynthesis.
In Methods of Enzymatic Analysis, p. 117
  • M W Slein
Slein, M. W. (1963). In Methods of Enzymatic Analysis, p. 117. Ed. by Bergmeyer, H. U. New York: Academic Press Inc.
RNA in bacteria have led to its wide acceptance as a messenger of information between DNA and sites of protein synthesis. This 'messenger RNA', which has been the subject of several recent reviews
Two features of a RNA in bacteria have led to its wide acceptance as a messenger of information between DNA and sites of protein synthesis. This 'messenger RNA', which has been the subject of several recent reviews (Jacob & Monod, 1961; Burna, 1962; Canellakis, 1962; Grunberg-Manago, 1962; Volkin, 1963), has a base composition similar to concomitantly synthesized DNA and exhibits a
  • R C Nordlie
  • H A Lardy
Nordlie, R. C. & Lardy, H. A. (1963). J. biol. Chem. 238,2259. Olavarria, J. M. (1960). J. biol. Chem. 235, 3058.
  • O Warburg
  • A W Geissler
  • S Lorenz
Warburg, O., Geissler, A. W. & Lorenz, S. (1961). Z. Naturf. 16b, 283.
In Methods of Enzymatic Analysis, p. 384
  • E Bernt
  • H U Bergmeyer
Bernt, E. & Bergmeyer, H. U. (1963). In Methods of Enzymatic Analysis, p. 384. Ed. by Bergmeyer, H. U. New York: Academic Press Inc.
Textbook of Quantitative Inorganic Analy8i8
  • I M Kolthoff
  • E B Sandell
Kolthoff, I. M. & Sandell, E. B. (1952). Textbook of Quantitative Inorganic Analy8i8, 3rd ed., p. 531. New York: Macmillan and Co.
  • C A Good
  • H Kramer
  • M Somogyi
Good, C. A., Kramer, H. & Somogyi, M. (1933). J. biol. Chem. 100, 485.
  • J Larner
  • R E Gillespie
Larner, J. & Gillespie, R. E. (1956). J. biol. Chem. 223, 709.
  • H G Sie
  • W H Fishman
  • V N Singh
  • T A Venkitasubramanian
Sie, H. G. & Fishman, W. H. (1958). Nature, Lond., 182,240. Singh, V. N. & Venkitasubramanian, T. A. (1963). Biochim. biophys. Ada, 78, 744.
  • C F Cori
  • G T Cori
  • A Dahlqvist
Cori, C. F. & Cori, G. T. (1929). J. biol. Chem. 81, 389. Dahlqvist, A. (1958). Acta chem. scand. 12, 2012. Dahlqvist, A. (1961). Biochem. J. 80, 547.
  • J Mendicino
Mendicino, J. (1962). Biochim. biophys. Acta, 62, 318.
a) In Methods of Enzymatic Analysis, p. 266
  • H J Hohorst
Hohorst, H. J. (1963 a). In Methods of Enzymatic Analysis, p. 266. Ed. by Bergmeyer. H. U. New York: Academic Press Inc.
  • J Raaflaub
Raaflaub, J. (1955). Helv. chim. acta, 38, 37.
  • R Takane
Takane, R. (1926). Biochem. Z. 171, 403.