The development of gluconeogenesis in rat liver: experiments in vivo.
Ontology highlight
ABSTRACT:
SUBMITTER: Philippidis H
PROVIDER: S-EPMC1184745 | biostudies-other | 1969 Jul
REPOSITORIES: biostudies-other
Similar Datasets
Project description:AimsTo understand the mechanism by which imeglimin (a new oral hypoglycemic agent whose phase 3 development program in Japan has now been completed) decreases hepatic glucose production.Materials and methodsWe compared the effect of imeglimin and metformin on glucose production, ATP/ADP ratio, oxygen consumption rate, mitochondrial redox potential and membrane potential in primary rat hepatocytes.ResultsWe found that both imeglimin and metformin dose-dependently decreased glucose production and the ATP/ADP ratio. Moreover, they both increased mitochondrial redox potential (assessed by mitochondrial NAD(P)H fluorescence) and decreased membrane potential (assessed by TMRM fluorescence). However, contrary to metformin, which inhibits mitochondrial Complex I, imeglimin did not decrease the oxygen consumption rate in intact cells. By measuring the oxygen consumption of in situ respiratory chain as a function of the concentration of NADH, we observed that imeglimin decreased the affinity of NADH for the respiratory chain but did not affect its Vmax (ie competitive inhibition) whereas metformin decreased both the Vmax and the affinity (ie uncompetitive inhibition).ConclusionsWe conclude that imeglimin induces a kinetic constraint on the respiratory chain that does not affect its maximal activity. This kinetic constraint is offset by a decrease in the mitochondrial membrane potential, which induces a thermodynamic constraint on the ATPase responsible for a decrease in the ATP/ADP ratio.
| S-EPMC8029524 | biostudies-literature
Project description:1. The normal development of the key enzymes of gluconeogenesis in rat liver, glucose 6-phosphatase, hexose diphosphatase, phosphopyruvate carboxylase and pyruvate carboxylase, was measured during the neonatal period. 2. Glucose 6-phosphatase, hexose diphosphatase and pyruvate carboxylase are all present in the late foetal liver, but all the enzymes show an increase in activity after birth. 3. Phosphopyruvate carboxylase is not present in liver extracts from foetal rats, but activity appears immediately after birth and increases rapidly over the first day and then more slowly to reach its maximum at the fourth postnatal day. 4. The fluorinated synthetic glucocorticoid, triamcinolone, was administered to foetal rats at various gestation times by intraperitoneal injection in utero and the animals were killed at intervals between 4 and 48hr. later. 5. The administration of triamcinolone results in slight depression of glucose 6-phosphatase, and a more significant depression of hexose diphosphatase to about one-half its normal activity in foetal rat liver. 6. Triamcinolone injection is without effect on pyruvate carboxylase activity and does not result in premature appearance of phosphopyruvate carboxylase in foetal rat liver. 7. Pyruvate kinase and aspartate amino-transferase activities in foetal rat liver are both depressed by triamcinolone treatment, whereas phosphofructokinase activity is elevated. 8. Tyrosine amino-transferase activity in foetal rat liver is markedly elevated in animals exposed to triamcinolone for 10hr. or more, but the effect is only observed in animals close to term. 9. The results are discussed in relation to mechanisms involved in the initial synthesis of tissue-specific enzymes in developing tissues, and it is concluded that glucocorticoids do not initiate the synthesis of the gluconeogenic enzymes.
| S-EPMC1198444 | biostudies-other
Project description:1. An assay method for the determination of phosphopyruvate carboxylase activity is described in which improved sensitivity is obtained by separation of the enzyme from interfering pyruvate kinase by zone sedimentation. 2. The molecular weight of rat liver phosphopyruvate carboxylase determined by zone sedimentation is about 68000. 3. Premature delivery of rat foetuses by uterine section results in the rapid appearance of phosphopyruvate carboxylase, but hexose diphosphatase and pyruvate carboxylase, already present in the foetal rat liver, are not significantly affected, and glucose 6-phosphatase activity is only slightly affected. 4. The rate of incorporation of [(14)C]pyruvate into glucose by liver slices is also greatly increased by premature delivery and there is a highly significant linear correlation between this process and the phosphopyruvate carboxylase activity.
| S-EPMC1198445 | biostudies-other
Project description:1. Measurements in livers of rats delivered by Caesarian section show a rapid change in the relative proportion of adenine nucleotides. By 20min the ATP/ADP ratio had increased from 1.76 to 8.7 and the value of the relationship [ATP][AMP]/[ADP](2) increased from 1.0 to 4.4. These changes are dependent on the availability of oxygen to the animal. 2. The free [NAD(+)]/[NADH] ratio in the liver cytosol increases from 180 after delivery to reach a maximum of 1010 at 2h, before falling to 540 in the 24h-old animal. 3. The mitochondrial NAD redox potential also shows a sharp increase towards a more oxidized state in livers of delivered rats. 4. These results probably indicate that the foetal liver is hypoxic, with oxygenation occurring in the first hour after delivery. 5. Measurements in livers of naturally born rats 2min after birth also suggest that this tissue is hypoxic with an ATP/ADP ratio of 1.83 and a free [NAD(+)]/[NADH] ratio of 117. 6. Concentrations of intermediates in the gluconeogenic pathway have been determined in livers of foetal, 1h-old and 1-day-old rats. These experiments imply a facilitation of lactate dehydrogenase and glucose 6-phosphatase activities by 1h after birth, and a stimulation of phosphoenolpyruvate carboxykinase and glucose 6-phosphatase steps by 1 day after birth. 7. The appearance of gluconeogenesis in livers of newborn rats seems therefore to involve an oxygenation stage followed by an increase in phosphoenolpyruvate carboxykinase activity.
| S-EPMC1177141 | biostudies-other
Project description:1. Administration of glucagon to foetal rats produced a 10-15-fold increase in hepatic phosphoenolpyruvate carboxykinase activity together with a similar increase in the overall pathway of pyruvate conversion into glycogen in liver slices. 2. Glucagon was without effect on gluconeogenesis in vivo, which remained at approx. 0.1% of the incorporation as measured in newborn animals. 3. The apparent discrepancy between these results was due to the ether anaesthesia that was required for experimentation in vivo. Under conditions when minimal ether was used, the rates of labelling of glycogen from [3-(14)C]pyruvate in vivo were increased 10-20-fold and there was an additional stimulus by glucagon. 4. Ether anaesthesia produced a more reduced redox state of the foetal liver cytosol and lowered the ATP/ADP concentration ratio. 5. It is proposed that these effects are significant in the limitation of gluconeogenesis in the foetal rat liver, so that only with high phosphoenolpyruvate carboxykinase activity, high ATP concentration and a relatively oxidized cytosol redox state will a functional gluconeogenic pathway be present.
| S-EPMC1179609 | biostudies-other
Project description:1. A modification of the methods of Miller and of Schimassek for the perfusion of the isolated rat liver, suitable for the study of gluconeogenesis, is described. 2. The main modifications concern the operative technique (reducing the period of anoxia during the operation to 3min.) and the use of aged (non-glycolysing) red cells in the semi-synthetic perfusion medium. 3. The performance of the perfused liver was tested by measuring the rate of gluconeogenesis, of urea synthesis and the stability of adenine nucleotides. Higher rates of gluconeogenesis (1mumole/min./g.) from excess of lactate and of urea synthesis from excess of ammonia (4mumoles/min./g. in the presence of ornithine) were observed than are likely to occur in vivo where rates are limited by the rate of supply of precursor. The concentrations of the three adenine nucleotides in the liver tissue were maintained within 15% over a perfusion period of 135min. 4. Ca(2+), Na(+), K(+), Mg(2+) and phosphate were found to be required at physiological concentrations for optimum gluconeogenesis but bicarbonate and carbon dioxide could be largely replaced by phosphate buffer without affecting the rate of gluconeogenesis. 5. Maximal gluconeogenesis did not decrease maximal urea synthesis in the presence of ornithine and ammonia and vice versa. This indicates that the energy requirements were not limiting the rates of gluconeogenesis or of urea synthesis. 6. Addition of lactate, and especially ammonium salts, increased the uptake of oxygen more than expected on the basis of the ATP requirements of the gluconeogenesis and urea synthesis.
| S-EPMC1270107 | biostudies-other
Project description:C/EBPalpha is a key transcription factor indispensable for the onset of gluconeogenesis in perinatal liver. However, C/EBPalpha was already expressed in fetal liver, suggesting that the expression of C/EBPalpha alone does not account for the dramatic increase of the expression of metabolic genes, and hence an additional factor(s) is expected to function cooperatively with C/EBPalpha in perinatal liver. We show here that expression of Foxo1 was sharply increased in the perinatal liver and augmented C/EBPalpha-dependent transcription. Foxo1 bound C/EBPalpha via its forkhead domain, and Foxo1 bound to the promoter of a gluconeogenic gene, phosphoenolpyruvate carboxykinase (PEPCK), in a C/EBPalpha-dependent manner in vivo. Insulin inhibited the expression of PEPCK in a culture of fetal liver cells, and also the C/EBPalpha-dependent transcription enhanced by Foxo1. These results indicate that Foxo1 regulates gluconeogenesis cooperatively with C/EBPalpha, and also links insulin signaling to C/EBPalpha during liver development.
| S-EPMC1949016 | biostudies-literature
Project description:1. The equations derived by Heath (1968) were applied to data from experiments on rats in four metabolic states: fed, post-absorptive, starved and 2hr. after an eventually lethal injury. The data used were: (a) The fractions of label injected as C1-, C2- and C3-pyruvate (where the prefix indicates the position of labelling) that are incorporated into carbon dioxide and glucose in post-absorptive and injured rats (yields). Yields could be corrected to yields on label taken up by the liver. (b) The (C5-label in glutamate)/(total label in glutamate) ratio in the liver after C2-pyruvate in rats in all four states. (c) The distribution of label within glutamate after C2-pyruvate or C2-alanine in the livers of fed, post-absorptive and starved rats. (d) The distribution of label within glucose after C2-lactate or C2-pyruvate in starved rats. (e) The relative specific radioactivities of pyruvate, aspartate, glutamate and (in two states only) of glucose 6-phosphate after injection of [U-(14)C]glucose into rats in all four states. These data were previously published, except those after (e) and some after (b) above, which are given in this paper. 2. In addition the concentrations of pyruvate, citrate, glutamate and aspartate in the livers of post-absorptive and injured rats were found. Injury decreased glutamate and citrate concentrations and to a smaller extent aspartate and pyruvate concentrations. 3. Non-steady-state theory showed that most of the data could be used without serious error in steady-state theory. Steady-state theory correlated all but one observation (the relative yields of (14)CO(2) from C2- and C3-pyruvate) listed after (a)-(e) above within the experimental errors, and gave rough estimates of the rates of pyruvate carboxylation, conversion of pyruvate and fat into acetyl-CoA and utilization of glutamate. The main conclusions were: (a) symmetrization of label in oxaloacetate both in the mitochondrion and in the cytoplasm was far from complete, because oxaloacetate did not equilibrate with fumarate in either. From this and other findings it was deduced: (b) that malate or fumarate or both left the mitochondrion, and not oxaloacetate; (c) that there was a loss from the mitochondrion of a fraction of the malate or fumarate or both formed from succinate, and (d) the resulting deficiency of oxaloacetate for the perpetuation of the tricarboxylic acid cycle was made up from pyruvate in fed and post-absorptive rats, but (e) in the starved rat could only be made up by utilization of glutamate. (f) In the fed rat the tricarboxylic acid cycle ran mostly on pyruvate, but in the post-absorptive and starved rat mostly on fat. (g) In the injured rat the tricarboxylic acid cycle was slowed, label in oxaloacetate was completely symmetrized (cf. conclusion a), and the tricarboxylic acid cycle utilized glutamate. (h) The conclusions were not invalidated by isotopic exchange, i.e. flux of label without net flux of compound, nor by interaction with lipogenic processes. (i) In the kidneys interaction between the tricarboxylic acid cycle and gluconeogenesis was different from in the liver, and was much less. The effects on the theory were roughly assessed, and were small. 4. The experiments and optimum experimental conditions required to check the theory are listed, and several predictions, open to experimental confirmation, are made.
| S-EPMC1187212 | biostudies-other
Project description:1. Rates of fluid endocytosis of rat liver, spleen, hepatocytes and sinusoidal liver cells have been determined, by using 125I-labelled poly(vinylpyrrolidone) as marker. Poly(vinylpyrrolidone) was injected intravenously into rats, and plasma clearance and uptake by liver and spleen were estimated. From these data, rates of fluid endocytosis of 1.2 and 1.8 ml of plasma/g of protein per day were calculated for liver and spleen respectively. Essentially the same results were found in nephrectomized rats. 2. Hepatocytes and sinusoidal cells were separately isolated by the collagenase/Pronase method, and sinusoidal cells were further fractionated by centrifugal elutriation. Hepatocytes, sinusoidal cells, Kupffer cells and endothelial cells showed rates of fluid endocytosis of 0.96, 9.0, 19 and 13 ml of plasma/g of cell protein per day respectively. Total-body X-irradiation did not influence uptake of poly(vinylpyrrolidone) by spleen, indicating that spleen lymphocytes are not significantly involved in fluid endocytosis. 3. For liver a rate constant of exocytosis of 5% per day was found, whereas for spleen no significant loss of accumulated label could be demonstrated during a 21-day period. 4. Distribution of label over a great number of organs and tissues was measured 9 days after the injection. Liver, skin, bone and muscle together contained about 70% of the label present in the carcass; only spleen and lymph nodes contained more label per g fresh weight of tissue than liver.
| S-EPMC1162377 | biostudies-other
Project description:1. The specific radioactivity-time relationships of glucose, glucose 6-phosphate, glycerol 1-phosphate and UDP-glucose were determined in rat liver after the intravenous injection of [U-(14)C]fructose, and a kinetic analysis was carried out. The glucose 6-phosphate pool was found to be compartmented into gluconeogenic and glycolytic components, and evidence was obtained that the triose phosphates were similarly compartmented. The glycolytic pathway was fed by glycogenolysis and glucose phosphorylation. There was no direct evidence that glycogenolysis fed only the glycolytic pathway, but this interpretation would make the liver resemble other organs in this respect. 2. UDP-glucose was not formed solely from gluconeogenic glucose 6-phosphate, as there was some dilution of label in the intervening glucose 1-phosphate pool, probably from glycogenolysis, though other pathways cannot be excluded. 3. The data cannot be explained by isotopic exchange.
| S-EPMC1187210 | biostudies-other