The effect of propionate on the metabolism of pyruvate and lactate in the perfused rat liver.
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ABSTRACT:
SUBMITTER: Chan TM
PROVIDER: S-EPMC1178695 | biostudies-other | 1972 Apr
REPOSITORIES: biostudies-other
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Project description:A preparation of isolated rat hindleg was perfused with a medium consisting of bicarbonate buffer containing Ficoll and fluorocarbon, containing glucose and/or lactate. The leg was electrically prestimulated to deplete partially muscle glycogen. The glucose was labelled uniformly with 14C and with 3H in positions 2, 5 or 6, and lactate uniformly with 14C and with 3H in positions 2 or 3. Glucose carbon was predominantly recovered in glycogen, and to a lesser extent in lactate. The 3H/14C ration in glycogen from [5-3H,U-14C]- and [6-3H,U-14C]-glucose was the same as in glucose. Nearly all the utilized 3H from [2-3H]glucose was recovered as water. Insulin increased glucose uptake and glycogen synthesis 3-fold. When the muscle was perfused with a medium containing 10 mM-glucose and 2 mM-lactate, there was little change in lactate concentration. 14C from lactate was incorporated into glycogen. There was a marked exponential decrease in lactate specific radioactivity, much greater with [3H]- than with [14C]-lactate. The 'apparent turnover' of [U-14C]lactate was 0.28 mumol/min per g of muscle, and those of [2-3H]- and [3-3H]-lactate were both about 0.7 mumol/min per g. With 10 mM-lactate as sole substrate, there was a net uptake of lactate, at a rate of about 0.15 mumol/min per g, and the apparent turnover of [U-14C]lactate was 0.3 mumol/min per g. The apparent turnover of [3H]lactate was 3-5 times greater. When glycogen synthesis was low (no prestimulation, no insulin), the incorporation of lactate carbon into glycogen exceeded that from glucose, but at high rates of glycogen deposition the incorporation of lactate carbon was much less than that of glucose. Lactate incorporation into glycogen was similar in fast-twitch white and fast-twitch red muscle, but was very low in slow-twitch red fibres. We find that (a) pyruvate in muscle is incorporated into glycogen without randomization of carbon, and synthesis is not inhibited by mercaptopicolinate or cycloserine; (b) there is extensive lactate turnover in the absence of net lactate uptake, and there is a large dilution of 14C-labelled lactate from endogenous supply; (c) there is extensive detritiation of [2-3H]- and [3-3H]-lactate in excess of 14C utilization.
| S-EPMC1144177 | biostudies-other
Project description:1. In aerobic conditions the isolated perfused liver from well-fed rats rapidly formed lactate from endogenous glycogen until the lactate concentration in the perfusion medium reached about 2mm (i.e. the concentration of lactate in blood in vivo) and then production ceased. Pyruvate was formed in proportion to the lactate, the [lactate]/[pyruvate] ratio remaining between 8 and 15. 2. The addition of 5mm- or 10mm-glucose did not affect lactate production, but 20mm- and 40mm-glucose greatly increased lactate production. This effect of high glucose concentration can be accounted for by the activity of glucokinase. 3. The perfused liver released glucose into the medium until the concentration was about 6mm. When 5mm- or 10mm-glucose was added to the medium much less glucose was released. 4. At high glucose concentrations (40mm) more glucose was taken up than lactate and pyruvate were produced; the excess of glucose was probably converted into glycogen. 5. In anaerobic conditions, livers of well-fed rats produced lactate at relatively high rates (2.5mumol/min per g wet wt.). Glucose was also rapidly released, at an initial rate of 3.2mumol/min per g wet wt. Both lactate and glucose production ceased when the liver glycogen was depleted. 6. Addition of 20mm-glucose increased the rate of anaerobic production of lactate. 7. d-Fructose also increased anaerobic production of lactate. In the presence of 20mm-fructose some glucose was formed anaerobically from fructose. 8. In the perfused liver from starved rats the rate of lactate formation was very low and the increase after addition of glucose and fructose was slight. 9. The glycolytic capacity of the liver from well-fed rats is equivalent to its capacity for fatty acid synthesis and it is pointed out that hepatic glycolysis (producing acetyl-CoA in aerobic conditions) is not primarily an energy-providing process but part of the mechanism converting carbohydrate into fat.
| S-EPMC1178032 | biostudies-other
Project description:High concentrations of urea were shown to induce a paradoxical regulatory volume decrease response with K(+) channel opening and subsequent hepatocyte shrinkage (Hallbrucker, C., vom Dahl, S., Ritter, M., Lang, F., and Häussinger, D. (1994) Pflügers Arch. 428, 552-560), although the hepatocyte plasma membrane is thought to be freely permeable to urea. The underlying mechanisms remained unclear. As shown in the present study, urea (100 mmol/liter) induced within 1 min an activation of β(1) integrins followed by an activation of focal adhesion kinase, c-Src, p38(MAPK), extracellular signal-regulated kinases, and c-Jun N-terminal kinase. Because α(5)β(1) integrin is known to act as a volume/osmosensor in hepatocytes, which becomes activated in response to hepatocyte swelling, the findings suggest that urea at high concentrations induces a nonosmotic activating perturbation of this osmosensor, thereby triggering a volume regulatory K(+) efflux. In line with this, similar to hypo-osmotic hepatocyte swelling, urea induced an inhibition of hepatic proteolysis, which was sensitive to p38(MAPK) inhibition. Molecular dynamics simulations of a three-dimensional model of the ectodomain of α(5)β(1) integrin in water, urea, or thiourea solutions revealed significant conformational changes of α(5)β(1) integrin in urea and thiourea solutions, in contrast to the simulation of α(5)β(1) in water. These changes lead to an unbending of the integrin structure around the genu, which may suggest activation, whereas the structures of single domains remained essentially unchanged. It is concluded that urea at high concentrations affects hepatic metabolism through direct activation of the α(5)β(1) integrin system.
| S-EPMC2937967 | biostudies-literature
Project description:1. The influence of ethanol on the redox level of the redox pair lactate/pyruvate has been studied in experiments with rat-liver slices. 2. Ethanol had no effect on oxygen consumption but strongly depressed carbon dioxide formation. On the assumption that ethanol is oxidized to acetate in the liver slices, it could be calculated that most of the oxygen that disappeared was consumed in this reaction. 3. Addition of ethanol to the incubation medium increased the lactate/pyruvate ratio and when all the ethanol had been oxidized the redox value decreased to the normal again. Ethanol depressed the pyruvate concentration, whereas the lactate concentration was not much influenced. 4. Acetaldehyde in the concentrations present during ethanol oxidation did not influence the lactate/pyruvate ratio. Higher concentrations, however, increased the redox state. 5. Acetate in the concentrations present during ethanol oxidation in the experiments, and also in higher concentrations, did not influence the lactate/pyruvate ratio. 6. The mechanism by which ethanol influences the lactate/pyruvate ratio is discussed.
| S-EPMC1264821 | biostudies-other
Project description:Aristolochic acids are natural nitro-compounds found globally in the plant genus Aristolochia that have been implicated in the severe illness in humans termed aristolochic acid nephropathy (AAN). Aristolochic acids undergo nitroreduction, among other metabolic reactions, and active intermediates arise that are carcinogenic. Previous experiments with rats showed that aristolochic acid I (AA-I), after oral administration or injection, is subjected to detoxication reactions to give aristolochic acid Ia, aristolactam Ia, aristolactam I, and their glucuronide and sulfate conjugates that can be found in urine and feces. Results obtained with whole rats do not clearly define the role of liver and kidney in such metabolic transformation. In this study, in order to determine the specific role of the kidney on the renal disposition of AA-I and to study the biotransformations suffered by AA-I in this organ, isolated kidneys of rats were perfused with AA-I. AA-I and metabolite concentrations were determined in perfusates and urine using HPLC procedures. The isolated perfused rat kidney model showed that AA-I distributes rapidly and extensively in kidney tissues by uptake from the peritubular capillaries and the tubules. It was also established that the kidney is able to metabolize AA-I into aristolochic acid Ia, aristolochic acid Ia O-sulfate, aristolactam Ia, aristolactam I, and aristolactam Ia O-glucuronide. Rapid demethylation and sulfation of AA-I in the kidney generate aristolochic acid Ia and its sulfate conjugate that are voided to the urine. Reduction reactions to give the aristolactam metabolites occur to a slower rate. Renal clearances showed that filtered AA-I is reabsorbed at the tubules, whereas the metabolites are secreted. The unconjugated metabolites produced in the renal tissues are transported to both urine and perfusate, whereas the conjugated metabolites are almost exclusively secreted to the urine.
| S-EPMC3276251 | biostudies-literature
Project description:1. The rates of gluconeogenesis from most substrates tested in the perfused livers of well-fed rats were about half of those obtained in the livers of starved rats. There was no difference for glycerol. 2. A diet low in carbohydrate increased the rates of gluconeogenesis from some substrates but not from all. In general the effects of a low-carbohydrate diet on rat liver are less marked than those on rat kidney cortex. 3. Glycogen was deposited in the livers of starved rats when the perfusion medium contained about 10mm-glucose. The shedding of glucose from the glycogen stores by the well-fed liver was greatly diminished by 10mm-glucose and stopped by 13.3mm-glucose. Livers of well-fed rats that were depleted of their glycogen stores by treatment with phlorrhizin and glucagon synthesized glycogen from glucose. 4. When two gluconeogenic substrates were added to the perfusion medium additive effects occurred only when glycerol was one of the substrates. Lactate and glycerol gave more than additive effects owing to an increased rate of glucose formation from glycerol. 5. Pyruvate also accelerated the conversion of glycerol into glucose, and the accelerating effect of lactate can be attributed to a rapid formation of pyruvate from lactate. 6. Butyrate and oleate at 2mm, which alone are not gluconeogenic, increased the rate of gluconeogenesis from lactate. 7. The acceleration of gluconeogenesis from lactate by glucagon was also found when gluconeogenesis from lactate was stimulated by butyrate and oleate. This finding is not compatible with the view that the primary action of glucagon in promoting gluconeogenesis is an acceleration of lipolysis. 8. The rate of gluconeogenesis from pyruvate at 10mm was only 70% of that at 5mm. This ;inhibition' was abolished by oleate or glucagon.
| S-EPMC1198388 | biostudies-other
Project description:1. Measurements were made of the activities of the four key enzymes involved in gluconeogenesis, pyruvate carboxylase (EC 6.4.1.1), phosphoenolpyruvate carboxylase (EC 4.1.1.32), fructose 1,6-diphosphatase (EC 3.1.3.11) and glucose 6-phosphatase (EC 3.1.3.9), of serine dehydratase (EC 4.2.1.13) and of the four enzymes unique to glycolysis, glucokinase (EC 2.7.1.2), hexokinase (EC 2.7.1.1), phosphofructokinase (EC 2.7.1.11) and pyruvate kinase (EC 2.7.1.40), in livers from starved rats perfused with glucose, fructose or lactate. Changes in perfusate concentrations of glucose, fructose, lactate, pyruvate, urea and amino acid were monitored for each perfusion. 2. Addition of 15mm-glucose at the start of perfusion decreased the activity of pyruvate carboxylase. Constant infusion of glucose to maintain the concentration also decreased the activities of phosphoenolpyruvate carboxylase, fructose 1,6-diphosphatase and serine dehydratase. Addition of 2.2mm-glucose initially to give a perfusate sugar concentration similar to the blood sugar concentration of starved animals had no effect on the activities of the enzymes compared with zero-time controls. 3. Addition of 15mm-fructose initially decreased glucokinase activity. Constant infusion of fructose decreased activities of glucokinase, phosphofructokinase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, glucose 6-phosphatase and serine dehydratase. 4. Addition of 7mm-lactate initially elevated the activity of pyruvate carboxylase, as also did constant infusion; maintenance of a perfusate lactate concentration of 18mm induced both pyruvate carboxylase and phosphoenolpyruvate carboxylase activities. 5. Addition of cycloheximide had no effect on the activities of the enzymes after 4h of perfusion at either low or high concentrations of glucose or at high lactate concentration. Cycloheximide also prevented the loss or induction of pyruvate carboxylase and phosphoenolpyruvate carboxylase activities with high substrate concentrations. 6. Significant amounts of glycogen were deposited in all perfusions, except for those containing cycloheximide at the lowest glucose concentration. Lipid was found to increase only in the experiments with high fructose concentrations. 7. Perfusion with either fructose or glucose decreased the rates of ureogenesis; addition of cycloheximide increased urea efflux from the liver.
| S-EPMC1177795 | biostudies-literature
Project description:Addition of phenylephrine to isolated perfused rat liver is followed by an increased 14CO2 production from [1-14C]glutamate, [1-14C]glutamine, [U-14C]proline and [3-14C]pyruvate, but by a decreased 14CO2 production from [1-14C]pyruvate. Simultaneously, there is a considerable decrease in tissue content of 2-oxoglutarate, glutamate and citrate. Stimulation of 14CO2 production from [1-14C]glutamate is also observed in the presence of amino-oxyacetate, suggesting a stimulation of glutamate dehydrogenase and 2-oxoglutarate dehydrogenase fluxes by phenylephrine. Inhibition of pyruvate dehydrogenase flux by phenylephrine is due to an increased 2-oxoglutarate dehydroxygenase flux. Phenylephrine stimulates glutaminase flux and inhibits glutamine synthetase flux to a similar extent, resulting in an increased hepatic glutamine uptake. Whereas the effects of NH4+ ions and phenylephrine on glutaminase flux were additive, activation of glutaminase by glucagon was considerably diminished in the presence of phenylephrine. The reported effects are largely overcome by prazosin, indicating the involvement of alpha-adrenergic receptors in the action of phenylephrine. It is concluded that stimulation of gluconeogenesis from various amino acids by phenylephrine is due to an increased flux through glutamate dehydrogenase and the citric acid cycle.
| S-EPMC1144094 | biostudies-other
Project description:ObjectivesTo assess the accuracy of blood lactate and lactate: pyruvate molar ratio (L:P) as a screen for mitochondrial, respiratory chain, or fatty acid oxidation disorders in children with pediatric acute liver failure (PALF); to determine whether serum lactate ≥ 2.5 mmol/L or L:P ≥ 25 correlated with biochemical variables of clinical severity; and to determine whether lactate or L:P is associated with clinical outcome at 21 days.Study designRetrospective review of demographic, clinical, laboratory, and outcome data for PALF study group participants who had lactate and pyruvate levels collected on the same day.ResultsOf 986 participants, 110 had lactate and pyruvate levels collected on the same day. Of the 110, the etiology of PALF was a mitochondrial disorder in 8 (7%), indeterminate in 65 (59%), and an alternative diagnosis in 37 (34%). Lactate, pyruvate, and L:P were similar among the 3 etiologic groups. There was no significant association between the initial lactate or L:P and biochemical variables of clinical severity or clinical outcome at 21 days.ConclusionsA serum lactate ≥ 2.5 mmol/L and/or elevated L:P was common in all causes of PALF, not limited to those with a mitochondrial etiology, and did not predict 21-day clinical outcome.Trial registrationClinicalTrials.gov: NCT00986648.
| S-EPMC5328928 | biostudies-literature
Project description:1. Loading the isolated perfused liver from well-fed rats with xylitol (20mm) caused a depletion of adenine nucleotides and P(i) and an accumulation of alpha-glycerophosphate. The ATP content fell to 66% of the control value after 10min and to 32% after 80min. The ADP and AMP contents also fell. After 80min 63% of the total adenine nucleotides and 59% of the P(i) had been lost. 2. The alpha-glycerophosphate content rose from 0.13 to 4.74mumol/g at 10min and reached 8.02mumol/g at 40min. 3. Xylitol was rapidly metabolized, the main products being glucose, lactate and pyruvate. 4. The [lactate]/[pyruvate] ratio in the presence of xylitol rose to 30-40. 5. On perfusion of livers from starved animals the main product of xylitol metabolism was glucose and the mean ratio xylitol removed/glucose formed was 1.29 (corrected for endogenous glucose and lactate production). This is close to the predicted value of 1.2. 6. Evidence is presented indicating that the loss of adenine nucleotides caused by xylitol is not due to the increased ATP consumption but to the accumulation of alpha-glycerophosphate and depletion of P(i). 7. The loss of adenine nucleotides accounts for the hyperuricaemia which can occur after xylitol infusion in man. 8. The relevance of the findings to the clinical use of xylitol as an energy source is discussed.
| S-EPMC1177829 | biostudies-other