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PubMed1995

Effects of endurance training on lactate removal by oxidation and gluconeogenesis during exercise.

This report describes the effects of 9 weeks of endurance-training on the relative rates of lactate removal via oxidation and gluconeogenesis in humans. Before and after training, eight subjects performed incremental (60 W plus 40 W every 6 min) exercise tests, while 14C-lactate was infused into one forearm vein and arterialized venous blood was sampled from the other forearm. During the trial, the volume of expired 14CO2 and circulating 14C-lactate and 14C-glucose specific radioactivities were measured. Such measurements revealed that training increased the estimated oxidation of equivalent venous blood lactate concentrations [VLa] of greater than 1.6 mmol/l. These increases in lactate oxidation were more than would be predicted from the approximately 40% higher O2 uptake values at any [VLa] after training. At a [VLa] of 6 mmol/l, rates of lactate oxidation were increased by some 100% following training, from 105 +/- 12 to 208 +/- 33 micromol/min/kg (P < 0.01). Improvements in lactate oxidation after training reduced the estimated rates of lactate-to-glucose conversion from 40 +/- 3 to 9 +/- 2 micromol/min/kg at a [VLa] of 2.5 mmol/l (P < 0.01). Thus, unlike in rats, human endurance-training does not increase gluconeogenesis. In the final stages of progressive exercise after training, more than 80% of lactate was oxidised and accounted for approximately 45% of overall carbohydrate oxidation.

Adult↗
PubMed1997

The influence of progesterone-induced proteins on glucose metabolism in early equine embryos.

The influence of different maternal plasma progesterone concentrations on embryonic glucose metabolism was studied. Uterine flushes were obtained after treating ovariectomized mares (n = 3) with 0 (control), 100 or 200 mg progesterone daily for 7 d. A group of progesterone-induced proteins (PIP) of Mr approximately 20,000 were identified in flushes from progesterone treatments by SDS-PAGE but were not observed in control flushes. Progesterone-induced proteins were removed from half the pooled flush in each treatment group by Sepharose blue CL-6B. In a 3 x 2 factorial (progesterone treatments, progesterone-induced proteins) experiment, 6 groups of Day 7 equine embryos (n = 6 per group) were incubated in culture media (MEM:DPBS; 1:3) containing radioactively-labeled glucose. Contributions of the Embden-Meyerhof pathway (EMP) and the pentose-phosphate pathway (PPP) to the total metabolism of glucose in early equine embryos were assessed separately. In the 200 mg progesterone treatment group, the presence of progesterone-induced proteins in the culture medium resulted in a 4-to 5-fold increase in the activities of the Embden-Meyerhof pathway and the pentose-phosphate pathway. These results lead to the following conclusions: 1)Addition of progesterone-induced uterine proteins from mares with high levels of circulating progesterone enhance the metabolic activities of the Embden-Meyerhof pathway and the pentose-phosphate pathway in Day 7.5 equine embryos in culture. 2)Uterine secretion of progesterone-induced proteins which is quantitatively and/or qualitatively adequate to modify embryonic glucose metabolism in vitro is dependent on a minimal concentration of maternal plasma progesterone.

Journal Article↗
PubMed1975

[Pentose phosphate pathway and nucleic acid synthesis in human funicular tissue. In vitro studies].

Umbilical cord slices were incubated with either 1- or 6-14C-glucose, the radioactivities of which were measured in CO2 evolved. The ratio, 1 CO2/6 CO2 was low, being comprised between 1 and 2. Furthermore, this incubation of cord slices with tritiated uridine or thymidine resulted in very low incorporations, especially for the latter. Therefore, both the pentose phosphate pathway and the synthesis of nucleic acid have a low activity in the cord tissue: these might be signs of senescence in this otherwise fetal organ.

Carbon Dioxide↗
PubMed1984

Energy metabolism of adult Haemonchus contortus in vitro: a comparison of benzimidazole-susceptible and -resistant strains.

In vitro biochemical characteristics of three strains of Haemonchus contortus, benzimidazole-susceptible, mebendazole-resistant and thiabendazole-resistant isolates, were investigated. Steady-state pool sizes of glucose and metabolic intermediates, including adenine nucleotides and end-products revealed no differences between adult worms resistant or susceptible to benzimidazoles in 30-60 min incubations. Possible regulatory steps in the glycolytic pathway are identified as those involving the enzymes hexokinase, phosphofructokinase and pyruvate kinase. The major component of carbohydrate reserves was trehalose, some glycogen was present and the glucose pool was small. On incubation for 18 h in vitro, carbohydrates were metabolised in all three strains. However, in the benzimidazole-susceptible worms there was a preferential use of the glycogen reserves to maintain energy metabolism. All three strains had similar levels of total lipid, total protein and free amino acid and these did not change on incubation. The major products found in the medium on incubation, in vitro, for 18 h were propionate, acetate and propanol, with smaller amounts of ethanol, lactate and malate. All three strains produced a similar sum total of end-products; however, in the mebendazole-resistant strain there appeared to be a diversion of carbon flow to the ethanol-producing pathway. Carbon dioxide production in 60 min incubations was measured using radioactively labelled glucose. A greater output of labelled CO2 was noted under aerobic than anaerobic conditions. This was particularly true of the mebendazole-resistant strain and, in this strain, was sensitive to cyanide. The extent to which metabolic differences noted in the three strains may be related to benzimidazole resistance is not readily apparent.

Amino Acids↗
PubMed1981

Formation of hydroxypyruvaldehyde phosphate in human erythrocytes.

Human erythrocytes when incubated with [U-14C]glucose formed radioactively labeled hydroxypyruvaldehyde-P (CHOCOCH2OPO3(2-)). Using a "diagonal" chromatographic procedure on an anion exchange column for isolation and quantitative detection, up to 0.3 mumol of hydroxypyruvaldehyde-P/liter of packed cells was found. If glycolysis was blocked by inhibition of glyceraldehyde-3-P dehydrogenase with N-ethylmaleimide and iodoacetate, 0.7 mumol of hydroxypyruvaldehyde-P/liter of packed erythrocytes was detected. Hydroxypyruvaldehyde-P, found for the first time in eukaryotic cells, might be one of the long sought natural substrates of the glyoxalases.

Aldehydes↗
PubMed1975

Initiation of protein synthesis in Ehrlich ascites tumour cells. Evidence for physiological variation in the association of methionyl-tRNAf with native 40-S ribosomal subunits in vivo.

Binding of methionyl-tRNAf to native 40-S ribosomal subunits is thought to be an early stage in the process of polypeptide chain initiation, and [35S]Met-tRNAf - 40-S-subunit complexes can be isolated from Ehrlich ascites tumour cells following a brief incubation with [35S]methionine. To determine whether this step is subject to modulation by physiological conditions, we have estimated the extent of binding of Met-tRNAf to native- 40S ribosomal subunits in Ehrlich cells under nutritional conditions known to affect the rate of protein synthesis in these cells. Deprivation of either an essential amino acid, lysine, or of glucose, results in a substantial reduction in the proportion of native 40-S subunits which have Met-tRNAf associated with them, and refeeding of lysine to cells deprived of this amino acid partially reverses this effect within 10 min. These effects on the concentration of Met-tRNA - 40-S-subunit complexes are paralleled by changes of similar magnitude in the rate of protein synthesis and in polyribosome profiles. Native 40-S subunits can be spearated by equilibrium density gradient analysis on caesium chloride into two species, with buoyant densities approximately 1.40 and 1.49 g X cm-3. In cells deprived of either lysine or glucose, the radioactivity from [35S]methionine is bound exclusively to the particle of buoyant density 1.40 g X cm-3. In well-fed cells, or in starved cells shortly after refeeding, a significant proportion of the label is associated with a region of the CsCl gradient corresponding to a particle of higher density. The results suggest that the binding of Met-tRNAf to native 40-S ribosomal subunits can be greatly affected by physiological conditions which alter the rate of protein synthesis. This is consistent with a regulatory role for this step in the sequence of reactions involved in initiation of translation.

Animals↗
PubMed1987

The postnatal development of stimulated deoxyglucose uptake into the mouse cochlea and the inferior colliculus.

The effect of acoustic stimulation on the postnatal development of deoxyglucose uptake into the mouse cochlea and the inferior colliculus was evaluated. Animals between postnatal day 4 and 20 were separated into four different groups depending on their age. Tritiated deoxyglucose was injected intraperitoneally into each animal and tracer uptake was quantitated by microdissection of the tissues and scintillation counting. Acoustic stimulation at a noise level of 100 dB (A) resulted in supra-normal levels of deoxyglucose uptake for all auditory tissues during postnatal days 13, 14, and 15. The lateral wall tissues, which are non-sensory and non-neuronal, also increased deoxyglucose uptake following acoustic stimulation in a manner that paralleled the uptake by the sensory structures. Serum radioactivity and glucose levels remained unchanged during postnatal development, with these parameters remaining stable with acoustic stimulation.

Acoustic Stimulation↗
PubMed1986

Non-enzymatic glycation of human albumin does not alter its palmitate binding.

The study described here makes use of a new technique to assess the level of non-enzymatic glycosylation (glycation) by purified radioactively labelled glucose. Glycation up to 3 molglc/mol protein of human serum albumin, in contrast to previous reports, did not affect the binding of up to 2 mol palmitate, which was reached at a ratio of 7.5 palmitate/HSA. The uptake of palmitate from albumin by either erythrocytes or HL-60 cells also was not influenced by glycation of 3 mol glucose/mol protein. The distribution of palmitate into neutral lipids, phospholipids, or the palmitate designated for oxidation was likewise not influenced. This suggests that levels of albumin glycation likely to be encountered in the blood of diabetic subjects (up to 1 molglc/mol HSA) do not affect fatty acid utilization.

Biological Transport, Active↗
PubMed1985

Gastric emptying and pancreatic polypeptide response to carbohydrate meals.

This study examined pancreatic polypeptide responses to isocaloric meals of radioactively labeled glucose or starch in six normal and seven vagotomized subjects. Liquid glucose meals were ingested with the subject both erect and supine and starch meals were ingested in the upright posture as a solution and as solid balls. In normal subjects, each meal left the stomach at a similar rate and the resultant pancreatic polypeptide responses were not significantly different from one another. Emptying rates varied markedly in vagotomized subjects depending upon the physical consistency of the carbohydrate ingested and the patient's posture. Despite these differences, pancreatic polypeptide responses to each meal were almost identical. These studies demonstrate that the pancreatic polypeptide response to carbohydrate meals is still present several years after vagotomy and is unaffected by alterations in the rate of gastric emptying after vagotomy and by the physical consistency and chemical nature of the carbohydrate ingested.

Adult↗
PubMed2007

Thiamine attenuates the hypertension and metabolic abnormalities in CD36-defective SHR: uncoupling of glucose oxidation from cellular entry accompanied with enhanced protein O-GlcNAcylation in CD36 deficiency.

BACKGROUND AND OBJECTIVES: The spontaneous hypertensive rat (SHR) is a widely studied model of hypertension that exhibits metabolic abnormalities, which share features with the human metabolic syndrome. Genetic linkage studies have revealed a defective CD36 gene, encoding a membrane fatty acid (FA) transporter, in hyperinsulinemia of the SHR. However, there is no unifying mechanism that can explain these phenotypes as a consequence of a defective CD36 gene. Impaired fatty acid uptake is compensated by increased glucose uptake. We hypothesized that (1) the abundant intracellular glucose is not oxidized proportionally and (2) the correction of the uncoupling of glucose oxidation to its cellular entry might be effective against the pathophysiology of CD36-defective SHR. Therefore, we attempted to activate glucose oxidation with the repletion of thiamine, a coenzyme for multiple steps of glucose metabolism. METHODS AND RESULTS: In one series of experiments, intracellular glucose fate was assessed by the ratio of [(14)C]glucose/[(3)H]deoxyglucose radioactivity, which suggested that glucose oxidation was uncoupled from its cellular entry in SHR. Protein O-GlcNAcylation was intense in the hearts of CD36-defective SHR compared with that of wild-type CD36 rats [Wister Kyoto rats (WKY)], indicating the shunt of glucose through the hexosamine biosynthetic pathway (HBP). In another series of studies, 4-week-old SHR were maintained with water containing 0.2% thiamine for 10 weeks. Systolic blood pressure, plasma insulin and norepinephrine levels were significantly lower in the thiamine-group, as compared with the untreated-group. In epididymal adipose tissue, thiamine repletion down-regulated the expression levels of mRNA transcripts for UDP-N-acetylglucosamine:peptide glycosyltransferase, angiotensinogen, angiotensin type 1 receptor, transforming growth factor-beta1 and plasminogen activator inhibitor-1. CONCLUSIONS: The hearts of CD36-defective SHR exhibited uncoupling of glucose oxidation from its cellular entry, accompanied with the enhanced protein O-GlcNAcylation, suggesting increased glucose shunt through the HBP. Thiamine repletion in CD36-defective SHR resulted in (1) the correction of the uncoupling of glucose oxidation to its cellular entry, concomitant with reduced protein O-GlcNAcylation, (2) the down-regulation of the expression of mRNAs involved in HBP, the renin-angiotensin system and adipokines in epididymal adipose tissue, and (3) the attenuation of the hypertension and hyperinsulinemia. We propose that interventions targeting glucose oxidation with thiamine repletion may provide a novel adjunctive approach to attenuate metabolic abnormalities and related hypertension.

Acetylglucosamine↗
PubMed1976

Impaired ganglioside synthesis in rat liver after D-galactosamine administration in vivo.

D-Galactosamine reduces the hepatic content of uridine phosphates, UDP-galactose, and UDPglucose due to an accumulation of UDP-amino sugars; this deficiency can result in severe hepatocellular damage. Alterations of glycosphingolipid synthesis in the early phase of this pathogenic process were studied by measurements of the incorporation of labeled galactose into glycosphingolipids of rat liver. [1-14C]Galactose was injected 2 h after galactosamine administration and the specific radioactivities of the glycosphingolipid precursors, UCPgalactose and UDPglucose, were determined. The specific radioactivity of UDPgalactose, when integrated over the whole period of radioactive synthesis, was four times higher in the galactosamine-treated animals than in the controls; the corresponding ratio of UDPglucose was 0.85. The pattern of the glycosphingolipids isolated from the livers of normal and galactosamine-treated rats resembled that described by Siddiqui and Hakomori (1970, Cancer Res. 30, 2930-2936); GL1, GM3,GM1, GD1, and a small amount of GT could be characterized. The specific radioactivities of glucose and galactose obtained from individual glycosphingolipids were determined in normal and galactosamine-treated livers. The synthesis of the glycosphingolipids was calculated using the respective data of the UDPhexoses. The labeling of glucosylceramide (GL1) was not altered and only a small change of GM3 could be detected; the synthesis of gangliosides GM1 and GD1, however, was inhibited by 95% or more between 4 and 6 h after galactosamine administration.

Animals↗
PubMedDate not supplied

Extraction of radioactive rubidium and D-glucose from the artificially perfused intervillous space of the human placenta.

Extraction (Et) of 86Rb and [14C]D-glucose from the artificially perfused intervillous space of the human placenta was measured using [3H]L-glucose as a reference tracer. E. of 86Rb increased slowly from initial values near zero to a late maximum, which indicates that Et was greatly influenced by heterogeneity of indicator transit times through the intervillous space. The ascending part of the plot of -1n(I-Et) against time (t) of 86Rb was approximately linear. In each experiment the time corresponding to zero extraction was estimated by linear extrapolation of the plot. The mean of the times obtained in the individual experiments corresponded to the most frequent transit time of the indicators through the system outside the placenta. These observations suggest that 86Rb is taken up by the trophoblast from the entire space perfused. Under such conditions the rate of the trophoblast uptake can be estimated from the slope of the above plot. Unlike that of 86Rb, Et of [14C]D-glucose increased rapidly to a relatively steady level. This time course of Et may result from combined effects of transit time heterogeneity and rapid back-flux of the tracer.

Biological Transport, Active↗
PubMed1981

A continuous assay method for glycogen synthesis from UDPglucose.

A light scattering assay was developed for continuous monitoring of glycogen synthesis from UDPglucose. A close linear correlation between light-scattering signal and the amount of radioactively labelled glucose incorporated into glycogen suggests that the scattering signal is determined by the average molecular weight of the glycogen molecules. The method has the advantage of continuity, and it is suitable to follow the time course of the reaction at different conditions and to determine the initial rate of glycogen synthesis in a relatively simple and fast way. The possibility of measurement of glycogen synthase activity in muscle extracts was also tested.

Animals↗
PubMed1990

Continuous synthesis of glycogen by individual worm pairs of Schistosoma mansoni inside the veins of the final host.

Hamsters infected with Schistosoma mansoni were operated upon to install a permanent canula into their blood stream. After recovery of the hamster, this canula was used for the injection of radioactively labelled glucose. In this way the glycogen metabolism of S. mansoni could be studied while the parasites remained undisturbed in their natural habitat. The consecutive injection of [U-14C]glucose and [1-3H]glucose permitted an analysis of possible changes in the glycogen synthesis of individual worm pairs with time. The results showed that the synthesis of glycogen by each worm pair was fairly constant with time. Furthermore, all individual worm pairs synthesised glycogen continuously; not even 2 min passed without its formation. Only small differences in glycogen synthesis were observed between parasites isolated from different locations in the veins of the hamster. These results exclude the possibility that the worm pairs had alternating periods of glycogen synthesis and degradation, and they also disprove the idea that synthesis and degradation occur at two different sites in the bloodstream of the hamster. The experiments further showed that glycogen synthesis was proportional to the amount of glycogen already present, which in turn was shown to be proportional to the size of the parasite. From this study it can be concluded that the replenishment of the endogenous glycogen reserves of S. mansoni is not induced by a marked decrease in the glycogen levels, but occurs slowly and continuously.

Animals↗
PubMed1976

Interactions of glucagon and fructose in the control of glycogenolysis in perfused rat liver.

By measuring the specific radioactivity of glucose released from isolated perfused livers of normal, fed rats in the presence of [U-14C]fructose, the gluconeogenetic and glycogenolytic contributions to glucose production were estimated. After 20 min of perfusion with 4 mM fructose, glycogenolysis was inhibited by 40% in the absence and by 70% in the presence of glucagon (3 nM). Glucagon decreased the release of lactate plus pyruvate and enhanced glucose formation from fructose without affecting its uptake. Glycerol (4 mM) and xylitol (3 mM) had qualitatively similar, but smaller effects on glucagon-stimulated glycogenolysis. The glucagon-mediated phosphorylase b to a conversion was not altered by fructose, indicating that glycogenolysis was decreased as a consequence of an inhibition of phosphorylase a. During the first minutes after the addition of fructose, decreased ATP/AMP ratios and tissue Pi levels correlated with a transient increase of phosphorylase a activity. It was concluded that the effects of fructose on the control of hepatic glycogenolysis and glucose production were the result of a complex interplay between a transient b to a conversion of phosphorylase and an inhibition of the a-form of the enzyme, possibly by fructose 1-phosphate and other phosphorylated metabolites.

Animals↗
PubMed1985

Isolation and quantitation of carbohydrates in sheep plasma by high-performance liquid chromatography.

The application of ultraviolet detection at 190 nm following chromatography on a Ca2+ cation-exchange column with a mobile phase of water enables the low amounts of carbohydrates present in plasma to be quantitated. The separation and quantitation of carbohydrates in maternal and fetal sheep plasma and amniotic fluid are described, as is the application of this method to the determination of specific radioactivities of glucose and fructose in plasma.

Amniotic Fluid↗