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At least 199 records · Page 11Linked to original sources
PubMed1965

[Metabolism of C(14)-glucose by Paramphistomum cervi]

The trematode Paramphistomum cervi empolyed in this experiment was obtained from the reticulum of cattle slaughtered at the local abbatoir. The worms were selected and washed several times in normal sterilized saline solution. Each about ten of intact worms were incubated in 50 cc volume of special incubation flasks with incubation mixture consisting of 50 cc of Krebs-Ringer phosohate buffer (pH 7.4) to which were added universally labeled C(14)-glucose and non-radioactive carrier glucose concentration of 200 mg per cent. The worms were allowed to incubate for 3 hours in the incubator at 38 degrees C. After incubation period, respiratory CO2 samples from central wall of incubation flask were analysed for total CO2 production rate and their specific activity of respiratory CO2. Glycogen samples isolated from worms were analysed for the tissue concentration and their radioactivities in order to determine the turnover rate of glycogen pool. 1. The glucose uptake rate was determined by analysing the difference of the glucose concentration in a medium before and after incubation period. Radioactivities of these series of experiments were counted by an endwindow Geiger-Muller counter as an infinitely thin samples. The quantitative analysis of C(14)-glucose utilized by Paramphistomum cervi was summerized as the following. The glucose uptake rate by Paramphistomum was a mean value of 2.32 +/- 0.27 micro M/hr/g of wet wt. and total CO2 production rate by the worms averaged 10.85 +/- 0.41 micro M/hr/g of wet wt. The relative specific activities of respiratory CO2 averaged 49.72 +/- 13.20 per cent. Thus, a mean of 49.72 per cent of total CO2 production rate was originated from the glucose in the medium, therefore the rate of CO2 production derived from medium glucose was mean of 5.24 +/- 2.16 micro M/hr/g of wet wt. Thus, the average value of 37.46 +/- 5.28 per cent of glucose utilized by the worms from the medium glucose was oxidized to respiratory CO2. 2. The tissue concentration of Paraphismum was a mean of 41.56 +/- 5.82 micro M/hr/g of wet wt or 4.16 +/- 0.72 %/g, and the turnover rate of glycogen pool yielded with a mean of 0.12 +/- 0.014 %/hr or 0.06 +/- 0.04 mg/hr/g of wet wt. Therefore, a mean value of 16.75 +/- 4.84 per cent of glucose was incorporated to the glycogen. 3. These data account for that at least 54.21 per cent of the utilized glucose by the worms participated in furnishing the oxidation into respiratory CO2 and the synthetic process into glycogen. According to the above data of the experiment, it is suggested in the metabolic process of glucose by the Paramphistomum that the synthetic process into the glycogen is less active than the oxidative process into the resppiratory CO2.

Journal Article↗
PubMed1984

Glucose induced inhibition of radioactive nucleotide efflux from mouse pancreatic islets is dissociated from an increase in islet oxygen uptake.

Glucose at 1.7 and 5.6 mmol/l, pyruvate (30 mmol/l) and glutamine (10 mmol/l) all stimulated islet respiration slightly. More marked stimulation was achieved with glucose 8.3 mmol/l. When pyruvate (30 mmol/l) was added to islets respiring in the presence of different concentrations of glucose (1.7, 3.3 or 5.6 mmol/l), a stimulatory effect was only observed at the highest glucose concentration. Stimulation of islet oxygen uptake was also achieved when glucose 8.3 (but not 5.6) mmol/l was added to islets respiring in glutamine 10 mmol/l. Radioactive nucleotide efflux was, however, progressively inhibited by increasing the glucose concentration up to 5.6 mmol/l both in the absence or presence of glutamine 10 mmol/l. It is concluded that the glucose-induced inhibition of radioactive nucleotide efflux is not obligatorily linked to respiration.

Adenine Nucleotides↗
PubMed1965

[Metabolism of C(14)-glucose by Ascaridia galli]

The fowl nematode Ascaridia galli employed in this experiment was obtained from the intestine of domestic fowls at the local market. The worms selected and washed several times in normal sterilized saline solution. Each about thirty of intact worms were incubated in 50 cc volume of special incubation flasks with incubation mixture consisting of 10 cc of Krebs-Ringer phosphate buffer (pH 7.4) to which were added universally labeled C14-glucose and non-radioactive carrier glucose so as to contain concentration of 200 mg per cent. The worms were allowed to incubation for 3 hours in Dubnoff metabolic shaking incubator at 38 degrees C. After incubation period, respiratory CO2 samples from central well of incubation flask were analysed for total CO2 production rate and their specific activity of respiratory CO2. Glycogen samples isolated from worms were analysed for uptake rate was determined by analyzing the difference of the glucose concentration in a medium before and after incubation period. Radioactivities of these series of experiments were counted by an endwindow Geiger-Muller counter as an infinitely thin samples. The quantitative analysis of C(14)-glucose utilized by Ascaridia galli was summarized as the following. 1. The glucose uptake rate by A. galli was a mean value of 1.73 +/- 0.32 micro M/hr/g of wet wt. and total CO2 production rate by the worms averaged 8.44 +/- 1.11 micro M/hr/g of wet wt. The relative specific activity of respiratory CO2 (R.S.A CO2) averaged 2.68 +/- 0.38 per cent. Thus, a man of 2.68 per cent of total CO2 production rate was originated from the glucose in the medium, therefore the rate of CO2 production derived from medium glucose was a mean of 0.23 +/- 0.03 micro M/hr/g of wet wt. Thus, the average value of 2.58 +/- 0.55 percent (R.G.D CO2)of glucose utilized by the worms from the medium glucose was oxidized to respiratory CO2. 2. The tissue concentration of glycogen in A. galli was a mean of 22.59 +/- 1.18 mg per gram of wet wt or 2.26 +/- 0.123 percent per gram, and the turnover rate of glycogen pool yielded with a mean of 0.17 +/- 0.04 percent per hour or 0.037 +/- 0.006 miligram per hour per gram of wet wt. Therefore, a mean value of 16.37 +/- 4.04 per cent (R.G.D gly) of glucose was incorporated to the glycogen. 3. These data account for that at least 18.95 per cent of the utilized glucose by the worms participated in furnishing the oxidation into respiratory CO2 and the synthetic process into glycogen. According to the above data of the experiment, it is suggested in the metabolic process of glucose by Ascaridia galli that the synthetic process into the glycogen is more active than the oxidative process into the respiratory CO2.

Journal Article↗
PubMed1981

Radioactive 2-deoxy-D-glucose incorporation into the prefrontal and premotor cortex of the monkey performing a forelimb movement.

Radioactive 2-deoxy-D-glucose (2-DG) incorporation into the monkey prefrontal and premotor cortex was studied in relation to extention-flexion movement at the wrist joint in two experimental and two control monkeys. With 2-DG injection and 45 min' intensive task performance thereafter, the following areas showed increased accumulations of radioactive glucose: the dorsomedial and dorsolateral prefrontal areas, including the lateral and medial banks of the principle sulcus; the ventral prefrontal and orbitofrontal areas; the cingulate gyrus, and the premotor cortex. In these areas, patch- or strip-like patterns were observed in the accumulation of 2-DG.

Animals↗
PubMed1976

Effect of heart work and insulin on the incorporation of [14C]glucose into hexose phosphates, uridine diphosphate glucose and glycogen in the normal and insulin-deficient perfused rat heart under working and non-working conditions.

1. The specific radioactivities of glucose 1-phosphate, glucose 6-phosphate, fructose 6-phosphate, UDP-glucose and glycogen, derived from [14C]gluocose, were determined in the normal and insulin-deficient (streptozotocin-diabetic and anti-insulin-serum-treated) perfused non-working and working rat heart. 2. The specific radioactivities of all glucose metabolities reached a plateau after about 10 min, except that for glycogen, which increased slightly but steadily over the whole observation period of 30min. 3. The specific radio-activities of fructose 6-phosphate, UDP-glucose and glycogen were slignificantly lower in the streptozotocin-diabetic heart than in the normal heart. 4. Mechanical work in the normal rat heart increased the specific radioactivities of glucose 1-phosphate, UDP-glucose and glycogen, but had little or no effect on those of gluose 6-phosphate and fructose 6-phosphate. 5. In the normal heart insulin strongly increased the specific radioactivities of all gluocse metabolites under all conditions tested. The maximum values achieved in the normal working heart in the presence of insulin were only about 15-20% above those in the normal non-working heart in the presence of insulin for the phosphorylated intermediates and about 40% above for glycogen. 6. In the streptozotocin-diabetic heart, work restored the specific radioactivities of all glucose metabolities to about normal values. 7. In the streptozotocin-diabetic heart insulin strongly increased the specific radioactivities of the direct glycogen precursors glucose 1-phosphate and UDP-glucose; the effect of insulin on glucose 6-phosphate and fructose 6-phosphate was less marked. These results confirm previous findings that the primary metabolic lesion in diabetic heart muscle is a defect of glycogen synthesis. The specific radioactivity of glycogen itself was increased sixfold. 8. Under all conditions tested the specific radioactivity of glucose 1-phosphate was always found to be higher than that of glucose 6-phosphate. This indicated either compartmentation of a small but metabolically very active pool of glucose 6-phosphate, or the existence of a hitherto unknown pathway of metabolism in which glucose 1-phosphate is the primary reaction product. For a number of reasons the authors prefer the first explanation, which could also account for the observation that in the perfused normal working and non-working heart the specific radioactivity of fructose 6-phosphate was always found to be higher than that of glucose 6-phosphate. This difference disappeared or was reversed in the rat hearts rendered insulin-insufficent by either streptozotocin or anti-insulin treatment.

Animals↗
PubMed1979

The reliability of rates of glucose appearance in vivo calculated from single tracer injections.

The rate of appearance of unlabelled glucose was calculated from changes in plasma glucose specific radioactivity after a single intravenous injection of labelled glucose and compared with the actual constant infusion rate of unlabelled glucose into an anaesthetized dog with all sources of endogenous glucose production surgically removed. The mean steady-state rate of appearance of unlabelled glucose calculated from the area under the specific radioactivity versus time curve was 7% higher than the actual infusion rate (n = 4), but the difference was not statistically significant. The variability in the rate calculated in this manner was, however, greater than the variability we have reported with rates determined from a primed constant infusion of tracer. Using 15- to 60- or 60- to 120-min specific radioactivity data the mean rate of appearance of glucose, calculated on the assumption of a one-pool model for glucose turnover in vivo, was approximately 60% higher than the actual infusion rate. The results also indicate that it is possible to construct multi-pool models, but it is difficult to equate specific physiological events with the individual terms of the multi-experimental equation which describes the changes in plasma glucose specific radioactivity.

Animals↗
PubMed1977

The influence of diurnal rhythms of carbohydrate metabolism in adult rat liver on the metabolic characteristics of isolated liver parenchymal cells.

Rats trained to the "8 + 16" controlled feeding cycle where food is only available for the first 8 h of the 12 h dark period exhibit a pronounced diurnal rhythm of hepatic glycogen metabolism. Glycogen is stored within the liver parenchymal cells during the dark period and subsequently mobilized for energy production during the light period. Hepatocytes, isolated by collagenase perfusion, from livers of such animals have differing capacities for glycogen synthesis when incubated with glucose. Cells prepared at the end of the 16 h period without food have very little capacity for synthesis compared with much higher rates obtained in cells obtained during the feeding period. Cells obtained from liver containing a large glycogen concentration produce a net breakdown of glycogen during incubations with glucose, however experiments using radioactively labelled glucose indicate that synthesis does occur in these cells. The changes in the capacity of the cells for glycogen synthesis appear to be due, in part, to changes in the percentage of the cell population involved in synthesis and in the activity of glycogen synthetase a. Attempts of influence the rate of glycogen synthesis at any time of day with insulin or dexamethasone were unsuccessful.

Animals↗
PubMed1990

Principles of the 2-deoxyglucose method for the determination of the local cerebral glucose utilization.

Sokoloff and co-workers developed the 2-deoxy-D-[1-14C]glucose (2DG) method in order to study the local cerebral glucose utilization (LCGU) of discrete brain regions in vivo. Energy metabolism of the adult mammalian brain is almost entirely dependent on glucose. The majority of the glucose taken up by the brain is needed for the maintenance of the membrane potentials and the electrical activity. The functional activity could thus be shown to be closely linked to energy metabolism. Consequently, examination of the energy metabolism by measuring the cerebral metabolic rate for glucose can provide information concerning functional activity in all of the neuroanatomically defined regions of the brain. Studying the fate of experimentally injected 2-deoxy-D-[1-14C]glucose, a radioactive labeled analogue of glucose, and, subsequently, employing quantitative autoradiographic techniques, it is possible to estimate the levels of the local cerebral glucose utilization in specific regions of the brain. According to Sokoloff (1982) the LCGU represents a "metabolic encephalography".

Animals↗
PubMed1994

Glucose- and ADPGlc-dependent starch synthesis in isolated cauliflower-bud amyloplasts. Analysis of the interaction of various potential precursors.

Recently, we have demonstrated that isolated cauliflower-bud amyloplasts incorporate glucose 6-phosphate at high rates into newly synthesized starch (Neuhaus et al. (1993) Plant Physiol. 101, 573-578). Here we have analyzed the incorporation of radioactively labeled glucose and ADPglucose into newly synthesized starch. It could be shown that glucose incorporation into starch exhibits a typical substrate saturation behaviour and is linear with time for at least 40 min. The incorporation of glucose is strongly dependent upon the intactness of the plastids and upon the presence of both, ATP and 3-phosphoglyceric acid. Using 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) we showed that glucose is taken up into isolated cauliflower-bud amyloplasts as the free glucose molecule, rather than as glucose 6-phosphate. Glucose incorporation into newly synthesized starch is strongly inhibited in the presence of low concentrations of glucose 6-phosphate. The radioactively labeled glucose moiety of ADPglucose is also incorporated into starch. This incorporation can be saturated at increased concentrations of ADPglucose. ATP significantly inhibits the incorporation of the glucose moiety of ADPglucose into starch. This inhibition can be reinforced by the additional presence of glucose 6-phosphate. Glucose 6-phosphate-dependent starch synthesis is not strongly inhibited in the presence of glucose or ADPglucose indicating that glucose 6-phosphate is the precursor for starch synthesis in isolated cauliflower-bud amyloplasts.

Adenosine Diphosphate Glucose↗
PubMed1990

Underestimation of glucose turnover corrected with high-performance liquid chromatography purification of [6-3H]glucose.

We have recently reported that during infusion of commercially available [6-3H]glucose, a radioactive nonglucose contaminant may accumulate in plasma causing errors in the measurement of glucose turnover. To determine whether purification of this tracer by HPLC (high-performance liquid chromatography) before infusion would eliminate the contaminant in plasma and remove the underestimation of glucose turnover reported during hyperinsulinemia, four normal subjects each underwent two 5-h euglycemic clamps during infusion of insulin (1 mU.kg-1.min-1). Glucose turnover was measured with either commercially available [6-3H]glucose or with HPLC-purified [6-3H]glucose. HPLC analysis of samples from the clamps done with commercially available [6-3H]glucose showed that 9.7% of the infused tracer and 26% of the "plasma glucose 3H radioactivity" were contaminants. In contrast, no contaminant was observed in the plasma during infusion of HPLC-purified [6-3H]glucose. During the last hour of the clamp, mean glucose turnover using commercially available [6-3H]glucose was less (P less than 0.01) than the mean glucose infusion rate (7.6 +/- 0.3 vs. 10.5 +/- 0.3 mg.kg-1.min-1) yielding apparent "negative" (P less than 0.001) hepatic glucose release. In contrast, when HPLC-purified [6-3H]glucose was employed, glucose turnover equaled the glucose infusion rate (10.4 +/- 0.9 vs. 10.2 +/- 0.9 mg.kg-1.min-1) and hepatic glucose release was no longer negative. We conclude that removal of a tritiated nonglucose contaminant in [6-3H]glucose by HPLC yields correct estimations of glucose turnover at steady state.

Adult↗
PubMed1967

Contribution of propionate to glucose synthesis in sheep.

1. The production rate of propionate in the rumen and the entry rate of glucose into the body pool of glucose in sheep were measured by isotope-dilution methods. Propionate production rates were measured by using a continuous infusion of specifically labelled [(14)C]propionate. Glucose entry rates were estimated by using either a primed infusion or a continuous infusion of [U-(14)C]glucose. 2. The specific radioactivity of plasma glucose was constant between 4 and 9hr. after the commencement of intravenous infusion of [U-(14)C]glucose and between 1 and 3hr. when a primed infusion was used. 3. Infusion of [(14)C]propionate intraruminally resulted in a fairly constant specific radioactivity of rumen propionate between about 4 and 9hr. and of plasma glucose between 6 and 9hr. after the commencement of the infusion. Comparison of the mean specific radioactivities of glucose and propionate during these periods allowed estimates to be made of the contribution of propionate to glucose synthesis. 4. Comparisons of the specific radioactivities of plasma glucose and rumen propionate during intraruminal infusions of one of [1-(14)C]-, [2-(14)C]-, [3-(14)C]- and [U-(14)C]-propionate indicated considerable exchange of C-1 of propionate on conversion into glucose. The incorporation of C-2 and C-3 of propionate into glucose and lactate indicated that 54% of both the glucose and lactate synthesized arose from propionate carbon. 5. No differences were found for glucose entry rates measured either by a primed infusion or by a continuous infusion. The mean entry rate (+/-s.e.m.) of glucose estimated by using a continuous infusion into sheep was 0.33+/-0.03 (4) m-mole/min. and by using a primed infusion was 0.32+/-0.01 (4) m-mole/min. The mean propionate production rate was 1.24+/-0.03 (8) m-moles/min. The conversion of propionate into glucose was 0.36 m-mole/min., indicating that 32% of the propionate produced in the rumen is used for glucose synthesis. 6. It was indicated that a considerable amount of the propionate converted into glucose was first converted into lactate.

Animals↗
PubMed1980

Nonenzymatic glycosylation of proteins. A warning.

Radioactively labeled glucose from several manufacturers contains radioactive impurities of to date unknown structure. These contaminants bind covalently to proteins, e.g. collagen, fibronectin, basic myelin protein, bovine serum albumin, and hemoglobin, and thus simulate nonenzymatic glycosylation.

Animals↗
PubMed1987

Metabolites of 2-deoxyglucose in rat brain at 12-24 h: bounds on kinetic constants.

Activities of 2-deoxy-D-glucose and its metabolites in rat brain were examined at 12, 16, 20, and 24 h after intraperitoneal injection of 14C-labeled 2-deoxy-D-glucose. Plasma radioactivity was monitored for 2 h before each of these determinations. As proportion of total brain radioactivity, 2-deoxy-D-glucose decreased monotonically from the unexpectedly high value of 22% at 12 h to 11% at 24 h after injection, 2-deoxy-D-glucose 6-phosphate decreased monotonically from 69% at 12 h to 23% at 24 h, and unphosphorylated products (of high and low molecular weight) increased from 10% at 12 h to 64% at 24 h. The data were analyzed in terms of a four-compartment model. Secure lower and upper bounds on the rate constant, k4*, for the dephosphorylation of 2-deoxy-D-glucose 6-phosphate were established: k4* was at least 0.0158 +/- 0.0014 . min-1 and at most 0.0385 +/- 0.0037 . min-1. If k4* is constant in time, then appreciable dephosphorylation occurs within the 45-min experimental period commonly used in the standard 2-deoxy-D-glucose method for estimating local cerebral glucose utilization. The possibility that the effective k4* is lower at such early times is reviewed in the light of a reanalysis of previously published data. Implications of these results for the 2-deoxy-D-glucose method are discussed from the points of view of numerical analysis and capillary heterogeneity.

Animals↗