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PubMed1978

Glycogen synthesis in the fungus Neurospora crassa.

An enzymic activity, obtained from Neurospora crassa, catalyzing the incorporation of [14C]glucose from ADP-[14C]glucose into a glucan of the glycogen type, is described. The properties of the ADPglucose : glycogen glucosyltransferase as compared with those of the already known UDP glucose : glycogen glucosyltransferase were studied. The radioactive products obtained with UDP-14C]glucose or ADP-[14C]glucose released all the radioactivity as maltose after alpha or beta amylase treatment. Glucose 6-phosphate stimulated the synthetase when UDP-[14C]glucose was the substrate but the stimulation was much greater with ADP-[14C]glucose as glucosyl donor. Glucose 6-phosphate plus EGTA gave maximal stimulation. The system was completely dependent &on the presence of a 'primer' of the alpha 1 leads to 4 glucan type.

Adenosine Diphosphate Glucose↗

PubMed1972

Glucose metabolism in the developing rat. Studies in vivo.

1. The specific radioactivity of plasma d-glucose and the incorporation of (14)C into plasma l-lactate, liver glycogen and skeletal-muscle glycogen was measured as a function of time after the intraperitoneal injection of d-[6-(14)C]glucose and d-[6-(3)H]glucose into newborn, 2-, 10- and 30-day-old rats. 2. The log of the specific radioactivity of both plasma d-[6-(14)C]- and d-[6-(3)H]-glucose of the 2-, 10- and 30-day-old rats decreased linearly with time for at least 60min after injection of labelled glucose. The specific radioactivity of both plasma d-[6-(14)C]- and d-[6-(3)H]-glucose of the newborn rat remained constant for at least 75min after injection. 3. The glucose turnover rate of the 30-day-old rat was significantly greater than (approximately twice) that of the 2- and 10-day-old rats. The relative size of both the glucose pool and the glucose space decreased with age. Less than 10% of the glucose utilized in the 2-, 10- and 30-day-old rats was recycled via the Cori cycle. 4. The results are discussed in relationship to the availability of dietary glucose and other factors that may influence glucose metabolism in the developing rat.

Age Factors↗

PubMedDate not supplied

Evidence for blood myo-inositol as a source of the epididymal secretion in the perfused cauda epididymidis of the rat.

The movement of radioactive inositol and glucose across the epididymal epithelium have been studied by perfusion of fluid, which has the major electrolyte compositions resemble those in the native epididymal fluid, through the lumen of a sperm free tubule of the distal cauda epididymidis of intact and nephrectomized rats. During intravenous infusion of (3H)-myo-inositol into the intact rats, labelled myo-inositol and its metabolites entered the lumen. However, only labelled inositol was found in the luminal perfusate when radioactive inositol was infused into the nephrectomized rat. On the other hand, after infusion of (14C)-glucose no trace of labelled inositol appeared in the lumen. Instead, the luminal radioactivity could be accounted for by labelled glucose. The results indicate that the myo-inositol present in the luminal fluid of the rat cauda epididymidis originates, in part, from blood inositol and, in part, from blood glucose.

Animals↗

PubMed1998

Metabolic labeling of a subset of glial cells by UDP-galactose: implication for astrocyte lineage diversity.

Astrocytes are implicated in many aspects of brain function; however, it remains unclear whether astrocytes arise from a single cell lineage. It is therefore important to obtain new markers for the astrocyte cell lineage. We show that exogenously added UDP-galactose (UDP-Gal) can be used to metabolically label a subset of glial fibrillary acidic protein-positive (GFAP+) cells. UDP-Gal was incorporated into the cultured embryonic mouse brain slices in a time-dependent manner. Surprisingly, the transferred sugar moiety was no longer Gal but was mainly glucose. Most of the radioactivity was transferred to a polymer of glucose, most likely to be glycogen, and also to glucosyl ceramide. In the slice culture, the reaction products were distributed densely in the ventricular zone and also on process-like structures extending to the pial surface. In dissociation culture, UDP-Gal labeled some of the GFAP+ cells and some of the vimentin+ cells. Because radial glial cells (RGCs) contain glycogen and change from vimentin+ to GFAP+, it is strongly suggested that UDP-Gal labeled RGCs and their descendants. Only 27% of the GFAP+ cells were labeled with UDP-Gal, which suggests that only a subset of astrocytes are derived from RGCs and that there is a discrete group of GFAP+ cells that is not generated from RGCs.

Animals↗

PubMed1978

Different effects of the ionophore A-23187 and D-glucose on 45Ca2+ fluxes in isolated islets of ob/ob-mice.

Fluxes of 45Ca2+ were studied in beta-cell rich islets of non-inbred ob/ob-mice, using LaCl3 to wash out extra-cellular and superficially bound 45Ca2+. The ionophore A-23187 (10 microM) increased the 45Ca2+ uptake in islets both at 3 and 20 mM D-glucose, the effect being more pronounced after 10 min than after 120 min of incubation. In incubations for 120 min, 20 mM D-glucose induced a higher uptake of 45Ca2+ than did A-23187. The ionophore enhanced the unidirectional efflux of 45Ca2+ from preloaded islets. Pretreatment of islets with 20 mM D-glucose in non-radioactive medium inhibited the subsequent D-glucose-induced 45Ca2+ uptake. Similar pretreatment with A-23187 increased the subsequent ionophore-induced 45Ca2+ uptake. The results suggest that A-23187 acts by catalyzing Ca2+ fluxes across the beta-cell plasma membrane. The different effects of D-glucose and A-23187 on 45Ca2+ fluxes suggest that the two agents act through different mechanisms in the beta-cells.

Animals↗

PubMed1968

Metabolism of carbohydrates by Pasteurella pseudotuberculosis.

Cell-free extracts of Pasteurella pseudotuberculosis and P. pestis catalyzed a rapid and reversible exchange of electrons between pyridine nucleotides. Although the extent of this exchange approximated that promoted by the soluble nicotinamide adenine dinucleotide (phosphate) transhydrogenase of Pseudomonas fluorescens, the reaction in the pasteurellae was associated with a particulate fraction and was not influenced by adenosine-2'-monophosphate. The ability of P. pseudotuberculosis to utilize this system for the maintenance of a large pool of nicotinamide adenine dinucleotide phosphate could not be correlated with significant participation of the Entner-Doudoroff path or catabolic use of the hexose-monophosphate path during metabolism of glucose. As judged by the distribution of radioactivity in metabolic pyruvate, glucose and gluconate were fermented via the Embden-Meyerhof and Entner-Doudoroff paths, respectively. With the exception of hexosediphosphatase, all enzymes of the three paths were detected, although little or no gluconokinase or phosphogluconate dehydrase was present unless the organisms were cultivated with gluconate. The significance of these findings is discussed with respect to the regulation of carbohydrate metabolism in the pasteurellae, related enteric bacteria, and P. fluorescens.

Carbon Isotopes↗

PubMed2004

Insulin-mimetic vanadyl(IV) complexes as evaluated by both glucose-uptake and inhibition of free fatty acids (FFA)-release in isolated rat adipocytes.

We have recently proposed the existence of some potent vanadyl complexes with blood glucose-lowering activity in experimental diabetic animals based on the results of an in vitro FFA (free fatty acids)-release assay in isolated rat adipocytes treated with epinephrine and evidence of an in vivo blood glucose lowering effect in experimental diabetic animals. However, the FFA assay depends indirectly on the glucose-uptake of vanadyl complexes in adipocytes. It is therefore necessary to develop a more reliable in vitro glucose-uptake assay, in place of the glucose uptake method using radioactive compounds such as (14)C-glucose, to identify insulin-mimetic vanadyl complexes. In the present study, we proposed a combined in vitro assay by using the conventional glucose oxidase method for glucose-uptake and FFA assay in isolated rat adipocytes. Insulin, vanadyl sulfate (VOSO(4)), bis(picolinato)vanadyl (VO(pa)(2)), and bis(6-methylpicolinato)vanadyl (VO(6mpa)(2)) complexes exhibited concentration-dependent uptake of (+)-D-glucose and inhibition of FFA release in the adipocytes treated with epinephrine. Vanadyl complexes were found to accelerate glucose-uptake at lower concentrations than VOSO(4). In vitro high insulin-mimetic activity of VO(pa)(2) and VO(6mpa)(2) were thus indicated by both glucose-uptake and FFA-release, with the insulin-mimetic activity of VO(6mpa)(2) being higher than that of VO(pa)(2), as suggested by the partition coefficient (0.330 for VO(pa)(2) and 0.595 for VO(6mpa)(2)). The proposed assay provides a more reliable method than each single method for the evaluation of in vitro insulin-mimetic activity of compounds.

Adipocytes↗

PubMed1973

The disorder of hyaluronic acid metabolism in cultured skin fibroblasts derived from a patient with the Hurler syndrome.

The metabolism of hyaluronic acid in cultured skin fibroblasts derived from a patient with the Hurler syndrome and from a normal subject was examined. 1. An increased net incorporation of [(3)H]glucose into the hyaluronic acid fraction of the Hurler-syndrome cells occurred when compared with normal cells. 2. During a ;chase' period, approx. 35% of the radioactivity derived from glucose was lost from the hyaluronic acid fraction of the Hurler-syndrome cells, whereas the normal cells retained all their radioactivity. 3. Although the Hurler-syndrome cells contained a ninefold greater amount of hyaluronic acid than normal cells, simultaneous determination of the specific radioactivity derived from the label revealed a value for the Hurler-syndrome cells one-half that of normal cells. These results are taken to indicate that the Hurler cells synthesize hyaluronic acid de novo at a higher rate than do normal cells. 4. Exposure of Hurler-syndrome cultured fibroblasts to a crude urine corrective-factor preparation (Neufeld & Cantz, 1971), now known to contain alpha-l-iduronidase, the specific Hurler-syndrome corrective factor (Bach et al., 1972), decreased the hyaluronic acid content to near-normal values before any effect was observed on [(3)H]glucose incorporation into the hyaluronic acid fraction. 5. In addition, the hyaluronic acid content of the normal cells decreased after exposure to the corrective factor of urine. 6. The mobilization of hyaluronic acid in Hurler-syndrome and normal cells exposed to the crude corrective-factor preparation of urine caused a decrease in specific radioactivity in the ;corrected' Hurler-syndrome cells and an increase in specific radioactivity in the ;corrected' normal cells.

Biological Transport↗

PubMed2003

[Positron emission tomography in oncology].

Positron emission tomography (PET) has been developed to visualize biochemical and physiological phenomena in living humans. Blood flow, blood volume, glucose metabolism, amino acid metabolism, neural transmission system functions can be quantitatively estimated by means of PET with various radioactive tracers. A glucose analog, 18F-fluoro-deoxy-glucose, has been utilized to evaluate glucose metabolism. The whole body PET scanner enables imaging of brain; heart, and neoplasms within an hour. Screening for cancer and evaluation of remote metastasis, recurrence, and effects of radio-chemotherapy are now performed clinically. Further development of the tracers may enable a visualization of gene expression by means of radioactive anti-sense nucleic acids. In regeneration medicine, functional recovery can be estimated by means of PET.

Adult↗

PubMed1994

Regulation of glucose transport in the NIH 3T3 L1 preadipocyte cell line by TCDD.

This study examined the changes in cellular glucose uptake induced by 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) as measured by quantification of intracellular radioactivity in the NIH 3T3 L1 preadipocyte cell line after a 30-minute incubation with the non-metabolizable radioactive analogue of glucose, 3-O-methyl-D-[1-3H] glucose. Treatment of differentiated NIH 3T3 L1 cells with TCDD produced a time- and dose-dependent decrease in the cellular uptake of glucose. Treatment of cells for 3 hr with 10(-8) M TCDD significantly reduced glucose uptake to about 10% of control values (p </= 0.05). Furthermore, cytochalasin B, a specific inhibitor of facilitative glucose transporter proteins totally abolished the portion of glucose transport activity that is sensitive to TCDD. The role of the Ah receptor in TCDD-mediated reduction in glucose uptake was investigated. Pretreatment of 3T3 L1 cells with the Ah receptor blocker 4,7-phenanthroline antagonized the effect of TCDD on glucose uptake. Structure-activity relationship studies with TCDD and two polychlorinated biphenyl (PCB) congeners revealed a rank order for their potency in the inhibition of glucose transport as follows: TCDD <<3,3',4,4' tetrachlorobiphenyl <2,2',5,5' tetrachlorobiphenyl (TCB). Such a rank order correlates both with previously determined biological activity of TCDD and the more active 3,3',4,4'- and less active 2,2',5,5'-TCB and with affinity for binding to the Ah receptor. The thyroid hormone T4, like TCDD, reduced glucose uptake and blocked the action of TCDD to further reduce glucose uptake. Experimental evidence is consistent with a proposed mechanism for TCDD to reduce the titer of functional glucose transporter proteins through its interaction with the Ah receptor.

3T3 Cells↗

PubMed1992

Absorption of Intralipid and interferences from nutrients infused into the peritoneal cavity of the rat.

We studied the peritoneal absorption and elimination of Intralipid after its intraperitoneal and intravenous infusion into rats, by means of a two-compartment model. Follow-up measurements of the plasma triglyceride rate were made. The peritoneal absorption of Intralipid gives the following absorption and elimination constants: Ka (absorption constant from the peritoneal cavity) is 0.106 +/- 0.08 h-1; Ke (elimination constant from the blood stream) is 0.0440 +/- 08 h-1; and BAa (absolute bioavailability) is 84.5 +/- 0.08% 8 hours after infusion. These results show that the intraperitoneal absorption of Intralipid is high and progressive during the first 8 hours, thus supplying the daily caloric needs of the animal through the administration of a single bolus administration, and the plasma triglyceride clearance is faster than the intraperitoneal absorption after the first 6 hours, thus avoiding dangerous overloads. We also studied the behavior of different combinations of glucose, amino acids, and fats infused into the peritoneal cavity of rats in order to observe possible interferences with the absorption of these nutrients. Two microcuries of radioactive L-glucose-1-C14 with 5 mL of 5% D-glucose, with 5 mL of 3.5% amino-acid solution, or with 5 mL of 20% fat emulsion were infused intraperitoneally into three different groups of animals. Slight differences of plasma radioactivity were registered among these three groups 1 hour after infusion. Likewise, small differences of plasma radioactivity were observed between the animals receiving an infusion of 1 microCi of five L-amino-acids-U-C14 diluted with 5 mL of 3.5% amino-acid solution, with 5 mL of 5% glucose solution, or with 5 mL of 20% fat emulsion 4 and 6 hours after infusion. No differences in the plasma triglyceride rates were observed between those groups of animals infused with 5 mL of 20% Intralipid plus 5 mL of glucose solution or with 20% Intralipid plus 3.5% amino-acid solution compared with the group receiving only 5 mL of 20% Intralipid. The infusion of fats does not seem to interfere with that of other substrates, possibly because of the different absorption route (lymphatic for fats and capillary vessels for amino acids and glucose solutions), but further research is needed to reach conclusive results. Perhaps the prolonged administration of fat, together with other substrates, produces precipitates and other galenic problems that hinder absorptive mechanisms of the preparations.

Absorption↗

PubMed1990

Effect of diet and substrate on the in vitro measurement of cholesterol and fatty-acid synthesis in hepatic tissue of Japanese quail.

A comparison of acetate, glucose, mevalonate, or water as radioactive substrates for the hepatic synthesis of cholesterol, fatty acids, and glyceride-glycerol was made in Japanese quail fed diets containing either beef fat or tuna oil. The quail fed a diet containing beef fat were fatter and had a significantly higher (P less than .01) concentration of serum cholesterol (5.6 mM per L) than that measured in the serum of quail given tuna oil (4.1 mM per L). Both in vitro cholesterol and fatty-acid synthesis were greater in the quail fed a diet of beef fat than in those fed a diet containing tuna oil. The results showed that mevalonate was the most-suitable radioactive substrate for measuring cholesterol synthesis, whereas glucose was the most-suitable radioactive substrate for measuring fatty-acid and glyceride-glycerol synthesis.

Animals↗

PubMed2003

A point mutation in the UDP-glucose pyrophosphorylase gene results in decreases of UDP-glucose and inactivation of glycogen synthase.

The regulatory role of UDP-glucose in glycogen biogenesis was investigated in fibroblasts containing a point mutation in the UDP-glucose pyrophosphorylase gene and, consequently, chronically low UDP-glucose levels (Qc). Comparisons were made with cells having the intact gene and restored UDP-glucose levels (G3). Glycogen was always very low in Qc cells. [(14)C]Glucose incorporation into glycogen was decreased and unaffected by insulin in Qc cells, whereas insulin stimulated glucose incorporation by approximately 50% in G3 cells. Glycogen synthase (GS) activity measured in vitro was virtually absent and the amount of enzyme in Qc cells was decreased by about 50%. The difference in GS activity between cells persisted even when G3 cells were devoid of glycogen. Incubation of G3 cell extracts with either exogenous UDP-glucose or glycogen resulted in increases in GS activity. Incubation of Qc cell extracts with exogenous UDP-glucose had no effect on GS activity; however, incubation with glycogen fully restored enzyme activity. Incubation of G3 cell extracts with radioactive UDP-glucose resulted in substantial binding of ligand to immunoprecipitated GS, whereas no binding was detected in Qc immunoprecipitates. Incubation of Qc cell extracts with exogenous glycogen fully restored UDP-glucose binding in the immunoprecipitate. These data suggest that chronically low UDP-glucose levels in cells result in inactivation of GS, owing to loss of the ability of GS to bind UDP-glucose.

Animals↗

PubMed1976

Decrease of uptake and exchange of neurotransmitter amino acids after depletion of their synaptosomal pools.

Synaptosomes prelabeled at 37 degrees C with radioactive amino acids (GABA, glutamate, glycine, taurine, alpha-aminoisobutyric acid, phenylalanine, leucine) and then washed at 0 degrees C on Millipore filters (DAWP 02500) lost 60-70% of the accumulated radioactivity. The loss was similar with exogenous tritiated GABA and glutamate, and with [14C]GABA and [14C]glutamate metabolically derived from [14C]glucose. In contrast, radioactive norepinephrine, dopamine and 5-hydroxytryptamine were almost totally retained by cold shocked synaptosomes. After pretreatment with reserpine and nialamide the loss of norepinephrine became significantly greater (about 25%). The uptake of radioactive GABA, glutamate and clycine after cold shock was about 50% reduced, whereas that of radioactive biogenic amines was less affected (reduction of 22% for norepinephrine, 29% for 5-hydroxytryptamine and 35% for dopamine). The loss of amino acids and the reduction of uptake could be minimized by performing the cold shock in hypertonic conditions. In synaptosomes prelabeled with [3H]GABA, a good correlation was observed among magnitude of amino acid pool depletion induced by cold shock or by 56 mM KCl, decrease of subsequent accumulation of [14C]GABA, and decrease of [14C]-GABA-stimulated [3H]GABA release (homoexchange).

Amino Acids↗

PubMed2004

Preserved direct hepatic insulin action in rats with diet-induced hepatic steatosis.

Recent in vivo studies have demonstrated a strong negative correlation between liver triglyceride content and hepatic insulin sensitivity, but a causal relationship remains to be established. We therefore have examined parameters of direct hepatic insulin action on isolated steatotic livers from high-fat (HF)-fed rats compared with standard chow (SC)-fed controls. Direct hepatic action of insulin was assayed in Wistar rats after 6 wk of HF diet by measuring the insulin-induced suppression of epinephrine-induced hepatic glucose output in an isolated liver perfusion system. Insulin-induced activation of glycogen synthase was measured by quantifying the incorporation of radioactive UDP-glucose into glycogen in HF and SC liver lysates. HF diet induced visceral obesity, mild insulin resistance, and hepatic steatosis. Both suppression of epinephrine-induced glycogenolysis and activation of glycogen synthase by insulin were sustained in HF rats; no significant difference from SC controls could be detected. In conclusion, in our model, triglyceride accumulation into the liver was not sufficient to impair direct hepatic insulin action. The data argue for an important role of systemic factors in the regulation of hepatic glucose output and hepatic insulin sensitivity in vivo.

Animals↗

PubMed1975

Glucose transport in the short loop of Henle of the rat kidney. Its characterisation by transport constants.

Short loops of Henle in rat kidneys were perfused with proximal tubular equilibrium solutions containing radioactive D-glucose. The transport rates follow 2-parameter kinetics: Km = 5.7 mmol/I. Vmax - 145 X 10(-12) MOL/MIN-1; Phlorrhizin inhibits transport almost completely, indicating little passive diffusion of D-glucose. The glucose transport capacity in the short loops of Henle, presumably in the pars rects, is much smaller than that in superficial segments.

Animals↗

PubMed1978

The effect of dietary fat or cholesterol and cholic acid on the rate of synthesis of rat liver glucose-6-P dehydrogenase.

The effect of dietary fat or cholesterol and cholic acid on the rate of synthesis of rat liver glucose-6-P dehydrogenase was measured by isolating hepatocytes from the livers of rats fed diets containing various amounts and types of lipid. Hepatocyte proteins were labeled with [3H]leucine and glucose-6-P dehydrogenase was immunoprecipitated with a specific antiserum. The immunoprecipitates were electrophoresed on sodium dodecyl sulfate-polyacrylamide gels and the radioactivity in the glucose-6-P dehydrogenase subunit was used to calculate the relative rate of synthesis of the enzyme. It is concluded that the activity of glucose-6-P dehydrogenase is primarily regulated by alterations in the rate at which the enzyme is synthesized. Dietary fat may decrease the rate of degradation of glucose-6-P dehydrogenase.

Animals↗

PubMed1976

Myocardial utilization of hypertonic glucose during hemorrhagic shock.

Awake pigs were rapidly bled 40% of total blood volume to induce hemorrhagic shock. Immediately after the induction of shock, all pigs received a single intravenous injection of radioactive-labeled glucose-U-14C. Simultaneously with glucose-U-14C injection, ten pigs received single central intravenous injections of unlabeled 50% glucose, four pigs received equiosmolar 25% mannitol, six did not receive either 50% glucose or mannitol, and two received 50% glucose plus insulin. Mean arterial pressure with 50% glucose was 89.9 mm. Hg at 15 minutes of shock and significantly higher than without 50% glucose, 48.3 mm. Hg or after mannitol, 46.7 mm. Hg (P = 0.05). Mean cardiac output at 10 minutes of shock with 50% glucose was 2.24 L. per minute and significantly higher than with mannitol, 1.34 L. per minute, or without 50% glucose, 0.94 L. per minute (P = 0.05.). Evidence for increased anaerobic myocardial utilization of the administered unlabeled 50% glucose was shown by a 12% greater production of unlabeled lactate in the venous coronary sinus blood from unlabeled 50% glucose in contrast to those not given 50% glucose at 10 minutes after shock (P = 0.05). Also, 50% glucose significantly increased mean arterial pressure, cardiac output, and survival over both control groups.

Anaerobiosis↗