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PubMed1977

The hepatocellular uptake of glucose, galactose and fructose in conscious sheep.

1. Surgical techniques for chronic catheterization of hepatic and portal veins in the sheep are described. These catheters remained usable for 2-6 months and did not alter hepatic morphology. 2. Hepatocellular uptake of monosaccharides was estimated from their ability to pass the boundaries of the sucrose space in a double indicator dilution procedure in conscious fed sheep. 3. A large proportion (81%) of D-glucose carried in the portal blood was found to enter an hepatic cellular compartment. 4. The radioactive label of D-glucose infused in the portal vein remained associated with D-glucose in hepatic venous blood samples during the experimental period. 5. A large proportion (74%) of an infused trace of D-galactose, a smaller proportion (33%) of D-fructose, and negligible amounts of L-glucose were taken up in a single passage through the liver. 6. Raised blood concentrations of sucrose or of methyl-alpha-D-glucoside (Me-alpha-DG) significantly diminished the proportional uptake of D-glucose. Raised blood concentrations of glucose, galactose or Me-alpha-DG diminished the proportional uptake of D-galactose. Raised blood concentrations of fructose diminished the proportional uptake of fructose. 7. Neither total hepatic blood flow changes nor competitive effects within the cell could account for these findings. 8. It is concluded that these monosaccharides enter the liver cell by facilitated diffusion, and share at least some of the membrane elements that mediate this process. It seems likely that only a proportion of the glucose-transporting apparatus is accessible to galactose.

Animals↗

PubMed1994

Hypometabolism and dipole localization in hemimegalencephaly: a case report.

A case of hemimegalencephaly was studied by means of neuroimaging (CT, MRI and PET) and magnetoencephalography (MEG). Hemimegalencephaly (HM) is a neuronal migration disorder. This is the first report of evaluation of HM with the use of PET and MEG from not only the morphological but also the functional point of view. PET with 11C-glucose showed a low radioactive concentration in the affected hemisphere, which suggested a metabolic deficit. MEG proved the epileptic foci existed mainly in the affected hemisphere, especially around a heterotopia and the pachygyric cortex, which was disclosed on MRI.

Brain↗

PubMed1987

Synthesis of IgA by human gastric mucosa in vitro.

Human gastric mucosa was removed at gastrectomy for duodenal ulcers. Intact mucosal layer and homogenized mucosal scrapings were incubated in vitro with L-[U-14C]leucine and with D-[U-14C]glucose and incorporation of radioactive label into IgA was investigated. 14C of both the precursors was incorporated into tissue IgA when intact gastric mucosa was incubated indicating synthesis of IgA by the tissue in vitro. IgA isolated from the media which bathed the luminal sides of the mucosae during incubation was also radioactive implying secretion of the newly-synthesized immunoglobulin into the media. When mucosal scrapings were incubated as homogenized suspensions, radioactivity of IgA was below the level of sensitivity of our methods. For analysis, IgA was separated from the bulk of radioactive mucosal proteins of the samples by isopycnic CsCl gradient centrifugation followed by gel filtration on Sephacryl S-200 or Sephadex G200 and then Sepharose 4B. The IgA-enriched Sepharose 4B fractions were subjected (1) to immunoprecipitation in agar gels by double diffusion against specific anti alpha-chain serum and (2) to SDS-polyacrylamide gel electrophoresis after reduction. Radioactivity of precipitated IgA, and of the protein band which corresponds to the alpha-chain of IgA on SDS-PAGE gels, was demonstrated autoradiographically. It is suggested that in vivo the mucosa is involved in local synthesis of the constituent IgA of gastric mucus.

Autoradiography↗

PubMed1980

Regulation of calcium fluxes in pancreatic islets: two calcium movements' dissociated response to glucose.

At normal extracellular 40Ca concentration (1.0--1.5 mM), D-glucose initially reduces and subsequently increases 45Ca efflux from prelabeled rat pancreatic islets, whether in the absence or presence of 20 mM Ca-EGTA. Thus, the initial fall cannot be attributed to a reuptake of effluent 45Ca. Both the fall and rise in effluent 45Ca represent sustained and rapidly reversible phenomena partially masked by one another. The dose-action relationship for the initial fall in 45Ca efflux (Km = 4.2 mM) differs vastly from that characterizing the secondary rise in 45Ca efflux (Km = 9.1 mM). Mannoheptulose, iodoacetate, and low temperature inhibit both the early fall and secondary rise in effluent radioactivity normally evoked by glucose. D-Glucose (8.3 mM) and D-glyceraldehyde (10 mM) exert comparable effects on 45Ca efflux. The initial fall and later increase in 45Ca efflux evoked by glucose, although dependent on the integrity of glucose metabolism, correspond to two distinct processes in the rapid regulation of Ca handling by the islet cells.

Animals↗

PubMed1999

Delayed labelling of brain glutamate after an intra-arterial [13C]glucose bolus: evidence for aerobic metabolism of guinea pig brain glycogen store.

Glycogen in glial cells is the largest store of glucose equivalents in the brain. Here we describe evidence that brain glycogen contributes to aerobic energy metabolism of the guinea pig brain in vivo. Five min after an intra-arterial bolus injection of d-[U-14C]glucose, 28+/-11% of the radioactivity in brain tissue was associated with the glycogen fraction, indicating that a significant proportion of labelled glucose taken up by the brain is converted to glycogen shortly after bolus infusion. Incorporation of 13C-label into lactate generated by brains made ischaemic after d-[1-13C]glucose injection confirms that these glucose equivalents can be mobilised for anaerobic glucose metabolism. Aerobic metabolism was monitored by following the time course of 13C-incorporation into glutamate in guinea pig cortex and cerebellum in vivo. After an intra-arterial bolus injection of d-[1-13C]glucose, glutamate labelling reached a maximum 40-60 min after injection, suggesting that a slowly metabolised pool of labelled glucose equivalents was present. As the concentration of 13C-labelled glucose in blood was shown to decrease below detectable levels within 5 min of bolus injection, this late phase of glutamate labelling must occur with mobilisation of a brain storage pool of labelled glucose equivalents. We interpret this as evidence that glucose equivalents in glycogen may contribute to energy metabolism in the aerobic guinea pig brain.

Aerobiosis↗

PubMed1991

Kinetics of lactate and glucose metabolism in the pregnant ewe and conceptus.

Two monotocous and two ditocous ewes were infused at 124-130 days of gestation with a mixture of L-[U-14C]lactate and D-[6-3H]glucose via a maternal or umbilical catheter, separate days being used for each infusion. Plateaux-specific radioactivities of plasma lactate and glucose were used to derive a four-pool model describing the fluxes between the lactate and glucose pools of the infused conceptus and mother. The average turnover rate of lactate was 23.3 and 13.2 mg carbon min-1 in the conceptus and 32.0 and 44.0 mg carbon min-1 in the mother for monotocous and ditocous ewes, respectively. Glycolysis rates within both conceptus and mother in all sheep were high, accounting for about 80 and 60% of the respective rates of lactate turnover. The synthesis of glucose from lactate accounted for 13 and 31% of the glucose turnover in the mother in monotocous and ditocous ewes, respectively, but was insignificant in the conceptus. Glycolysis within the conceptus used only glucose which had entered and mixed with the conceptus glucose pool; there was no direct transfer of carbon from the maternal glucose pool to the conceptus lactate pool. This finding is an important validation for the use of tracer methods to determine glucose use within the whole conceptus rather than within fetal corporeal tissues alone.

Animals↗

PubMed1988

Insulin action is altered in hyperthyroidism.

We have assessed insulin action in five hyperthyroid patients, pre- and post-radioactive iodine therapy using oral glucose tolerance tests, monocyte insulin binding and dose response curves generated with the euglycemic clamp technique. All patients had become euthyroid after radioactive iodine therapy with a decline in the plasma free T4 index level from 278 +/- 43 to 105 +/- 9. Fasting glucose was modestly, but significantly elevated in the thyrotoxic patients compared to when they were rendered euthyroid (p less than 0.05). Oral glucose tolerance tests showed no difference in either glucose or insulin values after the glucose load. Insulin receptor binding and affinity were similar regardless of their thyroid status. Hepatic glucose production in the basal state was elevated in the thyrotoxic patients, 61 +/- 5 mg/M2/min vs 49 +/- 3 mg/M2/min (p less than 0.05). At the lowest level of insulin infusion no difference in glucose disposal was found. At maximum insulin concentrations the glucose disposal rate was enhanced in the thyrotoxic patients, 686 +/- 19 vs 567 +/- 26 mg/M2/min (p less than 0.01). These results indicate that higher fasting glucose levels may result from increased hepatic glucose production in thyrotoxicosis, but as indicated by the oral glucose tolerance tests, this defect in insulin action is usually of minor significance. However, insulin responsiveness measured at pharmacological insulin levels is augmented in thyrotoxicosis.

Adult↗

PubMed1994

Absence of glycogen cycling in cultured rat hepatocytes.

Glycogen synthesis and degradation were studied in cultured rat hepatocytes prelabeled by incubation with [14C]glucose or [14C]galactose. During prelabeling about 75% of the accumulated glycogen was synthesized from glucose and about 25% from gluconeogenic precursors. Following the labeling period, glycogen synthesis and degradation were estimated at 5 and 12.5 mM glucose and varying concentrations of insulin and glucagon. At 12.5 mM glucose and 10 nM insulin the accumulation of glycogen was comparable to in vivo values, whereas the level of radioactivity in prelabeled glycogen remained constant. Further addition of 0.1 nM glucagon resulted in constant values of both content and radioactivity of glycogen. Increasing the concentration of glucagon to 10 nM resulted in a parallel decrease of content and radioactivity in glycogen. At 5 mM glucose, 10 nM insulin, and 0.1 nM glucagon both the content and the radioactivity of glycogen were constant, whereas addition of 10 nM glucagon resulted in a parallel decrease of content and radioactivity of glycogen, which was 64% higher than that observed with 12.5 mM glucose. In the absence of insulin, prostaglandin D2 had effects similar to those of 10 nM glucagon, whereas no effects was observed in the presence of insulin. From these results and from calculated rates of glucose 6-phosphate formation, it is concluded that the rate of glycogen degradation is less than 10% of the rate of synthesis under conditions favoring glycogen accumulation. At conditions favoring glycogen degradation (10 nM insulin plus 10 nM glucagon or prostaglandin in the absence of insulin) no synthesis could be detected. Results from cells prelabeled with [14C]galactose suggested that glycogen degradation is not an absolutely ordered process, but that some random degradation takes place.

Animals↗

PubMed1995

Characterisation of glucose transport in Helicobacter pylori.

The nature of the glucose transport system in the bacterium Helicobacter pylori was investigated employing radioactive tracer analysis. Fast D-glucose uptake was demonstrated by using two methods of measuring glucose transport. The transport of 2-deoxy-D-glucose was inhibited competitively by D-glucose; and the efflux of 2-deoxy-D-glucose from cells also was affected by the presence of D-glucose. The transport of 2-deoxy-D-glucose was saturable with a Km of 4.8 mM and Vmax of 146.6 pmol (microliter cell water)-1 at 20 degrees C. The transport was temperature-dependent with energies of activation of 6.8 and 51.0 kJ mol-1 for 0.2 and 20 mM 2-deoxy-D-glucose, respectively. The temperature dependence and saturable nature of transport suggested the presence of one or more glucose carriers. The substrate specificity of the transport system was studied by measuring the effects of mono- and disaccharides on the rates of transport of the glucose analogue. The most significant inhibitory effects were obtained with D-galactose and L-arabinose. Lack of transport inhibition by L-glucose established the stereospecificity of the transporters for the D-isomer of glucose. Higher rates of 2-deoxy-D-glucose transport were measured in the presence of sodium ions than for other monovalent cations, and the presence of amiloride inhibited transport of the monosaccharide. No inhibition was observed with cytochalasin B, phloretin or phloridzin. The results suggested the existence of specific D-glucose transporters and that the glucose transport system of H. pylori is significantly different from other known bacterial transporters.

Amiloride↗

PubMed1980

The role of carbon dioxide in the metabolism of adult Haemonchus contortus, in vitro.

Adult Haemonchus contortus worms simultaneously excrete and fix CO2. Their initial content of CO2 was measured as 4.55 mumoles/100 mg wet weight and their excretion rate in air as 1 mumol/100 mg wet weight/h for at least 4 h. When the worms were incubated either aerobically or anaerobically with 14CO2 most of the metabolized radioactivity was associated with propan-1-ol and propionate but small amounts were found in succinate and lactate. No radioactivity was associated with ethanol or acetate, two major catabolites of glucose. Stepwise degradation of the metabolized radioactive propanol and propionate showed that all the radioactivity in both compounds was associated with carbon atom no. 1. These results show that H. contortus has much in common with the anaerobic energy metabolism of Ascaris lumbricoides but they are not inconsistent with the utilization of the tricarboxylic acid cycle by the worm. H. contortus worms were found to metabolize their excretory products. When they were incubated with either [2,3-14C]succinate or [2-14C]acetate, 14CO2 was excreted under aerobic but not under anaerobic conditions. These results are consistent with a pathway similar to that used by Ascaris operating aloneunder anaerobic conditions and together with the tricarboxylic acid cycle under aerobic conditions.

1-Propanol↗

PubMed1978

Hyperglycaemic activity and metabolic effects of 3-aminopicolinic acid.

Administering 3-aminopicolinate to rats starved for 24h immediately initiated a progressive increase in blood glucose concentration. Hyperglycaemia was not the result of glycogenolysis, nor was it due to an inhibition of insulin release, since it caused marked hyperinsulinaemia. The rate of [6-(3)H]glucose disappearance from the blood of the intact rat was not altered by 3-aminopicolinate, indicating that it does not cause hyperglycaemia by inhibiting glucose utilization or by causing a redistribution of total body glucose. 3-Aminopicolinate increased the rate of fall in the specific radioactivity of blood [6-(3)H]-glucose, indicating dilution of the glucose pool by newly synthesized glucose. The rate of (14)C incorporation into blood glucose from [(14)C]alanine and [(14)C]lactate was increased 90 and 35% respectively, whereas that from [(14)C]glycerol and [(14)C]xylitol was either unaffected or slightly decreased by 3-aminopicolinate administration. Liver phosphoenolpyruvate of rats was increased to four to seven times the normal concentration 10min to 1h after injections of 50-300mg of 3-aminopicolinate/kg body wt. and the amounts of 2-phosphoglycerate and 3-phosphoglycerate were increased to three to four times normal. The high concentrations of liver phosphoenolpyruvate, 2-phosphoglycerate and 3-phosphoglycerate, as well as the enhancement of gluconeogenesis from lactate and alanine, but not from glycerol or xylitol, is compatible with an enhancement of gluconeogenesis at a step between pyruvate and the triose phosphates. After injections of 3-aminopicolinate, liver malate, citrate, aspartate, alanine, lactate and pyruvate were also increased, but to lesser extents than was phosphoenolpyruvate. The increases in some of these metabolites were approximated after an intravenous infusion of glucose, so their elevated concentration after 3-aminopicolinate administration could have been, in part, a consequence of the hyperglycaemia. The possibility is considered that 3-aminopicolinate stimulates gluconeogenesis in vivo by facilitating Fe(2+) activation of phosphoenolpyruvate carboxykinase as it does with the purified enzyme in vitro [MacDonald & Lardy (1978) J. Biol. Chem.253, 2300-2307]. In this effect 3-aminopicolinate may simulate the physiological role of the naturally occurring ferroactivator protein [Bentle & Lardy (1977) J. Biol. Chem.252, 1431-1440].

Animals↗

PubMed1991

A defect in insulin release in women at risk of future non-insulin-dependent diabetes.

1. A study on seven Caucasian glucose-tolerant women with previous gestational diabetes and seven matched control subjects is presented. The insulin response to oral glucose, insulin sensitivity and fasting glucose production rates were measured by using a 75 g oral glucose tolerance test, an insulin tolerance test and a non-radioactive tracer, [6,6-2H]glucose, respectively. 2. Fasting plasma glucose levels were similar between the women with previous gestational diabetes and the control subjects (4.8 +/- 0.3 versus 4.7 +/- 0.2 mmol/l), as were fasting plasma insulin levels (median 4 m-units/l, range 1-13 m-units/l versus median 4 m-units/l, range 1-24 m-units/l). After oral glucose the 60 min plasma glucose levels in the women with previous gestational diabetes were significantly higher (8.5 +/- 0.6 versus 6.7 +/- 0.8 mmol/l, P less than 0.05), whereas the plasma insulin level was significantly lower at both 30 min (median 23 m-units/l, range 4-47 m-units/l versus median 55 m-units/l, range 23-100 m-units/l, P less than 0.02) and at 60 min (median 23 m-units/l, range 4-43 m-units/l versus median 60 m-units/l, range 16-126 m-units/l, P less than 0.02). 3. Insulin sensitivity, expressed as the slope of the regression line of plasma glucose level against time after intravenous infusion of insulin (0.05 unit/kg), was similar in the women with previous gestational diabetes and the control subjects (mean slope, -0.17 +/- 0.01 versus -0.17 +/- 0.01). 4. Fasting glucose production rates were similar in the women with previous gestational diabetes and the control subjects (2.2 +/- 0.3 versus 1.9 +/- 0.1 mg min-1 kg-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

Effect of glucose on the distribution of iodine-123-IHA-16 between esterification and oxidation in canine myocardium.

To evaluate the effect of glucose perfusion on the myocardial metabolism of [123I]-16-iodo-9-hexadecenoic acid (IHA), the latter was injected intravenously into six fasting dogs perfused with a solution lacking glucose (controls) and seven fasting dogs perfused with glucose and insulin. The distribution of myocardial 123I among iodides, free IHA, and esterified IHA was measured in myocardial biopsy specimens. The increase in esterification and decrease in oxidation of IHA due to glucose were quantified using a compartmental mathematical model of myocardial IHA metabolism. Subsequently, in six control and six glucose-perfused dogs, cardiac radioactivity was measured with a scintillation camera for 1 hr following i.v. injection of IHA. Four different methods were used to analyze the myocardial time-activity curves and to calculate the distribution of IHA between oxidation and esterification. Results comparable to those provided by analysis of biopsy specimens can be obtained by considering the curve to be the sum of an exponential and a constant, or by analyzing it with a compartmental mathematical model.

Animals↗

PubMed1980

Use of a provocation test for objective assessment of dumping syndrome in patients undergoing surgery for duodenal ulcer.

It is difficult to assess the incidence of dumping after various operations for duodenal ulcer on clinical grounds alone. An objective assessment of dumping has been made with the help of a provocation test. The test, using 50% hypertonic glucose solution labeled with radioactive Indium 113m was performed on 39 preoperative patients and 107 times on 72 patients after operation for duodenal ulcer. The dumping status of all the patients prior to surgery was asymptomatic after ordinary food as well as on test. Among the postoperative studies the clinical status was asymptomatic in 69, uncertain in 32 and six had dumping symptoms. On the basis of the symptoms on-test, the status was asymptomatic in 61, uncertain in 14 and 32 had dumping symptoms. The objective indices further defined the status as 70 asymptomatics, none uncertain and 37 confirmed dumpers and thereby completely abolished the uncertain group. All the objective measurements of the dumping provocation test have clearly differentiated those patients with from those without dumping symptoms. Patients with dumping symptoms on-test had a significantly greater fall in plasma volume, more rapid rates of gastric emptying and steeper rise in blood sugar after ingestion of hypertonic glucose than did the patients without dumping symptoms on-test.

Administration, Oral↗

PubMed1995

Enzymatic formation of plant cerebroside: properties of UDP-glucose: ceramide glucosyltransferase in radish seedlings.

The activity of cerebroside synthase (UDP-glucose: ceramide glucosyltransferase) was found in the microsomal fraction of radish hypocotyls, and was studied. One % of the radioactivity due to UDP-[3H]glucose added to the membrane fraction was incorporated into cerebroside within 60 min. Optimum pH and temperature of the activity were pH 7.8 and 30 degrees C, respectively. No metal ions enhanced the cerebroside synthase activity, dissimilar to that in animal tissues. The apparent Km for UDP-glucose was approximately 200 microM. The same activity was also observed in radish roots and cotyledons, but proportions of UDP-[3H]glucose incorporation were slightly lower than that in hypocotyls. Exogenous ceramide species having trihydroxy sphingoid bases, which were major ceramide components of radish cerebrosides, usually stimulated cerebroside formation in microsomal fractions from radish seedlings, while any ceramide types having dihydroxy sphingoid bases were ineffective on the glucosylation reaction. It was assumed, therefore, that cerebroside synthase in radish seedlings would have substrate selectivity for ceramide species.

Brassica↗

PubMed1981

Substrate requirements for the phosphoinositide response in rat pancreatic islets.

The relationship between phosphatidylinositol hydrolysis and the first phase of insulin secretion has been investigated by briefly exposing rat pancreatic islets that had been prelabelled with myo-[2-3H]inositol to various agonists and antagonists of insulin secretion. The recovery of lipid-bound radioactivity progressively decreased as the D-glucose concentration of the incubation medium was increased. Those carbohydrates that stimulated insulin secretion evoked a phosphoinositide response, whereas non-stimulatory carbohydrates did not. With the notable exception of amino acids, non-carbohydrate secretagogues were also found to decrease the islet lipid-bound radioactivity. Inhibition of islet glucose metabolism was found to decrease the recovery of lipid-bound radioactivity, largely as a result of impaired de novo phosphoinositide synthesis. The phosphoinositide response to glucose was not affected by inhibition of microtubular function, but was dependent upon the availability of extracellular calcium ions. We conclude that the phosphoinositide response in carbohydrate-stimulated islets is not directly related to the activation of membrane-associated glucose receptors, but may occur as a consequence of the subsequent transmembrane movement of calcium ions. Finally, the observation that stimulatory amino acids did not evoke a phosphoinositide response suggests that, under certain circumstances, this phenomenon can be dissociated from insulin secretion.

Animals↗

PubMed1984

Incorporation of (U-14C)-glucose into glycogen in normal rat pancreatic islets.

The incorporation of glucose into glycogen was determined in pancreatic islets isolated from normal rats and incubated with glucose (5 or 20 mM) and compounds known to affect glycogen metabolism in other tissues. Incubation of pancreatic islets with glucose (20 mM) induced a marked increase in radioactive glycogen. Exposure to epinephrine in the presence of glucose (20 mM) slightly increased incorporation of glucose into glycogen. In contrast the incorporation of glucose into glycogen was not affected when isolated islets were exposed to glucagon or insulin, whereas anti-insulin serum in the incubation medium decreased radioactive glycogen formation.

Animals↗

PubMed1979

Production of [14C]rubratoxin B.

[14C]rubratoxin B was produced by culturing Penicillium rubrum Stoll for 13 days at 22 degrees C in medium containing [14C]glucose. The most efficient incorporation of glucose into rubratoxin occurred when Raulin-Thom medium enriched with 2.5% malt extract was supplemented with 2.5% added glucose. The presence of 1.0 mCi of radioactivity in 50 ml of medium with 2.5% added glucose resulted in the production of 38 mg of labeled, chromatographically pure rubratoxin with a specific activity of 0.47 Ci/mole.

Animals↗