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PubMed1981

Foetal and maternal rates of glucose production and utilization in chronically catheterized ditocous ewes.

1. Five well-nourished Scottish Blackface ewes carrying twin lambs were used. An umbilical artery and vein of each foetus in two sheep and one foetus in three sheep were catheterized at 109-112 days of gestation and both maternal jugular veins were catheterized 2 days before experiment. Two-day experiments were conducted between days 124 and 141 of gestation when [2-3H,U-14C]glucose was infused intravenously over 9 h into either the mother or one foetus, separate days being used for each infusion. 2. Plasma glucose specific radioactivities of the mother and infused foetus at plateau were used to determine the glucose flux rates within and between mother and foetus. The corresponding values for the uninfused foetus were calculated by using the relative weights of each twin foetus and were used to correct the maternal flux rates for the presence of the second foetus. 3. The net rate of glucose utilization by the foetus was 11.2 +/- 1.3 mg/min per kg of foetus (mean +/- S.E.M; n = 11). The corresponding rate in the mother was 1.1 +/- 0.1 mg/min per kg of live weight (n = 11). 4. The net rate of foetal uptake of glucose from the mother accounted for only 56 +/- 4% of the glucose used by the foetus. The remainder was provided by an input of 4.9 +/- 0.7 mg/min per kg of foetus to the foetal glucose pool via foetal gluconeogenesis. 5. The rate of glucose futile cycling in the foetus was high, equal to 95 +/- 19% of the net foetal glucose-utilization rate. 6. The rate of glucose utilization (mg/min per kg of foetus) decreased progressively over the observational period of 124-141 days of gestation. There was no increase in the rates of net foetal glucose uptake or of foetal gluconeogenesis to counter this decline.

Animals↗
PubMed1980

Rates of glucose production and utilization by the foetus in chronically catheterized sheep.

1. Six well-nourished Scottish Blackface ewes were each prepared at 110-112 days of gestation with indwelling catheters in an umbilical artery and vein and at 2 days before experiment with catheters in each maternal jugular vein. Two-day experiments were conducted between days 124 and 134 of gestation when [2-3H,U-14C]glucose was infused over 9 h into either the maternal or the foetal circulations, separate days being used for each infusion. 2. Plasma glucose specific radioactivities at plateau were used to determine, for a two-pool model representing the glucose system of the mother and foetus, the rates of glucose production, utilization and recycling by the mother and by the foetus and the rates of transfer of glucose between the mother and foetus. 3. The net rate of glucose utilization by the foetus, which we have called the 'foetal glucose requirement', was 7.6 +/- 0.6 mg/min per kg of foetus (n = 8). Compared with the corresponding rate in the mother of 1.1 +/- 0.1 mg/min per kg of mother (n = 8), this indicated a high rate of foetal metabolism. 4. The net rate of foetal uptake of glucose from the mother accounted for only 69 +/- 5% of the foetal glucose requirement, and it has been argued that the remainder was supplied by foetal gluconeogenesis. 5. The rate of glucose recycling within the foetus was high, equal to 108 +/- 16% of the net foetal glucose-utilization rate. The significance of this in terms of either Cori or futile cycling is discussed.

Animals↗
PubMed1969

Evaluation of three isotope-dilution techniques for studying the kinetics of glucose metabolism in sheep.

1. Comparisons have been made of three isotope-dilution techniques for measuring parameters of glucose metabolism in sheep given their daily ration in 12 equal amounts (i.e. from 07.00 to 18.00hr.) 2. [U-(14)C]Glucose was used in all experiments. After a single injection the specific radioactivity of plasma glucose was measured at specific times for up to 24hr. Primed infusions were made with various ratios of P, priming injection (nc), to F, infusion rate (nc/min.) (P/F ratios varying from 23:1 to 147:1) and the specific radioactivity of plasma glucose was measured at 60, 120, 150, 180, 210 and 240min. In continuous infusions the specific radioactivity of plasma glucose was followed for 9hr.; a constant specific radioactivity was observed after approximately 180min. 3. A computer programme was used to fit a multi-exponential equation to the log(specific radioactivity)-time curve after a single injection. A second- or third-order exponential equation was found to fit the results. 4. Conventional analyses of all results showed that similar estimates of the irreversible loss of glucose were obtained by using all three techniques. Estimates of glucose pool size and space by using the primed infusion technique were both significantly higher than estimates obtained by the single injection technique. In these experiments total entry rate could only be determined from the single-injection results and a wide variation in estimates was obtained. 5. Comparisons of the specific radioactivity-time relationships after a single injection of [U-(14)C]glucose in sheep given their ration either once daily or as a proportion at hourly intervals indicated that there were fluctuations in glucose synthesis in the former over the period of the experiment. The multi-exponential curves fitted to these results had larger residual variances than in sheep given food at hourly intervals. All parameters of glucose metabolism estimated were similar under both feeding regimes. 6. A number of methods of analysis are discussed and a model for glucose metabolism in sheep in suggested.

Animals↗
PubMedDate not supplied

[The metabolism of [2-(14)C] glycine in rat tissues in vivo].

It is found that two hours after intraperitoneal injection of [2-(14)C] glycine to rats its higher amount (83.6%) is used in the protein synthesis and 16.4% is catabolized. The carbonic chain of the amino acid is used to the greater extent in the synthesis of lipids than in the oxidation and glucogenesis. Radioactivity of the proteins in the investigated organs and tissues of rats varies within L7-50.6 thou. DPM per 100 mg of wet tissue and decreases in a series: small intestine mucosa, kidneys, liver, stomach mucosa, heart, lungs, cardiac muscle, skin, skeletal muscle, adipose tissue, brain. Radioactivity of lipids is within the limits of 0.2-5.1 thou. DPM per 100 mg of wet tissue 11.7-81.6% of protein radioactivity) and decreases in a series: liver, adipose tissue, kidneys, lungs, cardiac muscle, stomach mucosa, skin, skeletal muscle, brain. The total radioactivity of glucose+glycogen varies within 0.05-0.34 thou. DPM per 100 mg of wet tissue (0.8-10.7% of protein radioactivity) and decreases is a series: kidneys, liver, brain, skeletal muscle.

Animals↗
PubMed1980

Effects of somatostatin and glucagon on the utilization of [2-(14)C]propionate in glucose production in vivo in sheep.

This study examined the effects of hypoglucagonaemia and hyperglucagonaemia on the incorporation of 14C from [2-(14)C]propionate into plasma glucose of sheep in vivo. The sheep were adult ewes fed a maintenance diet of lucerne pellets delivered in equal aliquots hourly. The irreversible loss of glucose was determined by the continuous infusion of [6-(3)H]glucose. During the control period (the hour immediately preceding infusion of hormones) 63 +/- 2% of the propionate was converted to glucose, accounting for 30 +/- 2% of glucose production. Glucagon deficiency, induced by infusion of somatostatin (100 micrograms/h), did not affect gluconeogenesis and the irreversible loss of glucose significantly. However, glucagon infusion at 11.5 +/- 0.6 micrograms/h significantly increased the irreversible loss of glucose, with the greatest increase occurring in the first 15 min of infusion. The 14C specific radioactivity of glucose and the fraction of glucose derived from propionate decreased significantly during glucagon infusion. The data are consistent with glucagon have a marked glycogenolytic effect initially, but little or no selective effect in promoting the utilization of propionate for glucose synthesis in vivo in sheep.

Animals↗
PubMed1985

Absorption, distribution, excretion and metabolism of orally administered 14C-beta-cyclodextrin in rat.

The absorption, distribution, excretion and metabolism of orally administered universally labelled 14C-beta-cyclodextrin and 14C-glucose were compared in rat. The maximum radioactivity of the blood derived from 14C-beta-cyclodextrin was observed between 4th and 11th h and the value of the maximum in different experiments ranged between 5 and 17 0/00 of the total administered radioactivity. Following 14C-glucose treatment radioactivity reached the maximum within half-an-hour, with values of 15 to 82 0/00. In the 8th h after a high dose (313.5 mg/kg) of beta-cyclodextrin no more than 3-50 ppm beta-cyclodextrin was detectable in the blood by HPLC. After 14C-beta-cyclodextrin treatment 4.2-4.8% of the administered total radioactivity was excreted by the urine and about the same quantity (2-3.6%) in case of 14C-glucose. No specific accumulation was observed after 14C-beta-cyclodextrin treatment in the different organs. The large intestine contained 10-15% of the cyclodextrin radioactivity while this value was only 2% in case of 14C-glucose. Following p.o. administration of different doses of 14C-beta-cyclodextrin the radioactivity peak was detected in the exhaled air between the 4-6th and 6-8th h, respectively, depending on the administered doses, while in case of 14C-glucose treatment it was observed within 2 h. The total radioactivity exhaled by 14C-beta-cyclodextrin treated animals in 24 h was 55 to 64% of the administered radioactivity and 58% in case of 14C-glucose. It is assumed that beta-cyclodextrin is metabolized in rats slower but similarly to glucose, therefore p.o. administered beta-cyclodextrin cannot induce toxic symptoms.

Administration, Oral↗
PubMed1965

RATE OF UTILIZATION OF GLUCOSE AND 'COMPARTMENTATION' OF ALPHA-OXOGLUTARATE AND GLUTAMATE IN RAT BRAIN.

1. The rate of incorporation of (14)C into pyruvate, alpha-oxoglutarate, lactate and glucose of rat tissues was measured after the subcutaneous injection of uniformly labelled glucose. 2. In rat brain the specific radioactivities of lactate and glucose were similar to that of alanine. In liver the specific radioactivity of glucose was considerably higher than that of lactate or alanine. 3. The specific radioactivities of alpha-oxo acids of rat brain were lower than those of corresponding amino acids, alanine and glutamate. These findings have been explained in relation to metabolic compartments in vivo. 4. The approximate estimated rate of glucose utilization in rat brain in vivo is 0.96mumole/g. of brain/min.

Alanine↗
PubMed1981

Comparison of measurements of glucose flux rates in wethers and in pregnant and lactating ewes using C14 and H3 labelled tracers.

Glucose flux rates (GFR) were determined, from plateau glucose specific radioactivity values obtained during continuous infusions of [U - 14C] + [2 - 3H], [U - 14C] + [3 - 3H] and [U - 14C] + [6 - 3H] glucose tracers, in wethers fed either 800 g per day of poor quality hay plus 400 g barley per day. GFR determined with [U - 14C] glucose ranged from 15 to 24 mmoles per hour on the hay diet and from 22 to 34 mmoles per hour on the hay plus barley diet. The variation in GRF within animals and between days accounted for most of the total variability. GFR determined with [6 - 3H] glucose were similar to those estimated with [U - 14C] glucose but those determined with [2 - 3H] and [3 - 3H] glucoses were 14 per cent higher. GFR were also determined with [U - 14C] + [6 - 3H] glucose tracers in pregnant ewes fed 1000 g medium quality hay plus 400 g concentrate and in lactating ewes fed different amounts of medium quality hay plus concentrate. GFR, determined with [U - 14C] glucose, ranged from 27 to 49 mmoles per hour in pregnancy and from 54 to 83 mmoles per hour in lactation. At approximately 125 days' gestation there was a significant positive relationship between GFR and total lamb birth weight. Estimates of GFR with [6 - 3H] glucose were 21 per cent higher in pregnancy and 15 per cent higher in lactation than the simultaneous estimates with [U - 14C] glucose.

Animal Feed↗
PubMed1983

[Effect of application of a herbicide propyzamide into the soil by study of mineralization of glucose 14C(U) and distribution of radioactivity in various fractions of the soil (laboratory and open field tests)].

The effects of the herbicide PROPYZAMIDE are studied in laboratory and field conditions. The modifications involved are characterized by measurement of 14C-glucose mineralization and radioactivity incorporation into the soil fractions. In laboratory conditions, temperature and moisture are kept stable and the experiment is performed during less than 24 hours. In these conditions, Kerb 50 (commercial formulation of propyzamide) and the emulsifier (material used in propyzamide formulation) exert little effect on 14CO2 evolution. In field conditions, propyzamide andKerb 50 are applied once at two different doses: at field rate (1,5 kg/ha) and twentyfold this rate. Essays are duplicated. The herbicide (propyzamide in Celanol and Kerb 50) and the emulsifiers alone (Celanol and the material used in propyzamide formulation) are applied on the soil surface (application date: 3.02.81). Two weeks later and then every month during four months, samples are taken to the depth of about 5 cm (Propyzamide migrates very slowly in the first centimeters of the soil). The characterization experiment is performed on 10 g soil samples by 14C-glucose incubation at 28 degrees C during two hours. 14CO2 evolved is measured after incubation and acidification with HCl. Then radioactivity distribution in the soil is counted after chemical fractionation of soil. This distribution is about 10-16.5% as 14CO2, 22-37% in the acid-soluble fraction, 10-25% in the alkali-soluble fraction and 15-45% in the human fraction (measured as 14CO2 evolved after combustion). This distribution is little modified by the herbicides or the emulsifiers but its evolution is significantly related to environmental conditions (temperature). Nevertheless a few modifications are observed. They can be due to the herbicide propyzamide itself but the emulsifiers and the degradation products of propyzamide can also influence the measurement (After forty days in the soil, 70-95% of the starting active ingredient have disappeared). They can also be a result of the initial effects of the products (modification of the microflora and of the environment).

Benzamides↗
PubMed1975

The "hidden ligand" of the galactose-binding protein.

Following tryptophan fluorescence of the galactose-binding during dissociation of the ligand it has been found that glucose dissociates with a half life of less than 5 s. Similarly, fast dissociation was also observed by following release of radioactively labelled glucose from Sepharose-coupled galactose-binding protein upon dilution. Accordingly, a previous claim that the galactose-binding protein contains glucose as a non-dissociable "hidden ligand" [G. Richarme and A. Kepes (1974) Eur. J. Biochem. 45, 127-133] has to be reinterpreted

Carrier Proteins↗
PubMed1985

[Metabolic effects of exposure to air and the post-aeration response in the intertidal anthozoan Actinia equina L].

Metabolic adjustments occurring during air exposure have been studied in a population of Actinia equina submitted to long-lasting emersion periods. Oxygen consumption upon reimmersion seems to account for the discharge of an oxygen debt related to the accumulation of end-products derived from anaerobic pathways. Incorporation of radioactive labelled glucose into both submerged and air exposed animals has allowed identification of these final products. A correspondence between the length of exposure-time and the amount of oxygen debt is encountered, which parallels the evolution of the rate of radioactivity incorporation into amino acids. Increasing levels of amino acid synthesis from glucose in the exposed conditions appear as the main metabolic feature.

Adaptation, Physiological↗
PubMed1980

Transcriptional and translational control of glucose-stimulated (pro)insulin biosynthesis.

Islets of Langerhans were isolated from the pancreata of fed or 48-h-fasted Wistar rats. The islets were incubated with either [3H]leucine of [3H]uridine. Inhibition of RNA synthesis by actinomycin D or by alpha-amanitin for 4 h had no influence on the (pro)insulin biosynthesis of isolated islets of fed rats. The (pro)insulin biosynthesis was not inhibited after two days incubation of islets of fed rats with alpha-amanitin either. Incorporation of labelled uridine into total RNA for 3 h was stimulated by glucose in islets of fasted, but not of fed rats. Therefore, it was concluded that transcriptional control does not participate, even for longer periods than believed previously, in acute regulation of (pro)insulin biosynthesis of islets isolated fed rats. Despite the strong and preferential stimulation of (pro)insulin biosynthesis of islets of fed rats by glucose the radioactivity of the [3H]uridine-labelled polysomes active in proinsulin synthesis remained unchanged. To interprete these experimental data we suggest that glucose triggers the transformation of a translationally inactive form of pre-proinsulin mRNA to a translationally active form.

Amanitins↗
PubMed1977

Properties of carbohydrate utilising variants of Chinese hamster cells.

Variants of Chinese hamster ovary cells (CHO-K1) have been isolated which can grow on one of the following carbohydrates: lactose, sucrose, ribose or lactate. The ribose+ clones grow at the same rate on glucose as the parental cells whereas the others grow more slowly. With the exception of one ribose+ clone all excrete lactic acid while growing on glucose; none excrete significant amounts of lactic acid while growing on the alternative energy source. Wild-type cells and the variants accumulate radioactively labelled glucose and the corresponding radio-actively labelled alternative energy source to the same extent. The ribose+ variant that does not accumulate lactate while growing on glucose is also exceptional in its inability to utilise mannose.

Carbohydrate Metabolism↗
PubMed1977

Carbon dioxide fixation in the brain: its relation to glucose synthesis.

The incorporation in vivo of radiocarbon from 14C-bicarbonate in blood into relevant metabolites in rat brain is described. The animals, partially hepatectomized and nephrectomized, received the tracer bicarbonate via the intravenous route. The time course of label was followed in CO2 of blood and brain, in the anionic and cationic fractions of brain extract, in aspartate, glutamate, glutamine and in free glucose and in glycogen. From the tracer kinetic data a flux of 0.08 microgram atom fixed carbon min-1.g-1 brain tissue was calculated. Substantial amounts of 14C were found in free glucose, only a few percent in glycogen. The flux of newly synthetized glucose was approximated to 0.5--1.0 percent of the steady state level of glucose in brain tissue. In special experiments the localization of 14C in the carbon chain of aspartate and glucose was examined. 5 min following the tracer injection a practically total randomization of 14C between C-1 and C-4 aspartate was seen. From the radioactivity in glucose 94 percent were found in C-3 and C-4, only 6 percent in residual carbon. This 14C-pattern is typical for the labelling of glucose by CO2 fixation and retrograde Embden-Meyerhof pathway.

Animals↗
PubMed1997

Turnover of Galactans and Other Cell Wall Polysaccharides during Development of Flax Plants.

We investigated the synthesis and turnover of cell wall polysaccharides of the flax (Linum usitatissimum L.) plant during development of the phloem fibers. One-month-old flax plants were exposed to a 40-min pulse with 14CO2 followed by 8-h, 24-h, and 1-month periods of chase with ambient CO2, and radioactivity in cell wall sugars was determined in various plant parts. The relative radioactivity of glucose in noncellulosic polysaccharides was the highest compared with all other cell wall sugars immediately after the pulse and decreased substantially during the subsequent chase. The relative radioactivities of the other cell wall sugars changed with differing rates, indicating turnover of specific polysaccharides. Notably, after 1 month of chase there was a marked decrease in the proportional mass and total radioactivity in cell wall galactose, indicating a long-term turnover of the galactans enriched in the fiber-containing tissues. The ratio of radiolabeled xylose to arabinose also increased during the chase, indicating a turnover of arabinose-containing polymers and interconversion to xylose. The pattern of label redistribution differed between organs, indicating that the cell wall turnover processes are tissue- and cell-specific.

Journal Article↗
PubMed1994

Glucose translocation and metabolism in the rat jejunum perfused in once-through mode in vitro.

Simultaneous once-through luminal and vascular perfusions with glucose of rat jejunum in vitro were used in an attempt to resolve conflicting reports on glucose metabolism in jejuna perfused in once-through mode in vivo and in recirculation mode in vitro. Results include: (a) respiration rates during each perfusion, (b) CO2 production from absorbed glucose, (c) absolute rates of glucose absorption from the lumen into the epithelium, (d) absolute rates of glucose translocation from lumen to vascular bed, (e) absolute rates of lactate excretion into the two perfusion media, (f) recoveries of absorbed glucose, (g) the distribution of radioactivity among translocated glucose and its metabolites. About 50% of the total lactate originates in the glucose extracted from the vascular medium during concomitant absorption and translocation of luminal glucose. The results suggest what further experiments need to be done. Results from recirculation perfusions in vitro cannot contest or confirm the results quoted from experiments conducted with once-through perfusions in vivo.

Animals↗