[On the diffusion of substances of different size and solubility in nasal mucosa].
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Absorption↗
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Results for “GLUCOSE, RADIOACTIVE”
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Estimating rapid changes in the rates of glucose production from glycogenolysis and recycling through lactate.
In order to obtain independent estimates of changes in the rate of glucose production from glycogenolysis from the glucose carbon recycled throught lactate, previously validated nonsteady tracer methods are used. Changes in glycogenolysis are estimated by calculating the rate of appearance of a label ([6-3H]glucose) uniformly distributed through glycogen and simultaneously the rate of recycling of 14C is measured under nonsteady-state conditions. It is indicated that these results can be extended to the determination of absolute rates of glucose production from glycogen breakdown and gluconeogenetic precursors.
Animals↗
Analysis of the Radiorespirometric pattern after administration of [U-14C] glucose to Ehrlich ascites tumor-bearing mice.
Ehrlich ascites tumor-bearing mice were subjected to 14CO2 radiorespirometric analysis after administration of [U-14C]glucose, and the results were compared with the levels of host liver glycolytic enzyme activities and the uptake of the radioactivity into the liver. After IP administration of [U-14C]glucose, there was a progressive decline in respiratory 14CO2 after the transplantation of the Ehrlich ascites tumor cells. The peak time (PT) was about 10 min on day 1, but thereafter was increasingly delayed, and could not be determined on day 13. Peak height (PH) and yield value (YV) were both considerably decreased, and again the magnitudes of the changes increased with the time after transplantation of the tumor cells. Glycolytic enzyme activities in the host liver were at normal levels 13 days after transplantation of the tumor cells. The uptake of the radioactivity into the liver after IP administration of [U-14C]glucose began to decline from day 5 and was 50% the value in normal mice 13 days after transplantation of the tumor cells. THese results indicate that the radiorespirometric patterns with [U-14C]glucose reflects hepatic biochemical changes rather well.
Animals↗
Action of diethylstilbestrol on staphylococci: further observations on the effect of resting cells.
Diethylstilbestrol (DS) has been shown to be active against staphylococci and other gram-positive bacteria but not against gram-negative microorganisms. The present study extends these findings. Standardized suspensions of (14)C-labeled Staphylococcus aureus serotypes III and IV and Shigella flexneri were prepared and exposed to pharmacological concentrations of DS (1 to 20 mug/ml) under diverse environmental conditions; the cells were removed by membrane filtration and the presence of radioactive substances in release to the supernatant fraction was followed by standard radioisotopic techniques. Controls were exposed similarly to the hormone vehicle alone (buffer containing 2% ethyl alcohol). DS at bactericidal concentrations above 6 mug/ml caused significant leakage of cellular radioactivity of S. aureus labeled with (14)C-glucose and (14)C-glutamic acid within 1 to 4 hr after exposure to DS. Maximum leakage of radioactivity occurred under anaerobic conditions at 37 C. Absorption studies of (14)C-labeled DS indicated that the affinity of S. flexneri for DS is markedly less than that of S. aureus. This might be one reason for the resistance of gram-negative bacteria to DS.
Absorption↗
Functional imaging of head and neck tumors using positron emission tomography.
Positron emission tomography (PET) is an imaging modality that generates in vivo maps of tissue radioactivity originating from a labelled substrate of glucose metabolism: 18-fluorine labelled deoxy-glucose (FDG). This study was undertaken to evaluate PET in the detection of head and neck malignancies, and to determine its effectiveness in diagnosing recurrent cancer in operated or irradiated fields. PET revealed that each biopsy-proven tumour is an area of increased radioactivity. Tumour radioactivity ranged from 130% to 300% above that of the cerebellum, and up to 650% above the contralateral, normal side. By basing the maps on tissue metabolic function, PET proved capable of distinguishing tumour (increased radioactivity) from scar tissue (reduced radioactivity). Its application may facilitate the diagnosis of recurrent tumours amid the fibrosis and distortion of normal architecture in operated, irradiated fields.
Adult↗
Gluconeogenesis from lactate in the developing rat. Studies in vivo.
1. The specific radioactivity of plasma l-lactate and the incorporation of (14)C into plasma d-glucose, liver glycogen and skeletal-muscle glycogen were measured as a function of time after the intraperitoneal injection of l-[U-(14)C]lactate into 2-, 10- and 30-day-old rats. 2. Between 15 and 60min after the injection of the l-[U-(14)C]lactate, the specific radioactivity of plasma lactate decreased with a half-life of 20-33min in animals at all three ages. 3. At all times after injection examined, the specific radioactivity of plasma glucose of the 2- and 10-day-old rats was at least fourfold greater than that of the 30-day-old rats. 4. Although (14)C was incorporated into liver glycogen the amount incorporated was always less than 5% of that present in plasma glucose. 5. The results are discussed with reference to the factors that may influence the rate of incorporation of (14)C into plasma glucose, and it is concluded that the rate of gluconeogenesis in the 2- and 10-day-old suckling rat is at least twice that of the weaned 30-day-old animal.
Age Factors↗
Biosynthesis of glycosaminoglycans in bovine cornea. The effet of uridine diphosphate xylose.
1. The role of UDP-xylose in the regulation of corneal glycosaminoglycan biosynthesis was investigated. Bovine corneas were incubated with [U-(14)C]-glucose in the presence and in the absence of the nucleotide, and the radioactivity of chondroitin, chondroitin sulphate and keratan sulphate, as well as of their monosaccharide constituents, was determined. 2. A decrease in the rate of biosynthesis of chondroitin and chondroitin sulphate and an increase in that of keratan sulphate were observed in the samples incubated with UDP-xylose. 3. The UDP-glucuronic acid isolated after the incubation in the presence of UDP-xylose showed a noticeable decrease in the amount of radioactivity incorporated; this result suggests that UDP-xylose inhibits the UDP-glucose dehydrogenase, causing an accumulation of UDP-glucose and consequently an increase in the formation of UDP-galactose and keratan sulphate. 4. Galactose and galactosamine isolated from the polysaccharides showed variations in the amount of radioactivity incorporated in accordance with those observed for the macromolecules; this fact confirms that in the system we used in vitro a real biosynthesis of the polysaccharide chain took place and that the regulatory effect of UDP-xylose was active at the monosaccharide level.
Alcohol Oxidoreductases↗
Comparison of methods to determine glucose kinetics and measurement of recycling and lactose formation in lactating cows.
Several investigators have suggested that the conventional multicompartmental exponential analysis of in vivo glucose metabolism is arbitrary and possibly not the most accurate description of glucose kinetics, especially in the large animal. In support of that hypothesis, we found that in a systematic comparison of 3 methods, blood-specific radioactivity data in single-injection studies of glucose metabolism in lactating cows was better described graphically, or by a hybrid polynomial-biexponential curve fit, than by an exclusively exponential curve fit. We hypothesized that this finding was attributable to partial failure of linearity and steady-state assumptions that underlie the exponential model. Second, using both an irreversible tracer (3H-labeled glucose) and reversible tracer (14C-labeled glucose), we found that glucose carbon recycling had no effect during the first 2 hours, but became significant in lactating cows 7 hours after injection. Finally, we determined that approximately 52 to 55% of the glucose replacement rate was being used to generate lactose.
Animals↗
Wall regeneration by plasmolysed cells from tissue suspension cultures of Sphaerocarpos donnellii.
De novo synthesis of wall material by cells of Sphaerocarpos donnellii was followed using radioactive tracer techniques. Uniform uptake of [14C]glucose by plasmolysed suspension cultures was demonstrated autoradiographically. Liquid scintillation counts of acid- or alkali-soluble wall carbohydrates indicate that hemicellulose and cellulose make up the major wall fractions in control and plasmolysed tissues. The amount of label in walls of plasmolysed cells was significantly lower than in those of controls. Higher relative radioactivity in pectin and hemicellulose, and lower radioactivity in cellulose were found in plasmolysed tissue. These compositional changes may enhance wall stability by providing numerous sites for cross-linkage between cellulose microfibrils of regenerated walls.
Autoradiography↗
An autoradiographic study of [(18)F]FDG uptake to islets of Langerhans in NOD mouse.
To evaluate the potential of in vivo imaging of accumulation of lymphocytes to islets of Langerhans (insulitis), we compared 2-[(18)F]fluoro-2-deoxy-d-glucose ([(18)F]FDG) uptake in the pancreas and pancreatic islets of healthy BALB/c mice, phenotypically healthy NOD mice with insulitis and diabetic NOD mice. [(18)F]FDG was injected i.v. to 14 female BALB/c mice (age 13+/-3 weeks, plasma glucose 8+/-2 mmol/l) and 21 age-matched female NOD mice (plasma glucose 8+/-4 mmol/l, p=0.06). The mice were killed 90-min post injection and distribution of radioactivity was analysed using digital autoradiography. There was no correlation of plasma glucose concentration with the [(18)F]FDG uptake values. Uptake of radioactivity in NOD mice to the islets affected by insulitis was up to 2.3 times higher (p=0.001) than that to unaffected islets in the same pancreas. Uptake to NOD islets with insulitis was also clearly enhanced (1.0-2.3 times higher) compared to the islets in the BALB/c mice. In conclusion, NOD mouse islets with insulitis accumulate [(18)F]FDG markedly more than islets without insulitis or BALB/c islets. However, the relatively small difference in the [(18)F]FDG intensity between healthy and diseased islets, combined with the limited resolution ability of the positron emission tomography (PET), probably prevent the use of [(18)F]FDG in PET studies aiming at in vivo documentation of onset and progression of insulitis and prediabetes in mouse and man.
Animals↗
Taurocholic acid adsorption during non-starch polysaccharide fermentation: an in vitro study.
The association of radiolabelled taurocholic acid with the solid fraction of a faecal fermentation mixture was measured. A human faecal inoculum was incubated with [24-14C]taurocholic acid and several non-starch polysaccharide sources (pectin, wheat bran, ispaghula (Plantago ovata) husk and seed), glucose or a substrate-free control. Portions of fermentation mixture were taken at 0, 3, 6, 21 and 24 h and centrifuged to acquire a supernatant fraction and a pellet containing the fermentation residue. 14C was measured in supernatant fractions and pellets at all time points. Volatile fatty acids (VFA) were measured at 0 and 24 h to confirm bacterial growth. Radioactivity in the pellet increased over time for all substrates. Glucose resulted in the greatest incorporation of taurocholic acid into the pellet, followed by pectin. At 24 h the proportion of the total radioactivity found in the pellet was 92% for glucose, 79% for pectin, 60% for wheat bran, 59% for ispaghula seed, 53% for ispaghula husk and 26% for the control (mean of duplicates). Glucose and pectin produced the greatest quantity of VFA at 24 h. VFA production was highly correlated with radioactivity in the pellet (r0.976, P < 0.005). These results suggest that the bile acid binding capacity of a faecal culture mixture may be strongly influenced by the fermentability of the available substrate and hence related to bacterial metabolic activity.
Adsorption↗
Interaction of cytoplasmic dehydrogenases: quantitation of pathways of ethanol metabolism.
The interaction between xylitol, alcohol and lactate dehydrogenase has been studied in hepatocytes from rats by applying specifically tritiated substrates. A simple model, describing the metabolic fate of tritium from [2-3H] xylitol and (1R) [1-3H]ethanol is presented. The model allows calculation of the specific radioactivity of free, cytosolic NADH, based on transfer of tritium to lactate, glucose and water. From the initial labelling rate of lactate and the specific radioactivity of cytosolic NADH, we have determined the reversible flow through the lactate dehydrogenase catalyzed reaction to 1-5 mumol/min . g wet wt. The results suggest that xylitol, alcohol and lactate dehydrogenase share the same pool of NAD(H) in the cytoplasma. This finding allows estimation of the ethanol oxidation rate by the non-alcohol dehydrogenase pathways from the relative yield of tritium in water and glucose. The calculations are based on a comparison of the fate of the 1-pro-R hydrogen of ethanol and the hydrogen bound to carbon 2 of xylitol or carbon 2 of lactate under identical conditions.
Alcohol Dehydrogenase↗
Effects of insulin on steady state kinetics of GLUT4 subcellular distribution in rat adipocytes. Evidence of constitutive GLUT4 recycling.
We labeled rat adipocyte cell surface glucose transporters with an impermeable, photoreactive glucose analogue, 1,3-bis-(3-deoxy-D-glucopyranose-3-yloxy)-2-propyl 4-benzoylbenzoate (B3GL) and its radioactive tracer [3H]B3GL. The labeling did not affect glucose transporter subcellular distribution in basal and insulin-stimulated adipocytes. When basal or insulin-stimulated adipocytes were labeled with [3H]B3GL and incubated at 37 degrees C in steady state, labeled GLUT4 was rapidly reduced at the cell surface and stoichiometrically recovered in microsomes without any change in GLUT4 protein levels in either pool. The labeled GLUT4 equilibrium exchange was found to be a simple first order process describable by two first order rate constants, one for internalization (k(in)) and the other for externalization (kex). Insulin affected both rate constants, reducing k(in) by 2.8-fold and increasing kex by 3.3-fold. It is concluded that GLUT4 constantly and rapidly recycles in adipocytes between the cell surface and its storage pool, and insulin increases the cell surface GLUT4 level in rat adipocytes by modulating both the internalization and the externalization steps of constitutively recycling GLUT4.
3-O-Methylglucose↗
The glucose metabolism of adult Ostertagia circumcincta, in vitro.
Adult Ostertagia circumcincta from freshly killed sheep were incubated at 39 degrees C in a medium containing inorganic salts, antibiotics and D-[U-14C] glucose. The worms appeared healthy even after incubation for as long as 72 h. All the radioactivity was recovered either within the worms or in the incubation vessel in the form of metabolic products or unmetabolized glucose. Incubations were carried out at low oxygen tension except for those in which CO2 was measured. These were either aerobic or anaerobic. In terms of both quantity and radioactivity the main metabolic products of glucose were CO2, propan-1-ol, acetate and propionate. Smaller amounts of ethanol, lactate and succinate were formed. The results are compared with those found for the similar nematode Haemonchus contortus.
1-Propanol↗
Glutamate as a CNS transmitter. I. Evaluation of glucose and glutamine as precursors for the synthesis of preferentially released glutamate.
Slices of the molecular layer of the dentate gyrus of the hippocampal formation were incubated with either [14C]glucose, [14C]pyruvate or 14C glutamine and the efflux of endogenous and radioactive glutamate was monitored under various conditions. After prelabeling with either [14C]glutamine or [14C]glucose elevation of K+ concentration to 56 mM (Ca2+ free) increased efflux of endogenous and [14C]glutamate. Introduction of Ca2+ into the elevated K+ medium further increased the efflux of endogenous glutamate and radioactive glutamate derived from any of the precursors tested. In glutamine containing media, the increase in glutamate efflux as well as basal efflux was considerably higher than in the absence of glutamine and the specific activity of glutamate release was higher than that in tissue. Thus glutamine was superior to glucose or pyruvate as precursor and most specifically labeled the putative transmitter pool of glutamate. Similar experiments were carried out 4 and 14 days after a unilateral lesion in the entorhinal cortex which provides about 60% of the total synaptic input to the dentate granule cells. The Ca2+ dependent release of glutamate derived from either glucose or glutamine was markedly reduced on the operated side. This result suggests that the transmitter pool of glutamate is in perforant path terminals and can be synthesized from glucose or glutamine.
Animals↗
Biosynthesis and structure of glycosyl diglycerides, steryl glucosides, and acylated steryl glucosides.
A particulate enzyme fraction from Mycobacterim smegmatis catalyzed the transfer of -14C-glucose from the UDP--14C-glucose into neutral glycolipids. The two major radioactive components were purified by column chromatography on O-diethylamino ethyl cellulose (acetate) and thin layer chromatography on silica gel in several solvents. The first product yielded a water-soluble component upon saponification, which had a hexoseglycerol ratio of 1:1 with all of the hexose being identified as glucose. The second product yielded a water-soluble component upon saponification which contained hexose and glycerol in a 2:1 ratio and, in addition to glucose, contained lesser amounts of mannose and galactose. Palmitate and oleate were the predominant fatty acids and were present in equimolar amounts. The products thus have been identified as monoglycosyldiglyceride and diglycosyldiglyceride. The diglycosyldiglyceride could also be labeled with -14C-galactose when UDP--14C-galactose served as the donor, but the monoglycosyldiglyceride was only slightly labeled with -14C-galactose. Membrane fractions from mung bean seedlings catalyzed the transfer of -14C-glucose from UDP--14C-glucose into a neutral glycolipid which has been purified by thin layer chromatography and analyzed by combined gas liquid chromatography-mass spectrometry. It was determined to be a steryl glucoside with the two major sterol components being betasitosterol and stigmasterol linked to beta-D-glucose. Particulate fractions from developing cotton fibers also catalyzed the formation of steryl glucosides and, in addition, they catalyzed the esterification of steryl glucosides at the 6 position of glucose with fatty acids (primarily palmitate and oleate) from an andogenous acyl donor. Both the glucosyl transferase and the acyltransferase have been solubilized with Triton X-100 and partially purified by chromatography on Sephadex G-200. The acyltransferase activity was reconstituted by the addition of the steryl glucoside and a phospholipid acyl donor.
Acyltransferases↗
Glycogen turnover in skeletal muscle is stimulated along with glucose uptake in vivo during contraction.
We have shown previously that glycogen synthesis in the heart can be stimulated in vivo by epinephrine. Our aim in this study was to determine whether glycogen synthesis in skeletal muscle can be similarly affected during increased energy expenditure. Left sciatic nerves of anesthetized fasted rats were electrically stimulated to allow left hindlimb muscles to contract for 5, 10, and 20 min. Glycogen contents in the contracting muscles at the end of electrical stimulation were found to be approximately 40% less than resting muscles in the right hindlimbs in all three groups of rats. Accompanying the enhanced glycogenolysis was increased incorporation of the intravenously infused [3-(3)H]-glucose into glycogen. The rate of tritium incorporation into glycogen in the contracting muscle was found to be 34-fold greater than resting muscles. Glucose utilization was determined by the phosphorylation of the intravenously injected [14C]-2-deoxyglucose in the skeletal muscle. The rate of accumulation of [14C]-2-deoxyglucose-6-phosphate in the contracting muscles was found to be 28-fold greater than resting muscles. Glycogen synthesis and glucose uptake indexes, calculated by dividing the radioactivity in [3H]-glycogen and [14C]-2-DGP by the mean specific activity of their respective precursors in the plasma, were not found to be significantly different in the contracting muscle. In conclusion, our data indicate that: (i) glycogenesis and glycogenolysis can be stimulated concurrently in the skeletal muscle; and (ii) glucose utilization in the skeletal muscle during contraction may be mediated through glycogen turnover.
Animals↗
Nonenzymatic glycosylation of basement membranes: in vitro studies.
Incubation of purified rat glomerular basement membrane (GBM) with [14C]-glucose in vitro resulted in the incorporation of [14C] into acid-precipitable radioactivity in a reaction that was time and temperature dependent. Findings with rat lens capsule basement membrane (LCBM), an anatomically distinct but chemically similar extracellular matrix, incubated for varying times at different temperatures with [14C]-glucose at constant specific activity were similar. Nonenzymatic glycosylation of basement membrane, documented by hydroxymethylfurfuraldehyde generation after incubation with unlabeled glucose, increased in proportion to the ambient glucose concentration over a range of 5--100 mM. Acid-precipitable radioactivity also increased in proportion to [14C]-glucose concentration, although this method overestimated glycosylation about 15-fold at 5--20 mM glucose and 50-fold at 50--100 mM glucose. Coupled with recent in vivo studies, these findings indicate that exposure to increased glucose concentration alters the chemistry of glomerular and other basement membranes. Since accumulation of basement membrane characterizes several of the microangiopathic sequelae of diabetes, the role of increased nonenzymatic glycosylation on the structure, function, and metabolism of basement membrane warrants investigation.
Animals↗