Wide Range Of Glucose Concentrations Research Articles

Tissue glucose utilization during epinephrine-induced hyperglycemia.

The aim of this study was to investigate glucose utilization by individual tissues during epinephrine infusion. First, the applicability of the 2-deoxyglucose (2-DG) tracer technique during in vivo hyperglycemia was investigated in model systems in vitro. Epitrochlearis muscle and spleen cells were incubated with 1.25-20 mM glucose. The discrimination against 2-[14C]DG in glucose metabolic pathways, expressed by the lumped constant, remained unchanged over this wide range of glucose concentrations. It was concluded that in vivo hyperglycemia does not preclude the application of the 2-DG method. In a series of in vivo experiments, chronically catheterized conscious rats fasted for 24 h and were infused with epinephrine (0.2 microgram.kg-1.min-1), which produced a two-fold increase in plasma glucose concentration. 2-[14C]DG was injected 30 min after starting the epinephrine infusion and glucose utilization rates of individual tissues were calculated based on the concentration of phosphorylated 2-DG in samples excised at 70 min. The epinephrine infusion increased glucose utilization rates by 40-160% in hindlimb muscles, skin, ileum, liver, spleen, lung, epididymal fat, and kidney, although no change was found in the brain. Mass action of the increased plasma glucose is likely to play an important role in the enhanced rate of glucose utilization.

Evidence for functionally distinct glucose transporters in basal and insulin-stimulated adipocytes.

The activity and Km of glucose transport of rat adipocytes are quite variable in the basal state. This could be due to differing levels of highly saturable transport against a background of less saturable transport. Such heterogeneity could lead to differing conclusions as to the Km of basal cells compared to insulin-stimulated cells depending on the choice of substrate, the range of concentrations tested, and the rigor of data analysis. In the present work, we used a cell preparation which was stable and partially activated by constant agitation. We used a two-component model to fit the concentration dependence of D-glucose uptake. We defined two parallel pathways of glucose entry, a high-affinity/low-capacity pathway and a low-affinity/high-capacity pathway. Both pathways were stereospecific and were inhibited by cytochalasin B. The low-affinity pathway in basal cells had 97% of the total capacity (Vmax) with a high Km (greater than 50 mM). A second pathway had a very low Km (less than 1 mM) and only 3% of the total capacity, but contributed to 30-60% of glucose uptake at 8 mM glucose. In insulin-stimulated cells, a pathway with a Km of 4-5 mM dominated and contributed 85% of glucose transport. The low-affinity but not the very high affinity pathway persisted in stimulated cells, but its contribution was only 10-15% of transport at 8 mM glucose. These results suggest the presence of at least two functionally distinct transporters whose respective contributions can be characterized by nonlinear regression of data over a wide range of glucose concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Quality assessment of visual test strips for home blood glucose monitoring

AbstractA quality control filter‐paper method was applied to the assessment of two glucose enzyme reagent strips — Type A and Type B — in the home environment. Forty insulin‐dependent diabetics, experienced in home blood glucose monitoring, took part in a randomised, cross‐over trial. Marked variation was observed in the accuracy of readings with both strips over a wide range of glucose concentrations. Overall, Type B was found to read consistently higher than the reference filter‐paper method, whereas Type A read consistently higher for reference glucose concentrations < 10 mmol/l, but lower for concentrations ≥10 mmol/l. In particular, both strips were equally poor at detecting filter‐paper concentrations in the hypoglycaemic range. Although both strips have been modified since the study was initiated, the principle of quality control is equally applicable to all other currently used and visually read strips. Recommendations are provided for the quality assessment of all reagent strips employed by patients for home blood glucose monitoring.

Effects of cysteamine and antibody to somatostatin on islet cell function in vitro. Evidence that intracellular somatostatin deficiency augments insulin and glucagon secretion.

In this study we have characterized the effects of cysteamine (CHS) on the cellular content and release of immunoreactive somatostatin (S-14 LI), insulin (IRI), and glucagon (IRG) from monolayer cultures of neonatal rat islets. Incubation of cultures with 0.1-10 mM CHS for 1 h led to an apparent, dose-dependent reduction of cellular S-14 LI that was 50% of control at 0.3 mM, 87% at 1 mM, and 95% at 10 mM. IRI content was unaffected by CHS up to 1 mM, but at 10 mM 90% loss of IRI occurred. All concentrations were without effect on IRG content. The loss of S-14 LI and IRI was completely reversible with time, but with different recovery rates for the two hormones (48 h for S-14 LI, and 72 h for IRI). Released S-14 LI rose progressively with increasing doses of CHS from 21 +/- 2.5 pg/ml per hour to 41 +/- 1.4 pg/ml per hour at CHS concentrations of 5 mM and 10 mM. IRI and IRG secretion were both also significantly enhanced (by 55% and 88%, respectively), despite the elevated medium S-14 LI. Since CHS reduced cellular S-14 LI but augmented medium S-14 LI, the relative effects of CHS (1 mM) and immunoneutralization with antibody to S-14 LI on IRI and IRG secretion were tested. Anti S-14 LI alone stimulated basal IRG (67%) but not IRI. Cultures rendered S-14 LI deficient with both CHS and anti-S-14 LI exhibited threefold and 2.3-fold potentiation of IRG and IRI secretions, respectively, greater than that expected from the separate effects of the two agents. Increasing medium glucose from 2.8 mM to 16.7 mM stimulated IRI release by 86% and suppressed IRG by 53%. CHS (1 mM) and anti-S-14 LI further augmented stimulated IRI release, by 30%; although 16.7 mM glucose suppression of IRG was still maintained under these conditions, the quantitative IRG response was significantly greater. These results suggest that CHS induces an apparent loss of islet S-14 LI, and at high doses, of IRI as well, but has no effect on A cells. Complete islet S-14 LI deficiency augments IRI and IRG secretion over a wide range of glucose concentrations, suggesting a physiological role of D cells on B cell and A cell regulation. D cell modulation of B cells requires cellular but not extracellular S-14 LI, being mediated probably though direct intracellular communication, whereas the A cells seem to be regulated by both direct contact as well as through locally secreted S-14 LI.

Kinetics of sodium D-glucose cotransport in bovine intestinal brush border vesicles.

Brush border membrane vesicles ( BBMV ) purified from steer jejunum were used to study the kinetics of sodium D-glucose cotransport under voltage clamped, zero-trans conditions. When the initial rate of glucose transport ( Jgluc ) was measured over a wide range of glucose concentrations ([S] = 0.01-20 mM), curvature of the Woolf - Augustinsson -Hofstee plots was seen, compatible with a diffusional and one major, high capacity (maximal transport rate Jmax = 5.8-8.8 nmol/mg X min) saturable system. Further studies indicated that changes in cis [Na] altered the Kt, but not the Jmax, suggesting the presence of a rapid-equilibrium, ordered bireactant system with sodium adding first. Trans sodium inhibited Jgluc hyperbolically, KCl-valinomycin diffusion potentials, inner membrane face positive, lowered Jgluc , while potentials of the opposite polarity raise Jgluc . At low glucose concentrations ([S] less than 0.05 mM), a second, minor, high affinity transport system was indicated. Further evidence for this second saturable system was provided by sodium activation curves, which were hyperbolic when [S] = 0.5 mM, but were sigmoidal when [S] = 0.01 mM. Simultaneous fluxes of 22Na and [3H]glucose at 1 mM glucose and 30 mM NaCl yielded a cotransport-dependent flux ratio of 2:1 sodium/glucose, suggestive of 1:1 (Na/glucose) high capacity, low affinity system and a approximately 3:1 (Na/glucose) high affinity, low capacity system. Kinetic experiments with rabbit jejunal brush borders revealed two major Na-dependent saturable systems. Extravesicular (cis) Na changed the Kt, but not the Jmax of the major system.

Microcalorimetric Measurements of Glucose Metabolism by Marine Bacterium Vibrio alginolyticus

Microcalorimetric measurements of heat production from glucose by Vibrio alginolyticus were made to assess the viability of calorimetry as a technique for studying the metabolism of marine bacteria at organic nutrient concentrations found in marine waters. The results show that the metabolism of glucose by this bacterium can be measured by calorimetry at submicromolar concentrations. A linear correlation between glucose concentration and total heat production was observed over a concentration range of 8 mM to 0.35 muM. It is suggested that these data indicate a constant efficiency of metabolism for this bacterium over the wide range of glucose concentrations studied.

Islet cell function in gold thioglucose-induced obesity in mice.

Blood insulin, blood glucose and the biosynthesis and release of insulin have been studied in mice made obese with a single injection of gold thioglucose. In such mice, blood glucose levels were normal, though serum insulin rose in parallel with the development of obesity. When compared with controls, insulin secretion and synthesis were increased in isolated islets of Langerhans from obese mice, over a wide range of glucose concentrations. However, in obese animals, insulin biosynthesis was augmented above control levels at 2 mmol/l glucose, whilst the increase in insulin secretion accompanying obesity only became evident at glucose concentrations greater than 5 mmol/l. After 2 min incubation, cyclic AMP rose more in islets from obese mice than in controls, though cyclic AMP levels did not significantly differ in either group after 10 min incubation with glucose. Glucose oxidation was also increased in islets of Langerhans from obese mice. It seems possible that changes in glucose oxidation, as well as in cyclic AMP levels, contribute to the alteration in the B cell response in this type of obesity.

Stimulation of the hexosemonophosphate-pentose pathway by pyrroline-5-carboxylate in cultured cells.

delta 1-Pyrroline-5-carboxylic acid, an intermediate in the interconversions of proline, ornithine, and glutamate, is a potent stimulator of glucose oxidation through the hexosemonophosphate-pentose pathway. The effect is observed in cultured human fibroblasts, Chinese hamster ovary cells (CHO-K1), and rabbit kidney cells (LLC-RK1). In human fibroblasts, the magnitude of the stimulation of the hexosemonophosphate-pentose pathway is dependent on the concentration of added pyrroline-5-carboxylate and the effect is observed over a wide range of glucose concentrations. The mechanism of the effect is related to the generation of oxidizing potential in the form of NADP+ by pyrroline-5-carboxylate reductase concomitant with the conversion of pyrroline-5-carboxylate to proline. In LLC-RK1 cells, a cell line unique in having proline oxidase activity, proline also stimulated hexosemonophosphate-pentose pathway activity. Although pyrroline-5-carboxylate markedly stimulated the hexosemonophosphate-pentose pathway, it has no effect on glucose metabolism in the Embden-Meyerhof pathway or the tricarboxylic acid cycle. Since the hexosemonophosphate-pentose pathway is a source of ribose-5-phosphate, the precursor of phosphoribosyl pyrophosphate, the effect of pyrroline-5-carboxylate on the hexosemonophosphate-pentose pathway may link amino acid and nucleic acid metabolism.

Potentiation of Glucose-induced Insulin Release by Glucose in the Isolated Pancreas of Fed and Fasted Rats

Glucose, apart from its acute insulin-releasing effect, exerts a time-dependent potentiating action on subsequent stimulations of the pancreas. The influence of a 24-hour starvation on these two actions of glucose was studied with the completely isolated, perfused rat pancreas preparation. Starvation had no effect on the time kinetics of the insulin response, but the magnitudes of the early and late insulin-secretion phases were reduced to similar extents. It was demonstrated by using a wide glucose concentration range that the maximal insulin response is not significantly modified by starvation. In contrast, both the threshold of stimulation by and the Km for glucose were higher in the pancrease from fasted rats. Thus, starvation reduces the sensitivity of the islet for the insulin-releasing action of glucose. When the stimulatory concentrations of glucose were preceded for 40 minutes by the perfusion of 8.3 mM instead of the basal, 4.4 mM glucose, insulin secretion from the pancreas of fed animals was not modified. In contrast, raising the glucose concentration of the equilibrium period to 8.3 mM potentiated markedly the insulin response to subsequent stimulations in the pancreas from fasted rats. This potentiation expressed itself as increase in the maximal response: the Km for glucose was not reduced. Thus a 40-minute pretreatment with 8.3 mM glucose does not correct the diminished sensitivity induced by a 24-hour starvation. It is concluded that in starvation (1) the sensitivity for glucose of the mechanisms that initiate insulin release is diminished; (2) the sensitivity of the pancreas for the potentiation-inducing action of glucose is augumented. (3) In both respects, the insulin response of fasted rats is similar to that of mildly diabetic subjects. These and other findings suggest that the effect of glucose in initiation of insulin release and on generation of a state of potentiation in the islet are mediated by different mechanisms.

Placental glycogen.

The quantity and distribution of glycogen has been studied in 86 placentae from the last trimester of pregnancy and 8 of 8 to 16 weeks gestational age. In the first trimester glycogen concentrations were high, between 4-5 to 6-5 mg/g of blood-free tissue, but from about 12 weeks to term the concentrations were within a narrow range around 1-5 mg/g. The level did not deviate appreciably from normal in a range of clinical conditions: diabetes, intrauterine growth retardation, pre-eclampsia or acute fetal distress, and was unaffected by the length of labour and whether or not the mother had been given an infusion of dextrose. Nor was it affected by a wide range of glucose concentrations in the maternal and fetal plasma and in the placental tissue itself or by insulin concentrations in either circulation. After the first few weeks of pregnancy glycogen in the placenta was shown to be restricted to the vicinity of major fetal blood vessels. Here it may be presumed to act as an energy reserve for vasomotor activity. All the evidence suggests that any importance placental glycogen may have is likely to be local, in relation to the placental vessels; a more general role, as an emergency energy source for the fetus, seems unlikely.

Evaluation of Trinder's Glucose Oxidase Method for Measuring Glucose in Serum and Urine

Trinder's method for glucose has nearly all the attributes of an ideal automated colorimetric glucose oxidase procedure. The chemicals used in the color reaction with peroxidase are readily available, the solutions are stable and can be prepared by the user, the method is highly specific and largely free of interferences, the sensitivity can be adjusted by the user to cover a wide range of glucose concentrations, and the reagents are not hazardous. We found very good agreement between results by this method and by the hexokinase and Beckman Glucose Analyzer methods. The method has been modified and adapted to the AutoAnalyzer I and SMA 6/60 (Technicon) with manifolds that give very little interaction between specimens. A study of the method by the simplex technique revealed that the glucose oxidase activity in the reagent is the most critical variable.

Long-term effects of glucose on insulin release and glucose oxidation by mouse pancreatic islets maintained in tissue culture.

Rates of glucose oxidation and insulin release in response to a wide range of glucose concentrations were studied in short-term experiments in isolated mouse pancreatic islets maintained in tissue culture for 6 days at either a physiological glucose concentration (6.7mm) or at a high glucose concentration (28mm). The curves relating glucose oxidation or insulin release to the extracellular glucose concentration obtained with islets cultured in 6.7mm-glucose displayed a sigmoid shape similar to that observed for freshly isolated non-cultured islets. By contrast islets that had been cultured in 28mm-glucose showed a linear relationship between the rate of glucose oxidation and the extracellular glucose concentration up to about 8mm-glucose. The maximal oxidative rate was twice that of the non-cultured islets and the glucose concentration associated with the half-maximal rate considerably decreased. In islets cultured at 28mm-glucose there was only a small increase in the insulin release in response to glucose, probably due to a depletion of stored insulin in those B cells that had been cultured in a high-glucose medium. It is concluded that exposure of B cells for 6 days to a glucose concentration comparable with that found in diabetic individuals causes adaptive metabolic alterations rather than degeneration of these cells.

Krebszellkinetik und Krebs-Mehrschritt-Therapie / Cancer Cell Kinetics and Cancer Multistep Therapy

Basic to the proposed therapeutic usage of the difference in the in-vivo proliferation control between cancer and normal cells are the temporary selective increase in the proliferation rate and number of cancer cells in all kinds of tumors but without increase of the proliferative activity of normal cells. To further this aim, measurements of cellular kinetics are used, in connection with the glycolysis of different tumor tissues under saturation conditions, with the relationship between cancer cell cycle and glycolytic rate, or the local glucose level respectively, with the wide range of glucose concentrations in tumor regions which differ the conditions of supply, with the pO2-value critical for tumor growth (≈ 0.4 Torr), with the pO2-distribution in tumor tissues and the time distribution of cell cycles in human and animal cancerous tissues. From an approximative description of the cytostatic effects in different tumor regions and its validity limits it is estimated that the sensitivity towarts therapy is decreased to as low as one-tenth in poorly supplied tumor regions. These particular fractions of the tumor tissues determine the degree of tumor resistence. Additionally, from these considerations steps can be derived which could be important for multiplying the effect of the cytostatic attack on the critical tumor regions with poor supply conditions. These steps include: a) usage of combinations of cytostatic agents directed against all three sensitive phases of the cell cycle (S-G2-M); b) increase in blood glucose concentration to about 300 mg% for an optimum time span prior to the initiation of the main therapeutic process; c) increase in pO2 of the inspiration air to 320 or 400 Torr and in the degree of pO2 utilization by the use of specific pharmaceutic agents for the chosen time span preceding the main therapy; d) stimulation of tumor vascularization preceding the main therapy; e) decrease in the fraction of tumor cells utilizing glucose and O2 as a consequence of a post-therapy treatment 72 hours after the main therapy. The increase in the fraction of cells in a sensitive phase of the cell cycle is reached folowing synchronization after increasing the glucose concentration until saturation of the glycolytic capacity. Reasons are given, why the cytostatic attack has to be supplemented by other selective mechanisms which damage the tumor cell independent of the phase of the cell cycle. Such a mechanism is the lysosomal cytolytic chain reaction. Here, the death of tumor cells occurring during a sensitive phase of the cell cycle as a consequence of the cytostatic attack helps to damage cancer cells which are in the insensitive phase. A further mechanism of this kind is the immunological attack, which is also a component of multi-step cancer therapy

GLUCOSE METABOLISM IN NORMAL ERYTHROCYTES. I. KINETICS OF THE HEXOKINASE REACTION IN INTACT CELLS.

A method has been developed for determination of erythrocyte glucose consumption at a wide range of glucose concentrations. The method is based on paper chromatographic separation and quantitation of C14‐glucose and its labelled metabolites after incubation of intact cells.The glucose consumption was maximal at glucose concentrations above 0.4 mM.The inhibitory effect of inosine was investigated and found to be delayed, indicating an indirect action of this compound.The presence of EDTA in the medium increased the glucose consumption markedly, three to four times at 5–10 mM, whereas magnesium and calcium had no effect. EDTA removed easily exchangeable erythrocyte calcium during these conditions, but did not significantly penetrate the red cell membrane.Mercaptoethanol increased the glucose consumption, indicating the presence of potentially active SH‐groups on hexokinase in the intact cell.

Glucose oxidation in rat brain slices and homogenates

With the aid of C 14-labeling, various glycolytic and respiratory properties of rat brain preparations were studied. Glucose oxidation as well as glycolysis occurred readily in isotonic whole brain homogenates, fortified with ATP and DPN. Under optimal conditions glucose oxidation accounted for about 60 per cent of the total respiration. Added TPN markedly enhanced the oxidation of glucose carbon-1 but had no effect on the oxidation of other glucose carbons. In short-term experiments conducted over a wide glucose concentration range, glucose oxidation in homogenates was almost maximal at 0.0002 M, whereas in slices, maximal oxidation was reached at 0.001 M. Fructose-U-C 14 was readily oxidized by brain slices, but its oxidation was almost completely inhibited in the presence of glucose. Comparison of the radioactivity of lactic acid formed in brain slices and homogenates from glucose-1-C 14 and glucose-U-C 14 indicated the essential exclusive occurrence of the Embden-Meyerhof process. Although some glucose oxidation was observed with isolated brain mitochondria, it appeared this was due to contaminating cytoplasm, since glucose oxidation was greatly enhanced by the addition of the supernatant fraction.