No Effect of Hyperketonemia on Local Cerebral Glucose Utilization in Conscious Rats

Abstract: Local cerebral glucose utilization was measured by the [¹⁴C]2-deoxy- d -glucose method in conscious control and hyperketonemic rats. Hyperketonemia was induced by 3 days of starvation or by infusion of 3- hydroxybutyrate in fed rats. These treatments produced combined blood ketone body concentrations (acetoacetate + 3-hydroxybutyrate) of from 1.2 to 2.4 mM. Neither treatment significantly affected glucose utilization in any of the 15 brain regions studied. These observations indicate that hyperketonemia in resting, conscious rats does not interfere with brain uptake and phosphorylation of glucose.     

Alternative Pathways of Glucose Utilization in Brain; Changes in the Pattern of Glucose Utilization in Brain Resulting from Treatment of Rats with 6-Aminonicotinamide

The effect of 6-aminonicotinamide (6AN) treatment on the activities of alternative pathways of glucose metabolism in 20-day-old rat brain was evaluated by measurements of yields of 14CO2 from glucose labeled with 14C on carbons 1, 2, 3 + 4, or 6 and uniformly labeled glucose, and from the incorporation of 14C from specifically labeled glucose into lipids by brain slices from cerebral hemispheres and cerebellum. At the highest dose of 6AN used (35 mg/kg body weight) there was a significant decrease in the 14CO2 yields via the pentose phosphate pathway, the glycolytic route, tricarboxylic acid (TCA) cycle, and via the glutamate-gamma-aminobutyric acid pathway. Giving a graded series of doses (20-35 mg 6AN/kg body weight) revealed a hierarchy of responses in which the pentose phosphate pathway, lactate, glyceride-glycerol, and fatty acid formation were most sensitive, followed, in sequence, by the pyruvate dehydrogenase reaction, the glutamate-gamma-aminobutyrate route and, finally, the TCA cycle. The nature of the blocks in the various pathways was examined by the use of metabolite profiles.     

D-Glucose Transport in Cultured Cells of Neural Origin: The Membrane as Possible Control Point of Glucose Utilization

Abstract: The function of plasma membrane as control point of glucose metabolism has been studied in confluent monolayer of C1300 neuroblastoma (N2A) and glioma (C6) cells. In neuroblastoma, steady state intracellular glucose concentration reached the extracellular levels, while intracellular contents in C6 glioma cells remained very low. In C6 glial cells the amount of glycogen as source of energy was much higher than that found in C1300 neuroblastoma cells. Influx rates of D-glucose in C6 glioma cells were only half those found in neuroblastoma cells. During the influx period (0-40 s) the transport of glucose in these cells did not exceed the phosphorylation rate, whereas a steady, time-dependent increase in glucose content was observed in neuroblastoma cells. While glucose uptake in neuroblastoma cells seems to be regulated at the level of phosphorylating enzymes, the control point in C6 glioma is believed to be membrane transport.     

Regionally Selective Metabolic Effects of Hypoglycemia in Brain

Abstract: Regional CNS levels of glucose reserves, glycolytic intermediates, and high-energy phosphate reserves were measured in insulin-treated, hypoglycemic rats and correlated with EEG activity. Intravenous administration of insulin to paralyzed, ventilated animals causes concomitant reduction of blood glucose levels and progressive abnormality and eventual loss of EEG activity. In all regions of brain examined, glucose and glycogen levels decrease until they are essentially depleted, and glucose-6-phosphate and fructose-1,6-biphosphate fall approximately 80%. Pyruvate levels decrease 50% in cerebral cortex and brain stem and a lesser amount in striatum, hippocampus, thalamus, and cerebellum. Lactate levels fall 50–60% in all regions except cerebellum, where no change is observed. ATP and phosphocreatine levels remain normal until the EEG is isoelectric, and then decrease in all regions except cerebellum. These results demonstrate that hypoglycemia does not have a uniform effect on brain glucose and energy metabolism, and cerebellum seems to be relatively protected.     

The decomposition of organic compounds in soil

Summary The course of the CO₂ evolution rates of soil samples has been followed continuously in the absence and in the presence of various organic compounds. After an incubation period of 300 hours at 13 and 20°C the CO₂ evolution from pasture soil (containing 1.76% soil organic carbon) amounted to 0.13 and 0.44g CO₂–C.g soil^–1.h^–1, respectively. For arable soil (containing 1.20% soil organic carbon) the rates amounted to 0.04 and 0.09 g CO₂–C.g soil^–1.h^–1, respectively.At 20°C larger amounts of the organic substrates added to the soil supplied with 20 g NH₄NO₃–N.g soil^–1 were lost as CO₂ than at 13°C, indicating a higher efficiency of the growth of microorganisms at lower temperatures. In the absence of NH₄NO₃ the respiration rates were initially higher than in its presence, suggesting that a part of the soil microflora is inhibited by low concentrations of NH₄NO₃. The amounts of carbon lost were low for phenolcarboxylic acids with OH groups in the ortho position. The replacement of one of these groups by a methoxyl group resulted in a larger amount of the C lost as CO₂. The replacement of the COOH group by a C=C–COOH group had a decreasing effect on the decomposition of the phenolic acids tested. The decomposition of vanillic acid,p-hydroxybenzoic acid, and of the benzoic acids with OH groups in the meta position was as complete as that of glucose, amino acids or casein. The decomposition of bacterial cells to CO₂ was considerably less than that of glucose.No evidence could be obtained that the low percentage of substrate converted to CO₂ at the time of maximal respiration rate was due to the decreasing diffusion rate of substrate to the microbial colonies in the soil during the consumption of substrate.     

Influx of γ-Aminobutyric Acid and α-Aminoisobutyric Acid into Mouse Cerebrum Slices Incubated in a Pyruvate Medium with or without Added Glucose or Glucose Analogues Compared with Influx from a Glucose Medium

Concentrative influx of γ-aminobutyric acid (GABA) and α-aminoisobutyric acid (AIB) into incubated mouse cerebrum slices is decreased when pyruvate is substituted for glucose. Influx of GABA from pyruvate medium is not increased by presence of glucose, 2-deoxy-d -glucose (2-DOG), or 3-O-methyl-d -glucose (3-O-MeG). Influx of AIB is restored to the rate from glucose medium if 2-DOG is present initially, but is not restored if 2-DOG is added with AIB. Influx is not restored if 3-O-MeG is present initially, but is restored if 3-O-MeG is added with AIB. Influx is restored if glucose is present initially or is added with AIB.     

Influence of growth environment on the phosphoenolpyruvate: Glucose phosphotransferase activities of Escherichia coli and Klebsiella aerogenes: A comparative study

A consistent difference was found between glucose-limited cultures of Escherichia coli and Klebsiella aerogenes strains in the manner which their apparent cellular content of glucose: phosphoenolpyruvate phosphotransferase (glucose-PTS) varied with growth rate. With the former strains, activity increased as a function of growth rate; in the latter it decreased. However, under glucose-sufficient conditions (potassium-or ammonia-limitation) both species behaved similarly; the glucose-PTS activity was lower and bore no obvious relationship to the rate of glucose consumption expressed by the growing culture. These results are discussed in relation to the role of glucose as a regulator of glucose-PTS synthesis, and to the likely contribution which the glucose-PTS makes to the overall rate of glucose uptake, particularly by cells growing in glucose-sufficient environments.Abbreviation Glucose-PTS phosphoenolpyruvate phosphotransferase From May to November 1978 on study leave in the University of Amsterdam     

The catabolism of glucose in Tenebrio molitor: The effects of corpora cardiaca

During the development of the mealworm Tenebrio molitor, the effects of corpora cardiaca (CC) extracts on glucose catabolism were tested. In control insects and in insects receiving CC extracts, the activity of the pentose cycle and the glycolytic-citric acid cycle, were evaluated in vivo by a radiorespirometric method using [1-¹⁴C] glucose and [6-¹⁴C] glucose as substrates. The CC extracts strongly divert glucose from the pentose phosphate pathway, which is very active in Tenebrio molitor. Glucose oxidation is reduced by the CC extracts in pupae and adults but is increased in last instar larvae. It seems that the effects of CC extracts vary depending upon the state of carbohydrate reserves.     

Differences in the infectivity of Babesia incubated in plasma and serum and the role of glucose in prolonging viability

Babesia rodhaini was less infective to mice after incubation in rat serum than in rat plasma. This was explained by lower levels of glucose in serum than in plasma. Both serum and plasma were found to become metabolically depleted of glucose following prolonged contact with clotted and unclotted blood cells, respectively. When glucose concentrations in depleted samples were restored to those in freshly separated samples, infectivities of parasites were similar. This was shown for both B. rodhaini and B. argentina. Products of blood cell metabolism, produced when separation of plasma or serum was delayed for 24 h, were not shown to have any detrimental effects on the parasites. Average glucose values for plasma from rats and cattle were 153 mg/100 ml and 63 mg/100 ml, respectively, whereas serum and plasma remaining in contact with blood cells contained as little as 2 mg glucose/100 ml. Lactate values were correspondingly low in plasma and high in serum. Fibrinogen and platelets, factors involved in clotting, did not affect infectivity of B. rodhaini or B. argentina. The relevance of these findings to living babesial vaccines in which plasma- and serum-based diluents may be used is discussed.