The 2-deoxyglucose uptake method as a first screen for neurotoxic compounds

Our primary goal is to develop a screening procedure to detect and partially characterize neurotoxic compounds. There is a great need for a new approach to screening for neurotoxicants because our industrialized world abounds with untested and potentially neurotoxic compounds. A large number of new compounds are introduced each year. Although a number of testing approaches to the screening for neurotoxicants have been proposed in the recent years, a consensus on the most adequate approach is yet to emerge. The existing methods share a number of shortcomings. Thus, most methods only detect a fraction of the tested neurotoxicants. Other methods lack the necessary resolution to detect the neurotoxic damage reproducibly and reliably. Furthermore, many screening approaches are too time consuming and costly to be used for the large-scale screening of neurotoxicants. It is, therefore, imperative to develop reliable and efficient screening methods applicable in regulatory toxicology. In this report, we describe two versions of the same method that we feel may be very beneficial for the large-scale screening of neurotoxicants. The 2-deoxyglucose (2-DG) uptake method provides an indirect measure of neuronal activity in different areas of the brain. The ability of the method to detect most, if not all, neuroactive substances is reviewed in this report. In the context of this report, a neuroactive substance is defined as a substance acting directly on the central or peripheral nervous system neurons and (or) glia. The 2-DG method equals the sensitivity of the most sensitive alternative methods which were selectively designed to detect the effects of specific groups of compounds. The generality and sensitivity of the 2-DG method are of major importance. Thus, if a tested compound does not affect the uptake of 2-DG into the brain, it is not likely to be neuroactive. Since neurotoxic compounds are a subset of neuroactive compounds, a compound that is not neuroactive is also not neurotoxic. Thus, a single test may, in some instances, determine if a tested compound is nontoxic. In addition, it appears that each compound or, at least, each family of compounds produces a characteristic profile ("pattern") of the sites of altered 2-DG uptake. This pattern can be exploited to characterize the tested compound and help us decide whether it is neurotoxic or neuroactive. Preliminary results from our laboratory indicate classical neurotoxic agents such as acrylamide, triethyltin, and 2,5-hexanedione induce a generalized depression of the 2-DG uptake throughout the brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential 2-deoxyglucose uptake into chick brain structures during passive avoidance training

The pattern of [14C]2-deoxyglucose(-6-phosphate) accumulation in the brains of 14 chicks, 24 h post hatch was investigated. Isotope was injected 1 min prior to birds pecking either a water-coated or a methylanthranilate-coated bead (passive avoidance training). Birds were killed following testing for pecking or avoidance of a similar but dry bead 30 min later. Autoradiograms of coronal and parasaggital brain sections were scanned densitometrically and uptake into 12 identified and relatively heavily labelled structures measured. Three of the structures, hyperstriatum ventrale (posterior), palaeostriatum augmentatum and lobus parolfactorius showed significantly enhanced labelling (by 10, 13 and 11%; p less than 0.001, less than 0.05 and less than 0.05 respectively) in the birds which had been trained on the methylanthranilate bead by comparison with those which had pecked at the water-coated bead. The results are discussed in relationship to other observed biochemical changes consequent on passive avoidance training.

In vivo determination of transport and metabolism of deoxyglucose in intestinal tissues

Experiments were carried out on 11 anesthetized cats (Na-pentobarbital). Uptake of a glucose analogue (2-deoxy-D-glucose) by intestinal mucosa and muscularis from arterial plasma was studied in order to determine net rate of transport and phosphorylation of the material. The theoretical basis for calculating the rate constants of forward (kx1) and reverse (kx2) transport between plasma and tissue and also phosphorylation (kx3) and dephosphorylation (kx4) of 14C labeled deoxy-glucose (DG) was determined. The method can also be used for estimating tissue glucose uptake. The rate constants were found to be: kx1 = 0.669 and 0.873; kx2 = 2.285 and 4.656; kx3 = 0.057 and 0.067; kx4 = 0.091 and 0.097 [s-1] in the mucosa and muscularis, respectively. Glucose utilisation of intestinal mucosa was 2.69 and that of muscularis 2.46 mg/(min X 100 g) tissue, respectively. Arterial glucose concentration was constant during the studies, however, it showed a variation from 120 to 250 mg/100 ml of plasma from animal to animal. Tissue glucose uptake or any of the rate constants were not influenced by the plasma level over this range.

Cholinergic denervation of the hippocampal formation does not produce long-term changes in glucose metabolism

Decreased glucose metabolism is found in Alzheimer's disease associated with a loss of cholinergic neurons. The relationship between the chronic cholinergic denervation produced by medial septal lesions and glucose metabolism was studied using 2-deoxy-D-[3H]glucose in the rat hippocampal formation. Hippocampal glucose metabolism was increased 1 week after medial septal lesions. Three weeks after lesions, glucose metabolism was profoundly suppressed in all regions. By 3 months, intraregional hippocampal glucose metabolism had returned to control values. Our results demonstrate that chronic cholinergic denervation of the hippocampal formation does not result in permanent alterations of metabolic activity.

Hexose uptake in 7,12-dimethylbenz(a)anthracene-preexposed rat tracheal epithelial cells during the progression of neoplasia

Hexose uptake during the progression of neoplasia in rat tracheal epithelial cells was studied by measuring the uptake of 2-deoxy[3H]glucose (2-dGlc) in nontumorigenic (C-18) and tumorigenic (T-8, 1000-WT) rat tracheal epithelial cell lines with varying degrees of cell association as well as in: normal primary cell cultures (NPC) derived from explants of nonexposed tracheas; selected primary cell cultures (SPC) generated from explants of 7,12-dimethylbenz(a)anthracene-treated tracheal implants; and primary tumor cell cultures (TPC) derived from explants of 7,12-dimethylbenz(a)anthracene-induced tracheal carcinomas. The latter two groups represented cells from earlier and late stages in the progression of neoplasia, respectively, and each displayed an in vitro growth advantage that allowed for their survival and growth in medium devoid of supplements of pyruvate and insulin. This property was used in this study to select the carcinogen-altered cells from neighboring normal cells. Uptake of 2-dGlc per microgram of DNA was similar in subconfluent cultures of all cell lines. At confluency, uptake per microgram of DNA was reduced markedly (greater than 3-fold) in C-18 cells but it was reduced only 1.3-fold in T-8 cells and 1.6-fold in 1000-WT cells. Hexose uptake was further reduced in T-8 and 1000-WT cell cultures generated as outgrowths from explants of denuded tracheas bearing a reestablished epithelium from each cell line. Under these conditions, T-8 cells retained higher 2-dGlc uptake than did C-18, but uptake by 1000-WT was lower, indicating that tissue-like cell associations have a profound effect on hexose uptake in these epithelial cells. Results were generally similar when uptake was expressed per mg of protein although, in several instances, the interpretation of uptake data was affected by differences in the protein content between cultures (assessed by comparing protein:DNA ratios). Compared to NPC, hexose uptake was lower in SPC and one group of TPC. A second group of TPC, characterized by loose cell associations and much cell overlapping, had distinctly higher 2-dGlc uptake than did controls. Comparable results in these primary cultures were also observed when the number of cells per culture was used as a reference for 2-dGlc uptake. Under conditions of glucose deprivation, hexose uptake was increased in NPC and SPC. The production of lactic acid in each type of culture was dependent on the level of glucose in the medium, and this was nearly 2-fold greater in NPC than in SPC.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolic rate in different rat brain areas during seizures induced by a specific delta opiate receptor agonist

The glucose utilization during specific delta opiate agonist-induced epileptiform phenomena, determined by the [14C]2-deoxyglucose technique (2-DG), was examined in various rat brain areas at different time intervals. The peak in EEG spiking response and the most intensive 2-DG uptake occurred 5 min after intraventricular (i.v.t.) administration of the delta opiate receptor agonist. The most pronounced 2-DG uptake at this time interval can be observed in the subiculum, including the CA1 hippocampal area, frontal cortex and central amygdala. A general decrease of glucose consumption, compared to control values, is observed after 10 min, in all regions, with exception of the subiculum. Since functional activity and 2-DG uptake are correlated, we suggest that the subiculum and/or CA1 area, are probably the brain regions most involved in the enkephalin-induced epileptic phenomena.

Recovery from partial deafferentation increases 2-deoxyglucose uptake in distant spinal segments

2-Deoxy[14C]glucose autoradiography was used to study the responsiveness of the partially deafferented rat spinal cord to electrical stimulation of low-threshold afferent fibers. Unilateral extradural dorsal rhizotomies were carried out at L3 to S2, sparing L5. Postoperative sensory deficits were appropriate to the extent of the lesion. Acute, 7 day, and 14 to 20 day postrhizotomy animals and unoperated controls were anesthetized prior to isotope injection and electrical stimulation of Ia fibers in the L5 root. Quantitative densitometry was carried out on enlarged autoradiographs, subdividing the spinal gray matter into laminar divisions drawn from the corresponding stained sections. Optical densities from stimulated and unstimulated sides were compared using paired t tests for each experimental group at each lumbosacral segment (L1 to S2) and at T13 for the day 14 to 20 animals. This procedure provided an objective basis for statistical comparisons between homologous areas even where the differences in density were small. Unoperated animals showed activation in 11 of 23 dorsal horn zones extending to L2 and never involving the base of the dorsal horn (lamina V). Acute and day 7 groups did not appreciably differ from the control group except for activation of lamina V within the L4 segment. In the most delayed group, 18 dorsal horn regions were activated, extending to L1 with an additional zone in T13 . Lamina V contained significant labeling in three segments. In no group was there increased labeling of the ventral horn. The results are interpreted as showing that stimulus-related, neural activity increases after a 2-week delay in regions of spinal cord distant from the normal zone of significant metabolic change. This increase in neural activity during recovery is discussed in relation to time-dependent electrophysiologic, structural, and metabolic responses to deafferentation. The longitudinal spread of dorsal horn activation by preserved afferent fibers in the spared root may facilitate more effective central transmission of sensory information.

Stimulation of deoxy[3H]glucose uptake into slices from cerebral cortex elicited by excitatory amino acids

Slices from rat cerebral cortex incubated in the presence of 2-deoxy[3H]glucose accumulate the sugar mainly in the form of its phosphorylated derivative. 2-Deoxy[3H]glucose uptake, measured under conditions of initial velocity, is stimulated by 50-100% in the presence of depolarising agents (KCl, veratridine) or the excitatory amino acids L- and D-glutamate, L-aspartate and L-cysteate in millimolar concentrations. In contrast a variety of putative neurotransmitters are ineffective on this test. The stimulations elicited by KCl or excitatory amino acids consist in significant increases in both the apparent Km and Vmax values of the 2-deoxyglucose transport system. The effect of excitatory amino acids is not significantly modified in the presence of tetrodotoxin or when the extracellular Ca2+ concentration is diminished, whereas it is significantly reduced in the presence of ouabain. Hence stimulation of 2-deoxy[3H]glucose uptake and phosphorylation may indirectly reflect the activation of Na+, K+-adenosine 5'-triphosphatases triggered by excitatory amino acids in target cells. The stimulation of 2-deoxy[3H]glucose uptake elicited by the three excitatory amino acids is antagonised in an apparently competitive manner by glutamate diethyl ester (apparent Ki value of congruent to 15 mM) whereas the KCl-induced stimulation is not modified. In contrast a variety of other amino acid agonists (including quisqualate, kainate, N-methyl D-aspartate) or antagonists (including gamma-D-glutamyl glycine acid and 2-amino-5-phosphonovalerate) are inactive, indicating that the metabolic response is not mediated by any of the receptor subclasses identified electrophysiologically.

Local cerebral metabolic rates of glucose in movement and language disorders from positron tomography

Positron-computed tomography with [18F]fluorodeoxyglucose to measure glucose metabolism has shown changes in the brain distant to a focal area of infarction, demonstrating that what appears as a focal abnormality represents a more widespread functional process. Several approaches are presented to better understand quantitative metabolic data and focus on caudate and basal ganglia function. Area-to-area correlations in Parkinson's and Huntington's diseases showed decreases in the number of cortical relationships compared with control subjects, suggesting that the basal ganglia are involved with the ability of cortical regions to function together. In aphasia, caudate metabolism correlated with several language measures that suggested a role in some undefined basic process, seemingly related to Broca's area function. The studies presented suggest that the caudate may involve integrating the processing of language and cognition with the execution of the resulting response. Motor and cognitive function seem related to similar and overlapping brain systems. The disruption of such systems may result in loss of both cognitive and motor aspects of a function.

Local cerebral metabolic effects induced by nigral stimulation following ventromedial thalamic lesions. I: Basal ganglia and related motor structures

The effects of unilateral electrical stimulation of the substantia nigra (SN) were mapped in the extrapyramidal system of conscious rats bearing ventromedial thalamic (VM) lesions, using the quantitative autoradiographic 14C-deoxyglucose method. SN-stimulation in VM-intact rats resulted in metabolic activation within the deep layer of superior colliculus, subthalamic nucleus, ventrolateral thalamus and sensory-motor cortex ipsilaterally, and bilaterally in the reticulata, compacta, centrolateral and ventromedial thalamus, striatum, globus pallidus and entopeduncular nucleus. SN-stimulation 8 days following ipsilateral VM-lesion, induced activation only within the ipsilateral compacta, subthalamic and entopeduncular nuclei and the globus pallidus and in addition, the reticulata bilaterally. However, SN-stimulation 30 days following VM-injury elicited bilateral metabolic activation in all the examined structures. It is concluded that the VM-thalamic nucleus mediates information from one SN to the ipsilateral motor cortex and striatum, as well as to the extrapyramidal components of the contralateral hemisphere. Moreover, due to the plasticity of the central nervous system, one month following the VM-lesion transmission of information from the SN to all the bilateral components of this network is reestablished.

Thermal stabilization of antithrombin III by sugars and sugar derivatives and the effects of nonenzymatic glycosylation

A variety of neutral and acidic sugars and related compounds were evaluated in terms of their effect on the midpoint, Td, of the thermal denaturation curve of antithrombin III. The objectives were to determine which structural features of these molecules are responsible for their stabilizing properties and to identify more efficient stabilizers which combine the effects of lyotropic anions such as citrate with those of the polyols in a single molecule. The presence of one or more carboxylate groups in a sugar molecule invariably increased its stabilizing potency, whereas the number and position of hydroxyl groups appeared to have no influence on the molecules' stabilizing ability. Several compounds were shown to be effective in preserving antithrombin III activity during pasteurization for 10 h at 60 degrees C. However, the presence of reducing sugars invariably resulted in a decrease in activity following pasteurization, in spite of their ability to increase Td. In fact, when antithrombin III was pasteurized in the presence of 2 M glucose and 0.5 M citrate, it steadily lost its ability to inhibit thrombin even though Td under these conditions was 10 degrees C higher than in citrate alone where activity was preserved. This effect was shown to be coincident with the covalent incorporation of glucose into the protein molecule.

Inhibition of intracellular proteolysis in muscle cultures by multiplication-stimulating activity. Comparison of effects of multiplication-stimulating activity and insulin on proteolysis, protein synthesis, amino acid uptake, and sugar transport

The effects of the insulin-like growth factor, multiplication-stimulating activity (MSA), on chick myotube cultures were investigated. In serum-free media, MSA at levels reported to be present in fetal serum (5 ng/ml) significantly inhibited overall rates of protein degradation and stimulated protein synthesis and amino acid uptake. Half-maximal effects on protein degradation (-30%), synthesis (+25%), and amino acid uptake (+50%) occurred at approximately 0.05 micrograms/ml. In contrast, 10(2)-10(3)-fold higher concentrations (5 micrograms/ml) were required to stimulate transport of the glucose analog 2-deoxyglucose. The results indicate that MSA is an effective anabolic agent regulating protein metabolism and amino acid uptake, but not sugar transport in these cells. Parallel studies conducted with insulin demonstrated similar size effects on protein metabolism and amino acid uptake in serum-free media. However, unlike MSA, insulin levels (10(-2) units/ml) well in excess of its normal physiological range were required to produce significant effects. In addition, the relative sensitivity of sugar transport with respect to protein metabolic effects differed for insulin and MSA. Thus, 2-deoxyglucose transport was approximately 10 times more sensitive to insulin than protein synthesis, proteolysis, or amino acid uptake in contrast to MSA where the reverse was true. However, despite the relatively higher sensitivity of sugar transport to insulin, supraphysiological levels (10(-3) units/ml) of this hormone were still required for significant stimulation. These results suggest a generally low insulin sensitivity in cultured chick myotubes relative to adult tissues. In contrast, the effects of MSA are consistent with a possible role of this or similar factors in regulating growth and development of embryonic muscle.

The elimination of 1,5-anhydroglucitol administered to rats

Rat serum contains natural 1,5-anhydroglucitol. Injected or orally administered 1,5-anhydroglucitol was efficiently reabsorbed by the renal tubuli via a mechanism which had a saturation point at high serum 1,5- anhydroglucitol levels. The compound had a slow turnover rate in the body; its half-life is approximately 3 days. The compound was readily absorbed in the gut when administered orally.

Molecular events leading to enhanced glucose transport in Rous sarcoma virus-transformed cells

Transformation by Rous sarcoma virus results in a dramatic increase in the rate at which the transformed cells transport glucose across the cell membrane. The increased transport rate is a consequence of an increased number of transporters in the transformed cells. Utilizing antibody raised against the purified human erythrocyte glucose transporter, we have identified the glucose transporter as a membrane glycoprotein with a monomer Mr of approximately 41,000. The increased rate of glucose transport is dependent on the activity of pp60src, the transforming protein of Rous sarcoma virus. This protein has been shown to be a protein kinase that phosphorylates on tyrosine residues. We have examined the tyrosine phosphorylation of a major cellular protein of Mr 36,000 in cells infected with a panel of partially transforming mutants of Rous sarcoma virus. One of these mutants (CU2) increases the rate of glucose transport only slightly and does not render the infected cells fully anchorage independent or tumorigenic (although other transformation parameters are fully induced). Cells infected with this mutant display a 36,000-dalton protein that is phosphorylated to a considerably lesser extent than cells infected with wild-type virus. Analyses of this sort may help to identify the cellular targets of pp60src whose phosphorylation is necessary for the increased glucose transport rate.

Effects of valinomycin on hexose transport and cellular ATP pools in mouse fibroblasts

The K+ ionophore valinomycin at concentrations of 1 X 10(-8) M and over, stimulated 2-deoxy-D-glucose (2DG) and 3-O-methylglucose (3OMG) uptake in Swiss 3T3 fibroblasts. The rate-limiting step of 2DG uptake was transport rather than phosphorylation, in the control or valinomycin-treated cells. Kinetic analysis showed that valinomycin increased the Vmax for 2DG uptake without change of the Km. The valinomycin-stimulated 2DG uptake was insensitive to 10 micrograms/ml cycloheximide, and extracellular K+ concentrations between 0.1 and 50 mM. On the other hand, valinomycin at the concentration of 1 X 10(-8) M and over, induced a rapid decrease in cellular ATP content, followed by stimulation of 2DG uptake and recovery of the ATP content. A similar relationship between the reduction of cellular ATP content and the subsequent stimulation of 2DG uptake was observed when the cells were treated not only with 2,4-dinitrophenol and iodoacetic acid, but also with other monovalent cation ionophores or inhibitors of oxidative phosphorylation. These results suggest that valinomycin may posttranslationally stimulate hexose transport by increasing the number of functional carriers of hexose or changing their mobility, and the rapid decrease in cellular ATP pools by valinomycin may be a trigger of the stimulation of the hexose transport in Swiss 3T3 fibroblasts.

[Effects of bromazepam on cerebral neuronal activity in male Wistar rats with immobilized stress]

The [14C]2-deoxy-D-glucose technique has been applied to examine glucose utilization rate (GUR), as a measure of neuronal activity, of 42 cerebral nuclei, hypophysis and adrenals in male Wistar rats. Restraint and water-immersed stress for a 10 min period significantly increased GUR in the cortex frontalis, nucleus (n.) amygdaloideus centralis and lateralis, n. ventromedialis, substantia nigra, n. reticularis lateralis, n. ambiguus, lobus anterior of hypophysis, and adrenals. The elevation was predominant in the n. amygdaloideus centralis, n. ambiguus and lobus anterior of hypophysis. Bromazepam significantly prevented these elevations at the non-muscle relaxant dose of 1 mg/kg, p.o. Further prolongation (55 min) of stress caused a marked and non-selective increase of GUR in all cerebral nuclei and glands examined. In spontaneously hypertensive rats in the conscious, resting state, the pretreatment with bromazepam (3 mg/kg, p.o.) abolished the stress-induced pressor response and the release of epinephrine, norepinephrine and dopamine beta-hydroxylase into the circulation. These results suggest that the n. amygdaloideus centralis is mostly a sensitive site to stress and one of the major action sites of bromazepam.

Metabolic mapping of the brain during rewarding self-stimulation

Local rates of cerebral glucose utilization were measured in rats by the quantitative 2-deoxy-D-[14C]glucose autoradiographic method during electrical stimulation of the ventral tegmental area. Rats trained in intracranial self-stimulation showed a pattern of changes in forebrain metabolic activity distinctly different from the pattern seen in rats stimulated by the experimenter. These findings provide information about the distribution of local cerebral activity specific to reinforced instrumental behavior.

Kinetics of D-glucose and 2-deoxy-D-glucose transport by Rhodotorula glutinis

The yeast Rhodotorula glutinis (Rhodosporidium toruloides) is capable of accumulative transport of a wide variety of monosaccharides. Initial velocity studies of the uptake of 2-deoxy-D-glucose were consistent with the presence of at least two carriers for this sugar in the Rhodotorula plasma membrane. Non-linear regression analysis of the data returned maximum velocities of 0.8 +/- 0.2 and 2.0 +/- 0.2 nmol/min per mg (wet weight) and Km values of 18 +/- 4 and 120 +/- 20 microM, respectively, for the two carriers. Kinetic studies of D-glucose transport also revealed two carriers with maximum velocities of 1.1 +/- 0.4 and 2.4 +/- 0.4 nmol/min per mg (wet weight) and Km values of 12 +/- 3 and 55 +/- 12 microM. As expected, 2-deoxy-D-glucose was a competitive inhibitor of D-glucose transport. Ki values for the inhibition were 16 +/- 8 and 110 +/- 40 microM. These Ki values were in good agreement with the Km values for 2-deoxy-D-glucose transport. D-Xylose, the 5-deoxymethyl analog of D-glucose, appears to utilize the D-glucose/2-deoxy-D-glucose carriers. This pentose was observed to be a competitive inhibitor of D-glucose (Ki values = 0.14 +/- 0.06 and 5.6 +/- 1.6 mM) and 2-deoxy-D-glucose (Ki values = 0.15 +/- 0.07 and 4.6 +/- 1.2 mM) transport.

Transport and metabolism of 2-deoxy-D-glucose by Rhodotorula glutinis

2-Deoxy-D-glucose transport by Rhodotorula glutinis is an active process. The intracellular concentration of free deoxyglucose after 15 min incubation of Rhodotorula cells with this sugar was 230 times the extracellular concentration. Although cell extracts at this time contained more 2-deoxy-D-glucose 6-phosphate than deoxyglucose, pulse-labelling experiments demonstrated that deoxyglucose is transported as the free sugar and subsequently phosphorylated. After transport, Rhodotorula cells metabolize deoxyglucose. The major metabolites during 30-90 min incubations were determined to be 2-deoxy-D-glucose 6-phosphate, 2-deoxy-D-glucitol, 2-deoxy-D-gluconate and 2,2'-dideoxy-alpha, alpha'-trehalose. Rhodotorula glutinis also degrades deoxyglucose to CO2. The concentrations of intermediates in this pathway were too low to detect and resolve in extracts of control cells. In 2,4-dinitrophenol-poisoned cells, however, it appears that deoxyglucose degradation is restricted largely to loss of C-1 as CO2 and it was possible to identify 1-deoxy-D-ribulose 5-phosphate as an intermediate presumably arising from metabolism of deoxyglucose by the oxidative portion of the hexose monophosphate pathway.

The inhibitory effects of horse anti-rat AFP antiserum on the uptake of 2-deoxy-D-glucose by AFP-producing rat hepatoma cells

The inhibitory effects of horse antiserum against rat alpha-fetoprotein (AFP) on the uptake of 2-deoxy-D-glucose (2dG) by the AFP-producing rat ascites hepatoma AH66 cells was studied. AH66 cells cultured in medium containing 20% heat-inactivated antiserum had a 1.5-fold lower rate of sugar uptake than did AH66 cells which were cultured in medium containing 20% heat inactivated normal horse serum. The inhibition of 2dG uptake by antiserum was dependent on both the concentration and the exposure time of antiserum. Preincubation of AH66 tumor cells for 2 and 6 h with antiserum prior to the measurement of 2dG uptake resulted in a 70.1% and 58.2% decrease in 2dG uptake compared to control cells. Antiserum did not inhibit the rate of phosphorylation of 2dG by tumor cells. Kinetic constants for the uptake of 2dG in both AH66 cells treated with antiserum to AFP and in control cells were calculated from Lineweaver-Burk plots. The Km remained constant at approximately 1.2 mM, but the Vmax was twice as small for the cells treated with antiserum as for the control cells (571 vs 923 nanomoles/2 X 10(5) cells/min). These studies suggest that the inhibition of 2dG uptake by treatment with antiserum was the result of a decrease in the number of transport sites, or a decrease in the amount of carrier protein for the sugar which was present on the surface of the plasma membrane of the AH66 cells.

The effect of metrizamide on regional brain glucose metabolism in the rat

The X-ray contrast material metrizamide is structurally related to 2-deoxyglucose and inhibits brain glucose phosphorylation in vitro. In vivo, the present autoradiographic study with labeled 2-deoxyglucose revealed a global reduction of brain glucose phosphorylation after metrizamide administration in the cisterna magna of rats. The reduction averaged 18% of all regions.

Involvement of cellular cyclic AMP in theophylline-induced sugar accumulation in chicken intestinal epithelial cells

We have studied the possible involvement of cellular cyclic AMP in theophylline-induced sugar gradient enhancement in isolated chicken enterocytes. Theophylline increases 3-O-methylglucose accumulation 3-fold after 30 min incubation. Exogenous cyclic AMP enhances sugar accumulation by 48%. Adenylyl cyclase inhibitor RMI 12 330A reduces theophylline-induced sugar gradients by 22% and theophylline-induced cyclic AMP levels by 24.5%. At the concentration used, RMI 12 330A has no effect on 3-O-methylglucose accumulation or basal cellular cyclic AMP. Since theophylline has a rapid inhibitory effect on Na+-independent sugar permeability, we conclude that the effects of the drug on sugar gradients are the result of its acting by both direct - surface membrane - and indirect - cyclic AMP mediated - mechanisms. The effect of theophylline and exogenous cyclic AMP on sugar accumulation is independent of external chloride.

The effects of 1-methyl-3-isobutylxanthine on insulin-sensitive 2-deoxyglucose transport

The effect of 1-methyl-3-isobutylxanthine on insulin-sensitive 2-deoxyglucose uptake in rat adipocytes was studied. 1-Methyl-3-isobutylxanthine inhibited 2-deoxyglucose uptake rate substantially in both the absence and presence of insulin. The lag-time for the effect of insulin on 2-deoxyglucose uptake was prolonged. At the same time 1-methyl-3-isobutylxanthine caused a decrease in ATP levels. From experiments with isolated rat liver mitochondria it appeared that 1-methyl-3-isobutylxanthine inhibits glutamate plus malate oxidation in State 3.

Stimulatory and inhibitory effects of adrenaline and 8-bromo-cAMP on insulin-sensitive 2-deoxyglucose transport in rat adipocytes

The effects of adrenaline and 8-bromo-cAMP on 2-deoxyglucose uptake in isolated rat adipocytes were investigated under conditions of unidirectional flux, in which the transport process is rate limiting. Adrenaline showed a dualistic effect in the absence of insulin. At concentrations below 1 microM adrenaline stimulated 2-deoxyglucose uptake; at higher concentrations adrenaline inhibited the uptake. In the presence of insulin at the maximum effective concentration, addition of adrenaline further increased the 2-deoxyglucose uptake by about 50%. In the presence of insulin 8-bromo-cAMP had the same effect as adrenaline. In the absence of insulin, 8-bromo-cAMP only inhibited 2-deoxyglucose uptake.

Glucose utilization in the Papez circuit: effects of oxotremorine and scopolamine

The [14C]2-deoxy-D-glucose technique was used to test the effects of central muscarinic stimulation or antagonism on local cerebral glucose utilization (LCGU) in the rat limbic system. Systemic administration of the muscarinic agonist oxotremorine (OXO, 0.05, 0.1 or 0.7 mg/kg, i.p.), increased LCGU in the pre- and postsubiculum, anterior nuclei of the thalamus, mammillary bodies, retrosplenial medial cortex, medial septum, postcommissural fornix and mammillothalamic tract. Scopolamine (2.5 mg/kg, i.p.) blocked these effects, and independently decreased LCGU in the pre- and postsubiculum, anterior thalamic nuclei, and retrosplenial medial cortex. The affected brain regions are components of, or are connected with, the Papez circuit.