Different rates of functional development in the two visual systems of the chicken revealed by [14C]2-deoxyglucose

Age-dependent changes in neuronal metabolic activity in the visual systems of the male chicken were assessed using [14C]2-deoxyglucose (2-DG) autoradiography. Groups of 3 and 4 chicks aged either 2 or 23 days posthatching were injected with 2 DG and exposed for 30 min to a variety of visual stimuli in either the monocular or binocular condition. Control birds had both eyes occluded. All groups were subjected to the same auditory background. In the 2-day-old chicks high levels of metabolic activity occurred in the rotundal-ectostriatal system in a manner consistent with eye use and known neuro-anatomical connections, but very low levels of activity occurred in the thalamo-hyperstriatal visual system. In the 23-day-old chicks eye use resulted in high levels of metabolic activity in both visual systems. The distribution of higher activity within the rostral regions of the anterior hyperstriatum at this age was consistent with eye use and the known distribution of ipsilateral and contralateral projections to the region. Different rates of functional development in the hyperstriatal and ectostriatal systems may reflect a requirement for different visual information processing in young versus older chickens. This study indicates that the ectostriatal system subserves the majority of early visual behavior. Age-dependent changes in the regional arrangement of activity in the Field L auditory region were also noted.

Morphine-induced alterations of local cerebral glucose utilization in the basal ganglia of rats

The actions of various doses of morphine on the local cerebral glucose utilization (LCGU) were studied by means of the autoradiographic [14C]2-deoxyglucose technique. Morphine (1-15 mg/kg i.p.) decreased LCGU in most areas of the basal ganglia (caudate nucleus, globus pallidus, nucleus accumbens), but not in the substantia nigra pars compacta. LCGU was also decreased in limbic nuclei, such as septum, hippocampus and amygdala, and in most thalamic areas. In most cortical regions, a decrease was found as well. Findings in some efferent nuclei seemed of particular interest, namely in the substantia nigra pars reticulata, anteroventral and lateral nucleus of the thalamus and the subthalamic nucleus, where decreases in LCGU were found after administration of 7.5 mg/kg or sometimes lower doses, but not after 15 mg/kg of morphine. The decreases seem to reflect a general depressory effect of morphine on neuronal activity which is known from electrophysiological studies. Part of these effects might be, in addition, due to an activation of dopaminergic neurons, since dopamine mainly acts as an inhibitory neurotransmitter. This dopaminergic activation leads to characteristic behavioral effects after lower doses of morphine. The largest dose used (15 mg/kg) produces muscular rigidity, probably by a direct action on the striatum. This effect antagonizes and masks the dopaminomimetic effects. The results suggest that it also antagonizes the functional alterations in some efferent nuclei of the basal ganglia manifest after lower doses of morphine. Local injections of morphine (15 micrograms) led to decreases of LCGU in the various parts of the striatum, but to increases in lateral and anteroventral thalamus.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of NMDA antagonists, MK-801 and CPP, upon local cerebral glucose use

The effects upon cerebral glucose utilisation of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801, a non-competitive N-methyl-D-aspartate (NMDA, receptor antagonist) and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP, a competitive NMDA receptor antagonist) were examined in conscious, lightly restrained rats. Cerebral glucose utilisation was assessed quantitatively in 74 brain regions with [14C]2-deoxyglucose autoradiography. The intravenous (i.v.) administration of MK-801 (0.05-5 mg/kg) induced heterogeneous patterns of altered cerebral glucose utilisation with statistically significant increases being observed in 21 brain areas and statistically significant decrease in 8 brain regions. Pronounced dose-related increases in glucose use were observed after MK-801 in the subicular complex, hippocampus molecular layer, dentate gyrus, limbic system (posterior cingulate cortex; mamillary body; anteroventral thalamic nucleus), olfactory areas and substantia nigra (pars reticulata). Glucose use in the neocortex and inferior colliculus was particularly sensitive to reduction by MK-801 administration. The pattern of altered glucose use after administration of CPP (3-30 mg/kg, i.v.) differed markedly from that observed after MK-801 treatment. Statistically significant increases in glucose use after CPP were noted in 11 brain areas and statistically significant decreases in 5 of the regions examined. Regions in which increases were noted after CPP included hippocampus molecular layer, olfactory areas, cochlear nucleus, vestibular nucleus, cerebellar nucleus, superior olives and substantia nigra (pars reticulata). These data indicate that widespread, anatomically organised alterations in cerebral function are associated with the administration of NMDA receptor antagonists despite the minor role normally ascribed to these receptors in conventional fast synaptic transmission. The distinct patterns of response to competitive and non-competitive antagonists may be a reflection of the differential responses of the two modes of receptor blockade to increased glutaminergic transmission.

Endogenous regulation of 2-deoxyglucose uptake in C6 glioma cells correlates with cytoskeleton-mediated changes of surface morphology

The cellular basis of the membrane-limited state of glucose utilization and the mechanism of the endogenous regulation of hexose uptake in dense monolayers of C6 glioma cells were investigated. In an earlier study, it was shown that at high rates of glucose transport and phosphorylation combined with the inhibition of glycolytic adenosine triphosphate (ATP) production by iodoacetate, an endogenous regulatory response occurred that resulted in rapid, periodic variations of the glucose uptake rates (Lange et al., 1982). Similar time-dependent periodic changes of uptake rates also occurred during incubation of C6 glioma cells with 2 mM 2-deoxyglucose (2-DG) without pretreatment of the cells with iodoacetate. These changes were accompanied by variations of the intracellular ATP content, by distinct alterations of the shape and arrangement of microvilli and lamellae (lamellipodia) on the cell surface, and by changes of the cytoskeletal F-actin content. Because the changes of 2-DG uptake rates occurred independent of the intracellular 2-DG concentration, the bulk of this 2-DG pool was assumed to be localized apart from the membranal transport sites. Downregulation of 2-DG uptake appeared to be triggered by a rapid decrease of a small pool of the cellular ATP involved in the phosphorylation of transported hexose. Scanning and transmission electron microscopic observations of cells fixed in different states of the endogenous uptake regulation supported the assumption that the interior of lamellae and microvilli may represent a small entrance compartment for transported hexoses in which occurred the observed close coupling between hexose transport and phosphorylation as well as the rapid variations of ATP content. Hexose uptake is supposed to be regulated by cytoskeleton-mediated changes of volume and diffusional accessibility of this compartment, modulating the degree of its metabolic coupling with the cytoplasmic main compartment.

Effect of high-intensity sound on local cerebral glucose utilization in fetal sheep

The effects of external noise on fetal sheep cerebral glucose utilization were determined with the [14C]deoxyglucose method. Seventeen animals were prepared at 130 days gestation with catheters and electrodes for assessing fetal behavioral state. Five to 7 days later, 7 animals were studied under normal laboratory sound conditions (65-70 dB), 5 animals were exposed to 105-120 dB broadband noise levels produced by two earphones applied to the abdomen of the ewe, and 5 fetuses were stimulated with an electronic artificial larynx (EAL), positioned on the abdomen directly over the fetal head. There were no significant differences between local cerebral glucose utilization in controls and earphone ewes, and no obvious alteration in behavioral states. However, there were marked, significant differences in glucose utilization along the central auditory pathway during EAL stimulation. These autoradiographs revealed isofrequency-like bands in medial geniculate body and irregular darkening of cortex of the temporal lobe. Total time spent in clearly defined high and low voltage electrocortical activity did not change during EAL stimulation.

Determination of the deoxyglucose and glucose phosphorylation ratio and the lumped constant in rat brain and a transplantable rat glioma

Mitochondrially bound hexokinase (ATP-D-hexose-6-phosphotransferase; EC 2.7.1.1) was dissociatively extracted from normal rat brains and intracerebral and subcutaneous implants of the 36B-10 glioma. At least 70% of the total hexokinase enzyme activity in normal and glioma tissue was associated with the mitochondrial fraction. Purification of the crude tissue extracts by ion-exchange and affinity chromatography followed by analysis with sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a successive purification of the enzyme to homogeneity with a molecular size of 98 kilodaltons. Enzyme kinetics with glucose or 2-deoxyglucose (2-DG) as the substrate were measured spectrophotometrically by coupling the appropriate reactions to either NADPH or NAD+ formation. The Km of hexokinase with glucose as the substrate in the intracerebral glioma (0.138 mM) and subcutaneous glioma (0.183 mM) tissues was 2.1-2.7-fold higher than that observed in normal brain tissue (0.067 mM) (p less than 0.001). No significant differences were observed in the Km for hexokinase with 2-DG as the substrate in the glioma and normal brain tissue. The phosphorylation ratio for normal brain was 0.320 and was increased in the intracerebral glioma to 0.694 and in the subcutaneous glioma to 0.519. The ratios of deoxyglucose and glucose volumes of distribution in normal brain and intracerebral glioma tissues were 1.70 and 1.85, respectively. The lumped constants calculated directly from the phosphorylation ratios and the volumes of distribution of deoxyglucose and glucose were 0.517 in normal brain and 1.168 in intracerebral glioma. Our results indicate the lumped constant is increased 2.26-fold in intracerebral glioma compared with normal brain.

Altered glucose metabolism in microvessels from patients with Alzheimer's disease

Microvessels isolated from temporal cortex of patients with Alzheimer's disease showed decreased uptake of glucose when compared with vessels from age-matched or young control subjects. This was due to decreased hexokinase activity in the Alzheimer samples, as determined by ion exchange chromatography. This finding was confirmed independently by determination of the phosphorylation constant for hexokinase, K3, using positron emission tomography. The results suggest that Alzheimer's disease may result from a global defect in brain energy metabolism.

Design of a selective insulin receptor tyrosine kinase inhibitor and its effect on glucose uptake and metabolism in intact cells

An inhibitor of the insulin receptor tyrosine kinase (IRTK), (hydroxy-2-naphthalenyl-methyl) phosphonic acid, was designed and synthesized and was shown to be an inhibitor of the biological effects of insulin in vitro. With a wheat germ purified human placental insulin receptor preparation, this compound inhibited the insulin-stimulated autophosphorylation of the 95-kDa beta-subunit of the insulin receptor (IC50 = 200 microM). The ability of the kinase to phosphorylate an exogenous peptide substrate, angiotensin II, was also inhibited. Half-maximal inhibition of basal and insulin-stimulated human placental IRTK activity was found at concentrations of 150 and 100 microM, respectively, with 2 mM angiotensin II as the peptide substrate. The inhibitor was found to be specific for tyrosine kinases over serine kinases and noncompetitive with ATP. The inhibitor was converted into various (acyloxy)methyl prodrugs in order to achieve permeability through cell membranes. These prodrugs inhibited insulin-stimulated autophosphorylation of the insulin receptor 95-kDa beta-subunit in intact CHO cells transfected with human insulin receptor. Inhibition of insulin-stimulated glucose oxidation in isolated rat adipocytes and 2-deoxyglucose uptake into CHO cells was observed with these prodrugs. Our data provide additional evidence for the involvement of the insulin receptor tyrosine kinase in the regulation of glucose uptake and metabolism. These results and additional data reported herein suggest that this class of prodrugs and inhibitors will be useful for modulating the activity of a variety of tyrosine kinases.

The nucleus locus coeruleus modulates local cerebral glucose utilization during noise stress in rats

Local cerebral glucose utilization (LCGU), estimated by the quantitative autoradiographic 2-deoxyglucose technique, was studied in rats with bilateral 6-hydroxydopamine lesions of the locus coeruleus (LC) and in vehicle-injected controls. Unanesthetized animals were studied during exposure to stressful levels of white noise (95 dB) or in relative silence (50 dB). Results indicated that noise caused greater and more widespread increases in LCGU in animals with LC lesions than in vehicle-injected controls. Lesions alone had little or no effect in animals not subjected to noise. Analyses of variance revealed significant treatment interaction effects (intact/lesion x silence/noise) for 37 of 109 regions measured. The pattern of results suggests that the LC acts during stress to limit unnecessary cerebral activity that might interfere with efficient sensory processing and/or the organization of appropriate behavioral responses. In this respect LC function may be similar to those actions of the peripheral sympathetic nervous system that suppress vegetative functions during stress to allow for the performance of coping responses.

Learning-related activation in the auditory system of the rat produced by long-term habituation: a 2-deoxyglucose study

Autoradiography with [14C]2-deoxyglucose (2-DG) was used to examine the functional activity of the rat auditory system during long- and short-term habituation of the acoustic startle reflex. The data showed that presentation of the acoustic stimulus to long-term habituated rats resulted in a learning-related metabolic enhancement that was significantly greater than the response evoked by the same acoustic stimulus in the inexperienced rats. This enhancement was localized to brainstem and midbrain auditory nuclei and no significant changes occurred at thalamocortical levels of the auditory pathway. The largest difference in 2-DG uptake between long- and short-term habituated rats was in the lateral superior olivary nucleus (LSO). The LSO activation suggests that olivocochlear efferents may operate in a central feedback control of peripheral auditory input during long-term habituation. Findings of enhanced metabolism from the cochlear nuclei to the central nucleus of the inferior colliculus indicated that active processes of neuronal plasticity take place in the lower auditory system during long-term habituation. The results provide the first demonstration of how a nonassociative learning experience such as long-term habituation modifies the metabolic activity of the auditory system. The findings support the conclusion that auditory responses of behaving animals to acoustic stimuli are dependent not only on the physical parameters of a stimulus, but also on its learned behavioral significance.

Selective incorporation of 2-deoxyglucose into the developing spinal cord in vitro in response to target tissue and substratum

Differential uptake of [3H]deoxyglucose by larval frog spinal cord explants in vitro has demonstrated that metabolic activity is localized to the lateral motor columns in response to co-cultured target tissue or a neurite-promoting substratum. Autoradiographic data suggest that chemokinesis may be an integral component of motor neuron growth activation.

Deoxyglucose kinetics in a rat brain tumor

Accurate quantitation of local glucose metabolic rates (LMRglc) of abnormal tissues such as brain tumors with the 2-deoxyglucose (DG) method requires knowledge of the tissue rate constants and lumped constant. The deoxyglucose rate constants were measured in an experimental intracerebral glioma in 24 awake rats with a dual tracer [(3H)-DG and (14C)-DG] method. Tissue time points were obtained at 2, 5, 10, 18, 30, 60, 90, and 180 min after injection by decapitation and liquid scintillation counting. Blood samples were obtained at 1 min intervals initially and at longer intervals later. The rate constants were estimated with parameter estimation. LMRglc was calculated from the rate constants, assuming a lumped constant of 0.5. K1 for normal cerebrum was found to be 0.258 ml/g/min, and k2-k4 were 0.406, 0.075, and 0.0103 min-1; LMRglc = 65.1 mumol/100 g/min. The corresponding values for the glioma were 0.108, 0.126, 0.040, and 0.0019 with LMRglc = 41.7. The considerably lower k4 in the glioma was reflected in persistent higher activity in the glioma at longer times. Thus, tissue activity alone cannot be used to assess relative glucose metabolic rates in abnormal tissues such as gliomas, particularly at late times after injection.

Effects of self-administered phencyclidine on regional uptake of 2-deoxy-D-[1-14C]glucose in brain

Phencyclidine profoundly alters cerebral metabolism in the rat. This study explored whether cerebral metabolic effects of phencyclidine differed when the drug was self-administered by trained rats, compared with when it was given acutely to naive rats. The regional cerebral uptake of 2-deoxy-D-[1-(D14C] glucose (DG) was examined following two injections of phencyclidine (0.5 mg/kg/injection, i.v.) or saline in freely-moving, drug-experienced rats. Naive controls received phencyclidine or saline according to an identical dose regimen. In self-administering and naive rats, phencyclidine produced many of the same effects on uptake of DG, including the following: decreases in the habenula, inferior colliculus, sensory cortical areas and corresponding thalamic relay nuclei; and increases in limbic areas (entorhinal and retrosplenial cortices, subicular areas). Some regions (auditory and motor cortices, medial geniculate body, globus pallidus) showed different effects in self-administering and naive rats. Another study, in which rats were not self-administering phencyclidine, but had histories of treatment with drugs similar to those of the self-administering rats, indicated that chronic exposure to drug accounted for some of the differences. Furthermore, differences between the effects of phencyclidine in self-administering, versus non-self-administering rats with similar histories suggested that activity in some regions of the brain may relate to training in drug self-administration and/or behavior.

Analysis of the H+/sugar symport in yeast under conditions of depolarized plasma membrane

H+/sugar symport in the obligatory aerobic yeast Rhodotorula glutinis was analyzed under conditions where the plasma membrane was selectively depolarized by the lipophilic cation tetraphenylphosphonium (TPP+). Control experiments showed that this treatment did not impair the transmembrane delta pH, the cell energy charge, and the function of plasma membrane H+-ATPase. The kinetic data were fitted to elementary functions derived from a model constructed on the basis of some simplifying premises for ordered (either C + H+ + S or C + S + H+) and random reaction mechanisms. In addition, the comparison of the kinetic parameters in fully energized and depolarized cells provided information about the free carrier charge. It was concluded that the binding sequence of formation of the ternary carrier/H+/substrate complex follows a random mechanism and that the carrier bears a negative charge.

Transport processes of 2-deoxy-D-glucose in erythrocytes infected with Plasmodium yoelii, a rodent malaria parasite

The transport processes of D-glucose in Plasmodium yoelii-infected mouse erythrocytes were investigated using 2-deoxy-D-glucose (2DOG), a non-metabolizable analogue of D-glucose. Infected cells showed an increase in the uptake of 2DOG compared to uninfected controls, and an effect which was more prominent in cells with mature-stage parasites. Kinetic studies measuring the initial rates of 2DOG uptake revealed two components in infected cells with late trophozoite and schizont-stage parasites: a simple diffusion system and a carrier (transporter)-mediated system. The transporter was common for D-glucose and 2DOG and had a kinetic constant indicating a high affinity for 2DOG (the Km = 0.18 mM and the Vmax = 0.61 mmol/10(10) cells/min), as compared to the constant of the mouse erythrocyte carrier (the Km = 10 mM and the Vmax = 1.8 mmol/10(10) cells/min). Determination of the distribution of [3H]2DOG in infected cells and experiments with metabolic inhibitors indicated that the simple diffusion system localizes in the membrane of host cells and the transporter in the parasite plasma membrane. The parasite glucose transporter was much less sensitive to cytochalasin B than that of the host cells and the uptake of 2DOG via the transporter was dependent on energy. Based on these findings, the following features emerge: D-glucose first gains access to the cytosol of infected erythrocytes via the simple diffusion system, which appears after infection by the parasite, and an active uptake against the concentration gradient takes place at the parasite plasma membrane via the parasite glucose transporter in an energy dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Refinement of the kinetic model of the 2-[14C]deoxyglucose method to incorporate effects of intracellular compartmentation in brain

A translocase to transport hexose phosphate formed in the cytosol into the cisterns of the endoplasmic reticulum, where the phosphatase resides, is absent in brain (Fishman and Karnovsky, 1986). 2-Deoxyglucose-6-phosphate (DG-6-P) may therefore have limited access to glucose-6-phosphatase (G-6-Pase), and transport of the DG-6-P across the endoplasmic reticular membrane may be rate limiting to its dephosphorylation. To take this compartmentation into account, a five-rate constant (5K) model was developed to describe the kinetic behavior of 2-deoxyglucose (DG) and its phosphorylated product in brain. Loss of DG-6-P was modeled as a two-step process: (a) transfer of DG-6-P from the cytosol into the cisterns of the endoplasmic reticulum; (b) hydrolysis of DG-6-P by G-6-Pase and subsequent return of the free DG to the precursor pool. Local CMRglc (LCMRglc) was calculated in the rat on the basis of this model and compared with values calculated on the basis of the three-rate constant (3K) and the four-rate constant (4K) models of the DG method. The results show that under normal physiological conditions all three models yield values of LCMRglc that are essentially equivalent for experimental periods between 25 and 45 min. Therefore, the simplest model, the 3K model, is sufficient. For experimental periods from 60 to 120 min, the 4K and 5K models do not correct completely for loss of product, but the 5K model does yield estimates of LCMRglc that are closer to the values at 45 min than those obtained with the 3K and 4K models.

Regional cerebral blood flow and glucose utilization during hypoglycemia in newborn dogs

To assess alterations in regional cerebral blood flow and glucose utilization during perinatal hypoglycemia, newborn dogs (2-7 days postnatal age) were anesthetized with halothane, tracheostomized, paralyzed, and artificially ventilated with 70% N2O-30% O2 to maintain arterial normoxia and normocapnia (arterial PO2 greater than 60 mmHg; arterial PCO2: 35-42 mmHg; arterial pH: 7.35-7.45). Regional cerebral blood flow (rCBF) and glucose utilization (rCGU) were determined with iodo-[14C]antipyrine and 2-deoxy-[14C]glucose as the radioactive tracers, respectively. Hypoglycemia with blood glucose concentrations averaging 0.9 mmol/l was achieved within 90-120 min in 10 animals using intermittent intravenous injections of regular insulin; 10 control animals received 0.9% saline (blood glucose = 9 mmol/l). During hypoglycemia, mean arterial blood pressure was 81% of control, whereas heart rate was unchanged. Arterial O2 and acid-base balance were well maintained (arterial PO2 = 68 mmHg; PCO2 = 37 mmHg; pH = 7.35). Hypoglycemia was associated with significant increases in rCBF in all of 16 analyzed structures, ranging from 172% (parietal white matter) to 249% (thalamus) of control values (17-65 ml.100 g-1.min-1). During hypoglycemia, rCGU was relatively unchanged from normoglycemic values in 11 of 16 brain structures. Significant reductions in rCGU were seen only in occipital white matter (-31%) and in the cerebellar vermis and hemisphere (-31 and -43%, respectively). CGU actually increased slightly in the pons and medulla (+12 and +19%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

A rapid, extranuclear effect of 3,5,3'-triiodothyronine on sugar uptake by several tissues in the rat in vivo. Evidence for a physiological role for the thyroid hormone action at the level of the plasma membrane

T3 produced a prompt and biphasic change in the uptake of 2-deoxy-D-glucose (dGlc) by atria, ventricles, diaphragm, and fat in the rat in vivo. At the lower physiological doses T3 produced a dose-related increase in tissue dGlc uptake; the lowest effective concentration was 5-10 ng/100 g BW, and maximal effect of about 75-100% increase above control values was seen at a T3 dose of 25 (diaphragm) or 100 ng. At pharmacological doses of 5 and 50 micrograms/100 g BW T3 inhibited dGlc uptake by about 50%. Evaluation of the physiological related stimulatory effect of T3 on dGlc uptake in the four tissues revealed that it was independent of new protein synthesis, because it was not inhibited by cycloheximide which blocked [3H]leucine incorporation by more than 95%, and that it was thyroid hormone specific, as judged from the order of potency of several T3 analogs: 3'-isopropyl-L-T2 greater than or equal to L-T3 greater than L-T4 = D-T3 greater than D-T4; L-rT3, 3,5-L-T2, and DL-thyronine were without effect. Additional studies demonstrated that in the four tissues employed T3 acted to promote sugar uptake by increasing the activity of the sugar transport system located at the plasma membrane. The present study together with previous in vitro and in vivo studies, in the same and other tissues, provide a strong evidence in support of a physiological role for the action of thyroid hormone at the level of the plasma membrane to increase cellular sugar uptake.

Direct chemical measurement of the lambda of the lumped constant of the [14C]deoxyglucose method in rat brain: effects of arterial plasma glucose level on the distribution spaces of [14C]deoxyglucose and glucose and on lambda

The lumped constant in the operational equation of the 2-[14C]deoxyglucose (DG) method contains the factor lambda that represents the ratio of the steady-state tissue distribution spaces for [14C]DG and glucose. The lumped constant has been shown to vary with arterial plasma glucose concentration. Predictions based mainly on theoretical grounds have suggested that disproportionate changes in the distribution spaces for [14C]DG and glucose and in the value of lambda are responsible for these variations in the lumped constant. The influence of arterial plasma glucose concentration on the distribution spaces for DG and glucose and on lambda were, therefore, determined in the present studies by direct chemical measurements. The brain was maintained in steady states of delivery and metabolism of DG and glucose by programmed intravenous infusions of both hexoses designed to produce and maintain constant arterial concentrations. Hexose concentrations were assayed in acid extracts of arterial plasma and freeze-blown brain. Graded hyperglycemia up to 28 mM produced progressive decreases in the distribution spaces of both hexoses from their normoglycemic values (e.g., approximately -20% for glucose and -50% for DG at 28 mM). In contrast, graded hypoglycemia progressively reduced the distribution space for glucose and increased the space for [14C]DG. The values for lambda were comparatively stable in normoglycemic and hyperglycemic conditions but rose sharply (e.g., as much as 9-10-fold at 2 mM) in severe hypoglycemia.

Generalized decrease in brain glucose metabolism during fasting in humans studied by PET

In prolonged fasting, the brain derives a large portion of its oxidative energy from the ketone bodies, beta-hydroxybutyrate and acetoacetate, thereby reducing whole body glucose consumption. Energy substrate utilization differs regionally in the brain of fasting rat, but comparable information has hitherto been unavailable in humans. We used positron emission tomography (PET) to study regional brain glucose and oxygen metabolism, blood flow, and blood volume in four obese subjects before and after a 3-wk total fast. Whole brain glucose utilization fell to 54% of control (postabsorptive) values (P less than 0.002). The whole brain rate constant for glucose tracer phosphorylation fell to 51% of control values (P less than 0.002). Both parameters decreased uniformly throughout the brain. The 2-fluoro-2-deoxy-D-glucose lumped constant decreased from a control value of 0.57 to 0.43 (P less than 0.01). Regional blood-brain barrier transfer coefficients for glucose tracer, regional oxygen utilization, blood flow, and blood volume were unchanged.

Fetal glucose utilization in response to maternal starvation and acute hyperketonemia

The effects of maternal hypoglycemia and/or hyperketonemia on glucose utilization by individual fetal rat tissues have been studied in vivo. To decrease blood glucose and to raise fetal blood ketone body concentrations, 19-day pregnant rats were submitted to 48 or 96 h of starvation. To differentiate between the effects of decreased blood glucose and increased ketone body concentrations, fed pregnant rats were infused for 2 h with DL-beta-hydroxybutyrate. After 96 h of maternal starvation, fetal 2-deoxy-D-glucose (2DG) uptake decreased from 13.6 +/- 0.5 to 8.6 +/- 1.15 micrograms.min-1.g-1. This was mainly due to a decrease in 2DG uptake by fetal hindlimb muscles and heart. By contrast, 2DG uptake in fetal liver and brain was not affected by maternal starvation. Acute hyperketonemia in fed pregnant rats induced a 23% decrease in 2DG uptake by the whole fetus mainly as the result of a lowered 2DG uptake in fetal hindlimb muscles. These data suggest that fetal 2DG uptake does not simply depend on lowered blood glucose level during maternal starvation but that other hormonal, cardiovascular, or metabolic adaptations are implicated. In the rat, most of the fetal tissues including brain are protected against maternal hypoglycemia.

Glucose uptake and flux through phosphofructokinase in wounded rat skeletal muscle

Skeletal muscle injured with lambda-carrageenan has increased aerobic glycolysis. To assess the regulation of this process, the tissue concentrations of glycolytic intermediates, the flux through phosphofructokinase (PFK), and the intracellular concentrations of PFK effectors were examined in wounded rat skeletal muscle and in macrophages, the predominant inflammatory cell in the early stages of this wound model. Autoradiography demonstrated increased 2-deoxy-D-glucose uptake in wounded tissue compared with nonwounded muscle. 2-Deoxy-D-glucose was localized to the cellular infiltrate. The glycolytic intermediate concentrations demonstrated a facilitation of PFK in macrophages and wounded tissue as compared with nonwounded muscle. Wounded tissue had twice the flux through PFK compared with nonwounded muscle (10.0 +/- 0.6 wounded vs. 4.9 +/- 0.4 mumol.h-1.g-1 nonwounded). Macrophages had the highest flux through PFK (63.7 +/- 5.7 mumol.h-1.g-1) and when coincubated with muscle, the combined flux through PFK was equal to that of wounded muscle. The increase in glycolysis associated with wounded tissue may be explained by increased glucose uptake and increased flux through PFK by the inflammatory cells present in wounded tissue.