Suitability of the isolated perfused rat brain for studying effects on cerebral metabolism

Transport of the Proinflammatory Chemokines C-C Motif Chemokine Ligand 2 (MCP-1) and C-C Motif Chemokine Ligand 5 (RANTES) across the Intact Mouse Blood-Brain Barrier Is Inhibited by Heparin and Eprodisate and Increased with Systemic Inflammation

One important function of the vascular blood-brain barrier (BBB) is to facilitate neuroimmune communication. The BBB fulfills this function, in part, through its ability to transport cytokines and chemokines. C-C motif chemokine receptor 2 (CCL2) (MCP-1) and C-C motif chemokine receptor 5 (CCL5) (RANTES) are proinflammatory chemokines that mediate neuroimmune responses to acute insults and aspects of brain injury and neurodegenerative diseases; however, a blood-to-brain transport system has not been evaluated for either chemokine in vivo. Therefore, we determined whether CCL2 and CCL5 in blood can cross the intact BBB and enter the brain. Using CD-1 mice, we found that ¹²⁵I-labeled CCL2 and CCL5 crossed the BBB and entered the brain parenchyma. We next aimed to identify the mechanisms of ¹²⁵I-CCL2 and ¹²⁵I-CCL5 transport in an in situ brain perfusion model. We found that both heparin and eprodisate inhibited brain uptake of ¹²⁵I-CCL2 and ¹²⁵I-CCL5 in situ, whereas antagonists of their receptors, CCR2 or CCR5, respectively, did not, suggesting that heparan sulfates at the endothelial surface mediate BBB transport. Finally, we showed that CCL2 and CCL5 transport across the BBB increased following a single injection of 0.3 mg/kg lipopolysaccharide. These data demonstrate that CCL2 and CCL5 in the brain can derive, in part, from the circulation, especially during systemic inflammation. Further, binding to the BBB-associated heparan sulfate is a mechanism by which both chemokines can cross the intact BBB, highlighting a novel therapeutic target for treating neuroinflammation. SIGNIFICANCE STATEMENT: Our work demonstrates that C-C motif chemokine ligand 2 (CCL2) and C-C motif chemokine ligand 5 (CCL5) can cross the intact blood-brain barrier and that transport is robustly increased during inflammation. These data suggest that circulating CCL2 and CCL5 can contribute to brain levels of each chemokine. We further show that the transport of both chemokines is inhibited by heparin and eprodisate, suggesting that CCL2/CCL5-heparan sulfate interactions could be therapeutically targeted to limit accumulation of these chemokines in the brain.

Effects of the sodium channel blocker tetrodotoxin (TTX) on cellular ion homeostasis in rat brain subjected to complete ischemia

Anoxic depolarization (AD) and failure of the cellular ion homeostasis are suggested to play a key role in ischemia-induced neuronal death. Recent studies show that the blockade of Na+ influx significantly improved the neuronal outcome. In the present study, we investigated the effects of 10 microM tetrodotoxin (TTX) on ischemia-induced disturbances of ion homeostasis in the isolated perfused rat brain. TTX inhibited the spontaneous EEG activity, delayed the ischemia-induced tissue acidification, and significantly postponed the occurrence of AD by 65%. The [Ca2+]e elevation prior to AD was attenuated from 17.8% to 6% while the increase of the [Na+]e in this period was enhanced (from 2.9% to 7.3%). These findings implied that the ischemia-induced early cellular sodium load and the corresponding shrinkage of the extracellular space was counteracted by TTX. Our results suggest that the Na+ influx via voltage-dependent channels preceding complete breakdown of ion homeostasis is one major factor leading to cell depolarization. The massive Na+ influx coinciding with AD, however, may be mainly via non-selective cation channels or/and receptor-operated channels. Persistent Na+ influx deteriorates neuronal tissue integrity by favouring Ca2+ influx and edema formation. Blockade of ischemia-induced excessive Na+ influx is, therefore, a promising pharmacological approach for stroke treatment.

Neuronal protective effects of calcium antagonists in cerebral ischemia

We investigated the effects of calcium antagonists against ischemic injury in vivo and against excitotoxic damage in vitro. In vivo nimodipine protected significantly the CA1 hippocampal neurons from neurodegeneration after transient global ischemia in rats without changing the local cerebral blood flow. Furnidipine reduced the area of ischemia after permanent MCA-occlusion in mice. The results in vitro using the Ca(2+)-sensitive dye fura-2 showed that nimodipine reduced in a dose-dependent manner the elevation of [Ca2+]i in hippocampal neurons induced by K(+)-stimulation. The present in vitro and in vivo data show that calcium antagonists are potent agents in protecting neurons against the deleterious consequences of an excitotoxic or ischemic insult.

Neuroblastoma cells for testing neuroprotective drug effects

An attempt was made to use neuroblastoma cells for testing neuroprotective drug effects. To achieve cellular damage, cytotoxic hypoxia was induced in neuroblastoma cells after 10 days in culture by addition of sodium cyanide (1 mmol/L) to the culture medium and was terminated after 6 hr by replacing the cyanide-containing fresh nutrient medium. During this hypoxic period cells were additionally deprived of glucose. They were allowed to recover for another 7 days. Drugs were available to the cells from 30 min prior to hypoxia until 24 hr after hypoxia. Cell concentration of high-energy phosphates and culture protein content were determined as representatives for the posthypoxic development of cell damage, cell activity and viability. While barbiturates and phenytoin revealed neurotoxic effects when applied in doses higher than 300 mumol/L, chlorpromazine, dizocilpine, ketamine, ketazocine, naftidrofuryl, and flunarizine protected neuroblastoma cells against hypoxic damage. These results were comparable to those obtained from primary cultures of neurons under similar experimental conditions. In addition, they were in keeping with neuroprotective drug effects obtained from in vivo experiments. It is suggested that neuroblastoma cells are suitable for testing neuroprotective drug effects.

Preservation of integrative function in a perfused guinea pig brain

The mammalian brain has been one of the most difficult organs to maintain using artificial perfusion. Normal biochemistry, histology, and electrophysiology of the brain have been demonstrated for limited periods in vitro, but it has been more difficult to maintain complex, integrative neuronal activity such as the electroencephalogram (EEG) or programmed motor output. Normal motor output, other than reflex activity, has not previously been demonstrated in a perfused brain preparation. This paper reports the first preservation of normal function in a complete motor network, including intact afferent and efferent pathways, during perfusion of the mammalian brain. The brain, rostral spinal cord and peripheral nervous system of the guinea pig were perfused in situ using an artificial blood containing the oxygen carrier, perfluorotributylamine (FC-43). This preparation was maintained normothermic, whereas many other perfused brain preparations have been maintained hypothermic to prolong viability. Survival was enhanced by the addition of HEPES buffer to the perfusion medium, probably by increasing carbon dioxide transport. The duration of normal EEG was extended to 8 h. Spontaneous respiratory motor output with normal waveform and temporal pattern was recorded from the phrenic nerve for an average of 6 h. The respiratory motor output responded appropriately to blood pCO2, temperature, blood flow, drug concentrations, and electrical stimulation of vagal afferent fibers. This preparation represents a significant advance in the ability to preserve neural function during perfusion, and should offer advantages for studying cellular electrophysiology of intact, functioning neural networks, as well as neurochemistry and neuropharmacology.

Cultured neurons for testing antihypoxic drug effects

Cultured neurons of chick embryo cerebral hemispheres were used as an in vitro system for investigating the influence of several drugs on neuronal cell viability and metabolic activity under hypoxic conditions. Hypoxia was induced by addition of sodium cyanide to the nutrient medium, which led to a rapid depletion of energy stores. The ATP level of the cells and the protein content of the cultures were used to characterize the degree of neuronal damage after cytotoxic hypoxia and recovery, respectively, recovery lasting 15 min or 3 days. Various calcium antagonists, NMDA-antagonists, central depressants, central stimulants, nootropics, and miscellaneous drugs were tested. NMDA-antagonists and central depressants consistently protected the neurons against alterations caused by hypoxia. However, only one (flunarizine) out of five calcium antagonists, two (naftidrofuryl, pyritinol) out of 13 nootropics, the kappa-agonist ketazocine, and the ATPase inhibitor ouabaine exerted neuroprotection. The in vitro model seems to be suitable for testing neuroprotective drug effects and to be a valuable supplement for in vivo experiments, especially when the cellular mechanism of drug action has to be clarified.

Quantitative evaluation of optical reflection spectra of blood-free perfused guinea pig brain using a nonlinear multicomponent analysis

After developing a blood-free perfused preparation of the guinea pig brain a nonlinear multicomponent analysis (NLMCA) of the reflection spectra of the brain surface was worked out by which the redox state of cytochrome aa3, c, and b could be evaluated quantitatively and almost continuously. The NLMCA allowed to simulate the tissue reflection spectra in such a way that only a small statistical error remained between the recorded and the computed spectra. Using redox states of cytochrome aa3 and c as an intracellular oxygen probe it was found that in order to supply the guinea brain with sufficient oxygen by a saline medium equilibrated with 95% oxygen and 5% CO2 the temperature had to be reduced to 18-20 degrees C. At this temperature cytochrome aa3 was 95% oxidized.

Influence of an extract of Ginkgo biloba on cerebral blood flow and metabolism

The purpose of the present investigation was to examine the effects of an extract of Ginkgo biloba (EGB) on blood glucose levels, on local cerebral blood flow as well as on cerebral glucose concentration and consumption. The local cerebral blood flow (LCBF) was measured in conscious rats by means of the 14C-iodoantipyrine technique and local cerebral glucose utilization (LCGU) by 14C-2-deoxy-glucose autoradiography. EGB increased the LCBF in 39 analyzed, anatomically defined brain structures by 50 to 100 per cent. No influence of EGB on LCGU was demonstrable. However, EGB enhanced the blood glucose level dose-dependently. Substrates and metabolites of energy metabolism were measured in the cortex of the isolated rat brain perfused at constant rate and with 7 mmol/l glucose added to the perfusion medium. In these experiments EGB decreased the cortical glucose concentration without other substrate levels being changed. These results suggest that glucose uptake may be inhibited by EGB. It is argued that the effects of EGB on brain glucose concentration and blood flow may contribute to its protection of brain tissue against ischemic or hypoxic damage.

Evaluation of artificial plasma for maintaining the isolated canine brain

The use of canine erythrocytes suspended in artificial plasma to maintain the isolated brain was investigated in 18 preparations. Two plasmas were studied: One (AP1) contained electrolytes, amino acids, and albumin; the other (AP2) was similar to CSF and contained a mixture of 37 organic nutrients plus electrolytes and albumin. The CMRO2, CMRglu, and cerebral vascular resistance (CVR) were measured during 2 h of perfusion, and tissue high-energy phosphates were measured at the end of perfusion. The AP1 and AP2 groups were compared with control preparations perfused with canine red blood cells suspended in buffy coat-poor canine plasma. Both CMRO2 and ATP decreased to 60% of the control value; CVR increased to 187% of the control value in both groups following 2 h of perfusion. After 2 h of perfusion, the calculated value of intracellular pH (pHi)--based on creatine kinase equilibrium--remained normal (6.96) for the control brains, but decreased to 6.49 and 6.63, respectively, for the AP1- and AP2-perfused brains. Thus, there appears to be an eventual disruption of normal oxidative metabolism resulting in energy failure, possibly caused by the absence of an essential nutrient from the artificial plasma. For studies of intermediary metabolism in isolated normothermic brain, diluted whole blood appears to be the perfusate of choice.

Effect of gallopamil on energy metabolism of the isolated perfused rat brain in the postischemic period

The isolated perfused rat brain was used to demonstrate an effect of gallopamil on energy metabolism affected by ischemia. After a perfusion period of 30 min and 10 min of ischemia the isolated brain preparation was reperfused. From the onset of perfusion onwards, gallopamil (1 or 10 mumol/l) was present in the medium. The higher concentration of gallopamil accelerated significantly the restoration of the high-energy phosphates in the recovery stage: after 2 min of recirculation the ATP and the creatine-P levels were higher and the AMP level was lower in cortical tissue of drug-treated brains than in untreated controls. These results suggest that gallopamil protected brain energy metabolism against ischemic damage.

Effect of dihydroergocristine on energy metabolism studied in the isolated perfused rat brain affected by ischemia and in neuroblastoma cells deprived of oxygen and glucose

The effect of dihydroergocristine on energy metabolism was studied in the isolated perfused rat brain affected by ischemia and in cultivated C-1300 neuroblastoma cells deprived of oxygen and glucose. Creatine phosphate, ATP, ADP, AMP, glucose, glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-diphosphate, pyruvate, and lactate were measured enzymatically. After a perfusion period of 30 min, the cortex of the isolated perfused rat brain exhibited an energy state not different from that in vivo. Dihydroergocristine added to the perfusion medium (5 mumol/L) did not influence these substrate levels under normal perfusion conditions. However, this drug was able to retard the breakdown of high-energy phosphates during ischemia and to accelerate the restoration of the energy state during the postischemic reperfusion period. The perfusion rate was not changed by the drug, and therefore it was assumed that dihydroergocristine could act directly on cell metabolism. This view was supported by the results obtained from experiments using cultivated N-2a neuroblastoma cells. These cells were incubated in a buffered salt solution deprived of glucose and oxygen for 15 min. Under these conditions, dihydroergocristine (2 mumol/L) added to the incubation medium caused changes in the concentrations or the high-energy phosphates similar to those in the isolated brain preparation: It increased the ATP concentration and decreased the ADP concentration significantly.

P-31 nuclear magnetic resonance analysis of brain: II. Effects of oxygen deprivation on isolated perfused and nonperfused rat brain

Phosphatic metabolite (perchloric acid extractable) concentrations of cerebral tissues were analyzed by phosphorus-31 nuclear magnetic resonance (P-31 NMR) spectroscopy following external perfusion of the isolated rat brain (30 min or 60 min) under the following conditions: (a) constant perfusion pressure with either fluorocarbon- or erythrocyte-based medium, and (b) constant perfusate flow rate (3 ml/min) with the erythrocyte-based medium. Metabolite concentrations of control perfused brains were compared with those in nonperfused controls to provide a basis for detecting any qualitative or quantitative changes in cerebral metabolite composition. Metabolic responses of perfused brains to ischemia (incomplete ischemia, 83% reduction in flow for 10 min; transient complete ischemia for 1.5 or 2 min) were evaluated immediately after the ischemic episode and at selected time points during reperfusion (3 and 15 min). Alterations in cerebral metabolite levels induced by hypoxia were analyzed using a nonperfused rat brain model. Irrespective of the perfusion method employed, the phosphatic metabolites of control perfused rat brains were identical quantitatively to those of the nonperfused controls. Cerebral ischemia resulted in significantly increased levels of ADP, AMP + IMP, Pi, fructose 1,6-diphosphate, and glycerol 3-phosphate (global ischemia only), whereas ATP and phosphocreatine (PCr) levels declined significantly. The magnitude of these changes varied with the severity of the ischemia; however, following 15 min of control reperfusion metabolite levels had reverted to preischemic values. Significant perturbations in tissue phosphoethanolamine (3.84 delta resonance) content were evident at various time points during ischemia and postischemic recovery, which varied according to the perfusion conditions. In contrast to the changes observed in response to ischemia, hypoxia affected only cerebral high-energy phosphate levels. ATP and PCr levels were reduced, while a concomitant, essentially equimolar, increase in Pi and ADP was observed. The present studies indicate that in terms of phosphatic metabolites, the control equilibrated isolated perfused rat brain is quantitatively and qualitatively indistinguishable from the nonperfused rat brain in vivo regardless of the perfusion conditions (constant flow versus constant pressure). The metabolic responses to ischemia and hypoxia, as measured by P-31 NMR, were consistent with the pattern of changes reported elsewhere. Overall, P-31 NMR spectroscopic evaluation of the intact rat brain provides a potential experimental context for dynamic measures of cerebral metabolism under exogenously controlled conditions. Th

Recovery after hypoglycemic brain injury. Action of some biological substances on the cerebral metabolism

In artificially ventilated beagle dogs a severe hypoglycemic condition was induced by insulin injection, while the posthypoglycemic recovery was induced by glucose treatment at the end of a 20-min period of spontaneous electroencephalographic silence. The motor area of the cerebral cortex was analyzed for glycolytic metabolites, related amino acids, energy mediators, fatty acids, phospholipids and free fatty acids. The effects on the posthypoglycemic recovery of a intracarotid infusion with some agents (i.e. uridine, cytidine, DL-carnitine, DL-acetylcarnitine, papaverine) were tested. Severe hypoglycemia induced an extensive derangement of the brain metabolism, with partial restitution during the posthypoglycemic recovery. During this condition, the intracarotid perfusion with some biological pyrimidines (uridine, cytidine) interfered with the glycolytic and amino acid metabolites, inducing a decrease in glucose, pyruvate and lactate contents, and an increase in succinate, alanine and glutamine cerebral concns. The lipid carriers (DL-carnitine, DL-acetylcarnitine) interfered with the fatty acid degradation inducing a magnification of the decrease in the individual (palmitic acid, oleic acid) and total fatty acids, the vasodilating agent (papaverine) being practically inactive.

An improved method for perfusion of the isolated brain of the rat-influence of perfusion conditions and application of analeptic and anticonvulsant drugs

A method for the perfusion of the isolated brain of the rat with synthetic fluorocarbon emulsion is described. The functional states of the brains were investigated using biochemical, biophysical, and histological methods. After 4.5 h of perfusion, all brains were in excellent condition and comparable to the in vivo state. The influence of perfusion conditions on the viability of the brains was studied. Deep hypothermia was well tolerated; at 13 degrees the EEG exhibited a mean frequency of about 8 Hz, while the mean amplitude was about 40% lower than at 28 degrees or 36 degrees. Constant-pressure perfusion did not affect brain function, provided that the pressure amplitude was very slowly decreased. During application of pentylenetetrazole (PTZ) it was found that the threshold concentration of PTZ in the perfusion medium to induce epileptic seizure discharges was 0.13 mg/ml. However, after repeated application of PTZ, the threshold concentration decreased exponentially, indicating a kindling phenomenon. It could be shown that not PTZ as such, but the spike potentials provoked by PTZ, induced the kindling effect. This was inhibited by application of primidone or phenobarbital.

Drug action on the metabolic changes induced by acute hypoxia on synaptosomes from the cerebral cortex

The synaptosomal fractions obtained from the motor area of the cerebral cortex of normocapnic, normoxic, or hypoxic, untreated beagle dogs and of pentobarbital (Nembutal)- or cytidine diphosphate (CDP)-choline-treated dogs were incubated and analyzed for ATP, ADP, AMP, creatine phosphate, pyruvate, and lactate. The data were compared with data obtained by the surface freezing technique from the whole contralateral cortical area. The in vivo intracarotid perfusion of the drug differentially affected the content of the metabolites and their ratio. This occurred whether the evaluations were performed in the incubated synaptosomal preparations or in whole cerebral tissue, both during normoxia and after hypoxia (15 min; PaO2 = 17-19 mm Hg). Thus, intracarotid perfusion of nembutal increased the synaptosomal phosphorylation state both in normoxic and in hypoxic animals, whereas the effect on the metabolism of the contralateral cortical motor area as a whole was in all cases less than that observed in the synaptosomal fraction. Perfusion with CDP-choline increased synaptosomal phosphorylation after the hypoxic condition, but had no effect in normoxia or on the whole cortical tissue of the motor area. The possibility of obtaining a cerebral sparing action by utilizing molecules devoid of anesthetic action is suggested.

Characterization of the isolated perfused mouse brain as a system for neurochemical studies

The preparation of the isolated perfused mouse brain (IPMB) is described along with its electrophysiological, morphological, biochemical and pharmacological properties. Using high performance liquid chromatography with electrochemical detection, the primary metabolite of mammalian central nervous system norepinephrine, 3-methoxy-4-hydroxyphenethyleneglycol (MHPG), was measured in the perfusate at 15-min intervals. The rate of MHPG production was similar to literature values of the rate of norepinephrine turnover in mouse brain. MHPG production rate in the IPMB was blocked by pretreatment with 6-hydroxydopamine and was increased by pretreatment with reserpine.

Fluorocarbon perfusion medium applied to the isolated rat brain

In order to overcome the disadvantages of erythrocytes and albumin, a totally synthetic medium for the perfusion of the isolated rat brain was developed. the perfusion medium was based upon Krebs-Henseleit solution and contained in addition a fluorocarbon (FC 43) for oxygen transport and a polyol (Pluronic F 68) to furnish emulsifying and oncotic properties. The physico-chemical properties of this fluorocarbon perfusion medium allowed perfusion of an isolated rat brain to continue for more than 7 hr, while the medium could be stored as a stock emulsion for several months. The appropriate function of the isolated perfused rat brain is demonstrated by the EEG and by various substrates of the energy metabolism. The suitability of the fluorocarbon medium for perfusion of an isolated rat brain preparation is discussed.

Effects of chlorpromazine and some of its metabolites on the EEG and on dopamine metabolism of the isolated perfused rat brain

The study concerned the effects of chlorpromazine (CPZ), monodesmethyl-chlorpromazine (NOR1-CPZ), didesmethyl-chlorpromazine (NOR2-CPZ), and chlorpromazine-N-oxide (CPZ-NO) on the EEG and on dopamine metabolism of the isolated perfused rat brain. Isolated brains were perfused with 100 ml of a perfusion medium containing 30% bovine red cells (v/v), 2 g bovine serum albumin, 14 mM glucose as well as one of the agents in a concentration of 10 micrometers. The main dopamine metabolite homovanillic acid (HVA) was measured fluorimetrically in the striatum of the isolated brain. The EEG was recorded by two symmetrical bipolar leads from the parietal regions at various times during the 30 min perfusion period and was stored on magnetic tape. The recordings were evaluated visually and quantitatively by automatic analysis. CPZ-NO was found to be the most active agent both in changing the EEG and in elevating the HVA level in the striatum. The mean EEG amplitude and the slow wave activity increased significantly. The increase of the HVA level in the striatum was correlated with the increase of delta waves as well as excess of kurtosis and skewness calculated from the amplitude histography data. The desmethylated metabolites caused only moderate central effects.

Decreased GABA and glutamate concentration in rat brain after treatment with 6-aminonicotinamide

The effect of 6-aminonicotinamide (6-AN) on putative amino acid neurotransmitters, namely glutamate, GABA and aspartate was studied on brains of rats treated with this antimetabolite (35 mg/kg i.p.). After 6-AN application the following substrates and metabolites were determined: phosphocreatine, ATP, ADP, AMP, glucose, glucose 6-phosphate, fructose, glutamate, GABA, aspartate, ammonia, and 6-phosphogluconate. The alterations in the cerebral energy metabolism were found as reported in the literature (increased levels of glucose, glucose 6-phosphate, decreased levels of lactate and pyruvate) and could be interpreted as the result of a reduced glycolytic flux rate. After a prolonged period of 6-AN pretreatment (16-30 h) the GABA and glutamate concentrations were significantly reduced, whereas the level of aspartate remained unchanged. From the result presented the two following conclusions may be drawn: a) The changes in the concentration of neurotransmitters as GABA and glutamate could be responsible for some neurological symptoms produced by 6-AN. b) As 6-AN seems to affect the GABA-shunt it represents a model substance for studying this pathway in the nervous system.

Inhibition of glucose phosphorylation in rat brain by thiopental

The purpose of the present investigation was to shed some light on the suppression of the glycolytic pathway by anesthetics. The antimetabolite 6-aminonicotinamide (6-AN) was used to discriminate between the key enzymes hexokinase and phosphofructokinase which are suggested to be involved in the effect of anesthetics on glycolysis. The cerebral energy metabolism was studied in the isolated perfused rat brain after the addition of thiopental (0.15 mM) to the perfusion medium, after the administration of 6-AN (35mg/kg i.p.) to the intact animals 15 h before perfusion was started, as well as in brain preparations treated in the same manner with both 6-AN and thiopental. After a perfusion period of 30 min brain levels of the following substrates and metabolites were determined: phosphocreatine, ATP, ADP, AMP, glycogen, glucose, glucose 6-phosphate, fructose 6-phosphate, pyruvate, lactate, alpha-ketoglutarate, blutamate, ammonia, and 6-phosphogluconate. The metabolic alterations in the isolated rat brain caused by 6-AN or thiopental were such as reported in the literature. When the isolated brains of the 6-AN pretreated rats were perfused with thiopental we found as the most interesting result that the concentration of glucose 6-phosphate was reduced in comparison to that in brains only treated with 6-AN but still significantly higher than that in controls. The glucose concentration was significantly elevated and the lactate concentration decreased considerably. The effect of thiopental on cerebral glycolysis was interpreted as an inhibition of hexokinase activity.

The effects of increased glucose supply and thiopental anesthesia on energy metabolism of the isolated perfused rat brain

The effects of glucose concentrations in the perfusion medium ranging from 5 to 15 mM and thiopental, on cerebral energy metabolism were studied using the isolated perfused rat brain. After a perfusion time of 30 min brain levels of the following substrates and metabolites were determined: P-creatine, ATP, ADP, AMP, glycogen, glucose, glucose-6P, fructose-6-P, pyruvate, lactate, alpha-ketoglutarate, glutamate, ammonia. In control experiments increasing the glucose concentration in the perfusion medium produced an increase of intracellular brain glucose concentration only, revealing a linear relationship between glucose content in brain and blood. Neither high-energy phosphates nor glycolytic intermediates were markedly affected by the changes in blood glucose. With an anesthetic dose of thiopental (0.15 mM) in the perfusion medium identical metabolic alterations occured in all experiments: P-creatine and glucose were significantly increased whereas ADP, AMP, lactate and pyruvate were diminished. Also with thiopental brain glucose was linearly related with the glucose concentration in the perfusion medium. The calculated regression line was apparently parallel with that from control experiments; that means thipental always caused an elevation of brain glucose by the same amount of 0.9 mumoles/g--irrespective of the initial cerebral glucose content. The results yield further evidence that glucose transport is not the rate-limiting step in glycolysis. The action of thiopetal on glycolytic pathway is discussed.

Decreased glycolytic flux rate in the isolated perfused rat brain after pretreatment with 6-aminonicotinamide

Cerebral energy metabolism was studied in the isolated perfused rat brain after 6-aminonicotinamide (6-AN; 35 mg/kg i.p.) administered to the intact animals 7 hrs before perfusion was started. The metabolic alterations in the isolated rat brains were such as reported for rat and mouse brain in vivo: Inhibition of 6-phosphogluconate dehydrogenase was followed by an accumulation of 6-phosphogluconate, leading to a decreased activity of glucosephosphate isomerse. This was reflected by increased levels of glucose and glucose 6-phosphate and decreased levels of fructose 6-phosphate, pyruvate and lactate. Since the concentration of lactate in the perfusate of the isolated brain was also lowered, 6-AN must have reduced the glycolytic flux rate.