Metabolic Changes in Cerebral Cortex, Hippocampus, and Cerebellum During Sustained Bicuculline-Induced Seizures

Abstract— The objective of the present experiments was to study metabolic correlates to the localization of neuronal lesions during sustained seizures. To that end, status epilepticus was induced by i.v. administration of bicuculline in immobilized and artificially ventilated rats, since this model is known to cause neuronal cell damage in cerebral cortex and hippocampus but not in the cerebellum. After 20 or 120 min of continuous seizure activity, brain tissue was frozen in situ through the skull bone, and samples of cerebral cortex, hippocampus, and cerebellum were collected for analysis of glycolytic metabolites, phosphocreatine (PCr), ATP, ADP, AMP, and cyclic nucleotides. After 20 min of seizure activity, the two “vulnerable” structures (cerebral cortex and hippocampus) and the “resistant” one (cerebellum) showed similar changes in cerebral metabolic state, characterized by decreased tissue concentrations of PCr, ATP, and glycogen, and increased lactate concentrations and lactate/ pyruvate ratios. In all structures, though, the adenylate energy charge remained close to control. At the end of a 2-h period of status epilepticus, a clear deterioration of the energy state was observed in the cerebral cortex and the hippocampus, but not in the cerebellum. The reduction in adenylate energy charge in the cortex and hippocampus was associated with a seemingly paradoxical decrease in tissue lactate levels and with failure of glycogen resynthesis (cerebral cortex). Experiments with infusion of glucose during the second hour of a 2-h period of status epilepticus verified that the deterioration of tissue energy state was partly due to reduced substrate supply; however, even in animals with adequate tissue glucose concentrations, the energy charge of the two structures was significantly lowered. The cyclic nucleotides (cAMP and cGMP) behaved differently. Thus, whereas cAMP concentrations were either close to control (hippocampus and cerebellum) or moderately increased (cerebral cortex), the cGMP concentrations remained markedly elevated throughout the seizure period, the largest change being observed in the cerebellum. It is concluded that although the localization of neuronal damage and perturbation of cerebral energy state seem to correlate, the results cannot be taken as. evidence that cellular energy failure is the cause of the damage. Thus, it appears equally probable that the pathologically enhanced neuronal activity (and metabolic rate) underlies both the cell damage and the perturbed metabolic state. The observed changes in cyclic nucleotides do not appear to bear a causal relationship to the mechanisms of damage.     

Functional, Metabolic, and Circulatory Changes Associated with Seizure Activity in the Postischemic Brain

Abstract: The present study was undertaken to explore how transient ischemia in rats alters cerebral metabolic capacity and how postischemic metabolism and blood flow are coupled during intense activation. After 6 h of recovery following transient forebrain ischemia 15 min in duration, bicuculline seizures were induced, and brains were frozen in situ after 0.5 or 5 min of seizure discharge. At these times, levels of labile tissue metabolites were measured, whereas the cerebral metabolic rate for oxygen (CMRO₂) and cerebral blood flow (CBF) were measured after 5 min of seizure activity. After 6 h of recovery, and before seizures, animals had a 40–50% reduction in CMRO₂, and CBF. However, because CMRO₂ rose threefold and CBF fivefold during seizures, CMRO₂ and CBF during seizures were similar in control and postischemic rats. Changes in labile metabolites due to the preceding ischemia encompassed an increased phosphocreatine/ creatine ratio, as well as raised glucose and glycogen concentrations. Seizures gave rise to minimal metabolic perturbation, essentially comprising reduced glucose and glycogen contents and raised lactate concentrations. It is concluded that although transient ischemia leads to metabolic depression and a fall in CBF, the metabolic capacity of the tissue is retained, and drug-induced seizures lead to a coupled rise in metabolic rate and blood flow.     

Cyclic AMP Concentrations in Rat Neocortex and Hippocampus During and Following Incomplete Ischemia: Effects of Central Noradrenergic Neurons, Prostaglandins, and Adenosine

The concentrations of cyclic AMP, noradrenaline, glycogen, glucose, lactate, pyruvate, labile phosphate compounds, and free fatty acids were investigated in the rat neocortex and hippocampus during and following cerebral ischemia. An incomplete ischemia of 5 and 15 min duration was induced by bilateral carotid clamping combined with hypotension. The postischemic events were studied after 5, 15, and 60 min of recirculation. Five minutes of ischemia did not significantly alter the neocortical or hippocampal concentrations of cyclic AMP. After 15 min of ischemia the neocortical levels decreased significantly below control values. In the recirculation period following ischemia a significant elevation of the cyclic AMP concentrations was observed. Following 5 min of recirculation after 5 min of ischemia the levels increased from 2.53 +/- 0.21 nmol X g-1 to 5.18 +/- 0.09 nmol X g-1 in the neocortex and from 2.14 +/- 0.16 nmol X g-1 to 3.52 +/- 0.35 nmol X g-1 in the hippocampus. Five minutes of recirculation following 15 min of ischemia led to a significant increase in the levels of cyclic AMP, to 12.86 +/- 1.43 nmol X g-1 in the neocortex to 5.58 +/- 0.57 nmol X g-1 in the hippocampus. With longer recirculation periods the cyclic AMP levels progressively decreased and were similar to control values after 60 min. Depletion of cortical noradrenaline by at least 95% was performed by injections of 6-hydroxydopamine into the ascending axon bundles from the locus ceruleus. The lesion did not significantly change the ischemic or post-ischemic neocortical and hippocampal levels of cyclic AMP, glycogen, or free fatty acids including arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cerebral energy metabolism during experimental status epilepticus.

—The concentration of ATP, ADP, AMP, phosphocreatine and of 5 intermediates of carbohydrate metabolism were determined in rodent brain after single and repeated seizures induced by either electroshock (ES), flurothyl or pentylenetetrazol (PTZ). In paralysed-ventilated rats, one ES produced a 4–5 fold increase in cortical glycolytic flux (estimated from changes in glucose and lactate), and associated increases in pyruvate and in the lactate/pyruvate ratio. Total high energy phosphates declined during the seizure; a decrease was also calculated in cortical tissue pH and in the cytoplasmic [NAD⁺]/[NADH] ratio. Similar changes in brain were observed in ventilated mice after ES, but in paralysed animals, no decrease in high energy phosphates occurred during the first seizure. More vigorous and prolonged chemically-induced seizures in both rats and mice elicited a decrease in the cerebral energy reserves with a rise in lactate and in the lactate/pyruvate ratio. At all times during the seizures the cerebral venous blood had a higher oxygen tension than that of control animals (rats) or was visibly reddened (mice), implying that oxygen availability to brain exceeded metabolic demands. It is proposed that the development of‘non-hypoxic’cerebral lactacidosis during seizures is part of the overall metabolic response of the brain to an abrupt increase in energy consumption. The response constitutes a homeostatic influence which promotes cerebral vasodilatation, thereby increasing blood flow and the delivery of substrates. With repeated seizures, delivered 2 min apart, glycogen declined progressively, but concentrations of the adenine nucleotides appeared to plateau, suggesting that a new energy balance had been established. However, after 20–25 seizures, the attacks became self-generating and there was a further reduction in the tissue high energy phosphate stores, a fall in brain glucose and in the brain/blood glucose ratio. It is concluded that the brain possesses a limited capacity to adjust its metabolism to meet the increased energy requirements of single or repeated seizures, but that this mechanism ultimately fails during status epilepticus unless the abnormal electrical discharges, themselves, are brought under control.     

Regional Energy Balance in Rat Brain After Transient Forebrain Ischemia

Abstract: Phosphocreatine, ATP, and glucose were severely depleted, and the lactate levels were increased in the paramedian neocortex, dorsal-lateral striatum, and CA1 zone of hippocampus of rats exposed to 30 min of forebrain ischemia. Upon recirculation of the brain, phosphocreatine, ATP, and lactate concentrations recovered to control values in the paramedian neocortex and CA1 zone of hippocampus and to near-control values in the striatum. The phosphocreatine and ATP concentrations then fell and the lactate levels rose in the striatum after 6–24 h, and in the CA1 zone of hippocampus after 24–72 h. The initial recovery and subsequent delayed changes in the phosphocreatine, ATP, and lactate concentrations in the striatum and hippocampus coincided with the onset and progression of morphological injury in these brain regions. The results suggest that cells in these regions regain normal or near-normal mitochondrial function and are viable, in terms of energy production, for many hours before unknown mechanisms cause irreversible neuronal injury.     

Regulation of gluconeogenesis during exposure of young rats to hypoxic conditions

1. Two-day-old rats were exposed at constant temperature to atmospheres containing air and nitrogen with the air content varied in steps from 100 to 0%. By using this system of graded hypoxia a comparison was made between rates of gluconeogenesis from lactate, serine and aspartate in the whole animal and the concentrations of several liver metabolites. 2. Gluconeogenesis, expressed as the percentage incorporation of labelled isotope into glucose plus glycogen, proceeds linearly for 30min when the animals are incubated in a normal air atmosphere, but is completely suppressed if the atmosphere is 100% nitrogen. 3. Preincubation of animals for between 5 and 30min under an atmosphere containing 19% air results in the attainment of a new steady state with respect to gluconeogenesis and hepatic concentrations of ATP, ADP, AMP, lactate, pyruvate, beta-hydroxybutyrate and acetoacetate. 4. When lactate (100mumol), aspartate (20mumol) or serine (20mumol) was injected, it was shown that the more severe the hypoxia the greater the depression of gluconeogenesis. Under conditions when gluconeogenesis was markedly inhibited there were no changes in the degree of phosphorylation of hepatic adenine nucleotides, but free [NAD(+)]/[NADH] ratios fell in both cytosol and mitochondrial compartments of the liver cell. 5. Measurements of total liver NAD(+) and NADH showed that the concentrations of these nucleotide coenzymes changed less with anoxia, in comparison with the concentration ratio of free coenzymes. 6. Calculations showed that the difference in NAD(+)-NADH redox potentials between mitochondrial and cytosol compartments increased with the severity of hypoxia. 7. From the constancy of the concentrations of adenine nucleotides it is concluded that liver of hypoxic rats can conserve ATP by lowering the rate of ATP utilization for gluconeogenesis. Gluconeogenesis may be regulated in turn by the changes in mitochondrial and cytosol redox state.     

Metabolic recovery in herring larvae following strenuous activity

Larvae of spring spawning Clyde herring Clupea harengus L. were reared at 5 and 12° C. Metabolism following burst swimming was studied in 7-day-old larvae at their respective rearing temperatures. Escape responses were repeatedly elicited using tactile stimulation for a period of 3 min. Larval herring were hard to fatigue and still responded to tactile stimuli after 3 min. Whole larvae were freeze-quenched in liquid nitrogen, either immediately after exercise, or after periods of recovery of up to 24 h. Samples were freeze-dried and analysed for whole body creatine (Cr), phosphocreatine (PCr), ATP, ADP, AMP, lactate, glucose, and glycogen using high performance liquid chromatography and enzymatic methods. The exercise regime resulted in a marked decrease in PCr, ATP and glycogen concentrations and an increase in creatine, glucose and lactate concentrations whereas there was no significant change in either AMP or ADP concentrations. The extent of phosphagen hydrolysis (approx. 110 to 15μmol PCr g ⁻¹ dry body mass) and lactate accumulation (approx. 7 to 40 μmol lactate g⁻¹ dry body mass) over the exercise period was similar at the two temperatures, consistent with a relatively constant degree of effort. The rates of recovery of PCr and ATP were essentially the same at 5 and 12° C; returning to resting levels after approximately 30 min. Lactate and glycogen concentrations were restored 60 min after exercise at both temperatures. Maximum lactate clearance rates (1.2 μmol min ⁻¹ g ⁻¹ wet muscle mass) were an order of magnitude faster than reported for adult fish in the literature.     

IN VIVO EFFECTS OF AMPHETAMINE ON METABOLITES AND METABOLIC RATE IN BRAIN

—The concentrations of several metabolites, including glucose, glycogen, glucose-6-phosphate, lactate, ATP and phosphocreatine have been measured in the brains of mice rapidly frozen at various intervals after the intraperitoneal injection of d -amphetamine sulphate (5 mg/kg). During the initial 30 min following injection, amphetamine induced a fall in cerebral glycogen and phosphocreatine and an elevation of lactate. Changes in glucose and brain/blood glucose ratios were less marked over this period. The metabolite levels returned to control values at 60 min. The cerebral metabolic rate calculated by the ‘closed system’ technique also showed a biphasic change. An initial depression of energy flux over the first 15 min following amphetamine injection was followed by an increase that appeared to be closely associated with the increase in locomotor activity over this period. The results have been discussed in relation to the known catecholamine-releasing action of amphetamine, and differential effects on glial cells and neurons have been proposed.     

Role of NADH/NAD+ transport activity and glycogen store on skeletal muscle energy metabolism during exercise: in silico studies

Skeletal muscle can maintain ATP concentration constant during the transition from rest to exercise, whereas metabolic reaction rates may increase substantially. Among the key regulatory factors of skeletal muscle energy metabolism during exercise, the dynamics of cytosolic and mitochondrial NADH and NAD+ have not been characterized. To quantify these regulatory factors, we have developed a physiologically based computational model of skeletal muscle energy metabolism. This model integrates transport and reaction fluxes in distinct capillary, cytosolic, and mitochondrial domains and investigates the roles of mitochondrial NADH/NAD+ transport (shuttling) activity and muscle glycogen concentration (stores) during moderate intensity exercise (60% maximal O2 consumption). The underlying hypothesis is that the cytosolic redox state (NADH/NAD+) is much more sensitive to a metabolic disturbance in contracting skeletal muscle than the mitochondrial redox state. This hypothesis was tested by simulating the dynamic metabolic responses of skeletal muscle to exercise while altering the transport rate of reducing equivalents (NADH and NAD+) between cytosol and mitochondria and muscle glycogen stores. Simulations with optimal parameter estimates showed good agreement with the available experimental data from muscle biopsies in human subjects. Compared with these simulations, a 20% increase (or approximately 20% decrease) in mitochondrial NADH/NAD+ shuttling activity led to an approximately 70% decrease (or approximately 3-fold increase) in cytosolic redox state and an approximately 35% decrease (or approximately 25% increase) in muscle lactate level. Doubling (or halving) muscle glycogen concentration resulted in an approximately 50% increase (or approximately 35% decrease) in cytosolic redox state and an approximately 30% increase (or approximately 25% decrease) in muscle lactate concentration. In both cases, changes in mitochondrial redox state were minimal. In conclusion, the model simulations of exercise response are consistent with the hypothesis that mitochondrial NADH/NAD+ shuttling activity and muscle glycogen stores affect primarily the cytosolic redox state. Furthermore, muscle lactate production is regulated primarily by the cytosolic redox state.     

Responsiveness to glucagon by isolated rat hepatocytes controlled by the redox state of the cytosolic nicotinamide--adenine dinucleotide couple acting on adenosine 3'':5''-cyclic monophosphate phosphodiesterase.

1. The effects of changes in the cytoplasmic [NADH]/[NAD+] ratio on the efficacy of glucagon to alter rates of metabolism in isolated rat hepatocytes were examined. 2. Under reduced conditions (with 10mM-lactate), 10nM-glucagon stimulated both gluconeogenesis and urea synthesis in isolated hepatocytes from 48h-starved rats; under oxidized conditions (with 10mM-pyruvate), 10nM-glucagon had no effect on either of these rates. 3. The ability of glucagon to alter the concentration of 3':5'-cyclic AMP and the rates of glucose output, glycogen breakdown and glycolysis in cells from fed rats were each affected by a change in the extracellular [lactate]/[pyruvate] ratio; minimal effects of glucagon occurred at low [lactate]/[pyruvate] ratios. 4. Dose-response curves for glucagon-mediated changes in cyclic AMP concentration and glucose output indicated that under oxidized conditions the ability of glucagon to alter each parameter was decreased without affecting the concentration of hormone at which half-maximal effects occurred. 5. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.05 mM) significantly reversed the inhibitory effects of pyruvate on glucagon-stimulated glucose output. 6. For exogenously added cyclic [3H]AMP(0.1 mM), oxidized conditions decreased the stimulatory effect on glucose output as well as the intracellular concentration of cyclic AMP attained, but did not alter the amount of cyclic [3H]AMP taken up. 7. The effects of lactate, pyruvate, NAD+ and NADH on cyclic AMP phosphodiesterase activities of rat hepatocytes were examined. 8. NADH (0.01--1 MM) inhibited the low-Km enzyme, particularly that which was associated with the plasma membrane. 9. The inhibition of membrane-bound cyclic AMP phosphodiesterase by NADH was specific, reversible and resulted in a decrease in the maximal velocity of the enzyme. 10. It is proposed that regulation of the membrane-bound low-Km cyclic AMP phosphodiesterase by nicotinamide nucleotides provides the molecular basis for the effect of redox state on the hormonal control of hepatocyte metabolism by glucagon.     

Cerebral carbohydrate metabolism during acute hypoxia and recovery

Abstract— The levels of ATP, ADP, AMP and phosphocreatine, of four amino acids, and of 11 intermediates of carbohydrate metabolism in mouse brain were determined after: (1) various degrees of hypoxia; (2) hypoxia combined with anaesthesia; and (3) recovery from severe hypoxia. Glycogen decreased and lactate rose markedly in hypoxia, but levels of ATP and phosphocreatine were normal or near normal even when convulsions and respiratory collapse appeared imminent. During 30 s of complete ischaemia (decapitation) the decline in cerebral ATP and phosphocreatine and the increase in AMP was less in mice previously rendered hypoxic than in control mice. From the changes we calculated that the metabolic rate had decreased by 15 per cent or more during 30 min of hypoxia. Hypoxia was also associated with decreases of cerebral 6-phosphogluconate and aspartate, and increases in alanine, γ-aminobutyrate, α-ketoglutarate, malate, pyruvate, and the lactate :pyruvate ratio. Following recovery in air (10 min), increases were observed in glucose (200 per cent), glucose-6-phosphate, phosphocreatine and citrate, and there was a fall in fructose-1, 6-diphosphale. Similar measurements were made in samples from cerebral cortex, cerebellum, midbrain and medulla. Severe hypoxia produced significant increases in lactate and decreases in glycogen in all areas; γ-aminobutyrate levels increased in cerebral cortex and brain stem, but not in cerebellum. No significant changes occurred in ATP and only in cerebral cortex was there a significant fall in phosphocreatine. Phosphocreatine, ATP and glycogen were determined by quantitative histochemical methods in four areas of medulla oblongata, including the physiological respiratory centre of the ventromedial portion. After hypoxia, ATP was unchanged throughout and the changes (decreases) in phosphocreatine and glycogen were principally confined to dorsal medulla, notably the lateral zone. Thus there is no evidence that respiratory failure is caused by a ‘power’ failure in the respiratory centre. It is suggested that in extremis a protective mechanism may cause neurons to cease firing before high-energy phosphate stores have been exhausted.     

Inhibition of lipogenesis by halothane in isolated rat liver cells.

1. Halothane at clinically effective concentrations [2.5 and 4% (v/v) of the gas phase of the incubation flask] was found to inhibit significantly lipogenesis from endogenous substrates, e.g., glycogen, or from added lactate plus pyruvate. This was accompanied by a decrease in the ratio of the free [NAD+]/[NADH] of the mitochondrion and the cytoplasm, as shown by the [3-hydroxybutyrate]/[acetoacetate] ratio and the [lactate]/[pyruvate] ratio. 2. Acetoacetate or pyruvate decreased the inhibitory effect of halothane and restored lipogenesis to control rates. They were reduced rapidly by 3-hydroxybutyrate dehydrogenase or lactate dehydrogenase respectively, with the concomitant oxidation of NADH and the generation of NAD+. 3. These results suggest that the mechanism by which halothane inhibits lipogenesis from glycogen or lactate is by inhibition of the oxidation of NADH; this results in inhibition of flux of carbon through pyruvate dehydrogenase and a shortage of acetyl-CoA for fatty acid synthesis. Thus when NADH acceptors are added in the presence of halothane, the concentration of mitochondrial NAD+ is raised so that the flux of carbon through pyruvate dehydrogenase increases and lipogenesis is restored.     

Cerebral Metabolic State During the Ethanol Withdrawal Reaction in the Rat

Abstract: A severe ethanol withdrawal reaction was induced in rats by means of repeated intragastric intubation during a 4-day period. At the peak of the withdrawal reaction cerebral cortical tissue was frozen in situ for analysis of glycogen, glucose, phosphocreatine, creatine, ATP, ADP, AMP, lactate, pyruvate, GAB A, β-hydroxybutyrate, acetoacetate, cAMP and cGMP. Blood glucose concentration was also measured. The level of brain glycogen was decreased during ethanol withdrawal. Brain glucose concentration was increased, probably secondary to the increase in blood glucose concentration. The calculated NADH/NAD⁺ ratio was slightly increased during the withdrawal and brain ATP concentration and adenine nucleotide pool size were decreased. The adenylate energy charge remained unchanged. The overall changes in the metabolites were in agreement with the previously shown metabolic activation during ethanol withdrawal. The brain concentrations of ketone bodies (β-hydroxybutyrate and acetoacetate) during withdrawal did not deviate from controls, indicating that no abnormal ketone metabolism had developed as a consequence of the long-lasting ethanol intoxication. No changes were observed in the concentrations of GABA, cAMP, or cGMP in the rat cerebral cortex during ethanol withdrawal.     

The metabolic state of muscle in the isolated perfused rat hemicorpus in relation to rates of protein synthesis.

Measures of perfusion adequacy in perfused rat hemicorpus preparations were investigated as potential indices of tissue function during studies of muscle protein metabolism. Perfusion under normal conditions for up to 80 min resulted in rates of protein synthesis and concentrations of ATP in muscle that were similar to those in vivo, but phosphocreatine in muscle gradually decreased and muscle lactate increased. Hypoxic conditions led to lower rates of protein synthesis, lower phospho-creatine and raised lactate contents in muscle compared with normal perfusions, and ATP was slightly decreased. Hypoxic preparations also released more lactate and K+ into the medium and had higher perfusion pressures, but glucose uptake and muscle water content were not altered. In totally ischaemic muscle, concentrations of ATP and phosphocreatine were even lower than in hypoxic muscle, and that of lactate was higher. From 11 preparations perfused for 60 min under normal conditions, three were selected on the basis of lower muscle ATP content than the others. Preparations with low ATP also showed lower muscle phosphocreatine concentrations, O2 uptake and CO2 output, as well as higher perfusion pressure and muscle lactate concentrations than in the remaining preparations, but muscle water, ADP and AMP concentrations and lactate and K+ flux were no different. In perfusions extended to 3 h, deterioration of function was more apparent. There were significant correlations between rates of protein synthesis and the concentrations of ATP, phosphocreatine and lactate in two different muscles (r = 0.756-0.929), but not with any of the other indices investigated. Taken overall, these experiments showed that concentrations of ADP, AMP and water in muscle, rates of lactate and glucose metabolism, K+ output, perfusion pressure and blood gas parameters were unsuitable for distinguishing unsound from sound preparations, because they did not consistently demonstrate differences, or could not be ascribed to only muscle metabolism. It was found that ATP, phosphocreatine and lactate concentrations in muscle were the best indicators of impaired metabolic state in studies of protein synthesis. Measurements of these could be used on a routine basis for rejecting unsatisfactory preparations.     

The influence of adenosine on intermediary metabolism of isolated hepatocytes.

The effect of adenosine was tested on the energetic metabolism of fed rat liver cells after isolation. The cells were incubated in a buffered saline medium with glucose (5 mM) and adenosine (1 mM) for 30 minutes at 37 degrees C. This increased the concentration of the adenylic nucleotides ATP (+57 per cent, ADP (+39 per cent). Cyclic AMP was increased (+50 per cent) and the intracellular inorganic phosphate decreased (-22 per cent). These changes were accompaned by a decrease of glycogenolysis, glucose consumption and lactate production. Measurement of glycolytic intermediates showed decreased concentrations of fructose 1,6-bis-phosphate and 3-phosphoglycerate proportional to the increase in ATP concentration. The near-equilibrium of the glyceraldehyde 3-phosphate dehydrogenase-phosphoglycerate kinase system was not modified by adenosine. The decrease of the NAD+/NADH ratio along with the increase of the ATP/ADP X PO4 ratio explains the decrease of 3-phosphoglycerate. The decrease in glucose consumption can be explained by the cross over at the phosphofructokinase stage with the decrease of fructose 1,6-bisphosphate. The major part of adenosine was deaminated as indicated by an increase in the production of ammonia and urea. The effects of inosine, or adenosine along with an inhibitor of adenosine deaminase (pentostatin) suggest that adenosine acts on the glucose consumption through adenylic nucleotides. However the increase of the adenylic nucleotide level cannot totally explain the other metabolic changes: decrease of the NAD+/NADH cytoplasmic ratio, constancy of this ratio in mitochondria, decrease of gluconeogenesis from lactate. A direct action of adenosine can therefore be expected.     

EFFECT OF OLIGEMIA ON REGIONAL METABOLITE LEVELS IN CAT BRAIN

Abstract— Incomplete cerebral ischemia (oligemia) was produced in cat by carotid occlusion combined with arterial hypotension. Lowering arterial pressure to 50–60 Torr for 20 min caused marked alterations of the ATP, phosphocreatine, and lactate content of subcortical white matter. In contrast, metabolite levels in cerebral cortex and caudate nucleus were only moderately perturbed from control values. More severe oligemia resulted when arterial pressure was lowered to 30 Torr for 20 min following carotid occlusion. Metabolite levels in cortex, caudate nucleus, and white matter were greatly altered from control. In the gray matter there was regional heterogeneity of metabolic alteration, as evidenced from the pattern of NADH tissue fluorescence. The cortex contained micro-patches (0.1mm) of increased NADH, which frequently exhibited a columnar orientation.
These findings demonstrate two distinct types of cerebral inhomogeneity of metabolic failure with reduced blood flow; white matter fails before gray matter, and there is micro-heterogeneity of metabolic failure in the gray matter.     

PGF2 alpha, thromboxane B2 and HETE levels in gerbil brain cortex after ligation of common carotid arteries and decapitation.

The effects of ligation of both common carotid arteries in the gerbil on the levels of PGF2 alpha, TXB2, HETE and of energy metabolites in brain cortex, have been investigated. Also, in the same experimental conditions the changes of cyclic AMP in brain cortex, cerebellum, striatum and hippocampus have been monitored. ATP, glycogen, glucose and phosphocreatine decrease whereas, lactate and cyclic AMP are enhanced in the ischemic brain, as previously reported. In contrast, levels of arachidonic acid metabolites are not modified. During ischemia following decapitation, instead, PGF2 alpha, and TXB2, show considerable increase.     

Cyclic Nucleotide Response of the Hippocampal Formation to Septal Stimulation in Naive and Kindled Rats

Rats were kindled through nonmagnetic electrodes stereotaxically implanted into the medial septum. Concentrations of cyclic AMP and cyclic GMP were measured by radioimmunoassay in seven brain regions after microwave fixation during the development and expression of kindled seizures. Hippocampal concentrations were similar to untreated controls (cyclic GMP level in the left and right hippocampus, 0.66 +/- 0.04 and 0.68 +/- 0.07 pmol/mg of protein, respectively; cyclic AMP, 9.4 +/- 0.9 and 9.6 +/- 0.8 pmol/mg of protein, respectively), in kindled animals that were not stimulated, and in naive animals in response to septal stimulation, in spite of the presence in the latter group of bilateral hippocampal afterdischarges. Animals that failed to develop kindling and kindled animals that failed to have a seizure in response to stimulation also showed no change in cyclic nucleotide concentrations in any brain region. Kindled animals that developed a seizure following stimulation showed significant elevations in levels of both cyclic GMP and cyclic AMP in hippocampus and in several other brain regions. A single naive animal that had a seizure in response to its first stimulation also appeared to have elevated concentrations of both cyclic nucleotides in hippocampus. These data suggest that the elevation in levels of both cyclic GMP and cyclic AMP during kindled seizures is associated with seizure development rather than with the generation of afterdischarges or with the kindling engram.     

Dynamics of cerebral metabolism during moderate hypercapnia.

The effects of hypercapnia on the kinetics of cerebral energy metabolism were evaluated in adult rats by the closed system method of LOWRY et al. (1964). Moderate hypercapnia with a Pa_co2 of 61 torr sustained for 20 min resulted in intracellular brain acidosis (7.07-6.97). During hypercapnia the tissue content of glucose increased whereas phosphocreatine, ADP, pyruvate and lactate contents, and the lactate/pyruvate ratio decreased. The ATP/ADP ratio increased from 7.7 to 9.0; the cytoplasmic NADH/NAD + ratio decreased from 2.06 × 10^-3 to 1.49 × 10^-3. There was no change in Energy Charge. Turnover rate of phosphocreatine increased from 3.84 to 4.62 mmol/kg/min, but the turnover rates of ATP, glucose and glycogen were reduced (from 1.98 to 1.86, 6.24 to 4.80, and 3.96 to 2.94 mmol/kg/min, respectively). The utilization rate of total high energy phosphate decreased from 30.6 to 25.4 mmol/kg/min while the post-decapitation EEG during hypercapnia persisted longer than during normocapnia. These results indicate that moderate hypercapnia reduces the overall kinetic activity of cerebral energy metabolism. The steady Energy Charge suggests that the reduction in the rate of high energy phosphate use is proportionally balanced by a lowered production rate of ATP.     

The Role of Phosphometabolites in Cell Proliferation, Energy Metabolism, and Tumor Therapy

A common characteristic of tumor cells is the constant overexpression of glycolytic and glutaminolytic enzymes. In tumor cells the hyperactive hexokinase and the partly inactive pyruvate kinase lead to an expansion of all phosphometabolites from glucose 6-phosphate to phosphoenolpyruvate. In addition to the glycolytic phosphometabolites, synthesis of their metabolic derivatives such as P-ribose-PP, NADH, NADPH, UTP, CTP, and UDP-N-acetyl glucosamine is also enhanced during cell proliferation. Another phosphometabolite derived from P-ribose-PP, AMP, inhibits cell proliferation. The accumulation of AMP inhibits both P-ribose-PP-synthetase and the increase in concentration of phosphometabolites derived from P-ribose-PP. In cells with low glycerol 3-phosphate and malate-aspartate shuttle capacities the inhibition of the lactate dehydrogenase by low NADH levels leads to an inhibition of glycolytic ATP production. Several tumor-therapeutic drugs reduce NAD and NADH levels, thereby inhibiting glycolytic energy production. The role of AMP, NADH, and NADPH levels in the success of chemotherapeutic treatment is discussed.