The effects of intoxicating doses of ethanol upon intermediary metabolism in rat brain

Alterations in brain glucose utilization accompanying elevations in blood ethanol and acetate concentrations in the rat

BACKGROUND

Previous studies in humans have shown that alcohol consumption decreased the rate of brain glucose utilization. We investigated whether the major metabolite of ethanol, acetate, could account for this observation by providing an alternate to glucose as an energy substrate for brain and the metabolic consequences of that shift.

METHODS

Rats were infused with solutions of sodium acetate, ethanol, or saline containing (13)C-2-glucose as a tracer elevating the blood ethanol (BEC) and blood acetate (BAcC) concentrations. After an hour, blood was sampled and the brains of animals were removed by freeze blowing. Tissue samples were analyzed for the intermediates of glucose metabolism, Krebs' cycle, acyl-coenzyme A (CoA) compounds, and amino acids.

RESULTS

Mean peak BEC and BAcC were approximately 25 and 0.8 mM, respectively, in ethanol-infused animals. Peak blood BAcC increased to 12 mM in acetate-infused animals. Both ethanol and acetate infused animals had a lower uptake of (13)C-glucose into the brain compared to controls and the concentration of brain (13)C-glucose-6-phosphate varied inversely with the BAcC. There were higher concentrations of brain malonyl-CoA and somewhat lower levels of free Mg(2+) in ethanol-treated animals compared to saline controls. In acetate-infused animals the concentrations of brain lactate, alpha-ketoglutarate, and fumarate were higher. Moreover, the free cytosolic [NAD(+)]/[NADH] was lower, the free mitochondrial [NAD(+)]/[NADH] and [CoQ]/[CoQH(2)] were oxidized and the DeltaG' of ATP lowered by acetate infusion from -61.4 kJ to -59.9 kJ/mol.

CONCLUSIONS

Animals with elevated levels of blood ethanol or acetate had decreased (13)C-glucose uptake into the brain. In acetate-infused animals elevated BAcC were associated with a decrease in (13)C-glucose phosphorylation. The co-ordinate decrease in free cytosolic NAD, oxidation of mitochondrial NAD and Q couples and the decrease in DeltaG' of ATP was similar to administration of uncoupling agents indicating that the metabolism of acetate in brain caused the mitochondrial voltage dependent pore to form.

Ethanol modulates neuropeptide-degrading aminopeptidases at synapse level in calcium-dependent conditions

AIMS

To investigate the role of aminopeptidases in the pathways to peptides neurotransmission/neuromodulation ending in the actions of ethanol (EtOH) on the brain.

METHODS

The effects of EtOH on alanyl-, arginyl-, cystyl-, leucyl- and tyrosyl-aminopeptidase activities were studied under basal/resting and K+-stimulated conditions at the synapse level, using mouse frontal cortex synaptosomes and their incubation supernatant in a Ca2+-containing or Ca2+-free medium.

RESULTS

Under basal conditions, synaptosome aminopeptidase activities showed an inhibitory or biphasic response depending on the concentration of EtOH used and the aminopeptidase assayed, whereas supernatant activities showed a more complex response. Under K+-stimulated conditions, EtOH inhibited all synaptosome aminopeptidases assayed in presence of Ca2+. However, in absence of Ca2+, different responses were obtained depending on the concentration of EtOH used. In the supernatant, the highest concentration of EtOH inhibited the K+-stimulated increase on aminopeptidase activities, although the lowest concentration enhanced the release in presence of Ca2+. In absence of it, EtOH blocked the K+-stimulated decrease or increased the activity depending on the concentration of EtOH used.

CONCLUSIONS

The changes on aminopeptidase activities induced by EtOH may reflect the functional status of their corresponding endogenous substrates. EtOH may influence opioid peptides, oxytocin, vasopressin and the brain renin-angiotensin system through their degrading enzymes.

Brain imaging. Functional consequences of ethanol in the central nervous system

In recent years, sophisticated methods have been developed to view structure and function within the living brain. Functional imaging methods are used to visualize dynamic chemical processes that are linked to brain activity. Increased neural activity, for example, leads to greater glucose and oxygen consumption and greater regional rates of blood flow to meet elevated energy demands. Mapping these changes provides quantitative visual descriptions of localized changes in brain activity that result from behavioral or pharmacological manipulations. This chapter first describes several current methods and how they are used to study the effects of alcohol on brain function. In the second part, the effects of acute intoxication are discussed with emphasis on the complex nature of alcohol's effects in the central nervous system, which depend on dose, time since administration, and environmental context. In the final part, the functional consequences of long-term exposure to alcohol as well as diseases associated with chronic alcoholism are reviewed.

Effects of moderate alcohol consumption on the central nervous system

The concept of moderate consumption of ethanol (beverage alcohol) has evolved over time from considering this level of intake to be nonintoxicating and noninjurious, to encompassing levels defined as "statistically" normal in particular populations, and the public health-driven concepts that define moderate drinking as the level corresponding to the lowest overall rate of morbidity or mortality in a population. The various approaches to defining moderate consumption of ethanol provide for a range of intakes that can result in blood ethanol concentrations ranging from 5 to 6 mg/dl, to levels of over 90 mg/dl (i.e., approximately 20 mM). This review summarizes available information regarding the effects of moderate consumption of ethanol on the adult and the developing nervous systems. The metabolism of ethanol in the human is reviewed to allow for proper appreciation of the important variables that interact to influence the level of exposure of the brain to ethanol once ethanol is orally consumed. At the neurochemical level, the moderate consumption of ethanol selectively affects the function of GABA, glutamatergic, serotonergic, dopaminergic, cholinergic, and opioid neuronal systems. Ethanol can affect these systems directly, and/or the interactions between and among these systems become important in the expression of ethanol's actions. The behavioral consequences of ethanol's actions on brain neurochemistry, and the neurochemical effects themselves, are very much dose- and time-related, and the collage of ethanol's actions can change significantly even on the rising and falling phases of the blood ethanol curve. The behavioral effects of moderate ethanol intake can encompass events that the human or other animal can perceive as reinforcing through either positive (e.g., pleasurable, activating) or negative (e.g., anxiolysis, stress reduction) reinforcement mechanisms. Genetic factors and gender play an important role in the metabolism and behavioral actions of ethanol, and doses of ethanol producing pleasurable feelings, activation, and reduction of anxiety in some humans/animals can have aversive, sedative, or no effect in others. Research on the cognitive effects of acute and chronic moderate intake of ethanol is reviewed, and although a number of studies have noted a measurable diminution in neuropsychologic parameters in habitual consumers of moderate amounts of ethanol, others have not found such changes. Recent studies have also noted some positive effects of moderate ethanol consumption on cognitive performance in the aging human. The moderate consumption of ethanol by pregnant women can have significant consequences on the developing nervous system of the fetus. Consumption of ethanol during pregnancy at levels considered to be in the moderate range can generate fetal alcohol effects (behavioral, cognitive anomalies) in the offspring. A number of factors--including gestational period, the periodicity of the mother's drinking, genetic factors, etc.--play important roles in determining the effect of ethanol on the developing central nervous system. A series of recommendations for future research endeavors, at all levels, is included with this review as part of the assessment of the effects of moderate ethanol consumption on the central nervous system.

Ethanol binding to a model carbohydrate, glycogen

The binding affinity of ethanol for carbohydrates is unknown. Glycoconjugates are postulated to be sensitive targets of ethanol action. The glycogen content of muscle, liver, and brain is sensitive to ethanol. To explore whether carbohydrates as a class have a specific affinity to bind ethanol, we measured the binding of ethanol and other small molecules to the carbohydrate glycogen. Ethanol binding was found to be weak. The polar alcohol, glycerol, bound to glycogen with a greater affinity than ethanol did. Other small polar molecules (methanol, sucrose, acetate, glycine, and dimethyl sulfoxide) also bound more strongly than ethanol did. Ethanol and glycerol binding were concentration independent. No evidence of saturable or specific sites for these alcohols was obtained. Water binding was determined and was in agreement with hydrodynamic measures. Water binding exceeded the binding of all solutes studied. The loosely structured water of hydration in glycogen apparently was able to accommodate polar solutes, but tended to exclude ethanol and, to a lesser extent, methanol. We conclude that carbohydrates as a class exhibit no strong affinity or specificity for ethanol.

In vivo effects of lipopolysaccharide on hepatic free-NAD(P)(+)-linked redox states and cytosolic phosphorylation potential in 48-hour-fasted rats

This study was performed to determine the magnitude and time of onset of in vivo changes in hepatic bioenergetics in response to a sublethal dose of lipopolysaccharide (LPS), a bacterial endotoxin. Male rats (48-hour-fasted) were administered an intraperitoneal injection of LPS (5 mg/kg body weight) or vehicle alone, and the livers were freeze-clamped 5, 30, or 180 minutes or 24 hours later. Liver tissue was extracted with perchloric acid, and the metabolites necessary to calculate NAD(+)- and NADP(+)-linked redox states and the cytosolic phosphorylation potential were measured. There was no significant difference in hepatic cytosolic phosphorylation potential between LPS and control groups at any of the times investigated. This indicated that the ability of the liver to synthesize adenosine triphosphate (ATP) was not compromised under the conditions of the study. No changes in hepatic redox states were observed 5 or 30 minutes after LPS treatment. Three hours after LPS treatment, hepatic cytosolic and mitochondrial free-[NAD+]/[NADH] redox states and the cytosolic free-[NADP+]/[NADPH] redox state were more oxidized. By 24 hours, only NAD(+)-linked redox states were more oxidized than the time-matched controls. Hepatic urea content was elevated at both 3 and 24 hours, compatible with an increased rate of urea synthesis as a consequence of increased amino acid metabolism, whereas hepatic beta-hydroxybutyrate and total ketone bodies were decreased 24 hours after LPS treatment, indicating decreased hepatic ketogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional distribution of glycogen, glucose and phosphorylated sugars in rat brain after intoxicating doses of ethanol

Ethanol and anaesthetics increase glycogen levels in the brain. However, no data have been reported about the effect of ethanol on glycogen and glucose metabolism in specific brain regions. We have studied the concentrations of glycogen, glucose, glucose 6-P, glucose 1,6-P2 and fructose 2,6-P2 and the activities of glycogen synthase, glycogen phosphorylase and glycogen phosphorylase kinase in seven brain regions of starved rats following treatment with a single dose or several doses of ethanol. Our results show that: (1) the effect of ethanol on glucose metabolism depends on whether it is given in one single dose or in a series of doses; (2) glycogen concentration increases after a single dose of ethanol but not after long exposure; (3) glucose, glucose 6-P in some areas, and the bisphosphorylated sugar, fructose 2,6-P2 significantly increase after prolonged exposure to ethanol; and (4) the enzymatic activities of glycogen metabolism are not modified after a long exposure to ethanol. In summary, these data show that ethanol may modify the use of glycogen, glucose and derivatives in brain. Moreover, the changes produced depend on the pattern of ethanol intake and the brain area considered.

Metabolic changes in the rat brain after acute and chronic ethanol intoxication: a 31P NMR spectroscopy study

In this work, 31P phosphorus NMR (31P NMR) studies of the brain have been conducted in rats acutely and chronically intoxicated with ethanol. In both groups, changes in levels of high-energy phosphates were observed: increase of phosphocreatinine (PCr)/beta AaTP and PCr/inorganic phosphate (Pi) in acute and long-term ethanol exposure, and decrease of Pi/beta ATP after acute ethanol administration. These changes in high-energy phosphates, indicative of a reduction of adenosine triphosphate (ATP) and PCr consumption (PCr+ ADP+ H+ ATP+ Cr; ATP ADP+ Pi), suggest a reduction of cerebral metabolism both in acute and chronic ethanol exposure. In addition, in the group of rats chronically intoxicated with ethanol, there were variations in phosphodiester peak intensities (decrease of phosphomonoester (PME)/phosphodiester (PDE), increase of PDE/beta ATP), suggesting increased breakdown of membrane phospholipids. These changes could provide a metabolic explanation for the development of cerebral atrophy in chronic alcoholism.

In vivo measurements of ethanol concentration in rabbit brain by 1H magnetic resonance spectroscopy

In vivo 1H magnetic resonance spectroscopy was used to measure the cerebral ethanol concentration in the rabbit after both intraarterial and intragastric administration. There was good agreement between cerebral and blood ethanol concentrations at all times after administration by either route. Cerebral ethanol levels, measured using in vivo 1H spectroscopy, agreed well with those measured in perchloric acid extracts of brain, analyzed by both high-resolution 1H spectroscopy and gas chromatography. Ethanol may be useful as an indicator to measure cerebral blood flow by 1H spectroscopy and chemical shift-selective magnetic resonance imaging.

The effect of chronic ethanol consumption on [14C]deoxyglucose uptake in rat brain in vivo

The uptake of [14C]deoxyglucose by brains of rats that were given alcohol in drinking water for 7 months was investigated. There was a general, approximately 50%, increase in deoxyglucose uptake in brains of ethanol-treated rats with areas of the limbic system being particularly affected.

Effects of moderate ethanol sedation on brain regional 2-deoxyglucose uptake in alcohol-sensitive and alcohol-insensitive rat lines

Acute intraperitoneal ethanol administration (2 g/kg) decreased the accumulation of radioactivity after [14C]2-deoxy-D-glucose injection into grossly dissected brain regions of alcohol-sensitive (ANT) and alcohol-insensitive (AT) rat lines. In autoradiography, the balance of radioactivity uptake between different functional systems (as judged from relative optical density ratios) was changed after ethanol: especially in the ANT rats, areas associated with sensory input were damped but motor relay nuclei were relatively active, suggesting a tendency to motor overactivity relative to sensory input. The ANT rats furthermore showed slight relative damping of cortical associative areas and differences in limbic structures compared to the AT rats, which, provided that changes in the balance between brain regions with a decreased overall activity are meaningful, suggests that the higher level of ethanol-induced motor impairment of the ANT rats may be related to defects in their integration of sensory and motor processes.

Influence of ethanol on the energy metabolism of ischemic and postischemic brain

This study documents the effects of an intoxicating dose of ethanol on the energy metabolism and electrophysiological function of rat brain exposed for 0.5 h to ischemia produced by electrocautery of the vertebral arteries and reversible occlusion of the carotid arteries. One-hour exposure to 5 g kg-1 ethanol led to no significant alterations of the preischemic cerebral contents of glucose, lactate, or energy phosphates. Animals receiving ethanol or isovolumetric amounts of 0.9% saline showed statistically equivalent decreases in glucose, ATP, and phosphocreatine and increases in lactate, ADP, and AMP during 0.5 h of ischemia. Upon recirculation for 0.5-24 h, animals receiving ethanol again showed no significant differences from saline-treated animals in the rate of return of glucose, lactate, and energy metabolites to control levels. Animals receiving ethanol showed a trend for a faster and more complete normalization of the EEG during recirculation. It is concluded that under controlled experimental conditions, intoxicating doses of ethanol have no detrimental effect on the energy metabolism of ischemic and postischemic brain.

Ethanol inhibits some of the early effects of epidermal growth factor in vivo

Charles River male Wistar rats (200-300 g) were meal fed for 9-10 days, injected with either saline, epidermal growth factor (EGF), ethanol, or ethanol combined with EGF and their livers were freeze clamped 5 min after intraperitoneal injection of EGF. Metabolites were measured and the redox state and phosphorylation potential were calculated. Epidermal growth factor alone elevated hepatic content of glucose 1-P, glucose 6-P, fructose 6-P, and 3-phosphoglycerate 1.2-1.3-fold when compared to saline treatment. Ethanol alone decreased hepatic content of 3-phosphoglycerate and phosphoenolpyruvate 3.2-3.7-fold below saline-treated levels. Ethanol, in combination with EGF, decreased hepatic values for 3-phosphoglycerate and phosphoenolpyruvate 2.0-2.3-fold from saline treatment but elevated the content of phosphoenolpyruvate 1.6-fold over ethanol treatment alone. Epidermal growth factor inhibited pyruvate kinase activity 1.3-fold when compared to saline controls but ethanol in the presence of EGF facilitated the recovery of activity of this enzyme.

Adaptation of lipogenesis and lipolysis to dietary ethanol

The effect of dietary ethanol on metabolic fates of glucose and ethanol, and activities of lipoprotein lipase and hormone-sensitive lipase in several tissues of miniature pigs were determined in vitro. Ethanol and glucose were used at similar rates for fatty acid synthesis in liver and brain and CO2 production in liver. Ethanol was preferred over glucose for fatty acid and CO2 production in ileal mucosal cells. Glucose was the preferred substrate for lipogenesis and oxidation to CO2 in adipose tissue and skeletal muscle, and for oxidation to CO2 in brain. Dietary ethanol decreased glucose and ethanol conversion to fatty acids in ileal mucosa and brain, respectively. Dietary ethanol had no effect on the capacity of liver, adipose tissue, and skeletal muscle to convert either glucose or ethanol to long-chain fatty acids. The capacity to oxidize ethanol, but not glucose, to CO2 in liver was increased by dietary ethanol. No dietary ethanol effect was observed in other tissues. The capacity for removal of plasma triglycerides (based on lipoprotein lipase activity) tended to increase in adipose tissue and skeletal muscle of pigs fed ethanol. Mobilization of long-chain fatty acids from adipose tissue (based on hormone-sensitive lipase activity), triglyceride concentration in plasma, and percentage of lipid in liver remained unchanged when ethanol was fed. Livers of ethanol-fed pigs, however, were larger than livers of control pigs. Our results indicate that feeding miniature pigs 21-37% of total caloric intake as ethanol causes significant metabolic adaptations of lipid metabolism in liver and ileal mucosa, but not in adipose tissue, skeletal muscle, and brain. The ethanol feeding, however, did not cause fatty livers or hyperlipidemia.

Effects of long-term ethanol consumption on GABAergic neurons in the mouse hippocampus: a quantitative immunocytochemical study

The effects of 6 months' ethanol consumption by mice on hippocampal GABAergic neurons were investigated by means of an immunocytochemical method using GABA antibodies. Although ethanol treatment did not modify body or brain weights in our experimental conditions, two differences were observed in ethanol-treated mice, as compared to controls: a decrease in the labelling intensity of immunopositive neurons and fibers in the dorsal and the ventral parts of the hippocampus; and a decrease in the number of immunopositive neurons. This neuronal loss was statistically significant in the ventral hippocampus only, where it reached about 25% in the stratum radiatum. It is concluded that chronic ethanol consumption leads to a decrease in GABA content of hippocampal neurons and to a loss of GABAergic neurons, mostly in the ventral part of the hippocampus. These alterations in GABAergic transmission could be related to the well known functional deficits observed in chronic alcoholism.

The content of pentose-cycle intermediates in liver in starved, fed ad libitum and meal-fed rats

Liver content of pentose-cycle intermediates and the activity of the three major cytoplasmic NADPH-producing enzymes and pentose-cycle enzymes were measured in three dietary states: 48 h-starved rats, rats fed on a standard diet ad libitum, and rats meal-fed with a low-fat high-carbohydrate diet. Measured tissue contents of pentose-cycle intermediates in starved liver were: 6-phosphogluconate, 4.7 +/- 0.5 nmol/g; ribulose 5-P, 3.7 +/- 0.5 nmol/g; xylulose 5-P, 4.3 +/- 0.4 nmol/g; sedoheptulose 7-P, 25.5 +/- 1.3 nmol/g; and combined sedoheptulose 7-P and ribose 5-P, 30.6 +/- 0.7 nmol/g. These values were in good agreement with values calculated from fructose 6-P and free glyceraldehyde 3-P, assuming the major transketolase, transaldolase, ribulose-5-P 3-epimerase and ribose-5-P isomerase reactions were all in near-equilibrium. Similar results were found in animals fed ad libitum. These relationships were not valid in animals fed on a low-fat high-carbohydrate diet, with tissue contents of metabolites in some cases being more than an order of magnitude higher than the calculated values. Measured tissue contents of pentose-cycle intermediates in these animals were: 6-phosphogluconate, 124.2 +/- 13.9 nmol/g; ribulose 5-P, 44.8 +/- 7.1 nmol/g; xylulose 5-P, 77.2 +/- 9.4 nmol/g; sedoheptulose 7-P, 129.9 +/- 10.1 nmol/g; and combined sedoheptulose 7-P and ribose 5-P, 157.0 +/- 11.3 nmol/g. In all animals, regardless of dietary state, tissue content of erythrose 4-P was less than 2 nmol/ml. Liver activities of glucose-6-P dehydrogenase and 6-phosphogluconate dehydrogenase were increased from 3.5 +/- 0.9 mumol/g and 7.3 +/- 0.5 mumol/min per g in starved animals to 13.2 +/- 1.1 and 10.5 +/- 0.7 mumol/min per g in low-fat high-carbohydrate-fed animals. Despite these changes, the activities of transaldolase (3.4 +/- 0.3 mumol/min per g), transketolase (7.8 +/- 0.2 mumol/min per g) and ribulose-5-P 3-epimerase (7.5 +/- 0.4 mumol/min per g) were not increased in meal-fed animals above those observed in starved animals (3.4 +/- 0.2, 7.1 +/- 0.3 and 8.6 +/- 0.4 mumol/min per g respectively). The increase in the activity of oxidative pentose-cycle enzymes in the absence of any change in the non-oxidative pentose cycle appeared to contribute to the observed disequilibrium in the pentose cycle in animals meal fed on a low-fat high-carbohydrate diet.

Effects of ethanol and pentobarbital on neuronal hexose uptake in inbred mice

The effect of ethanol and pentobarbital narcosis on 2-deoxyglucose uptake into brain synaptosomes prepared from inbred C57BL/6J and DBA/2J mice which exhibit differential central sensitivity to ethanol and heterogeneous ICR mice was examined. A reversible depression of synaptosomal uptake was exhibited in all strains administered ethanol acutely, occurring at 2 min in ICR and C57BL/6J mice and 15 min in DBA/2J. Uptake returned to control values in all strains at 30 min although the mice remained intoxicated. Brain glucose concentration was significantly elevated at this time. Pentobarbital administration was without effect on synaptosomal hexose transport in DBA/2J and C57BL/6J mice but increased it significantly in ICR mice at 30 min. Pentobarbital anesthesia did not alter brain glucose concentration. No correlation was apparent between synaptosomal 2-deoxyglucose uptake and differential CNS sensitivity to ethanol and pentobarbital. The effects of ethanol and pentobarbital on neuronal hexose transport is discussed with respect to reported changes in glycolytic metabolism produced by these agents.

Energy metabolism in audiogenically seizure-prone chicks

Female chicks carrying the lethal, sex-linked recessive paroxysmal (px) gene are susceptible to spontaneous and audiogenic seizures. Because seizure activity does not begin until 1 to 2 weeks posthatching - coincidental with disappearance of the yolk-sac - it is postulated that a contributing factor to seizure activity may be a developmental failure of the chick's ability to switch from lipid to carbohydrate as a primary energy source. In testing this hypothesis, three experiments were performed: 1) to evaluate cerebral energy reserves - adenosine triphosphate (ATP), phosphocreatine - of px and normal chicks; 2) to determine effects of energy source (ethanol, glucose, insulin, and glucose-insulin combined) on audiogenically-induced seizure activity and electrical seizure threshold; 3) to evaluate energy source utilization as estimated by the respiratory quotient (RQ). Brain ATP and phosphocreatine levels in px chicks were both decreased (P less than .05) as early as 10 days posthatching. Ethanol increased electrical seizure threshold in 50% of px chicks and provided protection from audiogenic stimulation. No consistent effect was found with any of the other substances. The RQ of px chicks were lower (P less than .05) than those of controls by 18 days posthatching.

Purine nucleotide synthesis in adrenal chromaffin cells

The synthesis of purine nucleotides from the salvage precursors adenine and adenosine, and from the de novo precursors formate and glycine, was studied in isolated adrenal chromaffin cells. Both [8-14C]adenine and [8-14C]adenosine from extracellular medium are effectively incorporated into intracellular nucleotides. [14C]Formate and [U-14C]glycine are also incorporated, but de novo synthesis is clearly lower than synthesis from salvage precursors, although similar to de novo synthesis in liver. The enzymes responsible for adenine and adenosine salvage, adenine phosphoribosyltransferase and adenosine kinase, were purified about 1,500-fold. Both enzymes are mainly cytosolic and exhibit a similar molecular weight of around 42,000. The results suggest that chromaffin cells can replenish their intracellular nucleotides lost during the secretory event by an active synthesis from salvage and de novo precursors.

Lipid peroxidation in alcoholic myopathy and cardiomyopathy

The hypothesis is presented that lipid peroxidation is responsible for the damage in skeletal and cardiac muscle of chronic alcoholic subjects. The enhanced lipid peroxidation is caused by the accumulation of oxygen radicals. Both excessive production and decreased disposal of oxygen radicals can arise from the acetaldehyde formed in the oxidation of ethanol. Although acetaldehyde from hepatic sources may contribute, muscle itself can generate significant amounts of acetaldehyde through the action of muscle catalase. The effects of alcohol on other tissues, and its known long-term effects on membranes lend support to this hypothesis. The ultrastructural features of the alcoholic myopathies provide further support. The resemblance between vitamin E-deficiency myopathy and the alcoholic myopathies is strong additional evidence in favor of this hypothesis.

Regulation of glycogen metabolism in primary and transformed astrocytes in vitro

Glycogen metabolism was studied in primary and Herpesvirus-transformed cultures of neonatal rat brain astrocytes. A small fraction of the glucose consumed was conserved in glycogen in both the primary and the transformed astrocytic cell cultures. After addition of culture medium containing 5.5 mM glucose, glycogen increased to maximal levels within 2.5 h, the approximate time at which half of the medium glucose was consumed, and rapidly declined thereafter in both the primary and transformed astrocytic cultures. Maximum levels of glycogen were apparently related to the cell density of the Herpesvirus-transformed cultures, but primary cultures did not show this behavior. At any given cell density, maximal levels of glycogen were dependent on the concentration of extracellular glucose. Administration of glucose caused a transient activation of glycogen synthase alpha and a rapid inactivation of glycogen phosphorylase alpha.

Ethanol and acetaldehyde alter brain mitochondrial redox responses to direct cortical stimulation in vivo

To determine whether and how ethanol and acetaldehyde alter brain oxidative metabolic activity, reduction/oxidation shifts of components of the mitochondrial respiratory chain were optically measured, in situ, from cat cerebral cortex. Oxidative shifts of nicotinamide adenine dinucleotide (NADH) were recorded in response to increased energy demand provoked by stimulation of the cortical surface by electrical pulses. Ethanol or acetaldehyde did not alter the direction of the responses but each slowed the rates of oxidation with little effect upon the rates of subsequent re-reduction. There was no apparent change produced by either drug upon the kinetics of the negative shifts of the cortical steady potential in response to the stimulation. However, stimulus-evoked electrical and metabolic responses were decreased in amplitude with increasing drug doses. It is suggested that the slowed mitochondrial oxidation results from inhibition of Na+, K+-ATPase. This supports the concept that ethanol or acetaldehyde inhibit the processes that lead to increased oxygen consumption following cell depolarization in vivo, as has been demonstrated in vitro.

Acute effect of ethanol on metabolite concentrations of dog pancreas in vivo

Sections of dog pancreas were freeze-clamped before and 1 hr after oral administration of 1 g/kg of ethanol in anesthetized, respirated, 24-hr-fasted animals, and multiple metabolites were determined in the perchloric acid extract of the frozen tissue. In spite of the fact that the pancreas contained little or no alcohol dehydrogenase activity (less than 0.01 IU/g of tissue), significant metabolite changes did occur. Although arterial oxygenation was constant and adequate (pO2 = 100 +/- 7 mM Hg) there was a significant 1.7-fold rise in L-lactate and fall in the cytoplasmic free [NAD+]/[NADH] ratio from 719 +/- 87 to 453 +/- 88 after ethanol. Except for a tendency for L-malate and L-alpha-glycerolphosphate to parallel the rise in L-lactate, there was little consistent disturbance in the remainder of the glycolytic metabolites (glucose, glucose 6-phosphate, pyruvate, 2-ketoglutarate, citrate, 3-phosphoglycerate, etc.) or in high energy intermediates and related compounds (ATP, creatine phosphate, ADP, Pi, creatine). There was, however, an unexpected and significant fall in the levels of the major transaminating amino acids, L-glutamate, L-aspartate, and L-alanine. The results can be only partially explained by an influence of blood-borne metabolites and imply significant effects of ethanol on the metabolism of the pancreas in vivo not directly mediated through alcohol dehydrogenase. Evidence is presented suggesting that both L-alanine and L-aspartate aminotransferases are functioning near equilibrium in the pancreas in vivo.

The calculation of the cytoplasmic free [NADP+]/[NADPH] ratio in brain: effect of electroconvulsive seizure

This study has investigated the feasibility of calculating the cytoplasmic free [NADP+]/[NADPH] ratio in rat brain. The time course of the change in the substrate ratios of the malate dehydrogenase (decarboxylating) [E.C. 1.1.1.40], NADP+-isocitrate dehydrogenase (decarboxylating) [E.C. 1.1.1.42] and 6-phosphogluconate dehydrogenase (decarboxylating) [E.C. 1.1.1.44] reactions was followed for up to 10 min after a single, unmodified electroconvulsive seizure. From the results it has been concluded that during periods of low flux, the direction and magnitude of the change in the cytoplasmic free [NADP+]/[NADPH] ratio can, in fact, be reasonably determined even though there is some uncertainty in the absolute value of the ratio itself. It is recommended that reliance not be placed on a single enzyme system but that one or both of the other systems also be observed under a given experimental condition to increase confidence in the determination. The results also demonstrate that seizure and anoxia have a far lesser effect on the cytoplasmic free [NADP+]/[NADPH] ratio than on the free [NAD+]/[NADH] ratio in the same compartment. These results suggest that the pathways using the nicotinamide-adenine dinucleotide phosphate system are relatively protected from the rapid fluctuations that seizure and anoxia can produce.

The short-term toxicity of ethanol to neurons in rat cerebral cortex tested by topical application in vivo, and a note on a problem in estimating ethanol concentrations in tissue

In rats anesthetized with ethanol 4.0 g/kg i.p. the dura overlying the parietal cortex was exposed and superfused with 100% ethanol for 1 h. After 6 days survival the underlying cortex was stained with a silver method that is selective for degenerating axons and their terminals. No degeneration was found in the superfused cortex, although heat-lesioned tissue stained concurrently showed axonal degeneration and so validated the technique. Electron microscopy after 3-20 days survival did not show any degeneration, and synapses of normal appearance were present immediately beneath the cortical surface. In other rats the ethanol concentration in the superfused tissue was assayed in 0.4 mm thick discs sectioned with a vibratome from a 4-mm diameter core cut with a trocar from the cortex immediately after 1 h of superfusion. The ethanol was eluted in 2% TCA, and an aliquot assayed enzymatically. A second elution of the tissue disc contributed a further 5% of the ethanol content indicating a partition coefficient for ethanol between wet brain tissue and 2% TCA of about 10. The total concentration of ethanol in the superficial cortex was found to be about 0.82 M or 3.8%. This estimation was confirmed by superfusion with 14C-labelled ethanol and scintillation counting. Thus neurons in the cerebral cortex did not degenerate after exposure for 1 h to a concentration of ethanol that was 3 times greater than the concentration that causes death in a rat by paralysis of the respiratory centre (1.2%).

Effect of ethanol on superoxide dismutase activity in cultured neural cells

Superoxide dismutase (EC 1.15.1.1) activity was investigated in several types of neural cells cultivated in the presence of 100 mM ethanol. Superoxide dismutase was inhibited by acute treatment with ethanol. Chronic treatment with ethanol specifically inhibited superoxide dismutase in glial cells. In all instances withdrawal of ethanol produced a quick return to control values. Inhibition of superoxide dismutase by ethanol may increase toxic oxygen radicals in nervous tissue.

Chronic alcohol intake and some monogalactosyl glycolipids of the rat brain

The effect on monogalactosyl glycolipid complement (cerebrosides with hydroxy and non-hydroxy fatty acids, sulphatides and monogalactosyldiglyceride) after 38 weeks of feeding 25% sucrose-32% ethyl alcohol have been studied. Chronic alcohol intake produced a statistically significant increase of cerebrosides with hydroxy and non-hydroxy fatty acids and monogalactosyldiglycerides as well as decrease of sulphatides in male Wistar rats brain.

Characteristics of an acid active thiamine diphosphatase from beef brain

That thiamine has a role in nerve conduction as well as synaptic transmission is suggested by the following observations. (1) Thiamine phosphate esters are hydrolyzed and released from nerve membranes during nerve conduction. (2) Ultraviolet radiation of single nerve fibers at the wavelength specific for thiamine destroys the ability of that nerve to conduct an impulse. (3) Thiamine diphosphatase (TDPase) is present on synaptosomes. Previous articles have characterized an alkaline active TDPase in brain; this report characterizes a PH 5 active TDPase and compares it properties to the pH 9 enzyme. Both enzymes require a divalent cation for optimal activity. The pH 5 enzyme is more sensitive to ATP. Myelin fractions of brain have the highest specific activity for the acid TDPase, and the nerve ending particles the highest total activity. No PO4 3-inhibition was observed. Kinetic constants of this enzyme activity are reported.

Problems and pitfalls in acetaldehyde determinations

The determination of acetaldehyde in biologic samples is complicated by a variety of formation and disappearance reactions occurring in the present methods of acetaldehyde analyses. The acetaldehyde formation (ethanol oxidation) in deproteinized supernatant of tissue preparations is prevented by the use of thiourea. During deproteinization, however, it is not inhibited by thiourea, and this remains the main problem in blood acetaldehyde determinations. To circumvent this problem, the use of a correction curve is proposed which is generated by adding control blood samples to the deproteinizing agent such that the blood dilution, temperature, and the ethanol concentrations (the main factors affecting the artifactual acetaldehyde formation) in the controls are identical to those of the samples. Disappearance reactions mainly include loss of acetaldehyde due to binding and/or metabolism. The problem seems to be pronounced with human blood samples, and it is recommended that they be rapidly ( less than 5 sec) deproteinized.

Sources of energy for the brain and physical dependence on ethanol

This paper describes a proposed biochemical mechanism to account for physical dependence on ethanol. Long-term exposure to a continuous and plentiful supply of ethanol-derived hydrogens in NADH and ethanol-derived acetyl-CoA (AcCoA) may lead to a decreased rate of production of endogenous hydrogens in NADH and endogenous AcCoA in compensation. It is proposed that physical dependence on ethanol occurs when ketolytic- and glycolytic-based NADH and AcCoA synthetic rates fall below the rate of utilization by the brain; the brain then "depends" on alcohol-derived NADH and AcCoA for normal function.

The effect of the combination of lithium and haloperidol on brain intermediary metabolism in vivo

The effect of the chronic administration of the combination of lithium and haloperidol has been studied in rat brain in vivo. Lithium was administered in food in amounts sufficient to maintain serum lithium levels of 1.0 +/- 0.1 mEq/l; haloperidol (1.5 mg/kg) was given i.p. once daily. Control animals pair-fed with the lithium/haloperidol alone, or neither drug. Fifteen days after the beginning of the experiments the brains were instantaneously frozen with a rapid brain-freezing device and multiple metabolites were measured in the perchloric acid extract of the tissue. Intermediates examined included selected metabolites of the glycolytic pathway and the tricarboxylic acid cycle, N-acetylaspartate and cofactors such as ATP, CoA, and acetyl-CoA. Estimates of the effects of the treatments on cytoplasmic and mitochondrial redox states were also made. The results showed only minor effects of any of the treatments on any of the parameters studied and little or nothing to distinguish the combination of lithium and haloperidol from either treatment alone.

Acetaldehyde metabolism in vivo during ethanol oxidation

The liver is the primary site for the oxidation of ethanol-derived acetaldehyde (AcH) in the rat. Only a small amount of the total AcH formed in this organ escapes into the rest of the body, but this amount increases with increasing hepatic ethanol concentrations. The bulk of the hepatic AcH output is eliminated extrahepatically, thus drastically changing the AcH level from that initially leaving the liver. Nevertheless, the extrahepatic blood AcH levels can be used as relatively accurate indicators of the corresponding hepatic AcH levels, since they are highly correlated with them. Significant levels of brain AcH occur only at very high arterial blood AcH concentrations.