PATTERNS OF CHANGES IN BRAIN CARBOHYDRATE METABOLITES, AMINO ACIDS AND ORGANIC PHOSPHATES AT INCREASED CARBON DIOXIDE TENSIONS

—In order to study the time course of changes in cerebral metabolites in hypercapnia, anaesthetized and artificially ventilated rats were exposed to 11% CO₂ for 5, 15, 45, 90 and 180 min. In addition, the effect of anaesthetic levels of carbon dioxide was studied by exposing animals to 30 and 50% CO₂ for 45 min. In none of the groups were there significant changes in ATP, ADP or AMP, and a normal energy state was therefore obtained even in short-lasting hypercapnia, and at anaesthetic CO₂ concentrations (50% CO₂). In the group exposed to 11% CO₂ for 5 min there was a fall in glycogen but normalization occurred when the hypercapnia was prolonged. There were no changes in fructose 1,6-diphosphate, dihydroxyacetone phosphate or 3-phosphoglycerate but decreases in pyruvate, lactate, citrate, α-oxoglutarate, malate and glutamate at all exposure times. With 30 and 50% CO₂ glucose 6-phosphate accumulated. The results do not support the view that the depletion of pyruvate and of citric acid cycle intermediates is caused by H⁺-inhibition of rate-limiting enzymatic steps like the phosphofructokinase reaction. The glutamate concentration fell progressively during exposure to 11% CO₂. In the 5 and 15 min groups aspartate increased significantly indicating that the initial loss of glutamate was partly due to transamination to aspartate. With prolonged hypercapnia there was a secondary fall in aspartate to subnormal values. At 45 min and thereafter the glutamine concentration increased significantly. However, the sum of glutamate, aspartate and glutamine fell progressively after the initial 5 min period. Hypercapnia gave rise to similar increases in the lactate/pyruvate and malate/oxaloacetate ratios, and since the calculated NADH/NAD⁺ ratios remained close to normal in all groups, the results indicate that pH-dependent shifts occurred in the lactate and malate dehydrogenase equilibria.     

CHANGES IN CARBOHYDRATE SUBSTRATES, AMINO ACIDS AND AMMONIA IN THE BRAIN DURING INSULIN-INDUCED HYPOGLYCEMIA

—The influence of insulin-induced hypoglycemia upon carbohydrate substrates, amino acids and ammonia in the brain was studied in lightly anaesthetized rats, and the changes observed were related to the blood glucose concentration and to the EEG. Calculations from glucose concentrations in tissue, CSF and blood indicated the presence of appreciable amounts of free intracellular glucose at blood glucose concentrations above 3 μmol/g. When the blood glucose concentration fell below 3 μmol/g, there was no calculated intracellular glucose and decreases in the concentrations of glycogen, G-6-P, pyruvate, lactate and of citric acid cycle intermediates were observed. At blood glucose levels of below 1 μmol/g the tissue was virtually depleted of glycogen, G-6-P, pyruvate and lactate. When the blood glucose concentration was reduced below about 2·5 μmol/g there were progressive increases in aspartate and progressive decreases in alanine, GABA, glutamine and glutamate, and at blood glucose concentrations below 2 μmol/g the ammonia concentration increased. It is suggested that most of the changes observed can be explained as a result of a decreased availability of pyruvate and of NADH. The decrease in the concentration of free NADH was reflected in reductions of the lactate/pyruvate and malate/oxaloacetate ratios at an unchanged intracellular pH. Slow wave activity appeared in the EEG when the hypoglycemia gave rise to reduction of the intracellular glucose concentration to zero. Convulsive activity continued until carbohydrate stores in the form of glycogen and G-6-P were depleted. When this occurred the EEG became isoelectric. In all convulsive animals the concentration of the nervous system activity inhibitor, GABA, was decreased and stimulant, aspartate, was increased.     

THE EFFECT OF HYPERTHERMIA UPON OXYGEN CONSUMPTION AND UPON ORGANIC PHOSPHATES, GLYCOLYTIC METABOLITES, CITRIC ACID CYCLE INTERMEDIATES AND ASSOCIATED AMINO ACIDS IN RAT CEREBRAL CORTEX

The influence of hyperthermia on cerebral blood flow, cerebral metabolic rate for oxygen and cerebral metabolite levels was studied by increasing body temperature from 37° to 40°C and 42°C in rats under nitrous oxide anaesthesia maintained at constant arterial CO₂ tension. The metabolic rate for oxygen increased by 5-6% per degree centigrade. At 42°C the increase in cerebral blood Row was comparable to that in the metabolic rate. The increased temperatures were not accompanied by changes in organic phosphates (phosphocreatine, ATP, ADP or AMP) or in lactate/pyruvate ratio. There was an increase in the tissue to blood glucose concentration ratio. At steady state, there was an increase in glucose-6-phosphate but no other changes in glycolytic metabolites or citric acid cycle intermediates, and the only change in amino acids studied (glutamate, glutamine, aspartate, alanine and GABA) was an increase in glutamate concentration.     

THE EFFECT OF PHENOBARBITONE ANAESTHESIA UPON SOME ORGANIC PHOSPHATES, GLYCOLYTIC METABOLITES AND CITRIC ACID CYCLE-ASSOCIATED INTERMEDIATES OF THE RAT BRAIN

In order to study the effect of phenobarbitone anaesthesia upon the energy metabolism of the brain, organic phosphates, glycolytic metabolites and citric acid cycle intermediates were measured in rats anaesthetized with 175-200 mg/kg of phenobarbitone, and the results were compared to those obtained in rats anaesthetized with halo-thane or with nitrous oxide. An attempt was made to separate the effects of the phenobarbitone anaesthesia from those caused by the accompanying intracellular alkalosis by exposing one group of animals to hypercapnia of such a degree that normalization of the intracellular pH was achieved. Phenobarbitone anaesthesia did not alter the tissue concentrations of ATP, ADP or AMP, but led to a moderate increase in the phosphocreatine concentration. However, since this increase was reversed in the hypercapnic group it is concluded that it may be due partly to a pH-dependent shift in the creatine phosphokinase equilibrium. There was a decrease in the tissue concentrations of all measured substrates from pyruvate and onwards. The results indicate that phenobarbitone leads to a primary inhibition of glycolysis, which cannot be related to detectable changes in ATP, ADP or AMP. The resulting lowering of the tissue concentrations of a number of metabolic acids may be part of the explanation why barbiturate anaesthesia is associated with an intracellular alkalosis.     

EFFECT OF HYPOTHERMIA UPON ORGANIC PHOSPHATES, GLYCOLYTIC METABOLITES, CITRIC ACID CYCLE INTERMEDIATES AND ASSOCIATED AMINO ACIDS IN RAT CEREBRAL CORTEX

—The influence of hypothermia upon the metabolism of the brain was studied by reducing body temperature in N₂O-anaesthetized rats to 32, 27 or 22°C, with subsequent measurements of organic phosphates, glycolytic metabolites, citric acid cycle intermediates and associated amino acids. Hypothermia was maintained for either 1 or 2 h and the effect of anaesthesia was evaluated by maintaining unanaesthetized animals at 22°C. Hypothermia had no influence on the cerebral cortical concentrations of ATP, ADP or AMP and there was only a small increase in phosphocreatine. Since the tissue concentrations of glucose and glycogen were reduced, it is concluded that the well known resistance of the hypothermie brain to ischaemia is unrelated to increased energy stores. Hypothermia was accompanied by decreases in the tissue concentrations of fructose-1,6-diphosphate, dihydroxyacetone phosphate, 3-phosphoglycerate, pyruvate, lactate, α-ketoglutarate, succinate and malate, but not of glucose-6-phosphate or citrate. These results indicate that metabolic flux is retarded mainly at the phosphofructokinase and isocitrate dehydrogenase steps. The largest relative reduction was seen in α-ketoglutarate, which was possibly secondary to accumulation of ammonia. There was no change in GABA, but a decrease in glutamate and increases in aspartate and alanine. These, changes are compatible with shifts in the aspartate and alanine aminotransferase reactions, possibly induced by the fall in α-ketoglutarate.     

THE INFLUENCE OF HIGH PHENYLALANINE AND TYROSINE ON THE CONCENTRATIONS OF ESSENTIAL AMINO ACIDS IN BRAIN

—High circulating levels of phenylalanine caused depletions of threonine, valine, methionine, isoleucine, leucine, histidine, tryptophan, and tyrosine in immature and adult rat brains. The branched-chain amino acids were most affected. Their reductions ranged between 38–64 per cent of control values when phenylalanine was administered either parenterally or in the diet. The pattern of cerebral amino acid depletions found in phenylalanine-injected infant rats was similar to that of the adults. Phenylalanine loading caused depletions in serum amino acid levels in adult rats, but in infant rats the serum levels were either unchanged or somewhat elevated. Tyrosine, when administered to adult rats either parenterally or via the diet, caused cerebral depletions in essential amino acids, but the depletions were not as striking as with phenylalanine. In both the infant and adult rat, brain-blood ratios of most of the essential amino acids were significantly reduced by phenylalanine loading.     

几种蚜虫中的氨基酸

本文测定了七星瓢虫嗜食的桃蚜(Myzus persicae)、萝卜蚜(Lipaphis erysimi)及高粱蚜(Mclanaphis sacchari)的游离和水解氨基酸,供有关方面在进一步探讨七星瓢虫的食性营养时参考。     

DISTRIBUTION AND UPTAKE OF AMINO ACIDS IN VARIOUS REGIONS OF THE CAT BRAIN IN VITRO

—(1) The levels of the free amino acids were determined in five areas of the cat brain. The regional pattern was heterogeneous and fairly characteristic for each compound. (2) The uptakes of α-aminoisobutyric acid, taurine, d -aspartic acid, and l -histidine were measured in incubated slices from 31 regions of the cat CNS. Differences in uptake were found among the various areas; the regional pattern of uptake was different for each amino acid. The initial rate of uptake (5 min incubation) very often paralleled the rate at equilibrium (90 min incubation). (3) The regional correlation between distribution in vivo and uptake in vitro was good for aspartate, less so for histidine, and poor for taurine. (4) It is concluded that regional heterogeneity in exit processes, available energy, cell density, or protein content is unlikely to have decisive influence in determining regional differences in distribution and transport of metabolites; it seems that influx is the most important factor.     

THE AMINO ACIDS OF SOME MISTLETOES AND THEIR HOSTS

The following mistletoes and their hosts were studied: Phoradendron serotinum (Raf.) M. C. Johnst. (P. flavescens [Pursh] Nutt. var. macrophyllum Engelm.) on Juglans hindsii Jeps. (California black walnut), Arceuthobium campylopodum Engelmn. f. abietinum (Engelm.) Gill on Abies concolor (Gord. and Glend.) Lindl. (white fir) and A. magnifica A. Murr (red fir), Arceuthobium campylopodum Engelm. f. campylopodum (Engelm.) Gill on Pinus sabiniana Dougl. (Digger pine), and Amyema pendula (Spleng) Tiegh. on Eucalyptus macrorhyncha F. Muell. ex Benth. (stringybark). With the exception of the Amyema leaves, the mistletoes are richer in free and bound amino acids than their hosts; moreover, their amino acid composition closely resembles that of their hosts. Nevertheless, there is no satisfactory evidence that mistletoe specificity depends on the amino acid composition of the hosts. Some mistletoes contain γ-aminobutyric acid and asparagine, not found in all hosts. All the above mistletoes but no hosts contain free hydroxyproline. These results are discussed in relation to (1) the region in the mistletoes where hydroxyproline is formed and (2) the possibility of using certain amino acid analogs as selective poisons for mistletoes.     

THE INFLUENCE OF EXCESS METHIONINE ON THE FREE AMINO ACIDS OF BRAIN AND LIVER OF THE WEANLING RAT*

Abstract— —High circulating levels of l -methionine produced by inclusion in the diet or parenteral injection of the amino acid caused alterations in the free amino acid pattern of liver and brain tissues. Acute effects following l -methionine injection were more pronounced than those following long term feeding where adaptation played a role. The net effect following parenteral injection was to increase the total free amino acids of liver while decreasing those of brain. Individually, hepatic levels of aspartic acid, threonine, serine, glutamine, glutamic acid, glycine, and alanine were depressed while levels of taurine, cystathionine, methionine, lysine, and ornithine were markedly elevated. Brain levels of aspartic acid, threonine, serine, glutamic acid, glycine, alanine, and γ-aminobutyric acid were markedly depressed and increased levels of cystathionine, methionine, lysine, and glutamine were observed. A generalized aminoaciduria occurred shortly after excessive methionine intake. Disruption of the free amino acid pools was of two kinds. The first depended on the continued presence of excess l -methionine, the second did not.     

BIOSYNTHESIS OF FREE AMINO ACIDS IN THE BRAIN OF JIMPY MICE

—The metabolism of free amino acids: γ-aminobutyric acid (GABA), glutamine, glycine and glutathione has been studied. The labelling of these free amino acids in normal and in myelin-deficient brains of Jimpy mice was followed after intraperitoneal injection of ¹⁴C-labelled glucose precursor. The quantitative distribution of these amino acids in the two kinds of mouse brain has been compared. A higher level of GABA and a faster labelling of the amino acids in Jimpy than in normal mouse brain was observed.     

THE EFFECT OF HYPERCAPNIA UPON INTRACELLULAR pH IN THE BRAIN, EVALUATED BY THE BICARBONATE- CARBONIC ACID METHOD AND FROM THE CREATINE PHOSPHOKINASE EQUILIBRIUM

Abstract— Abstract-Intracellular pH in the brain was evaluated by the bicarbonate-carbonic acid method and from the creatine phosphokinase equilibrium, in rats exposed to 6–40 % CO₂ for 45 min. There was a very good agreement between the two methods, indicating that the creatine phosphokinase equilibrium in vivo shows the pH dependence predicted from previous in vitro studies. The stepwise increase in the tissue CO₂ tension from 45 to 265 mm Hg resulted in a lowering of the intracellular pH from 7.04 to 6.68. The regulation of intracellular pH in hypercapnia was far better than that which can be predicted from physicochemical buffering alone, and calculations indicate that the intracellular buffer base concentration increased by more than 10 mequiv./kg at the maximal P_co2 values encountered.     

THE EFFECT OF ELEVATED AMINO ACIDS ON AMINOTRANSFERASE LEVELS IN BRAIN AND LIVER OF THE MOUSE

Abstract— Adult mice were fed standard diets that were enriched with selected amino acids, i.e. 3% methionine, 6% valine, or 8% lysine. These diets caused the following changes in the amino acid pool of the brain measured at 7 and 21 days. The high methionine diet resulted in 50-fold higher levels of methionine and cysteine and somewhat lower levels of serine and glutamine. The valine and lysine-enriched diets also caused 2- to 4-fold increases in valine and lysine contents of brain, respectively. In spite of the large changes in amino acid levels, however, there were essentially no changes in aspartate: α-ketoglutarate, alanine: α-ketoglutarate, ornithine: α-ketoglutarate, methionine: α-ketoglutarate, and the branched chain aminotransferase activities of brain 3, 10, and 21 days after the onset of the dietary regimen. In contrast, these diets produced significant changes in some of these enzyme activities in liver. Changes in liver included a 2-fold increase in ornithine and alanine aminotransferase activities with the methionine-enriched diet. Liver ornithine aminotransferase activity also increased slightly in animals fed the valine-enriched or lysine-enriched diet.