Alternate cadmium exposure differentially affects amino acid metabolism within the hypothalamus, median eminence, striatum and prefrontal cortex of male rats.

This work was designed to analyze the possible changes in glutamate, aspartate and glutamine content induced by cadmium exposure in the hypothalamus, striatum and prefrontal cortex of rats, using an alternate schedule of metal administration. Pubertal-adult differences were also evaluated. In adult control rats, glutamate and aspartate contents in the anterior hypothalamus decreased as compared to pubertal controls. After cadmium administration from day 30 to 60 of life, the content of anterior hypothalamic glutamate and aspartate diminished. In adult control animals, the glutamine content increased in mediobasal hypothalamus as compared to pubertal controls. After cadmium exposure from day 30 to 60 of life, the mediobasal glutamine content increased, and after cadmium treatment from day 60 to 90 of life, the mediobasal aspartate content decreased. In adult control rats the content of glutamine, glutamate and aspartate of the posterior hypothalamus decreased significantly. After cadmium administration in pubertal animals, posterior hypothalamic contents of glutamine, glutamate and aspartate diminished. Cadmium treatment of adult animals caused a decrease in glutamine content, as compared to controls. In adult control rats, only glutamate and aspartate content increased in the prefrontal cortex as compared to the values found in pubertal controls. When cadmium was administered to adult animals, only the aspartate content decreased. In the striatum, cadmium decreased the glutamine and aspartate contents when administered from day 60 to 90 of life. These data suggest that cadmium differentially affects amino acid metabolism in the hypothalamus, striatum and prefrontal cortex. Age-dependent effects of cadmium on these brain areas appeared to have occurred.     

Possible role of glutamate, aspartate, glutamine, GABA or taurine on cadmium toxicity on the hypothalamic pituitary axis activity in adult male rats

This work was designed to evaluate the possible changes in glutamate, aspartate, glutamine, GABA and taurine within various hypothalamic areas the striatum and prefrontal cortex after oral cadmium exposure in adult male rats, and if these changes are related to pituitary hormone secretion. The contents of glutamine, glutamate, aspartate, GABA and taurine in the median eminence, anterior, mediobasal and posterior hypothalamus, and in prefrontal cortex in adult male rats exposed to 272.7 mol l^–1 of cadmium chloride (CdCl₂) in the drinking water for one month. Cadmium diminished the content of glutamine, glutamate and aspartate in anterior hypothalamus as compared to the values found in the untreated group. Besides, there is a decrease in the content of glutamate, aspartate and taurine in the prefrontal cortex. The amino acids studied did not change in median eminence, mediobasal and posterior hypothalamus or the striatum by cadmium treatment. Plasma prolactin and LH levels decreased in rats exposed to the metal. These results suggest that (1) cadmium differentially affects amino acid content within the brain region studied and (2) the inhibitory effect of cadmium on prolactin and LH secretion may be partially explained by a decrease in the content of both glutamate and aspartate in anterior hypothalamus, but not through changes in GABA and taurine.     

Changes with aging in the levels of amino acids in rat CNS structural elements I. Glutamate and related amino acids

Glutamate and related amino acids were determined in 53 discrete brain areas of 3-and 29-month-old male Fischer 344 rats microdissected with the punch technique. The levels of amino acids showed high regional variation-the ratio of the highest to lowest level was 9 for aspartate, 5 for glutamate, 6 for glutamine, and 21 for GABA. Several areas were found to have all four amino acids at very high or at very low level, but also some areas had some amino acids at high, others at low level. With age, in more than half of the areas, significant changes could be observed, decrease occurred 5 times more frequently than increase. Changes occurred more often in levels of aspartate and GABA than in those of glutamate or glutamine. The regional levels of glutamate and its related amino acids show severalfold variations, with the levels tending to decrease in the aged brain.     

INTERACTION OF CATECHOLAMINE AND AMINO ACID METABOLISM IN BRAIN: EFFECT OF PARGYLINE AND l-DOPA

Abstract— The combination of l -DOPA and pargyline caused a decrease in level of aspartate and an increase in that of glutamine in vivo in cerebral cortex, cerebellum, brain stem, hypothalamus, neostriatum and cervical cord of rat. There was also a decreased incorporation of radioactivity from [1-¹⁴C]acetate into amino acids in vivo , most notably in cerebellum and brain stem. The labelling of glutamine was especially affected. In addition, cortical slices were prepared from guinea pigs which had been pretreated with pargyline. These slices were incubated with and without 1 m m l -DOPA in media containing [1-¹⁴C]acetate. Pargyline alone caused a stimulation of the labelling of glutamate and aspartate but not glutamine and GABA; the levels of aspartate and GABA were greater than in control slices. The addition of l -DOPA to slices from pargylinized animals caused a severe decrease in glutamine labelling but not in that of glutamate or aspartate; the level of glutamine was increased while that of glutamate was decreased. The results are discussed in terms of the known biochemical and morphological compartmentation of amino acids in brain. It is suggested that catecholamines, in the process of functioning as transmitters, may also function as metabolic regulators of other transmitters, e.g. amino acids, as well as of the energy required for balanced neuronal function.     

Excitatory and inhibitory amino acid changes in ischemic brain regions in spontaneously hypertensive rats

Excitatory (glutamate, aspartate) or inhibitory amino acids (-aminobutyric acid: GABA, taurine) and glutamine contents were examined in acutely induced cerebral ischemia in spontaneously hypertensive rats. At 20 min ischemia most of these amino acids remained unchanged, but glutamine significantly decreased by 14% in the CA3 hippocampal subfield. At 60 min ischemia glutamate significantly decreased by 14% in the CA3, aspartate by 17–26% in the CA3, cingulate cortex, septum and striatum. In contrast, GABA significantly increased by 48–106% in the cortices (frontal, parietal and cingulate), striatum and nucleus accumbens, but insignificantly in hippocampal subrïelds. Likewise, taurine increased in the parietal cortex and nucleus accumbens. Glutamine showed heterogeneous changes (increase in the nucleus accumbens and decrease in the CA3). Amino acid levels change during ischemia, but their changes are varied in each area, implying that different reaction of amino acids may explain the selective vulnerability to cerebral ischemia.     

Amino acid utilization by L-M strain mouse cells in a chemically defined medium

Summary The amino acid requirements of strain L-M mouse cells grown in a chemically defined medium (2×Eagle) containing only the 13 essential amino acids (EAA) were investigated. Medium and acid hydrolysate samples were analyzed for amino acid content by the method of ion exchange chromatography. The extent of utilization of the EAA differed;e.g. after 120 hr of cell growth without medium change, glutamine was exhausted from the medium; methionine, leucine, isoleucine, cystine, arginine, and valine were depleted 60 to 80%; other EAA were used to lesser extents. Although the EAA were used in excess of their requirements for protein synthesis, a correlation could generally be made between utilization and protein amino acid composition. Glutamine appeared to be, a growth-limiting factor. Use of U-¹⁴C-labeled glutamine indicated that over one-half of the metabolized glutamine was converted to carbon dioxide, 17% to cell material, and 15% was extracted from the amino acid pools. Nonessential amino acids (NEAA), viz. alanine, aspartic acid, glutamic acid, glycine, proline, and serine, were released into the medium during growth, and some were reutilized. Exogenous provision of these did not improve cell growth. In contrast to the other NEAA, only serine showed net utilization when provided exogenously. When glutamic acid largely replaced the glutamine in the medium, it exerted a sparing effect on the glutamine requirement for protein synthesis. Suggestions are given for the improvement of Eagle medium for cell growth. Supported by Research Grants CA 03720 and CA 11802 from the National Institutes of Health. Predoctoral, fellow supported, by Grant F01-GM-42156-02 from the National Institutes of Health.     

Release of Excitatory Amino Acids from Cultured Hippocampal Astrocytes Induced by a Hypoxic-Hypoglycemic Stimulation

An excess release of excitatory amino acids (EAA) is an important factor for postischemic brain damage. In the present communication, we demonstrate that cultured hippocampal cells release EAA after hypoxic-hypoglycemic treatment. The amounts of EAA released from astrocytes were appreciably above those released from neurons. Furthermore, the amount of aspartate released from astrocytes was comparable to that of glutamate, although the endogenous content of aspartate was one-fifth that of glutamate. The endogenous content of aspartate in astrocytes increased even after hypoxic-hypoglycemic treatment. These results suggests that ischemic neuronal death is due, at least in part, to the excitotoxicity of aspartate and glutamate derived from surrounding astrocytes.     

Amino acid utilization by L-M strain mouse cells in a chemically defined medium

Summary The amino acid requirements of strain L-M mouse cells grown in a chemically defined medium (2×Eagle) containing only the 13 essential amino acids (EAA) were investigated. Medium and acid hydrolysate samples were analyzed for amino acid content by the method of ion exchange chromatography. The extent of utilization of the EAA differed;e.g. after 120 hr of cell growth without medium change, glutamine was exhausted from the medium; methionine, leucine, isoleucine, cystine, arginine, and valine were depleted 60 to 80%; other EAA were used to lesser extents. Although the EAA were used in excess of their requirements for protein synthesis, a correlation could generally be made between utilization and protein amino acid composition. Glutamine appeared to be a growth-limiting factor. Use of U-¹⁴C-labeled glutamine indicated that over one-half of the metabolized glutamine was converted to carbon dioxide, 17% to cell material, and 15% was extracted from the amino acid pools. Nonessential amino acids (NEAA), viz. alanine, aspartic acid, glutamic acid, glycine, proline, and serine, were released into the medium during growth, and some were reutilized. Exogenous provision of these did not improve cell growth. In contrast to the other NEAA, only serine showed net utilization when provided exogenously. When glutamic acid largely replaced the glutamine in the medium, it exerted a sparing effect on the glutamine requirement for protein synthesis. Suggestions are given for the improvement of Eagle medium for cell growth. Supported by Research Grants CA 03720 and CA 11802 from the National Institutes of Health. Predoctoral fellow supported by Grant F01-GM-42156-02 from the National Institutes of Health. Present address: Department of Community Medicine. Basic Science Building, University of California, San Diego, La Jolla, Calif. 92037.     

Effect of age and monosodium-L-glutamate (MSG) treatment on neurotransmitter content in brain regions from male fischer-344 rats

Peripheral administration of monosodium-L-glutamate (MSG) has been found to be neurotoxic in neonatal rats. When administered in an acute, subconvulsive dose (500 mg/kg i.p.), MSG altered neurotrnnsmitter content in discrete brain regions of adult (6 month old) and aged (24 month old) male Fischer-344 rats. Norepinephrine (NE) content was reduced in both the hypothalamus (16%) and cerebellum (11%) of adult rats, but was increased in both the hypothalamus (7%) and cerebellum (14%) of aged rats after MSG treatment. MSG also altered the dopamine content in adult rats in both the posterior cortex and the striatum, causing a reduction (23%) and an increase (12%), respectively. Glycine content in the midbrain of aged rats increased (21%) after MSG injection. Of particular interest is the widespread monoamine and amino acid deficits found in the aged rats in many of the brain regions examined. NE content was decreased (11%) in the cerebellum of aged rats. Dopamine content was reduced in both the posterior cortex (35%) and striatum (10%) of aged rats compared to adult animals. Cortical serotonergic deficits were present in aged rats with reductions in both the frontal (13%) and posterior cortex (21%). Aged rats also displayed deficits in amino acids, particularly the excitatory amino acids. There were glutamate deficits (9–18% reductions) in the cortical regions (posterior and frontal) as well as midbrain and brain stem. Aspartate, the other excitatory amino acid transmitter, was reduced 10% in the brainstem of aged rats. These data indicate that an acute, subconvulsive, dose of MSG may elicit neurochemical changes in both adult and aged male Fisher-344 rats, and that there are inherent age-related deficits in particular neurotransmitters in aged male Fisher-344 rats as indicated by the reductions in both monoamines and amino acids.     

INCORPORATION OF 14C FROM [U-14C]GLUCOSE INTO FREE AMINO ACIDS IN MOUSE BRAIN REGIONS UNDER CYANIDE INTOXICATION

—During anoxia induced by the administration of potassium cyanide, [U-¹⁴C]glucose was injected intraperitoneally into adult mice and they were decapitated at 5, 15 and 30 min after the injection. After freeze-drying in vacuo, differences in the uptake of radioactive carbon from [U-¹⁴C]glucose into free amino acids (glutamate + glutamine, aspartate + asparagine, GABA, alanine and glycine) in mouse cerebral neocortex, cerebellar hemisphere, caudate nucleus, thalamus, hypothalamus and medulla oblongata were investigated (by macroautoradiography and GLC separation) and compared with those obtained under normal conditions. (1) During anoxia, autoradiographical densities in the thalamus and medulla oblongata were higher than that in the cerebral neocortex and caudate nucleus. (2) Among specific radioactivities (d.p.m./μmol) of free amino acids, alanine gave the highest value during anoxia, except in the cerebellar hemisphere and hypothalamus at 5 min and the medulla oblongata at 30 min. (3) During anoxia, the specific radioactivities of alanine and glycine in each brain region did not significantly decrease at 15 and 30 min compared with those under normal conditions. During anoxia, the specific radioactivity of glutamate + glutamine in the cerebellar hemisphere and hypothalamus did not significantly decrease compared with the normal conditions, while that of GABA, aspartate + asparagine and glutamate + glutamine in the cerebral neocortex, caudate nucleus, thalamus and medulla oblongata showed an increase. (4) The percentage decrease of glutamate + glutamine and aspartate + asparagine at 5 and 15 min was highly significant in the cerebral neocortex and caudate nucleus.     

Alteration of amino acid metabolism in neuronal aggregate cultures exposed to hypoglycaemic conditions

The neuronal effects of glucose deficiency on amino acid metabolism was studied on three-dimensional cultures of rat telencephalon neurones. Transient (6 h) exposure of differentiated cultures to low glucose (0.25 mm instead of 25 mm) caused irreversible damage, as judged by the marked decrease in the activities of two neurone-specific enzymes and lactate dehydrogenase, 1 week after the hypoglycemic insult. Quantification of amino acids and ammonia in the culture media supernatants indicated increased amino acid utilization and ammonia production during glucose-deficiency. Measurement of intracellular amino acids showed decreased levels of alanine, glutamine, glutamate and GABA, while aspartate was increased. Added lactate (11 mm) during glucose deficiency largely prevented the changes in amino acid metabolism and ammonia production, and attenuated irreversible damage. Higher media levels of glutamine (4 mm instead of 0.25 mm) during glucose deprivation prevented the decrease of intracellular glutamate and GABA, while it further increased intracellular aspartate, ammonia production and neuronal damage. Both lactate and glutamine were readily oxidized in these neuronal cultures. The present results suggest that in neurones, glucose deficiency enhances amino acid deamination at the expense of transamination reactions. This results in increased ammonia production and neuronal damage.     

Maternal Undernutrition During Lactation: Effect on Amino Acids in Brain Regions of Offspring

Sprague-Dawley dams were fed either a protein-calorie deficient or control diet from day 5 to day 21 after parturition. The concentrations of seven amino acids (aspartate, glutamate, gamma-aminobutyric acid, glycine, glutamine, serine, and taurine) were determined in brain regions from 17-day-old undernourished offspring and from 35-day-old rehabilitated rats. The brain regions examined were the cortex, cerebellum, corpus striatum, hippocampus, hypothalamus, brainstem, and midbrain. At 17 days of age, taurine was the amino acid with the highest concentration, whereas at 35 days glutamate had the highest concentration. This change was due to the fact that the concentration of taurine decreased significantly in all brain regions between 17 and 35 days, whereas the concentration of glutamate remained high or increased somewhat in all brain regions except the hypothalamus and brainstem. When the age-matched offspring of control and undernourished rats were compared, several interesting and significant differences were found. The concentrations of glutamate and aspartate were significantly lower (decreased 16-34%) in the cerebellum, brainstem, cortex, and midbrain in 17-day-old undernourished rats. The aspartate level was also significantly decreased in the corpus striatum and hypothalamus in 17-day-old offspring. However, the deficiencies of aspartate and glutamate were transient and reversible. In contrast, the concentration of taurine was increased in the hypothalamus (31%) and hippocampus (12-33%) at both 17 and 35 days of age and in the midbrain (17%) at 17 days. Other transient abnormalities in amino acid levels were found in undernourished offspring. The results of these experiments suggest that undernutrition during lactation causes delayed CNS development, which is manifested in altered concentrations of the neurotransmitters aspartate, glutamate, and taurine.     

EFFECT OF CHRONIC HYPERPROLACTINEMIA ON DAILY CHANGES OF GLUTAMATE AND ASPARTATE CONCENTRATIONS IN THE MEDIAN EMINENCE AND DIFFERENT HYPOTHALAMIC AREAS OF MALE RATS

The 24h changes of glutamate (GLU) and aspartate (ASP) werestudied in the median eminence (ME) and hypothalamic areas. It was analyzedwhether prolactin may change their daily patterns. The hypothalamic concentrationof these amino acids was measured by high-performance liquid chromatography(HPLC) with fluorometric detection. Plasma prolactin levels increased overthe 24h light-dark cycle after pituitary grafting compared to controls, andits circadian rhythm was disrupted. In controls, aspartate and glutamate inthe hypothalamic areas studied followed a specific daily variation or showedno rhythmicity. In the median eminence, hyperprolactinemia seem to phase advancethe aspartate or glutamate peaks from 16:00 to 12:00. In the mediobasal hypothalamus,hyperprolactinemia altered daily changes of aspartate and significantly decreasedits concentration. Also, it seems to delay the nocturnal glutamate peak comparedto controls. In the posterior hypothalamus, hyperprolactinemia did not changeaspartate and glutamate concentrations and their daily changes, although itincreased the glutamine concentration. These data show the existence of 24hchanges of amino acid concentration in three of the hypothalamic regions studied.Increased plasma prolactin levels differentially affected these patterns dependingon the hypothalamic area analyzed. (ChronobiologyInternational, 17(5), 631–643, 2000)     

GLUCOSE AND AMINO ACID METABOLISM IN ISOLATED NEURONAL AND GLIAL CELL FRACTIONS IN VITRO

Abstract—

• 1 The metabolism of three substrates, [U-¹⁴C]glucose, [U-¹⁴C]pyruvate and [U-¹⁴C]glutamate has been studied in vitro in neuronal and glial cell fractions obtained from rat cerebral cortex by a density gradient technique.
• 2 The mixed cell suspension, after washing, metabolized glucose and glutamate in a manner essentially similar to the tissue slice. Exceptions were a reduced ability to generate lactate from glucose and alanine from glutamate, and a lowered effect of added glucose in suppressing the production of aspartate from glutamate.
• 3 After 2 hr incubation with [U-¹⁴C]glucose, the concentration of the amino acids glutamate, glutamine, GABA, aspartate and alanine were raised in the neuronal, compared to the glial fraction to 234 per cent, 176 per cent, 202 per cent, 167 per cent and 230 per cent respectively although both were lower than in the tissue slice. Incorporation of radio-activity was absolutely lower in the neuronal fraction, however, and the specific activities of the amino acids were: glutamate 12 per cent, GABA 18 per cent, aspartate 34 per cent, and alanine 33 per cent of those in the glial fraction.
• 4 After the incubation with [U-¹⁴C]pyruvate, the pool size of the amino acids were higher than after incubation with glucose, except for GABA, which was reduced to one-third. The concentrations of the amino acids glutamate, glutamine, GABA, aspartate, and alanine in the neuronal fraction were respectively 46 per cent, 143 per cent, 105 per cent, 97 per cent, and 57 per cent of those in the glial. Thus, with the exception of alanine, the specific activity of the neuronal amino acids compared to the glial was little increased when pyruvate replaced glucose as substrate.
• 5 After 2 hr incubation with [U-¹⁴C]glutamate in the presence of non-radioactive glucose, the pool sizes of all the amino acids were increased in both neuronal and glial fractions, with the exception of neuronal alanine and glial glutamine. The concentrations of the amino acids glutamine, GABA, aspartate and alanine were raised in the neuronal fraction, compared to the glial, to 425 per cent, 187 per cent, 222 per cent, and 133 per cent respectively. The specific activities of all the amino acids were higher than with glucose alone with the exception of alanine, and neuronal GABA. Neuronal glutamine and aspartate had specific activities respectively 102 per cent and 84 per cent of glial.
• 6 An unidentified amino acid, with R_F comparable to that of alanine and specific activity close to that of glutamate, was also present after incubation. It was relatively concentrated in the neuronal fraction.
• 7 The distribution of the enzymes glutamate dehydrogenase, aspartate aminotransferase, glutamate decarboxylase and glutamine synthetase between the cell fractions was studied. With the exception of glutamine synthetase, none of the enzymes was lost from the cell fractions during their preparation. Only 14 per cent of the glutamine synthetase, compared with 75 per cent of total protein, was recovered in the fractions. Of the enzymes, glutamate dehydrogenase activity was 406 per cent, and glutamate synthetase activity 177 per cent in the neuronal fraction compared to the glial in the absence of detergent. In the presence of detergent, glutamate dehydrogenase control was 261 per cent, aspartate aminotransferase activity 237 per cent is the neuronal as compared to the glial fraction.
• 8 Incorporation of radioactivity into acid-insoluble material from either glutamate or pyruvate was twice as high into the neuronal as the glial fraction.
• 9 The extent to which these differences may be extrapolated back to the intact tissue is considered, and certain correction factors calculated. The significance of the observations for an understanding of the compartmentation of amino acid pools and metabolism in the brain, and the possible identification of such compartments, is discussed.

     

Effect of chronic hyperprolactinemia on daily changes of glutamate and aspartate concentrations in the median eminence and different hypothalamic areas of male rats

The 24h changes of glutamate (GLU) and aspartate (ASP) were studied in the median eminence (ME) and hypothalamic areas. It was analyzed whether prolactin may change their daily patterns. The hypothalamic concentration of these amino acids was measured by high-performance liquid chromatography (HPLC) with fluorometric detection. Plasma prolactin levels increased over the 24h light-dark cycle after pituitary grafting compared to controls, and its circadian rhythm was disrupted. In controls, aspartate and glutamate in the hypothalamic areas studied followed a specific daily variation or showed no rhythmicity. In the median eminence, hyperprolactinemia seem to phase advance the aspartate or glutamate peaks from 16:00 to 12:00. In the mediobasal hypothalamus, hyperprolactinemia altered daily changes of aspartate and significantly decreased its concentration. Also, it seems to delay the nocturnal glutamate peak compared to controls. In the posterior hypothalamus, hyperprolactinemia did not change aspartate and glutamate concentrations and their daily changes, although it increased the glutamine concentration. These data show the existence of 24h changes of amino acid concentration in three of the hypothalamic regions studied. Increased plasma prolactin levels differentially affected these patterns depending on the hypothalamic area analyzed. (Chronobiology International, 17(5), 631-643, 2000)     

14C-LABELLED AMINO ACIDS AND GLUCOSE IN RAT BRAIN AND LIVER AFTER INJECTION OF [2-14C]PROPIONATE

Abstract— [2-¹⁴C]Propionate injected into rats was metabolized into [¹⁴C]glucose and ¹⁴C-labelled aspartate, glutamate, glutamine and alanine. The results are consistent with the conversion of propionate into succinate and the oxidation of succinate into oxaloacetate, the precursor of labelled amino acids and the substrate for gluconeogenesis.
The ratio of the specific radioactivity of glutamine to glutamate was greater than 1 during the 30 min period in the brain, indicating that propionate taken up by the brain was metabolized mainly in the 'small glutamate compartment' in the brain. The results, therefore, support the previous conclusion (G aitonde , 1975) that the labelling of amino acids by [¹⁴C]propionate formed from [U-¹⁴C>]-threonine in thiamin-deficient rats was metabolized in the 'large glutamate compartment' of the brain.
The specific radioactivity ratio of glutamine to glutamate in the liver was less than 1 during the 10 min period but greater than 1 at 30min. These findings which gave evidence against metabolic compartments of glutamate in the liver, were interpreted as indicative of the entry of blood-borne [¹⁴C]glutamine synthesized in other tissues, e.g. brain. The labelling of amino acids when compared to that after injection of [U-¹⁴C]glucose showed that [2-¹⁴C]propionate was quantitatively a better source of amino acids in the liver. The concentration of some amino acids in the brain and liver was less in the adult than in the young rats, except for alanine and glutathione, where the liver content was more than double that in the adult.     

INCORPORATION OF 14C FROM [U-14C]GLUCOSE INTO FREE AMINO ACIDS IN MOUSE BRAIN LOCI IN VIVO UNDER NORMAL CONDITIONS

By macroautoradiography and by GLC separation, differences in the uptake of radioactive carbon from [U-¹⁴C]glucose into free amino acids (glutamate + glutamine, aspartate + asparagine, GABA, alanine and glycine) in mouse cerebral neocortex, hippocampus, thalamus and hypothalamus were investigated. (1) The autoradiographical densities in the thalamus, cerebral neocortex and hippocampus measured with a microdensitometer were higher than that in the hypothalamus at 5 min after subcutaneous injection. At 180 min, densities in the cerebral neocortex, hippocampus and hypothalamus were higher than that in thalamus. (2) The free amino acid levels determined by GLC varied with each brain region. (3) The specific radioactivity (d.p.m./μmol) of alanine in each brain region was higher than that of the other amino acids at 5 min after the injection. The specific radioactivity of GABA in the brain regions was clearly higher than that of (glutamate + glutamine), (aspartate + asparagine) and glycine at 5 and 15 min. (4) The autoradiographical data were in good agreement with the chemical data at 5 min but were different at 180 min. (5) Variations in specific radioactivity of each free amino acid among brain regions at 5 min were influenced greatly by existing free amino acid concentrations in each region.     

Changes in plasma amino acid concentrations with increasing age in patients with propionic acidemia

The objective of the study is to analyze plasma amino acid concentrations in propionic acidemia (PA) for the purpose of elucidating possible correlations between propionyl-CoA carboxylase deficiency and distinct amino acid behavior. Plasma concentrations of 19 amino acids were measured in 240 random samples from 11 patients (6 families) with enzymatically and/or genetically proven propionic acidemia (sampling period, January 2001–December 2007). They were compared with reference values from the literature and correlated with age using the Pearson correlation coefficient test. Decreased plasma concentrations were observed for glutamine, histidine, threonine, valine, isoleucine, leucine, phenylalanine and arginine. Levels of glycine, alanine and aspartate were elevated, while values of serine, asparagine, ornithine and glutamate were normal. For lysine, proline and methionine a clear association was not possible. Significant correlations with age were observed for 13 amino acids (positive correlation: asparagine, glutamine, proline, alanine, histidine, threonine, methionine, arginine; negative correlation: leucine, phenylalanine, ornithine, glutamate and aspartate). This study gives new insight over long-term changes in plasma amino acid concentrations and may provide options for future therapies (e.g., substitution of anaplerotic substances) in PA patients.     

Glucose and amino acid metabolism in rat brain during sustained hypoglycemia

The metabolism of glucose in brains during sustained hypoglycemia was studied. [U-14C]Glucose (20 microCi) was injected into control rats, and into rats at 2.5 hr after a bolus injection of 2 units of insulin followed by a continuous infusion of 0.2 units/100 g rat/hr. This regimen of insulin injection was found to result in steady-state plasma glucose levels between 2.5 and 3.5 mumol per ml. In the brains of control rats carbon was transferred rapidly from glucose to glutamate, glutamine, gamma-aminobutyric acid and aspartate and this carbon was retained in the amino acids for at least 60 min. In the brains of hypoglycemic rats, the conversion of carbon from glucose to amino acids was increased in the first 15 min after injection. After 15 min, the specific activity of the amino acids decreased in insulin-treated rats but not in the controls. The concentrations of alanine, glutamate, and gamma-amino-butyric acid decreased, and the concentration of aspartate increased, in the brains of the hypoglycemic rats. The concentration of pyridoxal-5'-phosphate, a cofactor in many of the reactions whereby these amino acids are formed from tricarboxylic acid cycle intermediates, was less in the insulin-treated rats than in the controls. These data provide evidence that glutamate, glutamine, aspartate, and GABA can serve as energy sources in brain during insulin-induced hypoglycemia.     

Metabolic Abnormalities and Grade of Encephalopathy in Acute Hepatic Failure

Abstract: Acute hepatic failure is associated with many biochemical abnormalities in plasma and brain. Changes that correlate well with the degree of behavioral impairment may be important factors in the development of encephalopathy. We measured the concentrations of intermediary metabolites, ammonia, and amino acids in brain and plasma and the rate of whole-brain glucose utilization in rats with an acutely devascularized liver. In all rats an estimate of the grade of encephalopathy (reflected by behavioral impairment) was made. Rats underwent portacaval shunting and hepatic artery ligation (or sham operation) and were kept normoglycemic and normothermic thereafter. We sampled blood and whole brain (by near-instantaneous freeze-blowing) 2, 4, or 6 h later. There were no alterations in levels of high-energy phosphate metabolites in the brain or in metabolites associated with the glycolytic pathway and Krebs cycle, except lactate and pyruvate. Brain glucose use was decreased similarly at all times after surgery. Levels of ammonia and many amino acids were increased in brain and plasma; brain aspartate, glutamate, and arginine levels were decreased. The increases in content of plasma ammonia and brain glutamine, proline, alanine, and aromatic amino acids and the decreases in brain aspartate and glutamate were most strongly correlated with behavioral impairment.