Correlation between brain tryptophan and plasma neutral amino acid levels following food consumption in rats

Brain tryptophan increases significantly within two hr of the time that rats begin to consume a diet containing carbohydrate and fat, but fails to rise if the diet also contains 18–24% protein. The effects of particular diets on brain tryptophan are not well correlated with plasma tryptophan concentrations alone, but do correlate well with the ratio of plasma tryptophan to individual neutral amino acids (leucine, isoleucine, valine, tyrosine, phenylalanine) or to their sums. (These amino acids compete with tryptophan for uptake into the brain.) Carbohydrate ingestion raises brain tryptophan by elevating plasma tryptophan and depressing the plasma levels of the competing neutral amino acids; protein consumption prevents an increase in brain tryptophan by raising the plasma concentrations of the competing amino acids more than of tryptophan.     

Dose-response decrease in plasma tryptophan and in brain tryptophan and serotonin after tryptophan-free amino acid mixtures in rats

Rats fasted 15 hours were treated p.o. with increasing amounts (660 and 1320 mg/kg body weight) of a mixture containing a fixed proportion of seven essential amino acids (L-phenylalanine 13.6%, L-leucine 6.0%, L-isoleucine 12.1%, L-methionine 12.1%, L-lysine 30.3%, L-threonine 10.6%, L-valine 15.2%) and lacking tryptophan. The mixtures produced a dose-response decrease of free (by 34% after the lower dose and by 58% after the higher dose of the mixture) and total (by 10 and 31%) plasma tryptophan and of brain tryptophan (by 38 and 65%), serotonin (by 17 and 41%) and 5-hydroxyindole acetic acid (by 21 and 49%). The mechanisms of these changes are discussed.     

Diurnal rhythms in rat plasma amino acids

To obtain detailed data on the diurnal rhythm in rat plasma amino acids, groups of rats were killed every two hours during 24 hours and the amino acids in plasma were measured. By using such a short interval between the blood samples, it was possible to reveal differences in rhythmicity between the various amino acids, more detailed than those previously described. Furthermore, it was found that those large neutral amino acids (LNAA) which compete with each other for the carrier mediated transport from plasma into the brain demonstrated different rhythms, whereby also the relation between these competing amino acids varied during the day. This finding might have implications for the transport of the various LNAAs into the brain, and secondarily also for the synthesis of the monoaminergic neurotransmitters in the neurons, for which the LNAAs tyrosine and tryptophan serve as precursors.     

The effect of insulin deficiency, dietary protein intake, and plasma amino acid concentrations on brain amino acid levels in rats

The effect of diabetes (streptozotocin, 65 mg/kg ip), dietary protein intake (15-60%), and plasma amino acid concentrations on brain large neutral amino acid levels in rats was examined. After 20 days, the plasma concentrations of methionine and the branched chain amino acids (BCAA), valine, isoleucine, and leucine were increased in diabetic rats. In brain tissue, methionine and valine levels were increased but threonine, tyrosine, and tryptophan concentrations were depressed. Increased protein consumption promoted a diabetic-like plasma amino acid pattern in normal rats while enhancing that of diabetic animals. However, with the exception of threonine, glycine, valine, and tyrosine, there was little effect on brain amino acid levels. A good association was found between the calculated brain influx rate and the actual brain concentration of threonine, methionine, tyrosine, and tryptophan in diabetic animals. There was no correlation, however, between brain influx rate and brain BCAA levels. Thus, the brain amino acid pattern in diabetes represents the combined effects of insulin insufficiency and composition of the diet ingested on plasma amino acid levels as well as metabolic adaptation within the brain itself.     

The effect of tryptophan depletion on brain activation measured by functional magnetic resonance imaging during the Stroop test in healthy subjects

We investigated the role of serotonin in cognitive activation of the frontal cortex. The serotonergic system was affected by the administration of an amino acids mixture without tryptophan (tryptophan depletion). In a placebo-controlled double-blind cross-over study with 20 healthy volunteers, we tested the hypothesis that a tryptophan (serotonin) decrease affects the activation of prefrontal cortex by the Stroop test. Cognitive brain activation was evaluated by functional magnetic resonance imaging (fMRI). Tryptophan depletion decreased the plasma tryptophan level up to 90 % for five hours after the tryptophan-free drink had been consumed when compared with the same mixture with tryptophan (p?0.0001). Tryptophan depletion did not affect the Stroop test performance. We compared fMRI activation in both conditions (tryptophan depletion and placebo) with plasma tryptophan levels as the covariates. The tryptophan depletion increased the activation (fMRI signal) in the bilateral mediofrontal cortex, anterior cingulate and left dorsolateral prefrontal cortex. The present findings allow the postulate that serotonergic medial forebrain and cingulum bundle pathways play a role in the activity of cortical structures involved in Stroop test processing.     

Effects of Albumin, Amino Acids and Clofibrate on the Uptake of Tryptophan by the Rat Brain

Abstract: The influences of total tryptophan concentration, albumin binding and amino acid competition on the rate of tryptophan influx into rat brain were compared using a single-pass injection technique with tritiated water as a freely diffusible reference. Omission of 3% bovine albumin from a bolus containing tryptophan in Krebs–Ringer bicarbonate buffer injected into the carotid artery increased non-albumin bound (free) tryptophan concentration threefold but tryptophan uptake by only 35% and 30% into forebrain and hypothalamus, respectively. However, tryptophan uptake from injected rat plasma was more markedly elevated when free tryptophan concentration was raised. Thus, when free tryptophan was doubled, but total tryptophan unchanged, by in vitro addition of clofibrate to a plasma bolus, uptake was increased by 53% and 28% into forebrain and hypothalamus respectively. When clofibrate was injected in vivo so that plasma total tryptophan concentration was decreased by 45% but neither free tryptophan nor competing amino acid concentrations were altered, then uptake from a bolus of the rat's own plasma was unchanged. Addition of competing amino acids at physiological concentrations to tryptophan in Krebs-Ringer buffer significantly reduced tryptophan influx into both brain regions, but did not increase the effect of albumin binding. The results indicate that tryptophan uptake into rat forebrain is substantially influenced by albumin binding and competition from other amino acids, but that hypothalamic uptake is less influenced by these factors.     

Immobilization Decreases Amino Acid Concentrations in Plasma but Maintains or Increases Them in Brain

Immobilization for 2 h significantly decreased plasma concentrations of 13 of 16 amino acids assayed, including the transmitter amine precursors tyrosine and total tryptophan. The level of plasma free tryptophan, however, was increased. Despite the reduced plasma levels, corresponding brain concentrations of many large neutral amino acids (LNAAs) were increased (tryptophan, phenylalanine, valine, leucine, and isoleucine). Brain concentrations of tyrosine and the other amino acids measured were unaltered. The results for the LNAAs were not explained by calculated brain influx rates. Therefore, altered influx kinetics or perhaps altered brain protein metabolism or efflux may be responsible. Comparison of calculated brain influxes and brain concentrations of LNAAs suggests that the rise in level of plasma free tryptophan during immobilization is not responsible for the increase in level of brain tryptophan and that the mechanism responsible for the maintenance of or increase in brain concentrations of the other LNAAs is probably involved. Maintenance of brain concentrations of basic amino acids is explicable by reduced competition for brain uptake.     

Amino acid budgets in three aphid species using the same host plant

Abstract. Nutrient provisioning in aphids depends both on the composition of ingested phloem sap and on the biosynthetic capabilities of the aphid and its intracellular symbionts. Amino acid budgets for three aphid species, Rhopalosiphum padi (L.), Schizaphis graminum (Rondani) and Diuraphis noxia (Mordvilko), were compared on a single host plant species, wheat Triticum aestivum L. Ingestion of amino acids from phloem, elimination of amino acids in honeydew, and the content of amino acids in aphids tissue were measured. From these values, ingestion rates were estimated and compared to honeydew and to estimated composition of aphid proteins. Ingestion rate was lowest in D. noxia due to low growth rate and low honeydew production; intermediate in S. graminum due to higher growth rate and intermediate honeydew production; and highest in R. padi , which had the highest rates for both variables. Both D. noxia and S. graminum induced increases in the amino acid content of ingested phloem. These changes in phloem content, combined with differences in ingestion rates, resulted in large differences among aphids in estimated rates of ingestion of individual amino acids. In honeydew, most essential amino acids were found in low amounts compared with the amounts ingested, especially for methionine and lysine. A few amino acids (arginine, cystine, histidine and tryptophan) were more abundant in honeydew of some aphids, suggesting oversupply. Aphid species differed in the composition of free amino acids in tissue but showed very similar composition in protein, implying similar requirements among the aphids. In R. padi and D. noxia , most essential amino acids were ingested in amounts insufficient for growth, implying dependence on symbiont provisioning. In S. graminum , most amino acids were ingested in amounts apparently sufficient for growth.     

CORRELATION OF PLASMA AND BRAIN AMINO ACID AND PUTATIVE NEUROTRANSMITTER ALTERATIONS DURING ACUTE HEPATIC COMA IN THE RAT

During acute hepatic coma following two-stage hepatic devascularization in the rat, profound changes occurred in plasma and whole-brain amino acids and putative neurotransmitters. Brain ammonia, glutamine and GABA were increased, aspartate was decreased, while glutamate was unchanged. An increase in brain tryptophan was accompanied by a similar increase in plasma unbound tryptophan but decreased plasma total tryptophan. These changes occurred in the presence of high plasma levels of the other neutral amino acids, including the branched chain amino acids. Plasma insulin was unchanged while glucagon levels rose, resulting in a decreased insulin to glucagon ratio. These results suggest that while plasma unbound tryptophan may influence brain tryptophan levels, altered plasma concentrations of neutral amino acids which compete with tryptophan for transport into the brain do not contribute to the increase in brain tryptophan observed during acute hepatic coma.     

Glutamate ingestion: the plasma and muscle free amino acid pools of resting humans

Monosodium glutamate (MSG) ingestion is known to increase plasma glutamate concentration, and MSG infusion stimulates insulin secretion. We investigated the impact of MSG ingestion on both the plasma and intramuscular amino acid pools. Nine postprandial adults ingested MSG (150 mg/kg) and rested for 105 min. Venous blood was sampled preingestion and then every 15 min; vastus lateralis muscle biopsies were taken preingestion and at 45, 75, and 105 min postingestion. Venous plasma glutamate and aspartate concentrations increased (P 相似文献   

Effects of branched-chain amino acids on plasma amino acids in amyotrophic lateral sclerosis

Summary Although the cause of amyotrophic lateral sclerosis (ALS) remains unknown, biological findings suggest that the excitatory amino acid glutamate contributes to the pathogenesis of ALS. In previous studies of ALS, the therapeutic effect of the branched-chain amino acids (BCAAs) leucine, valine and isoleucine has been evaluated. The present study aimed at investigating the acute effect of BCAAs on plasma glutamate levels in ALS patients. Following two oral doses of BCAAs, significantly increased plasma levels were seen for valine (500%), isoleucine (1,377%) and leucine (927%), however the plasma level of glutamate was not affected. The plasma level of several other amino acids (tryptophan, tyrosine, phenylalanine and methionine) were found decreased after oral BCAAs, which may indicate a diminution in the rate of degradation of muscle protein and/or an increase in tissue disposal of amino acids.     

Variables Influencing the Effect of a Meal on Brain Tryptophan

Previous work from our laboratory points to plasma free tryptophan being a useful predictor of brain tryptophan concentration in many circumstances. Other work, in particular various studies on the acute effects of food intake, has emphasized the roles of plasma total tryptophan and of plasma large neutral amino acids that compete with tryptophan for transport to the brain. We have now studied associations between the above variables under different dietary conditions. Rats were allowed to feed for restricted periods during a 12-h light-12-h dark cycle. In the first study, rats were given access to a carbohydrate diet for 2 h midway through the light cycle and following an 18-h fast. The resultant rise of brain tryptophan was explicable largely by the associated fall in large neutral amino acids. In a second study, rats were adapted to a regimen whereby they were allowed access to the standard laboratory diet for 4 h during the dark cycle for 3 weeks. A postprandial decrease in brain tryptophan was associated with a fall in free tryptophan and of its ratio to competing amino acids. The brain change could be attributed neither to changes in plasma total tryptophan (which increased) nor to changes of its ratio to the competers (which remained unchanged). Results as a whole are thus consistent with changes of plasma free tryptophan and large neutral amino acid concentrations affecting brain tryptophan concentration under different dietary circumstances. It is suggested that these influences serve to maintain brain tryptophan when dietary supplies are defective.     

Indolic Substances in Plasma, Cerebrospinal Fluid, and Frontal Cortex of Human Subjects Infused with Saline or Tryptophan

Psychiatric patients undergoing the psychosurgical operation of stereotactic subcaudate tractotomy were infused intravenously with either saline or L-tryptophan (15 mg/kg/h). Plasma, lumbar cerebrospinal fluid (CSF), ventricular CSF and a specimen of frontal cortex were collected. The relationships of plasma concentrations of substances claimed to influence brain tryptophan concentration (total tryptophan, free tryptophan, large neutral amino acids) with the concentration of tryptophan in the cortex and CSF were investigated. Tryptophan infusion resulted in plasma tryptophan values comparable to those found after oral doses used in treating depression or insomnia, and about sixfold increases of tryptophan in the cerebral cortex. Increased brain 5-hydroxytryptamine synthesis was indicated by significant rises of CSF 5-hydroxyindoleacetic acid. The concentration of plasma free tryptophan was a better predictor than plasma total tryptophan of cortex tryptophan concentration. As all correlation coefficients of plasma versus brain or plasma versus ventricular CSF tryptophan concentrations were decreased when allowance was made for differences of concentration of large neutral amino acids, the results suggest that the role of these substances within their physiological range as inhibitors of tryptophan transport to the brain may previously have been overemphasised.     

Determination of amino acids in human plasma by liquid chromatography with postcolumn ninhydrin derivatization using a hydroxyapatite cartridge for precolumn deproteination

Amino acids in human plasma were determined by liquid chromatography with postcolumn ninhydrin derivatization using a hydroxyapatite cartridge for precolumn deproteination. S-Carboxymethyl-l-cysteine, d-phenylglycine and S-aminoethyl-l-cysteine were found to be suitable internal standards. The proposed method is simple, rapid (deproteination time less than 1 min) and reproducible [relative standard deviation below 3% except for low-level aspartic acid (n = 3)]. The average recovery of 25 amino acids was above 90%. The elution time of amino acids in human plasma was approximately 2 h. Protein binding of tryptophan was also determined by the proposed method. The analytical data for amino acids in human plasma deproteinated using the proposed and published methods (5-sulphosalicylic acid and ethanol) were compared.     

Plasma amino acids and sports injuries

Summary. The aim of this study was to explore the relationship between changes in plasma amino acids and the incidence of sports injuries during a soccer season. Fourteen plasma amino acids were assayed at monthly intervals in 12 young soccer players during a whole soccer season. Based on the number and severity of injuries the soccer players were divided into an injury-prone and a non-injury-prone group. The mean plasma level of the amino acid glycine was significantly lower (P=0.009) in the injury-prone group than the other group, while the mean plasma levels of tyrosine, tryptophan and lysine were higher in the injury-prone group during this period (P<0.05). However there were no significant differences in the calculated plasma tryptophan and tyrosine/large neutral amino acids ratios. Significant linear time trends were observed for taurine, ornithine, lysine and the tryptophan/large neutral amino acids ratio.These results indicate that the plasma concentrations of glycine and to a lesser extent those of tyrosine, tryptophan and lysine may be promising peripheral markers for injury-proneness in young soccer players. Whether a role for glycine substitution will be indicative to reduce the occurrence of sports injuries will need to be investigated in future studies.     

Decrease in plasma tryptophan after a tryptophan-free amino acid solution. A comparison between cirrhotic and control subjects

In healthy subjects the administration of an amino acid mixture devoid of tryptophan causes a marked decrease of plasma tryptophan. This is because amino acid mixtures induce protein synthesis and tryptophan in blood is incorporated into newly synthesized proteins. We hypothesized that a tryptophan-free mixture could differently affect plasma tryptophan levels in subjects with an impaired protein synthesis such as chronic liver patients. We studied tryptophan levels after a tryptophan-free amino acid solution in controls and cirrhotics fasting 12 hours. Plasma total tryptophan fell to 91% of the initial level 60 minutes after the administration of the diet, to 71% after 120, and to 50% after 210' in controls. In cirrhotics the solution caused a decrease of plasma tryptophan that began significantly later than in controls, the delay being proportional to the severity of the disease. Cirrhotics were subdivided into two groups in accordance to the Pugh modification of the Child-Turcotte criteria. Total plasma tryptophan was 100% of base line levels after 60', 88% after 120', and 65% after 210' in less severe clinical condition; total plasma tryptophan was 102% of base line levels after 60', 98% after 120', and 75% after 210' in more severe clinical condition.     

Application of the Phenomenex EZ:faast™ amino acid analysis kit for rapid gas-chromatographic determination of concentrations of plasma tryptophan and its brain uptake competitors

The Phenomenex EZ:faast™ amino acid analysis kit is available for gas (GC) or liquid (LC) chromatographic analysis of amino acids (AA) using mass spectrometry (MS) and other GC detectors. We used it for rapid GC determination of plasma tryptophan, its brain uptake competitors (Val, Leu, Ile, Phe and Tyr) and many other amino acids. Based on solid-phase extraction, this fast method enables one person to process two plasma samples in 8–10 min and six samples in ∼15 min up to GC injection and a 7-min GC run per plasma sample. Using a Perkin-Elmer Clarus 500 GC, a Total Chrome software, a flame-ionisation detector (FID) and norvaline as internal standard, we used this method to analyse ∼1,000 plasma samples from normal subjects undergoing acute tryptophan depletion and loading tests. The limit of detection for most amino acids is 1 nmol/ml (1 μM) and in many cases less. With manual injection, coefficients of variation for the above six amino acids were 1.5–6.2% (intra-assay) and 3.8–9.7% (inter-assay). This simple, rapid and elegant method will be valuable to the amino acid analyst and researcher, as it can save much manpower time and meet urgent emergency requests and the demands of a high-throughput laboratory.     

Effect of Age on Variables Influencing the Supply of Tryptophan to the Brain

Abstract: The relations of plasma concentrations of substances claimed to influence brain tryptophan concentration (total tryptophan, free tryptophan, large neutral amino acids) with the concentrations of tryptophan, 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in the forebrain were investigated in rats of different ages (from 8 days to 16 months after birth). In brain, tryptophan fell by 46%, whereas 5-HT rose by 20% between 8 and 40/42 days after birth. Thereafter, the levels of both tryptophan and 5-HT remained essentially constant. Brain 5-HIAA showed a more complex pattern, rising by 63% between 8 and 19 days, falling between 19 and 40/42 days, and then gradually rising until values at 16 months were significantly higher than those at 40/42 days. In plasma, the concentrations of free fatty acids, free and total tryptophan, and large neutral amino acids all decreased between 8 and 19 days and thereafter either remained constant or increased slowly, the exception being total tryptophan values, which showed large increases between 28/30 and 60/70 days. Also, the unidirectional uptake of tryptophan from blood to brain was determined using a carotid artery injection technique. Uptake values obtained using a tracer concentration of tryptophan in the injection solution decreased progressively with age. Kinetic analysis of the data in terms of the Michaelis-Menten equation for carrier-mediated transport indicated significantly lower values for V_max and K_D (a component for nonsaturable transport) in 6-month-old rats as compared to 19-day-old suckling rats, whereas K_m values were the same at both ages. Detailed analysis of these results indicated that the age-related changes in brain tryptophan were largely explicable in terms of plasma free tryptophan in association with blood-brain transport characteristics; moderate differences in concentration of amino acids competing for transport were without apparent effect between 19 days and 16 months. The larger differences between 8 and 19 days after birth could be important.     

Brain Serotonin Content: Physiological Regulation by Plasma Neutral Amino Acids

When plasma tryptophan is elevated by the injection of tryptophan or insulin, or by the consumption of carbohydrates, brain tryptophan and serotonin also rise; however, when even larger elevations of plasma tryptophan are produced by the ingestion of protein-containing diets, brain tryptophan and serotonin do not change. The main determinant of brain tryptophan and serotonin concentrations does not appear to be plasma tryptophan alone, but the ratio of this amino acid to other plasma neutral amino acids (that is, tyrosine, phenylalanine, leucine, isoleucine, and valine) that compete with it for uptake into the brain.     

The metabolism of L-tryptophan by isolated rat liver cells. Effect of albumin binding and amino acid competition on oxidatin of tryptophan by tryptophan 2,3-dioxygenase.

1. Novel methods, using L-[ring-2-14C]tryptophan, are described for the measurement of tryptophan 2,3-dioxygenase activity and tryptophan accumulation in isolated rat liver cells. 2. The effects of bovine serum albumin, non-esterified fatty acids and neutral amino acids on tryptophan oxidation by hepatocytes and on the partition of tryptophan between free and albumin-bound forms were investigated. 3. Oxidation of physiological concentrations (0.1 mM) of tryptophan was inhibited by approx. 50% in the presence of 2% (w/v) bovine serum albumin; no effects were found at tryptophan concentrations of 0.5 mM and above. 4. Increases in free tryptophan concentrations produced by displacement of 0.1 mM-tryptophan from albumin-binding sites by palmitate resulted in increased flux through tryptophan dioxygenase. 5. Addition of a mixture of neutral amino acids, at plasma concentrations, to hepatocyte incubations had no effect on the rate of tryptophan oxidation. 6. It is concluded that alterations in free tryptophan concentrations consequent to changes in albumin binding may be an important factor in regulating tryptophan uptake and catabolism by the liver. The results are briefly discussed with reference to possible consequences on brain tryptophan metabolism.