Content Of Aromatic Amino Acids Research Articles

Nutritional composition of chickpea ( Cicer arietinum L.) as affected by microwave cooking and other traditional cooking methods

The effects of microwave cooking and other traditional cooking methods such as boiling and autoclaving on the nutritional composition and anti-nutritional factors of chickpeas ( Cicer arietinum L.) were studied. Cooking treatments caused significant ( P < 0.05 ) decreases in fat, total ash, carbohydrate fractions (reducing sugars, sucrose, raffinose and stachyose, while verbascose was completely eliminated after cooking treatments), antinutritional factors (trypsin inhibitor, haemagglutinin activity, tannins, saponins and phytic acid), minerals and B-vitamins. Cooking treatments decreased the concentrations of lysine, tryptophan, total aromatic and sulfur-containing amino acids. However, cooked chickpeas were still higher in lysine, isoleucine and total aromatic amino acid contents than the FAO/WHO reference. The losses in B-vitamins and minerals in chickpeas cooked by microwaving were smaller than those cooked by boiling and autoclaving. In-vitro protein digestibility, protein efficiency ratio and essential amino acid index were improved by all cooking treatments. The chemical score and limiting amino acid of chickpeas subjected to the various cooking treatments varied considerably, depending on the type of treatment. Based on these results, microwave cooking is recommended for chickpea preparation, not only for improving nutritional quality (by reducing the level of antinutritional and flatulence factors as well as increasing in-vitro protein digestibility and retention rates of both B-vitamins and minerals), but also for reducing cooking time.

Branched-Chain Amino Acids and Brain Function

Branched-chain amino acids (BCAAs) influence brain function by modifying large, neutral amino acid (LNAA) transport at the blood-brain barrier. Transport is shared by several LNAAs, notably the BCAAs and the aromatic amino acids (ArAAs), and is competitive. Consequently, when plasma BCAA concentrations rise, which can occur in response to food ingestion or BCAA administration, or with the onset of certain metabolic diseases (e.g., uncontrolled diabetes), brain BCAA concentrations rise, and ArAA concentrations decline. Such effects occur acutely and chronically. Such reductions in brain ArAA concentrations have functional consequences: biochemically, they reduce the synthesis and the release of neurotransmitters derived from ArAAs, notably serotonin (from tryptophan) and catecholamines (from tyrosine and phenylalanine). The functional effects of such neurochemical changes include altered hormonal function, blood pressure, and affective state. Although the BCAAs thus have biochemical and functional effects in the brain, few attempts have been made to characterize time-course or dose-response relations for such effects. And, no studies have attempted to identify levels of BCAA intake that might produce adverse effects on the brain. The only "model" of very high BCAA exposure is a very rare genetic disorder, maple syrup urine disease, a feature of which is substantial brain dysfunction but that probably cannot serve as a useful model for excessive BCAA intake by normal individuals. Given the known biochemical and functional effects of the BCAAs, it should be a straightforward exercise to design studies to assess dose-response relations for biochemical and functional effects and, in this context, to explore for adverse effect thresholds.

QSAR of Human Steroid 5α‐Reductase Inhibitors: Where are the differences between isoenzyme type 1 and 2?

AbstractQuantitative Structure Activity Relationships have been established for inhibitors of human steroid 5α‐reductase including 6‐azasteroids and non‐steroidal compounds. From the applied descriptors, those related to the molecular geometry, electronic properties, and the electrostatic surface were derived from semi‐empirical AM1 calculations. A chemical reaction as part of the inhibitory action is indicated by the presence of the ionization potential in the descriptor space. Strong similarities between the variables for the prediction of the binding affinity to the type 1 and IC50 values for the type 2 isoform of the 5α‐reductase were observed. The most pronounced differences in the linear regression QSAR equations were found for the descriptors accounting for the hydrogen‐bonding interaction, suggesting a different hydrogen‐bonding pattern in the binding pocket of both isoforms. Furthermore, the topological indices together with the surface related descriptors point towards a lower content of aromatic amino acids in the binding site of the type 2 isoenzyme. Consequences for the design of new inhibitors are discussed.

Peptides from milk protein hydrolysates to improve the growth of human keratinocytes in culture

Abstract Milk and colostrum are known to contain constituents having growth promoting activities on various human cell lines. Peptides from milk protein hydrolysates have also been shown to have various nutraceutical and biological properties. The aim of this research was to establish conditions for the in vitro hydrolysis of milk proteins and for the separation and identification of peptides that could promote growth of human skin cells in culture. Milk protein hydrolysates were obtained by using trypsin and chymotrypsin with various enzyme to substrate ratios (E/S) and degrees of hydrolysis (DH). Peptides contained in a 6% DH hydrolysate obtained with chymotrypsin were separated by size exclusion chromatography and supplemented in in vitro culture media to measure their efficacy to promote growth of keratinocytes isolated from human skin. The results indicated that growth promoting activity was increased up to 108% for keratinocytes cultured in medium supplemented with 300 μg mL −1 of one peptide fraction. Fifteen peptides isolated from this fraction by RP-HPLC and characterized by Pico-Tag amino acids analysis were shown to have an average molecular weight of 800 Da and to contain high concentrations of hydrophobic and aromatic amino acids.

Amino acid ratios in plasma and tissues in a rat model of liver cirrhosis before and after exercise

In human liver cirrhosis (LC), the Fischer ratio (branched-chain amino acid (BCAA)/aromatic amino acid (AAA)) is used as a marker of hepatic encephalopathy. Similarly, the plasma BCAA levels decrease while AAA levels increase in LC rats. However the BCAA and AAA ratio and the influence of exercise on this ratio remains to be clarified in various tissues of the LC rat model. Normal and LC rats received 2-weekly injections of olive oil or CCl 4 for 10 weeks, respectively, and half of the rats from each group were subjected to one time exercise on a treadmill. BCAA, AAA, glutamate (GLU) and glutamine (GLN) concentrations were measured in plasma, liver, brain, heart and skeletal muscles. Decreased BCAA and increased AAA concentrations in brain and heart were also observed in LC rats and these changes were significantly amplified by exercise. The Fischer ratio in the LC group with and without exercise was decreased in skeletal muscles, while it remained unchanged in the liver. Decreased GLU and increased GLN concentrations were shown in most LC samples following exercise. In conclusion, specific alterations of the amino acid patterns were observed in various tissues in the LC group. These alterations were further emphasized by exercise.

Chemical characterization of protein-like fluorophores in DOM in relation to aromatic amino acids

A systematic survey of the protein-like fluorescence intensities was conducted at 11 stations along the 137°E transect from bay to oceanic areas in the northwestern Pacific using three-dimensional excitation emission matrix (3DEEM) spectroscopy and the concentrations of aromatic amino acids obtained by high-performance liquid chromatography (HPLC) in dissolved organic matter (DOM). The 3DEEM patterns of tyrosine-like and tryptophan-like peaks in protein-like fluorophores were variable across different marine environments. The tyrosine-like peak was observed at all stations and depths, while the tryptophan-like peak was only distinguishable as a clear peak in bay and coastal surface waters. These distribution patterns were similar to those of actual concentrations of tyrosine and tryptophan in total hydrolyzable amino acids (THAA) in DOM. Consequently, the tyrosine- and tryptophan-like fluorescence intensities were interpreted to be correlated to the concentrations of tyrosine and tryptophan, respectively, indicating that tyrosine and tryptophan were responsible for the protein-like fluorescence intensities of DOM. The protein-like fluorescence intensities were also correlated to the concentrations of THAA, suggesting that the dynamics of aromatic amino acids were similar to those of THAA. In addition, protein-like fluorescence intensities may be useful indicators as to the dynamics of not only aromatic amino acids but of THAA in bulk DOM as well. Comparison of the tyrosine- and tryptophan-like fluorescence intensities with the concentrations of aromatic amino acids and THAA suggests that the dissolved amino acids were components of relatively small peptides and not protein molecules.

Cats Require More Dietary Phenylalanine or Tyrosine for Melanin Deposition in Hair than for Maximal Growth

In 1986, the NRC recommended a dietary concentration of 4.0 g/kg of phenylalanine and 8.5 g/kg of total aromatic amino acids for growing kittens on the basis of maximal growth rate and nitrogen balance. Black hair-coated cats were given purified diets containing the following phenylalanine + tyrosine (Phe + Tyr) concentrations (g/kg diet): 4 + 2, 4 + 4, 4 + 6, 4 + 8, 10 + 0, 10 + 2, 10 + 4, 10 + 6, 10 + 8, 10 + 10, 24 + 0 for at least 6 mo. All other amino acids were present at about twice the requirements. Total melanin and the oxidation product of eumelanin, pyrrole-2,3,5-tricarboxylic acid (PTCA) were measured in hair. There was a significant linear relationship between the concentrations of tyrosine in plasma and PTCA in hair. The relationship between PTCA concentration in hair and Phe + Tyr in the diet had a point of inflection at approximately 16 g/kg Phe + Tyr. Cats fed diets with <16 g Phe + Tyr developed "red hair." We confirmed the anecdotal reports that the black hair of cats can change from black to reddish brown. An aromatic amino acid concentration > or =18 g/kg is recommended for the prevention of visually discernible red hair in black-coated cats. Dietary concentrations >18 g total aromatic amino acids/kg diet promote a greater ratio of PTCA:total melanin in hair. We are unaware of a secondary nutrient requirement being so much greater than the requirement for growth.

Nutritional composition and antinutritional factors of chickpeas (Cicer arietinum L.) undergoing different cooking methods and germination.

The effects of cooking treatments (boiling, autoclaving and microwave cooking) and germination on the nutritional composition and antinutritional factors of chickpeas were studied. Cooking treatments and/or germination caused significant (p < 0.05) decreases in fat, total ash, carbohydrate fractions, antinutritional factors, minerals and B-vitamins. Germination was less effective than cooking treatments in reducing trypsin inhibitor, hemagglutinin activity, tannins and saponins; it was more effective in reducing phytic acid, stachyose and raffinose. Cooking treatments and germination decreased the concentrations of lysine, tryptophan, total aromatic and sulfur-containing amino acids. However, cooked and germinated chickpeas were still higher in lysine, isoleucine and total aromatic amino acid contents than the FAO/WHO reference. The losses in B-vitamins and minerals in chickpeas cooked by microwaving were smaller than in those cooked by boiling and autoclaving. Germination resulted in greater retention of all minerals and B-vitamins compared to cooking treatments. In vitro protein digestibility, protein efficiency ratio and essential amino acid index were improved by all treatments. The chemical score and limiting amino acid of chickpeas subjected to the various treatments varied considerably, depending on the type of treatment. Based on these results, microwave cooking appears to be the best alternative for legume preparation in households and restaurants.

Female-specific expression of a hexamerin gene in larvae of an autogenous mosquito.

Fourth-instar larvae of the autogenous mosquito, Aedes atropalpus, synthesize three hexamerins or hexameric storage proteins which are distinguished by different methionine and aromatic amino-acid contents. One protein, Hexamerin-1.2 (AatHex-1.2) is only found in female larvae and pupae. In order to investigate the molecular basis for this sex-specific accumulation, we have cloned and sequenced the cDNA encoding AatHex-1.2 and isolated and sequenced over 1 kb of the 5' flanking region of the AatHex-1.2 gene. The AatHex-1.2 transcript encodes a 81.6-kDa hexamerin subunit which contains 19.8% phenylalanine, tyrosine and tryptophan and 8.6% methionine residues. The single-copy AatHex-1.2 gene consists of three exons and two small introns located at its 5' end. A 2.3-kb AatHex-1.2 mRNA accumulates only in female larvae and pupae and is expressed at very low levels in adult female mosquitoes. The temporal expression profile of this transcript is typical of other mosquito hexamerin genes, with rapid disappearance of the mRNA shortly after pupation. Hence this is the first observation of exclusively female-specific gene activity during preadult development of an insect. In the 5' flanking region of the AatHex-1.2 gene, we identified putative binding sites for transcription factors, such as GATA, C/EBP and Doublesex, typically involved in fat body- and female-specific gene activity in Diptera. These findings suggest that mechanisms for sex-specific transcription in the fat body may be well conserved between flies and mosquitoes.

Spectrophotometric and Colorimetric Determination of Protein Concentration

AbstractSpectrophotometric and Colorimetric Determination of Protein Concentration (Michael H. Simonian, Beckman‐Coulter, Inc., Fullerton, California, and John A. Smith, University of Alabama at Birmingham, Birmingham, Alabama). Measuring absorbance at 280 nm (A280) is one of the oldest methods for determining protein concentration. This method is still widely used because it is simple and does not require incubating the sample with exogenous chromophores. Accordingly, the quantitation of proteins by peptide bond absorption at 205 nm (A205) is more universally applicable. Furthermore, the absorptivity for a given protein at 205 nm is several‐fold greater than that at 280 nm. Thus, lower concentrations of protein can be quantitated with the A205 method. The disadvantage of this method is that some buffers and other components absorb at 205 nm. The aromatic amino acids also exhibit fluorescence emissions when excited by light in the UV range. Measurement of intrinsic fluorescence by aromatic amino acids is primarily used to obtain qualitative information. However, with a protein standard whose aromatic amino acid content is similar to that of the sample, intrinsic fluorescence can be used for quantitation. The most frequently employed colorimetric methods for determining protein concentration are those of Bradford and Lowry.

Local expression and distribution of a storage protein in the ovary of Hyphantria cunea.

Storage protein-1 (HcSP-1) is a major storage protein found in the hemolymph and fat body of Hyphantria cunea. HcSP-1 has a high methionine (6.0%) and low aromatic amino acid content (8.5%) (Cheon et al., 1998). In this study, the accumulation and expression of HcSP-1 in ovary was investigated using biochemical and immunocytochemical methods. HcSP-1 was detected in the ovaries in 6-day-old pupae and accumulated toward the end of pupal life, when HcSP-1 transcripts were detectable by Northern blot analysis and RT-PCR. In situ hybridization showed that the HcSP-1 mRNA was located in the nurse cells and follicular epithelial cells, but not in the oocyte. Though most of the HcSP-1 that is incorporated in the yolk bodies of the oocyte is probably sequestered from the surrounding hemolymph, HcSP-1 is an important yolk protein contributing to early yolk body formation before the development of patency by the follicular epithelium.

Streptokinase Triggers Conformational Activation of Plasminogen through Specific Interactions of the Amino-terminal Sequence and Stabilizes the Active Zymogen Conformation

Cleavage of Arg(561)-Val(562) in plasminogen (Pg) generates plasmin (Pm) through a classical activation mechanism triggered by an insertion of the new amino terminus into a binding pocket in the Pg catalytic domain. Streptokinase (SK) circumvents this process and activates Pg through a unique nonproteolytic mechanism postulated to be initiated by the intrusion of Ile(1) of SK in place of Val(562). This hypothesis was evaluated in equilibrium binding and kinetic studies of Pg activation with an SK mutant lacking Ile(1) (SK(2--414)). SK(2--414) retained the affinity of native SK for fluorescein-labeled [Lys]Pg and [Lys]Pm but induced no detectable conformational activation of Pg. The activity of SK(2--414) was partially restored by the peptides SK(1--2), SK(1--5), SK(1--10), and SK(1--15), whereas Pg(562--569) peptides were much less effective. Active site-specific fluorescence labeling demonstrated directly that the active catalytic site was formed on the Pg zymogen by the combination of SK(1--10) and SK(2--414), whereas sequence-scrambled SK(1-10) was inactive. The characterization of SK(1--10) containing single Ala substitutions demonstrated the sequence specificity of the interaction. SK(1--10) did not restore activity to the further truncated mutant SK(55-414), which was correlated with the loss of binding affinity of SK(55--414) for labeled [Lys]Pm but not for [Lys]Pg. The studies support a mechanism for conformational activation in which the insertion of Ile(1) of SK into the Pg amino-terminal binding cleft occurs through sequence-specific interactions of the first 10 SK residues. This event and the preferentially higher affinity of SK(2--414) for the activated proteinase domain of Pm are thought to function cooperatively to trigger the conformational change and stabilize the active zymogen conformation.

Severe hepatitis treated with an artificial liver support system

We designed an artificial liver support system (ALSS) including plasma exchange, charcoal hemoperfusion, plasma bilirubin absorption, charcoal plasma perfusion, hemofiltration and hemodialysis. We chose different methods or their combinations according to the patient's conditions. We investigated the effect of ALSS in 154 patients with severe hepatitis, 72 of whom survived. All data were analyzed by SPSS. The effectiveness of ALSS treatment was compared at different stages (i.e. early, middle and end stages). After each ALSS treatment, the liver function of these patients greatly improved, serum endotoxin and HBV-DNA concentrations were significantly decreased, and the serum concentration of aromatic amino acids (AAA) such as methionine decreased while BCAA/AAA ratio increased. Patients treated with ALSS in the early or middle stages of disease had much higher survival rates than patients in the end stage of disease. Thus, we concluded that ALSS is a reliable therapy for advanced liver diseases and treatment in early or middle stages is appropriate.

SUITABILITY OF ANIMALS' PURIFIED MILK CASEINS AND THEIR SUBUNIT κ−CASEINS AS SUBSTRATES FOR SUBTILISIN AND TRYPSIN

Acid casein and κ-casein were purified from different species of animal's milk, such as cow, sheep, goat, and water buffalo. These caseins were used as substrates for commercially available subtilisin and trypsin. It was established that, when acid caseins were used as a substrate for subtilisin, cow acid casein was found to be a better substrate for the enzymes, compared to other animals' milk casein. It was suggested that this acid casein has significantly more aromatic amino acids, as compared to arginine and lysine. KM and Vmax values, which were obtained for cow κ-casein, showed that cow κ-casein was a better susbstrate for trypsin than the others, suggesting that cow κ-casein has a rich content of lysine, arginine, and aromatic amino acids by comparison with the others. The calculated C/N ratio also supports this suggestion.

NMR spectroscopy based metabonomic studies on the comparative biochemistry of the kidney and urine of the bank vole ( Clethrionomys glareolus), wood mouse ( Apodemus sylvaticus), white toothed shrew ( Crocidura suaveolens) and the laboratory rat

The metabolic profiles of three wild mammals that vary in their trophic strategies, the herbivorous bank vole ( Clethrionomys glareolus), the granivorous wood mouse ( Apodemus sylvaticus), and the insectivorous white-toothed shrew ( Crocidura suaveolens), were compared with that of a widely used strain of laboratory rat (Sprague Dawley). In conjunction with NMR spectroscopic investigations into the urine and blood plasma composition for these mammals, high resolution magic angle spinning (HRMAS) 1H-nuclear magnetic resonance (NMR) spectroscopy was applied to investigate the composition of intact kidney samples. Adaptation to natural diet affects both renal metabolism and urinary profiles, and while these techniques have been used to study the metabolism of the laboratory rat little is known about wild small mammals. The species were readily separated by their urinary profiles using either crude metabolite ratios or statistical pattern recognition. Bank vole urine contained higher concentrations of aromatic amino acids compared with the other small mammals, while the laboratory rats produced relatively more hippurate. HRMAS 1H-NMR demonstrated striking differences in both lipid concentration and composition between the wild mammals and Sprague Dawley rats. Bank voles contained high concentrations of the aromatic amino acids phenylalanine, tyrosine and tryptophan in all tissue and biofluids studied. This study demonstrates the analytical power of combined NMR techniques for the study of inter-species metabolism and further demonstrates that metabolic data acquired on laboratory animals cannot be extended to wild species.

Degradation of Latex and of Natural Rubber by Streptomyces Strain La 7

Streptomyces strain La 7 was isolated from the banquete of a city high way in Karlsruhe. According to partial 16S rRNA gene sequencing it was identical with Streptomyces albogriseolus and Streptomyces viridodiastaticus. DNA-DNA-similarity studies revealed 80.3-82.4% similarity between each of two of the three strains. Although phylogenetically closely related, Streptomyces strain La 7 differed from the two reference strains by morphological as well as physiological features and might represent a new species aside of S. albogriseolus and S. viridodiastaticus. The new Streptomyces strain La 7 was grown in a medium containing a latex emulsion or squares of natural rubber gloves as the only carbon source. On agar plates with a latex overlay agar, translucent halo formation around the colonies was observed. The unvulcanized latex was metabolized and the carbon from the isoprene units was apparently used for cell growth. In shake cultures with unlimited oxygen supply, during 60 days of incubation, 140 mg of the 175 mg totally emulgated latex were degraded exponentially. In sterile control flasks about 3% of the initial amount of latex could not be recovered after incubation on a shaker, presumably due to photochemical transformation. During static incubation of sterile medium, the latex formed a sticky layer at the surface of the medium and on the glass walls and recovery of the material was more difficult. Estimation of the protein content of cells from total nitrogen resulted in about 50% of the degraded latex being incorporated into cells, if a standard cell composition was assumed. Direct protein analysis according to Bradford (1976) gave much lower estimates, presumably due to a low content of aromatic amino acids. Stripes of natural rubber were degraded by Streptomyces strain La 7 during 70 days to an extent of about 30%. Scanning electron microscopy demonstrated, that hyphes of Streptomyces strain La 7 colonized and penetrated the latex surface with a concomitant deterioration of the latex material.

Metabolism of Tryptophan in the Liver: Interference with Decarboxylation of Other Aromatic Amino Acids

Decarboxylation of aromatic amino acid in mammalian tissues is catalyzed by aromatic amino acid decarboxylase (EC. 4.1.1.28, AAD). The enzyme differs in its affinity to individual aromatic amino acids, the best substrates being 3,4-dihydroxyphenylalanine (dopa) and 5-hydroxytroptophan. Surprisingly, AAD is abundant in the liver, where the substrates with rather low affinity to AAD as tryptophan, phenylalanine, and tyrosine are offered to decarboxylation. In the present paper, the possibility of interference of tryptophan with decarboxylation of phenylalanine, tyrosine as well as dopa in the liver was investigated. The AAD activity was measured radiometrically with 1-14C-labeled aromatic amino acid substrates using the rat liver enzyme. The influence of tryptophan on decarboxylation of tyrosine was formally competitive with Ki = 9.2 x 10(-3) M, while the inhibition of decarboxylation of phenylalanine by tryptophan was non-competitive with Ki at 2.75 x 10(-2) M. The effect of tryptophan on decarboxylation of dopa was small and it could not be expressed in terms of inhibition kinetics and inhibition constant. At physiological concentrations of aromatic amino acids in plasma, tryptophan does not seem to have remarkable effects on decarboxylation of phenylalanine, tyrosine, and dopa in the liver.

Molecular cloning and expression of two hexamerin cDNAs from the mosquito, Aedes aegypti.

Fourth-instar larvae of Aedes aegypti synthesize two types of hexamerins, Hexamerin-1 (AaHex-1) and Hexamerin-2 (AaHex-2), whose subunits are distinguished by different methionine and aromatic amino acid contents. In early female pupae only the methionine-rich AaHex-1gamma subunit accumulates to two-fold higher levels than in males. To investigate the relationship between hexamerin structure and the roles of Hex-1 and Hex-2 during mosquito development and reproduction, we have cloned and sequenced cDNAs encoding the AaHex-2alpha, -2beta and AaHex-1gamma subunits. Comparison with other insect hexamerins revealed that the Aedes Hex-1 and Hex-2 proteins belong, respectively, to the two hexamerin subfamilies previously defined for brachyceran Diptera. Probes specific for the Hex-2alpha and Hex-1gamma transcripts showed that expression of both genes follows the same developmental timetable. However, greater Hex-1gamma mRNA accumulation may contribute to the higher levels of Hex-1 gamma protein in early female pupae.

Relationships between phenylalanine hydroxylation and plasma aromatic amino acid concentrations in humans

We investigated the relationships between phenylalanine hydroxylation (Phe Hy) and plasma concentrations of phenylalanine, tyrosine, and glucagon in healthy male volunteers (N = 13; age, 29 ± 3 years). Phe Hy, as well as the Phe and Tyr rate of appearance (Ra), were measured during l-[ 2H 5]-Phe and l-[ 2H 2]-Tyr continuous intravenous (IV) infusions both under basal postabsorptive conditions (N = 13) and following divergent changes of plasma aromatic amino acids (AAA) concentrations. Namely, AAA were increased by administration of a balanced synthetic mixed meal (n = 6) or selectively decreased by IV infusion of insulin along with a Phe-deficient, Tyr and tryptophan—deprived amino acid mixture ([IAA] n = 7). Following the meal, plasma Phe (54 ± 3 to 81 ± 12 μmol/L), plasma Tyr (54 ± 4 to 91 ± 7), Phe Hy (0.09 ± 0.01 to 0.15 ± 0.02 μmol/kg · min), Phe Ra (0.65 ± 0.04 to 0.96 ± 0.07), and Tyr Ra (0.51 ± 0.03 to 0.93 ± 0.11) all significantly increased ( P ≤ .05 v basal). IAA infusion significantly decreased plasma Phe (to 47 ± 3 μmol/L), plasma Tyr (to 25 ± 4), Phe Hy (to 0.07 ± 0.004 μmol/kg · min), and Tyr Ra (to 0.29 ± 0.02; all P ≤ .05 v basal), while Phe Ra did not change (0.64 ± 0.04, NS). Plasma glucagon did not change in the three experimental periods (basal, 85 ± 7; meal, 72 ± 10; IAA, 92 ± 14 pg/mL; NS). Using linear regression analysis, plasma Phe was positively related to both Phe Hy ( R 2 = .76, P < .001) and plasma Tyr ( R 2 = .80, P < .001); Phe Hy and plasma Tyr were also significantly correlated ( R 2 = .60, P < .001). No correlation was found between Phe Hy and basal plasma glucagon ( R 2 = .04, NS). Using multiple regression analysis with plasma Tyr as the dependent variable, plasma Phe was still correlation with plasma Tyr ( t = 4.29, P = .0002), while the relationship between Phe Hy and plasma Tyr was no longer significant ( t = 0.69, P = .49). These data indicate that plasma Phe is closely associated with its own hydroxylative disposal in humans, and confirm that Phe conversion to Tyr may play a physiological role in maintaining balanced plasma phenylalanine and tyrosine concentrations.

The Effects of Branched Chain Amino Acid Infusion on Pain Perception and Plasma Concentrations of Monoamines

KIRVELÄ, O. A., J. JAATINEN, H. SCHEININ AND J. KANTO. The effects of branched chain amino acid infusion on pain perception and plasma concentrations of monoamines in healthy volunteers. PHARMACOL BIOCHEM BEHAV 60(1) 77–82, 1998.—Infusions of branched chain amino acids (BCAA) have been shown to have several CNS-mediated effects including antinociceptive action. We investigated the effects of BCAA infusion on pain perception, respiratory control, and plasma monoamine concentrations. Six healthy female volunteers were given in a double-blind, random, crossover design an 8-h infusion (1.75 ml/kg/h) of either (a) Ringers lactate, (b) conventional 4% amino acid solution, or (c) 4% BCAA solution with intervals of at least 48 h. Respiratory control was evaluated with continuous capnography. Pain perception was measured using dental dolorimetry for sharp pain, and pain transmitted by afferent C-fibers was evaluated with tourniquet test. Changes in vigilance were measured using critical flicker fusion technique. Evaluations were made for baseline, and after 2.5, 5, and 8 h. Plasma samples were collected at the same time points for amino acid and monoamine analysis. BCAA infusion resulted in significant increases of plasma concentrations of all BCAAs, with a simultaneous decrease in concentrations of aromatic amino acids. Of the measured monoamines and their metabolites dihydroxyphenylacetic acid (DOPAC) decreased, showing significant treatment effect for BCAA. Despite these changes no significant effect of BCAAs on respiratory control, vigilance, or pain perception was observed. In conclusion, despite significant changes in plasma concentrations of both amino acids and DOPAC, BCAA infusion did not show any clinically relevant antinociceptive effect.