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PubMed1978

Effects of proteins and their corresponding amino acid mixtures on nitrogen balance and body composition in the growing rat.

The efficiencies of nitrogen utilization from intact proteins (casein, gluten, soybean, egg albumin) were compared to that of the respective synthetic amino acid mixtures. Food intake, growth, NER (nitrogen efficiency ratio), (Nitrogen retained/Nitrogen intake) X 100, BV (biological value), TD (true digestibility), liver weight and body composition were estimated on growing rats. Rats fed amino acid mixtures simulating casein, egg albumin and soybean consumed more food and showed more rapid growth than rats fed the intact proteins. Differences in nitrogen utilization and body composition were occasionally observed between the respective intact protein and amino acid mixtures but were in most cases not significant. It is concluded that nutrition with intact proteins cannot be assumed to be equivalent to nutrition with the corresponding amino acid mixture. However, general differences between the two types of feeding regimens were not obvious since the results were influenced by factors such as the amino acid composition of the protein and the amino acid mixture as well as the methodology used for nutritional evaluation. (Nitrogen retained/Nitrogen intake) X 100 and BV but not NER of an amino acid mixture formulated according to a commercial elementary diet was found to be low compared to casein.

Amino Acids↗
PubMed1994

Dependence of the utilization of a phenylalanine-free amino acid mixture on different amounts of single dose ingested. A case report.

For patients with phenylketonuria the daily ingested phenylalanine-free amino acid mixture is the most important source of nitrogen. It is recommended to ingest one third of the total amount combined with main meals. Some patients, especially the older ones, do not follow this recommendation; they ingest the entire daily amount of amino acid mixture in one portion. This intake mode leads to an increased oxidative utilization of the amino acids. To set up an example for this metabolic phenomenon, a 13C-leucine breath test was performed in one female phenylketonuric patient. She ingested a third of her daily amount of the amino acid mixture combined with an oral tracer of 3 mg 13C-leucine/kg body weight at breakfast. The breath test was carried out by a standardized time schedule over 5 h. Three days later the breath test was repeated when she ingested the total amount of amino acid mixture in only one portion at breakfast. Total daily caloric intake and food composition were not changed. On both days a 24 h urine was collected to determine total nitrogen loss. The 13C-content of expired air was analysed by gas isotope ratio mass spectrometry, the total nitrogen content was determined using a combustion unit. The 13C-elimination rate as a percentage of the applied 13C-tracer was 9.5% on the first test day as compared to 19.6% on the 2nd day. The corresponding total nitrogen excretion was increased (4.3-6.9 g/24 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1974

Design and evaluation by nitrogen balance and blood aminograms of an amino acid mixture for total parenteral nutrition of adults with gastrointestinal disease.

This study was undertaken to assess the efficacy of an amino acid mixture formulated for intravenous use from estimates of requirements for essential amino acids of human adults, and from data previously derived from a study using casein hydrolysate as the amino acid source. This mixture contained 39.4% essential amino acids, with glycine, alanine, arginine, histidine, and proline selected to supply the nonessential nitrogen. Nitrogen balance and blood aminograms were measured in six adult patients with gastrointestinal disease, fed intravenously for 1 wk at each of three levels of amino acid intake, while all other nutrients were constant and adequate in relation to body weight. Four of the patients were then fed 1.0 g/kg of egg or meat protein orally for 1 wk at the end of the 3 wk study, while all nutrients other than the amino acids were fed intravenously. Average nitrogen balances of -0.8, 0.5, and 2.2 g/day were observed when the amounts of amino acids infused were 0.25, 0.5, and 1.0 g/kg, respectively. Fasting levels of threonine, glycine, cystine, methionine, isoleucine, tryptophan, and arginine, but not of the other amino acids, increased with the increment in input, although the levels were generally lower than normal. The increase in blood concentration observed during infusion was similar for each of the essential amino acids, indicating that the supply of each of the amino acids was much better balanced for utilization than casein hydrolysate. However the blood aminograms did suggest that some changes in composition of the mixture for the malnourished adult were desirable, such that the amino acid mixture resembled that needed by the normal growing child. Nitrogen balance in the four patients fed orally with high-quality protein averaged 2.0 g/day, showing that an amino acid mixture given intravenously, provided it is well-balanced, can be utilized as efficiently as protein given orally. It is concluded that the prediction of oral requirements for amino acids should be combined with observations on changes in blood aminograms during infusion over a range of amino acid input in the development of amino acid mixtures for intravenous feeding.

Adult↗
PubMed1984

[Absorption of enzymatic protein hydrolysates and equimolar amino acid mixtures in the perfused small intestine of the rat].

Casein, wheat gluten or field-bean protein isolate (vicia faba) was hydrolyzed enzymatically by trypsin or thermitase (proteinase from Thermoactinomyces vulgaris). The degree of splitting of the protein peptide bounds was, resp., 18% or 30% for casein, 8% or 30% for wheat gluten and 16% or 29% for the field-bean protein isolate. The peptide pattern of the protein hydrolysates was measured by gel chromatography. The absorption of the enzymatic protein hydrolysates was compared with the absorption of the equimolar mixtures of free amino acids by perfusion of the distal or proximal part of the small intestine of nonanaesthesized rats. The absorption was measured on the basis of the amino acid disappearance from the perfused part of the small intestine and expressed as absorption of the total amino acids, of each single amino acid and as coefficient of variation of amino acid absorption. There are no differences in the total amino acid absorption of the tryptic casein hydrolysate and the three thermitatic protein hydrolysates compared with their corresponding mixtures of free amino acids. The absorption is decreased in case of larger oligopeptides. Their preceding mucosal hydrolysis is slower than the absorption of the splitting products. This is true for tryptic hydrolysates of wheat gluten and field-bean protein. The absorption patterns of the single amino acids are different for protein hydrolysates compared with their equimolar mixtures of amino acids in case of a same total absorption, too. The coefficient of variation is low (more equal amino acid absorption) in hydrolysates consisting of a homogeneous mixture of low molecular weight peptides. It is more increased in mixtures of free amino acids or in hydrolysates containing longer-chain peptides.

Animals↗
PubMed1984

Biliary steroid excretion in rats fed soybean protein and casein or their amino acid mixtures.

Male Wistar rats were fed 1% fat, cholesterol-free semipurified diets containing soybean protein isolate and casein or amino acid mixtures simulating these proteins for 28-30 days. The animals then underwent surgery for biliary diversion, and bile was collected for 2 hours. The rate of bile flow was not influenced by the type of dietary protein. The concentration and output of biliary cholesterol in rats fed soybean protein were significantly higher than in those fed casein, while biliary bile acid excretion was comparable. The group given the soy protein-type amino acid mixture also tended to excrete more biliary cholesterol relative to the casein-type amino acid mixture, although the difference was not significant, while biliary bile acid output was comparable. When 5% fat diets containing 0.5% cholesterol were given to rats, concentrations of both biliary cholesterol and bile acid were elevated significantly on a vegetable protein diet. In these experiments, there was a significant negative correlation between serum cholesterol and biliary cholesterol levels. Stimulation of the biliary excretion of cholesterol seems at least relevant to the cholesterol-lowering action of soybean protein.

Amino Acids↗
PubMedDate not supplied

[Pancreatic exocrine secretion to the introduction into the blood of amino acid mixtures of varying composition].

Tests conducted on dogs with a fistula of the pancreatic duct evidenced that various amino acids mixtures containing all the essential amino acids and differing mainly in the replaceable nitrogen dissimilarly act on the external secretion of the pancreas after their introduction into the blood. The most intensive secretion produces a mixture in which the replaceable nitrogen is represented by glycine alone. The mixture, one of its constituent is one of the dicarboxylic acids (glutamic) very poorly stimulates this function. At the same time, the action of all the studied amino acids mixtures is less pronounced than is the effect of the caseine hydrolysate. The commercial agent aminofusin L-600, containing all the essential amino acids with addition of polyols (xylitol and sorbitol) with no dicarboxylic amino acids in its composition, produces an intensive pancreatic secretion close to that caused by the caseine hydrolysate.

Amino Acids↗
PubMed2003

Effect of a selected amino acid mixture on the recovery from muscle fatigue during and after eccentric contraction exercise training.

The effect of an amino acid mixture on the recovery from muscle fatigue after eccentric exercise (ECEX) training was examined in twenty-two male college students. The administration of 5.6 g of the amino acid mixture twice daily resulted faster recovery of muscle strength than that with a placebo. The oral administration of the amino acid mixture was proved to effective for muscle strength recovery after the eccentric exercise.

Administration, Oral↗
PubMed1980

A comparison of the gastrointestinal tract in germ-free and conventional mice fed an amino acid mixture or purified whole-egg protein.

An amino acid mixture diet(AA) simulated with purified whole-egg protein and a purified whole-egg protein diet(WE) were given to ICR strain male germ-free(GF) and conventional(CV) mice for three weeks from five to eight weeks of age. All mice were killed at eight weeks of age and the gastrointestinal tracts were removed. The lengths of the small intestine were measured and six parts, i.e., the stomach; upper, middle and lower parts of the small intestine; cecum; and colon and rectum were separated, and each part (with contents) was weighed immediately. The contents were removed from each part by washing with distilled water. For the gut without contents, only total nitrogen(TN) was estimated and for the gut contents, TN, protein nitrogen(PN) and water-insoluble nitrogen(WIN) were estimated. The fresh weight of cecum with contents per 100 g of body weight of GF mice fed on AA diet, 2.07 +/- 0.11 g (mean +/- SE), was lighter than that of GF mice fed on WE diet, which was 4.51 +/- 0.28 g. The weight and length of the small intestine of AA diet groups were smaller than those of WE diet group. TN and PN(mg) in whole gut contents per 100 g of body weight in the WE diet group were higher than those in the AA diet group and high TN and PN were observed in GF mice. The PN per TN and WIN per PN of gut contents were affected more by the presence of the flora than by the difference in diets, and CV mice showed high values. The TN of the intestinal tract excluding contents showed no differences in GF and CV mice fed on either diet.

Amino Acids↗
PubMed1989

[Procedure for calculating various parameters of the metabolism of amino acid mixtures].

For the evaluation of indirect calorimetry, elements are used, which specify the relation between nitrogen (N) excretion and amount of oxidized amino acids (AS/N) and between nitrogen excretion and oxygen-/carbon dioxide-exchange of the corresponding amounts of amino acids (O2/N, CO2/N). These elements are only valid for the amino acid mixture which was used for their determination, and only under the condition of complete combustion of deaminized amino acid skeletons. We developed a computer program, which is able to simulate complete oxidation, maximal gluconeogenesis, and maximal lipogenesis for a given amino acid mixture of any composition. The parameters AS/N, O2/N and CO2/N were calculated by the program for various parenteral amino acid solutions. Range of error was determined exemplarily for the use of standard parameters. The calculations demonstrate errors up to 50% for the calculation of substrate turnover in indirect calorimetry, depending on composition and actual metabolism of amino acid mixtures. As long as these influencing factors are not known in stress metabolism, we recommend to use those elements, which were calculated for the amino acid solution in use, assuming complete combustion.

Amino Acids↗
PubMed1975

Induction of multiple forms of tyrosine aminotransferase by amino acid mixtures of different compositions.

Hepatic tyrosine aminotransferase (EC 2.6.1.5) was induced in rats by intubation of amino acid mixtures (complete or tryptophan-free). Enzyme activity was increased 4-fold by the complete mixture and 8-fold by the tryptophan-free mixture. The enzyme was analyzed by chromatography on CM-Sephadex. Chromatographic patterns were characteristic of the type of inducer rather than of the chronology of the induction cycle: after induction by the complete amino acid mixture the three forms of the enzyme were equally increased whereas after induction by the tryptophan-free mixture Form I was preferentially increased.

Amino Acids↗
PubMed1997

Growth hormone release induced by an amino acid mixture from primary cultured anterior pituitary cells of goats.

The effects of amino acids on growth hormone (GH) release and cytosolic calcium concentration ([Ca2+]i) were investigated in caprine anterior pituitary cells cultured for 3 d in Dulbecco modified Eagle medium. The addition of an amino acid mixture consisting of seven nonessential amino acids (NEAA: L-Asp, Gly, L-Ala, L-Ser, L-Pro, L-Asn, and L-Glu; concentration of each 12.5-200 mumol/l) in the medium significantly raised GH release from the cultured cells in a concentration-dependent manner with the maximum release at 200 mumol/l NEAA. Although an addition of L-Asp (0.1-100 mumol/l) caused a significant rise in GH release in a concentration-dependent manner, neither the individual amino acids contained in NEAA except L-Asp nor others (L-Leu, L-Phe, L-Gln, L-Met, and L-Arg) caused a rise in GH release when added alone to the medium. The rise in GH release induced by NEAA (200 mumol/l) and GH-releasing hormone (GHRH, 10 nmol/l) was significantly reduced by the addition of EGTA (1.8 mmol/l) and nifedipine (1 mumol/l) to the medium, respectively. The addition of NEAA (200 mumol/l) caused a rapid and transient [Ca2+]i increase, followed thereafter by a steady increase. The prior addition of nifedipine (1 mumol/l), which itself significantly reduced the basal [Ca2+]i, completely abolished the response induced by NEAA or GHRH. From these findings, we conclude that: 1) NEAA raises GH release and [Ca2+]i in cultured caprine anterior pituitary cells, and 2) Ca2+ influx from the medium may be responsible for the cellular action of NEAA.

Amino Acids↗
PubMed2004

Tyrosine-free amino acid mixture attenuates amphetamine-induced displacement of [11C]raclopride in striatum in vivo: a rat PET study.

Previous neurochemical and behavioural studies show that tyrosine depletion using a nutritionally balanced tyrosine-free amino acid mixture attenuates the dopamine-releasing and psychostimulant properties of amphetamine. Here we investigate the effect of a tyrosine-free amino acid mixture on striatal binding of [(11)C]raclopride, and amphetamine-induced [(11)C]raclopride displacement, using positron emission tomography in the rat. Rats were scanned for 60 min after an i.v. injection of approximately 11 MBq [(11)C]raclopride using a quad-HIDAC system. Amphetamine (2 mg/kg i.p., 30 min prior to scan) caused a 12% reduction in [(11)C]raclopride distribution volume ratio (DVR) compared to saline-injected controls. The tyrosine-free amino acid mixture (1 g/kg i.p.) caused a small (+7%) but statistically insignificant increase in [(11)C]raclopride DVR and attenuated, although it did not fully block, the amphetamine-induced reduction. These data are in keeping with previous neurochemical, immunocytochemical, and behavioural studies showing that tyrosine-free amino acid mixtures reduce dopamine function and offer promise for future PET studies testing the effect of tyrosine-depleting paradigms on dopamine release in humans.

Amino Acids↗
PubMed1992

[The clinical implications of the use of an amino acid mixture without tryptophan in liver cirrhosis].

The ingestion of an amino acid mixture lacking tryptophan causes a rapid fall of plasma tryptophan in healthy subjects. This is because amino acids elicit protein synthesis and endogenous tryptophan is incorporated into new proteins. If protein synthesis is the mechanism through which tryptophan-free solution decrease blood tryptophan, it may be interesting to study tryptophan levels after a tryptophan-free mixture in subjects with impaired protein synthesis. In the present paper we show that in 27 cirrhotics the administration of a tryptophan-free solution caused a fall of total plasma tryptophan that began significantly later than in 14 control subjects, the delay being significantly proportional to the severity of the disease. The difference between control and cirrhotic subjects was due to the bound fraction of plasma tryptophan. The diagnostic and clinical usefulness of our findings are discussed.

Amino Acids↗
PubMed1993

Comparative effect of proteins, peptides, and amino acid mixtures on recovery from 70% hepatectomy in rats.

The effects of proteins, peptides, and amino acid mixtures on the recovery from 70% hepatectomy were compared in rats. In Experiment 1, the most suitable time for the comparison was studied. Rats weighing 250 g after 70% hepatectomy were fed 20% casein diet. On day 0,1,2,3,4,6,8,11,15 post-operation, 3-5 rats were killed for the observation of recovery. The recovery time, evaluated by daily food intake, body weight gain, liver weight and compositions, and hematologic values was about 10 days. For the comparison of different nitrogen sources, we estimated that the 6th day after the operation when the animals did not fully recover was suitable. In Experiment 2, rats of each group after hepatectomy were fed one of 14 experimental diets containing protein (3 types), peptides (8 types), or amino acid mixture (3 types) for 5 days and killed on the 6th day after the operation. Daily food intake, body weight gain, liver weight and compositions, and hematologic values were measured and pathological examination was also done. The effect of different nitrogen sources were similar on the recovery after 70% hepatectomy with only a few minor exceptions in rats.

Amino Acids↗
PubMedDate not supplied

Response of muscle protein synthesis to parenteral administration of amino acid mixtures in growing rats.

Previous studies have shown that 1-hour infusions of neither glucose nor an amino acid mixture alone stimulates muscle protein synthesis in postabsorptive rats (Biosci Rep 1986;6:177-183). We have therefore investigated whether longer periods of infusion are required to initiate responses. The effects of intravenous infusions of various substrates for 6 hours on rates of skeletal muscle protein synthesis in fasted rats were studied. Fractional rates of protein synthesis (ks, the percent of muscle protein renewed each day) and the ribonucleic acid activity (kRNA, the amount of protein synthesis per unit of ribonucleic acid [milligrams of protein per day per milligram of ribonucleic acid]) were measured with a flooding dose of L-[4-3H]phenylalanine. Infusion of mixed amino acids (15 mg of nitrogen per hour per rat) increased ks and kRNA by approximately 50% in comparison with saline-infused rats, but rates of muscle protein synthesis remained below those observed in fed animals. Doubling the infusion rate of amino acids to 30 mg of nitrogen per hour per rat had no additional effect on ks and kRNA, and addition of glucose (0.3 g/h per rat) or glucose plus lipid also had no significant additive effect. However, infusion of glucose alone (0.3 g/h per rat) increased ks and kRNA by 25% when compared with saline-infused controls. Infusion of the branched-chain amino acids in the same amounts as present in the amino acid mixture increased ks and kRNA by 20% compared with saline-infused controls, but the rate remained significantly lower than that obtained by infusion of mixed amino acids.

Amino Acids↗
PubMed2006

Effect of acute tyrosine depletion in using a branched chain amino-acid mixture on dopamine neurotransmission in the rat brain.

Central dopamine function is reduced by decreasing the availability of the catecholamine precursor, tyrosine, using a tyrosine-free amino acid mixture containing multiple large neutral as well as branched chain amino-acids, which compete with tyrosine for uptake into the brain. Current mixtures are cumbersome to make and administer, and unpalatable to patients and volunteers. Here, we investigate whether individual or limited amino-acid combinations could reduce brain tyrosine levels and hence dopamine function. Measurements of regional brain tyrosine levels, catecholamine and indoleamine synthesis (L-DOPA and 5-HTP accumulation, respectively) were used to identify an effective paradigm to test in neurochemical, behavioral and fos immunocytochemical models. Administration of leucine or isoleucine, or a mixture of leucine, isoleucine, and valine reduced tyrosine and 5-HTP, but not L-DOPA accumulation. A mixture of leucine, valine, and isoleucine supplemented with tryptophan reduced brain tyrosine and L-DOPA, but not 5-HTP. In microdialysis experiments this amino-acid mixture reduced basal and amphetamine-evoked striatal dopamine release, as well as amphetamine-induced hyperactivity. This mixture also reduced amphetamine-induced fos expression in striatal areas. In conclusion, the present study identified a small combination of amino acids that reduces brain tyrosine and dopamine function in a manner similar to mixtures of multiple amino acids. This minimal mixture may have use as a dopamine reducing paradigm in patient and volunteer studies.

3,4-Dihydroxyphenylacetic Acid↗