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Amino acid preparations were used in experiments on rats which received intravenous nutrition for 15 days. It has been demonstrated that electron microscopy and morphometry of hepatocyte structures provide an objective assessment of the protein-synthesizing system of the liver. This criterion combined with other ones may be used for the evaluation of nutritive mixtures.
We tested the effect of equicaloric loads of glucose (0.89 g) or a balanced amino acid mixture (0.85 g) on extracellular amino acid concentrations in the brains of freely moving rats. At 15:30 hours, the microdialysis probe was inserted into the lateral hypothalamic area of ambulatory rats, and food and water were removed. Dialysates were collected every 20 min from 1 h prior to gavage (18:00 hours) and until 3 h after the gavage. Amino acid concentrations in the dialysate were determined by reverse-phase HPLC. Following the amino acid gavage, extracellular amino acid concentrations significantly increased from baseline for alanine, isoleucine, leucine, methionine, threonine, tyrosine, and valine. Those elevations occurred within 20-40 min following the amino acid load, and lasted up to 100 min. After the glucose and water treatments, amino acid concentrations were either not affected or gradually diminished from baseline. We conclude that extracellular amino acid concentration in the lateral hypothalamus is influenced by the composition of food consumed.
To identify a role for amino acids in cholestasis associated with total parenteral nutrition, we measured bile formation by the isolated perfused rat liver in the presence and absence of added amino acids. All livers were infused constantly with sodium [14C]taurocholate (0.28 mumoles per min) for 90 min. At 40 min, a primed-constant infusion of a synthetic L-amino acid mixture (121 + 19.3 mumoles of N per min) was administered for an additional 50 min. Mean bile flow rates during the amino acid infusion were reduced from 15.4 microliter per min per 10 gm liver weight to 10.4 microliter per min per 10 gm (p less than 0.005). There was no significant change during saline infusion of control livers, and there was no significant difference in perfusate osmolalities in the two groups. Although biliary recovery of infused taurocholate was slightly lower in the experimental perfusions than in controls (95.3% vs. 101.7%, p less than 0.05), there was no significant reduction in taurocholate excretion rate during the infusion in either group. Bile flow changes were related to ambient concentrations and net fluxes of individual amino acids in the perfusate. Of the 14 infused amino acids, glycine and arginine achieved levels greater than 3 times greater than reported physiological postprandial portal venous concentrations in the rat, and together constituted about 25% of the 90-min perfusate amino acids (8.3 mM). The highest net hepatic uptake was for glycine (125 mumoles per hr per 10 gm), which was almost 50% of its infusion rate.(ABSTRACT TRUNCATED AT 250 WORDS)
Prolactin levels are elevated in patients with liver cirrhosis and hepatic encephalopathy. Patients with hepatic encephalopathy also have an abnormal plasma amino acid composition, with a relative excess of aromatic amino acids, and a relative decrease in branched chain amino acid levels. In order to study the effect of the plasma amino acid composition on prolactin release, we measured plasma PRL at 0, 10, 20, 30, 40, 50 and 60 minutes after 400 micrograms TRH, both after infusion of a conventional amino acid mixture and after a branched chain amino acid enriched mixture (BCAA) in 5 patients with cirrhosis of the liver and hepatic encephalopathy. After conventional amino acid infusion, a depressed branched chain/aromatic amino acid ratio was found in all patients, together with an increased PRL response to TRH. After BCAA infusion the branched chain/aromatic amino acid ratio normalized. At the same time the excessive PRL response to TRH stimulation was significantly lower in all patients. This suggests that the elevated PRL levels in hepatic encephalopathy are caused by a disturbance of hypothalamic neurotransmitter systems, due to altered amino acid-neurotransmitter precursor levels.
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The postprandial plasma amino acid response to test meals containing different amino acid mixtures was analysed in six young adults. The amount of amino acids given in each test meal was equivalent with 3.5 g of nitrogen. Each test meal also contained a large amount of carbohydrate (mainly as wheat starch). Five different amino acid mixtures were used, and the effects on the plasma amino acid response of different dietary levels of lysine, isoleucine and methionine were studied in detail. The plasma amino acid responses were evaluated both by a modified Longenecker and Hause procedure (PAA ratios) and by the procedure proposed by Graham and Placko (percentage changes in the postprandial essential amino acid molar ratios). The plasma amino acid response of lysine was found to be less sensitive to reductions in the dietary supply than the isoleucine and methionine responses evaluated by these procedures. The influence of altered levels of dietary supply on the postprandial plasma concentrations of isoleucine and methionine seemed to be specifically great at the intake levels where these essential amino acids become limiting for protein utilization according to the amino acid score of the test mixtures. The nutritional significance of the postprandial pattern and level of essential amino acids is discussed on basis of the present results. Experimental conditions and evaluation models are examined with regard to the use of single-meal plasma amino acid responses to assess the protein quality of human diets.
A mixture of amino acids designed to maintain normal plasma amino acid concentrations of infants and children requiring parenteral nutrition was evaluated in 40 infants and children receiving only parenteral nutrients (2.39 +/- 0.26 g/kg/d of amino acids and 110.3 +/- 10.4 kcal/kg/d) for five to 21 days. The children ranged in weight from 2.0 to 12.6 kg (median weight, 3.83 kg; fifth to 95th percentile, 2.06 to 11.1 kg) and in age from 1 week to 43.6 months (median age, 2.7 months; fifth to 95th percentile, 0.2 to 25.3 months). Mean weight gain was 11.0 +/- 5.0 g/kg/d; mean nitrogen balance was 242 +/- 70 mg/kg/d. Plasma concentrations of all amino acids except tyrosine were within the normal range (ie, within the 95% confidence limits of the two-hour postprandial plasma concentrations observed in 30-day-old, healthy, normally growing, breast-fed, term infants) throughout the period of study. Mean prestudy and poststudy serum total protein, albumin, and transthyretin (prealbumin) concentrations were not significantly different. However, plasma transthyretin concentration increased in all children with low prestudy concentrations. Mean poststudy serum total bilirubin concentration of the total population was not different from the mean prestudy concentration. This was true also for the 31 children who received the parenteral amino acid mixture for more than ten days. In contrast to the expected 30% to 50% incidence of cholestasis, only one of these 31 experienced an unexplained increase in serum total bilirubin concentration during study, suggesting that normalizing plasma amino acid concentrations and/or providing taurine during parenteral nutrition may decrease the incidence of cholestasis associated with this therapy.
Plasma and intraluminal amino acid profiles were compared in normal subjects 30, 60, 120, 180 minutes after meals containing either a peptide-rich protein hydrolysate (H) or an equivalent free amino acid mixture (AA) as the nitrogen source. Except for asparagine (30 minutes) and glutamine (30 and 60 minutes), which were absorbed to a significantly (p less than 0.05) greater extent from the peptide mixture, there were no significant differences in the plasma increments of the remaining 13 amino acids at any time interval after the meals. Positive correlations (p less than 0.01 or less) between the amino acid composition of the hydrolysate and amino acid meals and both (1) the post-prandial increments in the individual plasma amino acids and (2) the residual intraluminal amino acid content suggested that the amino acid composition of ingested protein, rather than specialised free amino acid and peptide transport systems, dictated the pattern of amino acid absorption. The studies provide no evidence that peptides rather than free amino acids are the ideal nitrogen source in elemental diets.
To assess the possible role of altered central serotonin function in psychiatric disorders, investigators have utilized pharmacological challenge testing with an amino acid mixture to decrease blood tryptophan concentration and, indirectly, brain serotonin levels. The aim of this pilot study was to assess the effectiveness of a modified amino mixture, administered in capsule form, in decreasing plasma tryptophan levels. Studies were conducted in six healthy, medication-free female volunteers. Following double-blind, randomized, cross-over design, subjects received on separate days capsules containing a tryptophan-free amino acid mixture (31.5 grams) or lactose placebo. Over the six hours following amino acid administration, plasma tryptophan concentrations decreased to 21% of baseline values, while the tryptophan/large neutral amino acid ratio decreased to 6% of baseline. Subjects reported minimal symptoms of nausea or other side effects following amino acid administration. The results suggest that the modified amino acid mixture may be useful in assessing behavioral responses to acute tryptophan depletion challenge testing.
Amino acid mixtures corresponding to either casein or egg yolk protein when fed to rabits ina low fat, cholesterol-free semipurified diet, produced the same degree of hypercholesterolemia as the proteins themselves. Amino acid mixtures corresponding to soy protein isolate or sunflower protein gave low plasma cholesterol levels, but not as low as those obtained with the intact proteins. Experiments were designed to identify amino acids responsible for the differential in plasma cholesterol produced by casein or soy protein amino acid mixtures. Plasma cholesterol levels obtained with a casein amino acid mixture containing half the amounts of essential amino acids were significantly higher than he corresponding soy protein mixture. Feeding trials based on systematic modifications to the casein and soy protein mixtures indicated that interaction between essential and non-essential amino acids was important in determining plasma cholesterol levels. In further experiments, protein components were formulated by adding amino acids to casein to give a mixture corresponding to soy proteins, or by adding amino acids to soy protein, or by adding amino acids to soy protein to give a mixture equivalent to casein. These diets failed to reverse plasma cholesterol levels which suggests differences in digestion and absorption of proteins relative to amino acid mixtures.
A mixture of amino acids designed to maintain normal plasma amino acid concentrations in infants and children requiring parenteral nutrition was evaluated in 28 low birth weight (LBW) infants (birth weight, 750 to 1750 g; postnatal age, 1 to 4 weeks) who required parenteral nutrients for optimal nutritional management. Sixteen babies received only parenteral nutrients for five to 21 days. Ten of these received a typical regimen by peripheral vein (1.91 +/- 0.16 g/kg/d of amino acids and 44.7 +/- 4.4 kcal/kg/d) and six received a typical regimen through a central vein (2.39 +/- 0.11 g/kg/d of amino acids and 95.9 +/- 14.5 kcal/kg/d). Mean weight gain of the peripheral vein subgroup was 10.3 +/- 10.6 g/kg/d; mean nitrogen balance was 230 +/- 66 mg/kg/d. Both the mean rate of weight gain (17.2 +/- 5.1 g/kg/d) and the mean rate of nitrogen retention (267 +/- 49 g/kg/d) of the central vein subgroup were similar to intrauterine rates. In these two subgroups as well as the total population, plasma concentrations of all amino acids except phenylalanine were within the 95% confidence limits of the plasma concentrations observed in LBW infants fed sufficient amounts of human milk to result in a rate of weight gain similar to the intrauterine rate. However, although plasma tyrosine and cyst(e)ine concentrations were within the 95% confidence limits of the plasma concentrations goals, the LBW infant's ability to use N-acetyl-L-tyrosine and cysteine HCl appears to be even less than that of the term infant and older child. In toto, these data support the efficacy of the amino acid mixture evaluated for LBW infants. Of equal importance, they suggest that the LBW infant's ability to use parenterally delivered amino acids is not as limited as commonly thought.
Effects of a glucose and amino acid mixture prescribed for parenteral alimentation on anti-Candida activity of neutrophils were examined. Neutrophils obtained from peripheral blood of healthy humans inhibited the growth of Candida albicans in vitro. More than 1.0% of glucose inhibited the anti-Candida activity of the neutrophils in a dose-dependent manner. This glucose effect was reduced by the addition of an amino acid mixture clinically prescribed with a carbohydrate solution (PN-twin) in Japan. The amino acid mixture neutralized the suppression of anti-Candida activity of neutrophils by dexamethasone. These results suggest that an amino acid mixture prescribed in an alimentation solution may play a role as a neutralizer of the suppressive action of glucose for anti-Candida activity of neutrophils in a limited area near the top of a catheter in a blood vessel.
Previous studies suggested that the ingestion of a mixture of amino acids inhibited the fat-stimulated increase in colonic motility. This study determine the effect of the ingestion of an amino acid mixture on the postprandial distal colonic spike potential (SP) response to a standard 1000-calorie meal in normal subjects and in patients with the irritable bowel syndrome. The distal colonic response was measured following a standard meal with and without the preadministration of a protein hydrolysate solution. After the meal, normal subjects had their maximum response within the first 30-min postprandial period (41.0 +/- 6.3 SP/30 min). Spike activity returned to fasting activity by 60 min. Most patients with irritable bowel syndrome did not have a significant early postprandial distal colonic spike response (P > 0.05), but all patients had a large late increase in spike activity occurring 60-90 min postprandially (50.0 +/- 5.0 SP/30 min) (P < 0.001). Ingestion of the protein hydrolysate solution prior to the meal resulted in suppression of the early colonic spike response in normal subjects (P < 0.01) and the late colonic spike response in the irritable bowel patients (P < 0.01). This study suggests that amino acids can modulate postprandial colonic motility and that dietary alteration may be beneficial in the irritable bowel syndrome.
The effect of energy on nitrogen balance was examined in young men given amino acid mixture. The minimum amino acid nitrogen requirement for nitrogen equilibrium was determined together with the egg protein requirement. In experiment 1, the nitrogen sparing effect of energy was evaluated in four male students receiving diet containing an amino acid mixture and a constant nitrogen intake of 3.5 g N/day, which was equivalent to the nitrogen requirement with excess energy intake determined by Rose and Wixom (1). When the dietary energy supply was 45 kcal/kg, which is approximately the maintenance level, the mean nitrogen balance was negative, being -23.9 +/- 9.3 mg N/kg. However, with an excess energy intake of 55 kcal/kg, the nitrogen balance improved significantly, being -6.1 +/- 7.7 mg N/kg. In experiment 2, the nitrogen requirement of egg-pattern amino acid mixture for apparently zero balance was evaluated at maintenance energy intake in 28 Japanese young men and was compared with that of egg protein. After receiving standard diet, the subjects were given a semi-purified experimental diet containing egg-pattern amino acid mixture at nitrogen intake levels of 60, 75, 100, and 130 mg N/kg for two weeks. Then all groups except the 60 mg N/kg group were given isonitrogenous egg protein diet for another week. Energy intake was kept constant at approximately the maintenance level of 44.4 +/- 1.4 kcal/kg throughout the experiment. Nitrogen balance was not significantly different in groups given egg-pattern amino acid mixture and intact egg protein in each nitrogen intake level. From regression analysis, the nitrogen requirement for nitrogen equilibrium of the amino acid mixture was calculated to be 110.1 +/- 50.2 mg N/kg, which was not significantly different from the value of 88.4 +/- 40.6 mg N/kg of egg protein. It was concluded that the total amino acid requirement estimated by Rose and Wixom (1) was too low because they gave excess energy, and that there was no difference between the nitrogen requirement of egg protein and that of the corresponding amino acid mixture.
1. Starving rats were given complete and tryptophan-deficient amino acid mixtures by stomach tube and were killed from 1 to 7hr. later. The polysome profile in the livers of rats fed with the tryptophan-deficient mixture showed a shift in distribution such that the large aggregates were decreased and the small aggregates were increased, particularly dimers. This polysome shift was reversed when the complete amino acid mixture was given by stomach tube 2hr. after administering the tryptophan-free amino acid mixture. 2. After removal of liver polysomes by centrifugation, some smaller ribosomal aggregates (oligosomes) remaining in suspension were harvested by prolonged centrifugation of the supernatant fluid. A large increase in the dimer population of this fraction was observed in the rats receiving the incomplete mixture. 3. When the polysome and oligosome fractions were incubated with cell sap, an energy-generating system and labelled amino acids dl-[1-(14)C]leucine and l-[Me-(14)C]tryptophan were incorporated into the cell fractions in the ratio 4.5:1. Preparations of polysomes and oligosomes from rats fed with the tryptophan-free amino acid mixture showed a decreased amino acid-incorporating activity compared with particulate preparations made from rats fed with the complete mixture. 4. The yield of free ribosomes prepared from the unfractionated liver microsomes by treatment with iso-octane was 40-50% greater in rats fed with the amino acid mixture deficient in tryptophan. 5. A post-microsomal fraction was prepared from cell sap and was shown to consist of ribosomal sub-units. When the animals were fed with the tryptophan-deficient mixture, there was an increase in content of this post-microsomal fraction and in the ratio 30s RNA/19s RNA. Rats were also given [5-(3)H]orotic acid at the time of feeding with the amino acids. Lack of tryptophan in the mixture caused a decrease in the specific activity of both RNA fractions which affected the 30s RNA more extensively than the 19s RNA. 6. These changes in the distribution and quantity of the cellular components engaged in protein synthesis are discussed in relation to RNA metabolism and amino acid-incorporating activity of the liver cell and their response to feeding with the tryptophan-free amino acid mixture.
Radioprotective efficacy of differently composed amino acid mixtures (e. g. swine brain hydrolyzate, mixtures of several crystalline amino acids, etc.) was estimated. The survival rate and average life of exposed animals increased after the administration of amino acid preparations. The most pronounced effect was produced by the mixtures composed of several crystalline amino acids.
1. The characteristics of absorption of individual amino acids from amino acid mixtures simulating casein and from enzymic hydrolysates of casein containing oligopeptides as well as free amino acids are known to be different. The differences, which are attributable to mucosal uptake of small peptides, involve more rapid absorption from the enzymic hydrolysates of certain amino acids which are relatively slowly absorbed from the amino acid mixtures. This could lead to more effective utilization of amino acids from the enzymic hydrolysates than from the amino acid mixtures. 2. To obtain further information bearing on this hypothesis, we have used a recently developed technique for portal cannulation in the guinea pig to make a preliminary investigation of amino acid concentrations in the portal venous plasma at intervals after the infusion into the duodenum of equivalent amounts of (a) an amino acid mixture simulating casein and (b) a partial enzymic (papain followed by kidney peptidases) hydrolysate of casein, the two preparations being infused in separate experiments. 3. For some amino acids, such as leucine, isoleucine, valine, phenylalanine and lysine, the curves after the enzymic hydrolysate were fairly similar to the corresponding curves after the amino acid mixture, though usually slightly lower. With other amino acids, the curves after the enzymic hydrolysate were very much lower than the corresponding curves after the amino acid mixture. With serine, glutamine, proline and glycine this discrepancy was particularly great. 4. The results cannot yet be fully explained, but their main features are explicable by the hypothesis that the lower amino acid concentrations in portal plasma after the enzymic hydrolysate are the result of entry of amino acids into the portal blood in peptide form, in which they would not be detectable by the analytical technique employed, and possibly also of more rapid clearance of amino acids from the blood during absorption of this preparation.
We report the effects of a tyrosine (and phenylalanine)-free amino acid mixture on tyrosine levels, ex vivo catecholamine synthesis and in vivo catecholamine release in brain regions of the rat. Administration of a tyrosine-free amino acid load reduced tissue levels of tyrosine (-50% after 2 h) in all brain regions examined (frontal cortex, hippocampus, striatum). The tyrosine-free amino acid mixture also reduced DOPA accumulation: this effect was most marked in striatum (-44%) and nucleus accumbens (-34%), areas with a predominantly dopaminergic innervation. Smaller decreases (-20-24%) were detected in other areas (cortex, hippocampus and hypothalamus). The effect on DOPA accumulation was prevented by supplementing the mixture with tyrosine/phenylalanine. The tyrosine-free amino acid mixture did not alter 5-HTP accumulation in any region. In microdialysis experiments, the tyrosine-free amino acid mixture did not consistently alter striatal extracellular dopamine under basal conditions but markedly, and dose-dependently, reduced the release of dopamine induced by amphetamine. In contrast, the tyrosine-free amino acid mixture did not alter either basal or amphetamine-evoked release of noradrenaline in hippocampus. Overall, these studies indicate that administration of a tyrosine-free amino acid mixture to rats depletes brain tyrosine to cause a decrease in regional brain catecholamine synthesis and release. Dopaminergic neurones appear to be more vulnerable to tyrosine depletion than noradrenergic neurones.