Plasma Free Amino Acid Levels Research Articles

Plasma amino acid pattern during the first month of life in calves fed the first colostrum at 0-2 h or at 24-25 h after birth.

Calves are born with a mostly inadequate essential amino acid (EAA) status. Studies were designed to test the hypothesis that delaying the intake of the first colostrum for 24 h, besides its early effects, also has late effects on plasma free amino acid levels and on the protein status. There were marked and rapid elevations (within 2 h) of plasma levels of various amino acids, and especially of EAA, after the intake of the first colostrum, whereas changes after the intake of mature milk on day 28 of life were mostly absent or concentrations even decreased. The EAA and non-essential amino acid (NEAA) status was rapidly normalized after intake of the first colostrum, but normal plasma levels of some amino acids were also reached during the first 24 h of life even when the first meal was withheld. Delaying colostrum intake had only transient effects on EAA and NEAA (except hydroxyproline), in contrast to its effects on plasma immunoglobulin G and total protein levels.

Plasma Free Amino Acids in Workers Working under Different Stress Conditions

Plasma Free Amino Acids in Workers Working under Different Stress Conditions: Tang‐Chun Wu et al. Institute of Occupational Medicine, Tongji Medical University—Many harmful occupational factors induce the stress response and result in both the induction of heat stress proteins and the inhibition of the synthesis of other cellular proteins. Since amino acid levels are intimately linked to protein synthesis, we examined the free amino acid levels in the plasma of workers subjected to prolonged exposure to heat, carbon monoxide (CO) or both. The results showed that the levels of most amino acids tended to increase in the plasma of workers in stressful environments, and that free methionine and tryptophan increased significantly (p<0.05) in the heat, CO, and heat+CO groups when compared to a control group. The largest increase was seen in the heat+CO group, followed by the heat group, and finally the CO group. The changes in plasma free amino acid levels in the stress‐exposed workers correlate to the induction of heat stress proteins. These findings suggest that the regulation of plasma amino acids levels, by preventing amino acid accumulation possibly resulting from a decrease in the rate of protein synthesis following exposure to stressors, may help to protect workers from these extreme conditions.

Effects of exercise on plasma nonesterified fatty acids and free amino acids in Arctic char (Salvelinus alpinus)

AbstractThe plasma nonesterified fatty acids (NEFA) and free amino acids (AA) of exercised and rested Artic char (Salvelinus alpinus) were measured. Total nonesterified fatty acids, total saturated fatty acids and total monoenes were significantly elevated in the plasma of the exercised group. Plasma levels of palmitate (16: 0) were also significantly elevated in the exercised fish. No significant changes with exercise were observed in the total polyenes.The total plasma free amino acid and total nonessential amino acid levels were significantly elevated in the exercised group. The concentrations of glutamate, alanine, taurine, and tryptophan increased with exercise. The percent contribution of total essential amino acids to total free amino acids in the exercised fish was lower than that of the rested group.It is suggested that mobilization of specific nonesterified fatty acids and amino acids largely reflect increased oxidation of metabolic substrates by exercising red muscle. © 1995 Wiley‐Liss, Inc.

Clearance rate of plasma branched-chain amino acids correlates significantly with blood ammonia level in patients with liver cirrhosis

Reduced plasma free branched-chain amino acid (BCAA; valine, isoleucine and leucine) levels appear often in patients with liver cirrhosis and relate closely to the pathogenesis of hepatic encephalopathy and protein malnutrition in cirrhotics. To elucidate possible mechanism(s) of the BCAA decrease, plasma amino acid clearance rates were estimated by analyzing disappearance curves of amino acids which were infused at a rate of 0.1 g/kg per 5 min in ten patients and eight controls. The clearance rate of total amino acids (TAA) was significantly lower while that of BCAA was significantly higher in cirrhotics than in controls. The relative clearance rate of BCAA (% TAA clearance) correlated significantly with the blood amimonia level. Since BCAA is required for the detoxication of ammonia in skeletal muscles, enhanced clearance of plasma BCAA may indicate the increased muscular uptake of BCAA. In conclusion, plasma BCAA reduction in cirrhotics is due, at least in part, to the enhanced plasma BCAA clearance, and hyperammonemia seems to be responsible for this enhancement. Supplementation with BCAA in these patients is reasonable to rescue this pathophysiological state of relative BCAA deficiency.

Dietary carbohydrate utilization in cod (Gadus morhua): metabolic responses to feeding and fasting

Moist diets with increasing amounts of carbohydrate (0.5%, 10% and 21% on a dry weight basis) were each fed to duplicate groups of cod (initial weight 370 g) for 8 weeks, after which all groups were fasted for 4 weeks. Protein energy was high and accounted for more than 70% of the gross energy content in all feeds, and the diets were maintained isocaloric by substituting lipid energy for carbohydrate energy. No indigestible binder was added. Excellent growth and feed conversion were obtained in all groups. After 4 weeks of fasting, fish previously fed diets with either 10% or 21% carbohydrate showed significantly higher weight loss than fish fed the diet without carbohydrate. Liver glycogen reached 10% of liver wet weight in fish fed diets containing 10% or 21% carbohydrate and 5% in fish receiving 0.5% carbohydrate after 8 weeks. Following 4 weeks of fasting, liver glycogen was reduced to similar levels in all fish. Plasma glucose levels 4 h after feeding were higher in fish fed the diets with 10% or 21% carbohydrate and plasma free amino acid levels (FAA) were lower, than in fish fed the diet containing 0.5% carbohydrate. Blood lactate concentrations were unaffected during the first 24 h after feeding. After 4 weeks of food deprivation, the levels were significantly reduced only in the 21% carbohydrate group. A link between glucagon and protein metabolism is suggested because plasma glucagon concentration followed the same pattern as the concentrations of plasma FAA throughout the study. Insulin and glucagon-like peptide (GLP) showed a covariation throughout the experiment. Reduced plasma insulin levels were seen after fasting concomitant with reduction in the levels of FAA and glucose. It is suggested that insulin secretion in cod is affected both by plasma FAA and glucose and that cod meets food deprivation by slowing down metabolism.

Interactive effects of dietary levels of tryptophan and protein on voluntary feed intake and growth performance in pigs, in relation to plasma free amino acids and hypothalamic serotonin.

The effects of dietary level of tryptophan (TRP) and CP content and composition on voluntary feed intake, growth performance, and carcass characteristics in finishing pigs were studied in two experiments, with an equal number of females and castrated males. In Exp. 1, involving 120 Large White pigs from 44 to 99 kg BW with ad libitum access to feed, six treatments were compared according to a 2 x 3 factorial arrangement: 1) two levels of TRP (.09 and .13%), suboptimal and optimal for growth, respectively, 2) three types of CP supply (a 12.5% CP diet based on corn-soybean meal, and adequately balanced for essential amino acids [EAA] other than TRP; 15.7% CP diet with additional protein from corn gluten meal; 16.2% CP diet with additional nonessential amino acids [NEAA, in the form of L-glutamic acid.HCl and glycine], and the same levels of EAA as in the 12.5% CP diet. In Exp. 2, including four of the six previous factorial combinations (.09 and .13% TRP, 12.3 and 15.8% CP with additional protein), 32 pigs of 50-kg initial BW were used during 21 d, and further observations on meat quality characteristics, plasma free amino acid levels, and serotonin concentrations in the posterior hypothalamus were made. The major observed effects were interactions of different magnitude according to sex between TRP level and the amount and the composition of additional CP. At the suboptimal level of .09% TRP, the increase in protein content severely decreased daily feed intake and growth compared with the .13% level, especially in females. Conversely, the addition of NEAA at both TRP levels had little effect on daily feed intake and growth. Deficiency of TRP exerted a significant increase of pH in adductor femoris and semimembranosus muscles measured 45 min and 24 h postmortem, but only in females. Voluntary feed intake, as affected by dietary TRP and CP levels, was linearly related with concomitant changes in TRP to large neutral amino acids (TRP:LNAA) ratio both in feed and in plasma, which in turn was directly associated to hypothalamic serotonin concentration. It was concluded that an overly low concentration of serotonin in the hypothalamus, especially in females, as a result of TRP:LNAA imbalance, could be involved in the reduction of voluntary feed intake.

Efficacy of ornithine-alpha-ketoglutarate (OKGA) as a dietary supplement in growing rats

New substrates of potential benefit to critically ill patients receiving traditional nutritional support have been suggested to meet organ or tissue specific needs. The addition of an anabolic stimulus during nutritional support therefore appears to be a reasonable adjunct to augment protein synthesis. The purpose of this investigation was to evaluate the efficacy of the neutral salt ornithine alphaketoglutarate (OKGA) as a dietary supplement to promote growth in young rats by enhancing protein metabolism. A group of 16 male Sprague-Dawley rats (150–170g) were housed in individual metabolic cages and after dark-light cycle adaptation were fed ad libitum an oral liquid diet for 7 days. Half of the animals were given the control diet and the other half was fed a test diet. This isonitrogenous test diet contained the control diet with 2.3% of nitrogen (N) replaced by N from OKGA. Daily weight, food intake and urinary excretions of N, creatinine, urea, orotic acid, polyamines and amino-acids were determined. At the end of 7 days of free-feeding, the rats were sacrificed and blood was collected for free amino-acids. Rats fed the OKGA supplemented diet consumed 16% more diet, retained 11% more nitrogen and gained 15% more weight. The accelerated protein metabolism is reflected in the changes in plasma and urinary free amino-acid levels. Enhanced protein anabolism is evident from the increased urinary excretion of polyamines in the OKGA fed rats. The increased ratio of urinary urea N to total N and the decreased orotic acid excretion in OKGA fed rats suggests thata NH 4 + was efficiently diverted through urea cycle. It is concluded that in growing rats, supplementing isonitrogenous diet with OKGA significantly stimulates food intake compared to controls. This results in better weight gain and improvement in protein metabolism.

The Nutritional Value of Oat Flour for Very Young Children

SummaryWhole groat flour was consumed by nine infants and young children as 22.5, 45, or 67% of total diet energy (one half of 6.4%, all of 6.4%, or all of 9.6% protein energy). Isonitrogenous and isoenergetic casein control diets were given. Apparent absorption of oat nitrogen (N) was consistently around 75% of intake (casein, 87%), but absorptions of oat energy, carbohydrate, and fat, as percentages of intake, decreased disproportionately as oat flour intake was doubled and then tripled. Apparent retentions were 39 ± 5% of mixed oat‐casein protein intake in the 22.5% diet, the preceding and following casein controls being 38 ± 8% (NS) and 44.4% (p<0.05) of the intakes; 32 ± 6% from oats in the 45% diet, controls 38 ± 5 and 46 ± 5% (both p<0.05), and 33 ± 11% from oats in the 67% diet, controls, 36 ± 9% (NS). Fasting plasma free total essential amino acid (TEAA) levels of children consuming 45% oats were low (562 ± 119 μmol of TEAA/L) and did not change significantly after meals. Fasting molar proportions of individual essentials (millimoles of EAA per mole of TEAA) were similar to those from milk protein diets and did not vary significantly 3 and 4 h after feeding, suggesting that no individual amino acid, but rather protein digestibility, was first limiting to N retention. Oats are a satisfactory source of energy, protein, and fat for very young children and many infants.

The Nutritional Value of Oat Flour for Very Young Children

Whole groat flour was consumed by nine infants and young children as 22.5, 45, or 67% of total diet energy (one half of 6.4%, all of 6.4%, or all of 9.6% protein energy). Isonitrogenous and isoenergetic casein control diets were given. Apparent absorption of oat nitrogen (N) was consistently around 75% of intake (casein, 87%), but absorptions of oat energy, carbohydrate, and fat, as percentages of intake, decreased disproportionately as oat flour intake was doubled and then tripled. Apparent retentions were 39 +/- 5% of mixed oat-casein protein intake in the 22.5% diet, the preceding and following casein controls being 38 +/- 8% (NS) and 44.4% (p less than 0.05) of the intakes; 32 +/- 6% from oats in the 45% diet, controls 38 +/- 5 and 46 +/- 5% (both p less than 0.05), and 33 +/- 11% from oats in the 67% diet, controls, 36 +/- 9% (NS). Fasting plasma free total essential amino acid (TEAA) levels of children consuming 45% oats were low (562 +/- 119 mumol of TEAA/L) and did not change significantly after meals. Fasting molar proportions of individual essentials (millimoles of EAA per mole of TEAA) were similar to those from milk protein diets and did not vary significantly 3 and 4 h after feeding, suggesting that no individual amino acid, but rather protein digestibility, was first limiting to N retention. Oats are a satisfactory source of energy, protein, and fat for very young children and many infants.

Adaptation to High Protein Intakes, with Particular Reference to Formula Feeding and the Healthy, Term Infant

The purpose of this paper is to attempt to define the upper limit of the safe range of protein intake, with particular reference to the protein content of prepared fixed-formulas used for feeding healthy, term infants. For discussion purposes we use the current upper limit proposed by the U.S. Food and Drug Administration (FDA), namely, 4.5 g protein per 100 kcal, as our initial reference level. To help reach a conclusion, the concept and definitions of nutritional adaptation and accommodation are considered, followed by a brief review of selected studies in full-term infants fed varying levels of protein intake. Based on growth and blood biochemical data, principally plasma free amino acid levels, we conclude that the currently proposed FDA upper limit is probably too high. The available data support a recommendation for lowering the value to about 3.5 g of protein per 100 kcal. Concerns for renal solute load (RSL) may require a further, desirable refinement in the value proposed. Indeed RSL should perhaps serve as the primary basis for establishing a rational and safe upper limit for the protein content of prepared fixed-formula diets for the very young, healthy infant.

Adaptation to High Protein Intakes, with Particular Reference to Formula Feeding and the Healthy, Term Infant

The purpose of this paper is to attempt to define the upper limit of the safe range of protein intake, with particular reference to the protein content of prepared fixed-formulas used for feeding healthy, term infants. For discussion purposes we use the current upper limit proposed by the U.S. Food and Drug Administration (FDA), namely, 4.5 g protein per 100 kcal, as our initial reference level. To help reach a conclusion, the concept and definitions of nutritional adaptation and accommodation are considered, followed by a brief review of selected studies in full-term infants fed varying levels of protein intake. Based on growth and blood biochemical data, principally plasma free amino acid levels, we conclude that the currently proposed FDA upper limit is probably too high. The available data support a recommendation for lowering the value to about 3.5 g of protein per 100 kcal. Concerns for renal solute load (RSL) may require a further, desirable refinement in the value proposed. Indeed RSL should perhaps serve as the primary basis for establishing a rational and safe upper limit for the protein content of prepared fixed-formula diets for the very young, healthy infant.

Altered plasma free and protein-bound sulfur amino acid levels in patients undergoing maintenance hemodialysis

The plasma sulfur amino acid status of maintenance hemodialysis (MHD) patients has not previously been comprehensively investigated. We measured plasma sulfur amino acid levels in 24 MHD patients (12 fasted, 12 nonfasted) both before and after a routine 4-h hemodialysis and in 13 normal individuals (seven fasted, six nonfasted). Plasma free cystine, homocystine, cysteine-homocysteine-mixed disulfide (MDS), methionine, and taurine and protein-bound cysteine and homocysteine were measured. In nonfasted patients, plasma homocystine and MDS were not measured. Fasted patients predialysis had elevated plasma free cystine, homocystine, MDS, methionine, and taurine; all of these, except taurine, fell during dialysis. In nonfasted patients, plasma free cystine was elevated. Protein-bound cysteine and homocysteine were elevated predialysis and postdialysis in all patients; protein-bound cysteine fell during dialysis but remained above normal. In MHD patients predialysis, plasma free cystine levels correlated with plasma MDS, protein-bound cysteine, and age. These findings indicate pervasive alterations in plasma sulfur amino acid levels in MHD patients.

Effect of meal schedules and fasting on selected plasma free amino acids in horses.

The effects of meal frequency and fasting on selected plasma free amino acids (PFAA) was studied in horses. Six 22-mo-old Quarter Horses were used in a replicated 3 X 3 Latin-square design in which each horse received one meal per day (1M), two meals per day (2M) or six meals per day (6M) for 2 wk. A complete pelleted ration was fed at a rate of 1.75% of body weight daily. The consumption of a meal by the horses fed 1M and 2M daily was followed by an increase (P less than .05) in plasma methionine. The highest levels were observed at 5 h and 3 h in the 1M and 2M treatments, respectively. The horses receiving the larger meal (1M) also had higher methionine levels. There were no significant changes in plasma methionine levels in the 6M group. Feed was withheld from the 1M group for 48 h and blood samples were obtained for alanine, glutamine, glutamate, lysine and leucine levels. These amino acids also peaked at 5 h, then declined through 19 to 25 h. During the last 24 h PFAA levels increased (P less than .05). Although glutamine and lysine appeared to level off at 49 h after the meal, alanine, glutamate and leucine were still increasing.

The effect of food deprivation on the plasma free amino acid levels of sturgeon, Acipenser transmontanus

Plasma levels of free amino acids were compared in recently fed sturgeon and in those deprived of food for over two weeks. Fed animals had elevated levels of branched chain amino acids. It is suggested that the higher levels of these amino acids are due to reduced metabolism of these amino acids as well as high levels in the food.

The Influence of Level of Valine on Nitrogen Status and Plasma Free Amino Acid Levels in Infused Sheep

A 4 × 4 Latin square design with an extra period was used to determine the influence of different levels of valine (Val) on the nitrogen metabolism of sheep receiving all nutrients by infusion. Glucose, amino acids and water-soluble vitamins were introduced in the jugular vein while inorganic nutrients and volatile fatty acids were given intraruminally. The amino acid mixture contained 1, 3, 5 or 7 g of Val with varying amounts of glycine (Gly) to balance the nitrogen level. The infusion in the extra period was isonitrogenous but contained no Val. When Val was omitted from the infusion, nitrogen balance (NB) was significantly reduced and plasma urea nitrogen (PUN) was significantly increased compared with all levels of added Val. The level of Val infusion that supported the numerically highest NB and the lowest PUN and urinary urea nitrogen (UUN) was 3 g/day, although NB and PUN, at all levels of added Val, were not statistically different. Plasma free Val increased abruptly at infusion levels above 3 g of infusion. It was concluded that Val is metabolically essential for the sheep and the best estimate of the requirements would be 200 mg/(kg body weight)0.75 per day in animals of this age and sex.

Comparison of the Effect of Semisynthetic Human Insulin and Porcine Insulin on Glucose Kinetics, Plasma Free Fatty Acid and Amino Acid Levels in Man

The effect of semisynthetic human insulin on hepatic glucose output, peripheral glucose clearance, plasma levels of C-Peptide, free fatty acids and amino acids was compared with purified pork insulin using the glucose clamp technique. 8 normal overnight-fasted subjects received intravenous infusions of either human or porcine insulin at 20 mU/m2.min(-1) during 120 min achieving plasma insulin levels of approximately equal to 50 mU/l. Plasma glucose levels were maintained at euglycaemia by variable rates of glucose infusion. Hepatic glucose production measured by continuous infusion of 3-(3) H-glucose was similarly suppressed by both insulins to rates near zero. The metabolic clearance rate of glucose increased during infusion of human insulin by 120%, C-peptide levels decreased by 41% and plasma FFA concentrations fell by 74%. The respective changes during infusion of pork insulin were similar, 118%, 48% and 72%. Both insulins decreased the plasma levels of branched-chain amino acids, tyrosine, phenylalanine, methionine, serine and histidine similarly. Thus, the results demonstrate that semisynthetic human and porcine insulin are aequipotent with respect to suppression of hepatic glucose output, stimulation of glucose clearance, inhibition of insulin secretion, lipolysis and proteolysis.

Effects of a glandless cottonseed protein diet on fasting plasma amino acid levels in college women

Plasma amino acids were determined and correlated to the level of dietary amino acids consumed over a 42-day period. Six college women, ages 19 to 23, were fed meals in which 99% of the dietary protein was supplied by glandless cottonseed flour. The protein content was decreased weekly from 14.6 to 9.9, 8.7, 7.5, 6.9, and 6.3 g nitrogen per day, until that amount was found that would not maintain nitrogen equilibrium. Fasting blood samples were obtained after subjects had consumed a specific protein level for 1 week. Significant (P less than 0.05) decreases in fasting plasma free amino acid levels occurred from day 0 to 7 of the study for threonine, proline, isoleucine, leucine, tyrosine, and lysine. There were no significant differences in these plasma amino acids thereafter. Of the essential amino acids, leucine, valine, histidine, and lysine appeared to have similar graphical trends between the plasma and dietary amino acid concentrations over the entire 6-week period. However, only leucine had a significant (P less than 0.05) correlation. Results indicated that fasting plasma free amino acid concentrations of young women on a cottonseed protein diet appear to drop initially, but rarely fall beyond the realms of normal values during nitrogen equilibrium.

Blood Glucose and Plasma Amino Acid Concentrations in Infants of Diabetic Mothers

Postnatal blood glucose and individual plasma free amino acid levels were measured in 14 newborn infants of diabetic mothers. All infants had a significantly lower blood glucose concentration than normal controls but no significant correlation was observed between the blood glucose values and any of the amino acids determined. As regards the quantitative and qualitative changes of the plasma aminogram, the total concentration of amino acids and the level of a few individual amino acids (glycine, alanine, taurine, and valine) were significantly elevated in full-term babies. However, no significant difference was found in the total plasma concentration of amino acids between premature infants of diabetic mothers and premature control infants, but the plasma alanine level was higher in the former. It is of interest that total plasma amino acid, alanine, and glycine levels were elevated in the asphyxiated babies. This suggests that the postnatal hyperaminoacidemia observed in infants of diabetic mothers was due to birth asphyxia rather than to impaired gluconeogenesis. The possible role of a defective gluconeogenesis in the etiology of postnatal hypoglycemia in infants of diabetic mothers is not supported by these data.

Utilization of amino acids by pre-ruminant lambs. III.* The influence of age and the dietary proportions of essential and non-essential amino acids on the levels of urea, ammonia and free amino acids in the blood plasma of milk-fed lambs

Jugular blood samples were obtained from 10.5 kg and 28 kg lambs receiving a diet of reconstituted cows' whole milk. The lambs were then given diets in which the proportion of essential amino acids (BAA) in the dietary crude protein was altered over a wide range. A second blood sample was taken after lambs had received such diets for 12 days. Plasma obtained from these samples was analysed for free amino acids, urea and ammonia. The pattern of plasma free amino acids (PFAA) in lambs given reconstituted cows' whole milk is described. In both the pre-treatment and post-treatment samples, the heavier lambs appeared to have lower plasma levels of all EAA, and high plasma levels of glycine, serine, urea and ammonia. In the lighter lambs, there were pronounced responses of PFAA levels to changes in the dietary proportion of EAA. At low proportions, the levels of most EAA in plasma were low. Lysine and phenylalanine were exceptions. In addition, levels of many non-essential amino acids (non-EAA), particularly serine and glycine, were high. At high proportions of EAA, plasma levels of all EAA, especially methionine, rose markedly. Within the non-EAA, serine, proline and glycine were reduced, while taurine and cystathionine increased. In the plasma of the heavier lambs, the response of some amino acids to a given dietary change differed from the response in the lighter lambs. This was especially true of methionine, tyrosine, phenylalanine and arginine. There was also marked between-animal variation in plasma levels. When expressed as molar proportions of total PFAA, results were similar to those of the lighter lambs. There was a pronounced similarity between the response of the PFAA to diets with a low proportion of EAA, and the PFAA pattern characteristic of developing kwashiorkor. __________________ *Part II, Aust. J. Agric. Res., 28, 933 (1977).

Plasma free amino acid levels in human subjects after meals containing lactalbumin, heated lactalbumin, or no protein

Plasma free amino acids were measured in six adult human subjects at four consecutive 1/2 hr intervals following meals containing either 50 g lactalbumin, 50 g heated lactalbumin, or no protein. After the lactalbumin meal, all essential and several nonessential amino acids increased in the plasma. After the heated lactalbumin meal, these increases were either much less or did not appear. Following the no protein meal all measured plasma amino acids fell. The absence of a response to the heated lactalbumin meal was considered to be related to a drop in digestibility of heated lactalbumin as measured in rats.