Feeding and arginine deficient diets differentially alter free amino acid concentrations of hindlimb muscle in young rats

Summary The objective of these experiments was to examine short- and long-term (7 d) effects of arginine-deficient diets on free amino acid concentrations in hindlimb muscle of rats. In rats fed the control diet containing arginine (+Arg), muscle alanine and methionine concentrations were higher 1 and 2h after feeding compared to food-deprived rats, whereas branched-chain amino acids, arginine and asparagine concentrations were lower postprandially. In Experiment 1, rats were fed an arginine-deficient (–Arg) diet with glutamate (+Glu) substituted for arginine; alanine (+Ala), ornithine (+Orn) or citrulline (+Cit) were substituted for arginine in Experiment 2. In Experiment 1, arginine concentrations decreased in blood but not in muscle. This contrasts with rats fed –Arg/+Ala or –Arg/+Orn diets which had muscle arginine concentrations less than half the concentrations in controls or in rats fed the –Arg/+Cit diet. Muscle essential amino acids in Experiment 2 did not differ by diet, but muscle branched-chain amino acids were elevated relative to controls in the rats fed –Arg/+Ala or –Arg/+Orn diets; however, rats fed the –Arg/+Cit diet had levels similar to the controls. Also, muscle branched-chain amino acids were correlated with glutamine concentrations in both blood and muscle. The measurements in the post-meal period suggest that muscle amino acid concentrations may more closely reflect dietary amino acid patterns than do blood amino concentrations.Abbreviations BCAA branched-chain amino acids - BCKADH branched-chain ketoacid dehydrogenase - EAA essential amino acids - LNAA large neutral amino acids - NEAA nonessential amino acids - PDV portal-drained viscera - SELSM standard error of least squares means - SSA 5-sulfosalicylic acid - TAA total amino acids Mention of a trade name, proprietary product or specific equipment does not constitute a guarantee by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.     

Studies on the uptake of (14C) amino acids derived from both dietary (14C) protein and dietary (14C) amino acids by rainbow trout, Salmo gairdneri Richardson

Previous studies have shown that rainbow trout fed on diets containing whole protein have superior growth rates compared to fish fed on diets of similar amino acid composition but containing a high proportion of free amino acids. The influence of several nutritional factors on the uptake of radioactivity from food pellets containing either [U-^I4C] protein or [U-¹⁴C] amino acids into the systemic blood of trout has been investigated. The time taken for radioactivity in the free amino acid fraction of blood to reach a peak after a meal containing [U-¹⁴C] protein had been given was much shorter, and the level of radioactivity in the blood higher, in trout with almost empty stomachs than in fish with almost full stomachs; uptake of radioactivity into blood amino acids was also more rapid and reached much higher concentrations when pellets containing [U-¹⁴C] amino acids were fed than when [U-¹⁴C] protein was fed. Incorporation of radioactivity into blood protein continued for a much longer period and reached higher levels when a pellet containing [U-¹⁴C] protein was fed than when a pellet containing [U-¹⁴C] amino acids was fed. Previous dietary history (low or high protein intake) did not appear to affect the rate of absorption of amino acids from either protein or free amino acid pellets. The uptake rates from pellets containing free amino acids could be slowed by mixing the dietary amino acids with albumin. The distribution, postabsorption, of radioactivity in the different fractions of blood and liver suggested that incorporation of carbon residues into glycogen and lipid from an amino acid diet was greater than from a protein diet. The converse was true of incorporation of radioactivity into tissue protein.     

Indispensable amino acid concentrations decrease in tissues of stomachless fish,common carp in response to free amino acid- or peptide-based diets

Summary. The premise that free amino acid or dipeptide based diets will resolve the nutritional inadequacy of formulated feeds for larval and juvenile fish and improve utilization of nitrogen in comparison to protein-based diets was tested in stomachless fish, common carp (Cyprinus carpio L.) larvae. We examined the postprandial whole body free amino acid (FAA) pool in fish that were offered a FAA mixture based diet for the duration of 2 or 4 weeks. We found that the total amount and all indispensable amino acids concentrations in the whole body decreased after a meal. We then fed juvenile carp with dietary amino acids provided in the FAA, dipeptide (PP), or protein (live feed organisms; brine shrimp Artemia salina nauplii, AS) forms. Histidine concentrations in the whole fish body increased in all dietary groups after feeding whereas all other indispensable amino acids decreased in FAA and PP groups in comparison to the AS group. Taurine appears to be the major osmotic pressure balancing free amino acid in larval freshwater fish which may indicate a conditional requirement. We present the first evidence in larval fish that in response to synthetic FAA and PP diets, the whole body indispensable free AA concentrations decreased after feeding. This study shows that amino acids given entirely as FAA or PP cannot sustain stomachless larval fish growth, and may result in depletion of body indispensable AA and most of dispensable AA. The understanding of these responses will determine necessary changes in diet formulations that prevent accelerated excretion of amino acids without protein synthesis.     

Influence of exercise on plasma and muscle free amino acids in trained rainbow trout

Variations in the concentration of free amino acids in the muscle and plasma of trout submitted to 5 minutes of intense exercise have been studied. The responses of untrained fish and those trained performing the same type of exercise twice daily for 28 days are compared. Total amino acid concentrations in muscle tend to diminish after intense exercise. Significant decreases are observed in muscle content of alanine, beta-alanine, isoleucine and ornithine. Plasma amino acids tend to increase after exercise with significant differences in glutamate, GABA, methionine and NH4+. The small variations due to intense exercise suggest that the amino acids are mobilised. Training led to a decrease in total amino acid concentration in plasma but not in muscle, where levels of aspartate and ornithine increased. This suggests a metabolic adaptation to exercise, with amino acid level retention in the muscle.     

Free amino acids in plasma and tissue of rats born to underfed dams.

Amino acids were determined in plasma, muscle, and liver tissues of adult male rats born of mothers on restricted or nonrestricted diets during pregnancy and lactation. The concentrations of plasma alanine, glutamic acid, glycine, proline, arginine, and valine were significantly lower in the progeny of restricted mothers as compared to non-restricted mothers. Similar changes were observed in liver tissues. The concentrations of free amino acids in muscle of the perinatally malnourished progeny, however, did not differ significantly from those of the controls. The differences determined in this study are of special significance in view of the fact that the animals studied had been maintained on an adequate diet since weaning. The demonstrated effect of the maternal diet on the plasma aminogram of the off-spring some months later must be considered when interpreting plasma aminograms in studies of malnourished children.     

Comparative aspects of protein digestion and amino acid absorption in fish and other animals

1. Molar concentrations of amino acids in the content of subsequent parts of alimentary tract of rainbow trout and common carp have been calculated. 2. The ratio of free amino acid concentration in intestinal content to blood of carp most commonly was between 10 and 20 and decreased as digestion proceeded. 3. Free amino acid concentration in gut content of fish appeared several times higher than that in reptiles or mammals. 4. Absorption rate of amino acids in carp was most intense during the first 3 hr after feeding and generally similar to that found in caymans. 5. Release rate of amino acids from dietary protein was most intense in the second segment of carp intestine where most of amino acids were also absorbed. 6. Requirements of essential amino acids based on their absorption rate were determined.     

Beta-Alanine and other free amino acids during salinity adaptation of the polychaete Nereis japonica

The free amino acid pool was measured in the body wall muscle and in coelomic cells (eleocytes) of the polychaete Nereis japonica following adaptation to salinities between 6 and 44 per thousand. Beta-Alanine and glycine were the major amino acids comprising 35-60% of the total free amino acid pool in the body wall. In eleocytes, glutamate and lysine in addition to beta-alanine and glycine were the dominant free amino acids. In the body wall, the concentrations of beta-alanine were closely correlated with the ambient salinity between 12 and 35 per thousand. The concentrations of glycine rose initially but remained unchanged at concentrations above 26 per thousand. In both body wall and eleocytes, the mean total primary amine concentrations were correlated with the ambient salinities between 12 and 35 per thousand. The sum of amino acids determined by HPLC showed the same correlation in both tissues, but accounted only for 60-85% of the concentrations of total primary amines. The total protein content of the body wall was slightly higher at 44 per thousand compared to the lower salinities indicating dehydration of the tissues. Eleocytes swell at 6 per thousand and showed irregular amino acid concentrations indicating a loss of metabolic integrity.     

Variation in the free amino acid content of skeletal muscle of Ophicephalus punctatus (Bloch)

The skeletal muscle of Ophicephalus punctatus contains nine essential free amino acids, arginine, histidine, isoleucine, leucine, methionine, phenylalanine, threonine, valine and lysine, and eight non-essential amino acids, alanine, aspartic acid, cystine, glutamic acid, glycine, tyrosine, proline and serine. Histidine and lysine dominated the free amino acids pool. Seasonal variation was detected in the levels of histidine, arginine, leucine, phenylalanine, glycine, cystine and serine with highest values occurring in April and again in November. Changes were also detected in the concentrations of certain amino acids as the fish grew in size. Levels of free amino acids did not significantly differ between sexes. Factors effecting variation are discussed.     

Correlations between amino acid concentrations in brains of seizure-susceptible and seizure-resistant rats

We have examined the relationship between free amino acid concentrations in the brains of genetically seizure-susceptible and seizure-resistant rats. The concentrations of free amino acids in the two strains do not differ significantly in the inferior colliculus or the cortex. However, animal-to-animal variations in the concentrations of numerous amino acid pairs are highly correlated. Glutamic acid decarboxylase activities did not vary between the two strains.We conclude that the strong correlations reported between glutamate and taurine levels in several species are not unique to this amino acid pair. Furthermore, unlike the situation with some experimentally-induced epilepsies, genetic epilepsy is not associated with major disturbances in free amino acid concentrations. The high correlations between amino acid pairs in some cases may reflect variations in cellular and subcellular compartment sizes that are shared by several amino acids.     

Metabolic adjustments to varying protein intake in harbor seals (Phoca vitulina): evidence from serum free amino acids

Effects of varying dietary protein intake on serum free amino acid (FAA) concentrations were studied in harbor seals (Phoca vitulina) fed two different prey fish diets: either exclusively low-fat, high-protein walleye pollock (Theragra chalcogramma) or high-fat, relatively high-energy-density Pacific herring (Clupea pallasi). Significant differences in FAA concentrations and patterns were observed between the two diets. All essential amino acids (EAA), except methionine and phenylalanine, and two nonessential amino acids (NEAA), glycine and tyrosine, decreased when the diet was switched from herring to pollock and increased on switching back to herring. Both total EAA concentrations and EAA : NEAA ratios decreased with the elevated protein intake typical of a low-fat pollock diet, indicating an inverse correlation between EAA concentrations and dietary protein intake levels. We propose that differing dietary protein intake, caused by differences in macronutrient composition of the two prey fish species, induced a change in protein metabolism that was reflected in blood-circulating amino acids. These findings suggest that surveys of amino acid profiles may be useful to partially determine the protein metabolic status of harbor seals.     

Non-essential amino acid sources in crystalline amino acid diets for trout (Oncorhynchus mykiss)

A study was conducted over a 84-day period to evaluate glycine, L-glutamic acid and L-glutamine as sources of non-essential amino acids (NEAA) in dietary 'protein' consisting of crystalline amino acids only. The study was performed with a total of 1200 rainbow trout fingerlings ( Oncorhynchus mykiss ) of 48 g mean body mass. The addition of non-essential amino acids (NEAA) to essential amino acids (EAA) evidently improved growth and feed efficiency: glutamine was superior to glycine and glycine superior to glutamic acid. However, the best results in growth were obtained by adding a mixture of all three NEAA. The improvement of trout performance by glutamine may hypothetically be traced back to a better amino acid absorption capacity by a less acidic intestinal milieu. In consequence, the optimal EAA to NEAA ratio may have to be redefined.     

Impact of potassium,sodium, and salinity on the protein-and free amino acid content of wheat grain

A lysimeter study was conducted on Cajeme wheat (Triticum aestivum L.) to investigate the impact of salinity on protein and free amino acid content of the grain. Cross correlations were obtained between 16 different soil-plant-water based parameters and the concentration and total accumulation of amino acids. The results indicated that after 3 years of irrigation, the majority of protein bound and free amino acids increased in concentration in the grain. However, both free tryptophan and free proline revealed decreasing concentrations with increasing salinity. Free tryptophan showed a synergism between total accumulation, yield and concentration. Free proline concentrations decreased in association with increasing protein concentrations. Cross correlations of the 16 soil-plant-water based parameters with free and protein bound amino acids revealed significant correlations for free aspartic acid and glycine with total accumulation but not with concentrations. Only methionine plus cystine was lower than suggested FAO levels for essential amino acids and was lower in the third year than in the first year.     

Patterns of amino acid utilization by aquatic hyphomycetes

Summary The utilization of amino acids in leaf protein and leaf leachate by aquatic hyphomycetes was studied during decomposition in a combined field and laboratory experiment. Leaves were sampled from a stream which exhibited a seasonal variation in free amino acid concentration in surface water, reaching peaks in autumn and winter. In the leaf drift environment the concentration of amino acids was approximately two orders of magnitude higher than in surface water. Protein amino acid content, which was higher in alder leaves than in beech leaves, decreased exponentially and faster in alder leaves, so that protein amino acid content was similar in the two leaf types after 9–10 weeks decomposition. From 55% to 75% of leaf amino acids were used instantaneously by attached fungi, which grew well, especially on alder leaves, regardless of the presence of a grazing amphipod. If nitrogen was a limiting nutrient source for fungi, it appeared to be more advantageous to colonize alder leaves. Four times more fungal species were found on alder leaves than on beech leaves. The changes in concentration of amino acids in leaves and water was described by a set of differential equations. Rate constants for the transfer of amino acids from leaves and water were estimated from experimental data and the preference in fungi for protein-bound and free amino acids evaluated.The amounts of free amino acids in water absorbed by fungi varied between leaf types and leaves at different stages of decay. Experimental data showed a switching behaviour in fungal absorption of dissolved amino acids so that absorption became superproportional at a certain proportion of free amino acids available in the water.     

Uptake of intact amino acids by plants depends on soil amino acid concentrations

Studies in different ecosystems have shown that plants take up intact amino acids directly but little is known about the influence of free amino acid concentrations in the soil on this process. We investigated the effect of three different soil amino acid N concentrations (0.025, 0.13 and 2.5 μg N g^?1 soil) on direct uptake of four dual labelled (¹⁵N, ¹³C) amino acids (glycine, tyrosine, lysine, valine) in a greenhouse experiment using Anthoxantum odoratum as a model plant.Our results revealed that 8–45% of applied ¹⁵N was incorporated into plant root and shoot tissue 48 h after labelling. Additional ¹³C enrichment showed that 2–70% of this incorporated ¹⁵N was taken up as intact amino acid. Total ¹⁵N uptake and ¹⁵N uptake as intact amino acids were significantly affected by soil amino acid N concentrations and significantly differed between the four amino acids tested.We found a positive effect of soil amino acid concentrations on uptake of mineralized ¹⁵N relative to amino acid concentrations for all amino acids which was presumably due to higher diffusion rates of mineralized tracer to the root surface. However, intact amino acid uptake relative to amino acid concentrations as well as the proportion of total ¹⁵N taken up directly decreased with increasing soil amino acid N concentrations for all amino acids, irrespective of their microbial degradability. This effect is most likely controlled by the mineral N concentration in soil and perhaps in plants which inhibits direct amino acids uptake.Overall, we conclude that plant internal regulation of amino acid uptake controlled by mineral N is the main mechanism determining direct uptake of amino acids and thus a lower contribution of intact amino acid uptake to the plants N nutrition has to be expected for higher amino acid concentrations accompanied by mineralization in soil.     

Influence of dietary non-essential amino acid profile on growth performance and amino acid metabolism of Nile tilapia, Oreochromis niloticus (L.)

The quality of dietary protein is an important factor influencing the growth performance of fish. To evaluate the quality of protein, the variables commonly studied are the composition of the essential amino acids, the digestibility and the protein use efficiency. The goal of the present experiment was to test the effect of the dietary non-essential amino acid composition on the growth of Nile tilapia (Oreochromis niloticus). The fish were fed three purified diets differing only in their non-essential amino acid composition. The influence of the experimental diets on the growth performance, on the activity of enzymes involved in the amino acid metabolism, aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT), and on whole body delta(15)N values was investigated. Body mass, lipid, protein and energy gain differed significantly between the feeding groups. The activity of ASAT in the whole liver was significantly higher in fish with a positive protein balance compared to fish which lost protein. Whole body delta(15)N values of fish were negatively correlated with their body mass gain. Despite the poor utilisation of synthetic amino acids, the experiment indicates the importance of the dietary non-essential amino acid composition for the growth performance of fish. The study reveals the possibility to trace the utilisation of synthetic amino acids by determining the isotopic composition of dietary amino acids and tissues or whole bodies of animals.     

Plasma amino acid levels in rainbow trout (Oncorhynchus mykiss)

The time course of plasma amino acid concentrations was studied in adult rainbow trout (300 g mean body weight). After a starvation period of 2 days fish were force-fed either with fish protein concentrate or a mixture of acidic casein and Na-caseinate at a rate of 0.32% CP (N' 6.25) of body weight. Peak levels occurred for feeding fish protein concentrate 6–12 h and for the casein mix 18 h post-feeding. The increase of the essential amino acids was closely correlated to the amino acid profile of the test proteins, whereas the concentration differences of the non-essential amino acids were at no time correlated to the amino acid pattern of fish protein concentrate or even negatively correlated in case of casein. The limiting amino acids in the test proteins were determined by ranking the average concentration increases (decreases) of the individual essential amino acids. Accordingly, arginine and histidine were most deficient in casein; in fish protein concentrate tryptophan seems to be the first limiting amino acid, followed by isoleucine.     

Free amino acids in brain, liver, and skeletal muscle tissue of voles infected with Trypanosoma brucei gambiense.

The concentrations of several acidic and neutral amino acids of brain, liver, and skeletal muscle were determined in field voles, Microtus montanus, and compared to values obtained from voles harboring a chronic infection of Trypanosoma brucei gambiense. All of the amino acids examined were found at comparable levels in brain tissue from both groups of animals with the exception of tyrosine, which was reduced by approximately 45% in the infected voles. Similarly, the only difference noted in liver tissue was 32% decrease of free tyrosine in the infected animals. With respect to muscle tissue, in addition to a 45% reduction of free tyrosine in the infected voles, decreases of a smaller magnitude were also noted for threonine, glutamate, and valine. The relatively specific alteration of free tyrosine concentrations in the investigated tissues of trypanosome-infected animals suggests an alteration in host metabolism of this amino acid and/or parasite utilization.     

Hind leg muscle amino acid balances in cold-exposed rats

The changes in hind leg tissue (muscle and skin) amono acid pool size and arteriovenous balance were measured in rats subjected to 0–90 min of cold exposure (4°C). Tissue free amino acid pools presented a different composition pattern from protein amino acids. Muscle rapidly reacted to cold exposure by releasing small amounts of some amino acids (alanine, aspartate), with only small changes in pool size during the first 30 min. Amino acid oxidation was very limited during the whole period of cold exposure, since at all times tested there was either nil ammonia efflux or net absorption of ammonia and glutamine; i.e. the muscle was in positive nitrogen balance throughout the period studied. Thus most of the amino acid nitrogen taken up from the blood and not found in the free amino pools must have been incorporated into protein, since it was not oxidized, as shown by the glutamine and ammonia blance. The data on amino acid incorporation into proteins indicate that hind leg protein turnover is rapidly and widely modulated from a low initial setting upon cold exposure to a higher protein synthesis rate immediately afterwards, suggesting that protein turnover may have an important role in short-term events in cold-exposed muscle, in addition to its influence in long-term adaptation.     

Dietary protein content affects the profiles of extracellular amino acids in the medial preoptic area of freely moving rats

This study examined the effect of protein consumption on extracellular amino acid concentrations in the medial preoptic area (MPOA) of rats. Rats were given free access to diets containing 0, 25 or 50 % protein for 3-h duration, starting from the onset of dark cycle (1800 h). The microdialysis probe was implanted into the MPOA at 1500 h. Dialysates were collected every 20 min from 1700 h to 2100 h. Amino acid concentrations in dialysate samples were determined by reverse phase-HPLC. Extracellular amino acid concentrations in the MPOA were elevated by protein consumption within 20 to 40 min following the start of the meal. The 50 % protein diet resulted in increased (p<0.05) alanine, glutamine, isoleucine, leucine, methionine, tyrosine and valine concentrations, when compared with both baseline and the 0% protein diet. When the 25 % protein diet was fed, amino acid concentrations in the MPOA were between those after the 0 and 50% protein diets. The ratio of tryptophan to the total branched-chain amino acids in extracellular fluid was highest after the 0% protein diet and increased with time. We conclude that extracellular amino acid profiles in the MPOA are affected by dietary protein content.     

The establishment of essential and metabolically derived amino acid profiles in developing chick embryo organs

The accumulation of certain essential and metabolically derived amino acids in the free amino acid pools of three excitable tissues has been studied in the chick embryo. Valine together with leucine are at the onset present in the yolk at higher concentrations than any of the other essential amino acids. By 15 days all the amino acids studied have accumulated in the embryonic pools at a higher rate than valine, although certain amino acids, such as phenylalanine or methionine, always remain at lower relative concentrations than valine. This reflects their low supply in the yolk, rather than a more rapid rate of disappearance (utilization). During early embryogenesis (E₂–E₄), tissues preferentially concentrate glutamic acid, besides taurine and phosphoethanolamine (6). The next distinct stage of development (E₄–E₇) is marked in the brain by a gradual rise in glutamic acid, glutamine and aspartic acid; the same three amino, acids do not demonstrate a further increase in the pool of the heart, while in the whole eye the amino acid profile begins to resemble the blood. Leucine in all three tissues declines rapidly, to reach isoleucine levels by day 7 of development; tyrosine increases slowly in apparent reciprocity to an equally gradual phenylalanine decrease. Into the second week of embryo growth (E₇–E₁₅), GABA appears in the mesencephalon (E₇) and the eye (E₉–E₁₀). In the mesencephalon, the free amino acid pool composition exhibits a rather sudden increase of most metabolically derived amino acids. Glutamic acid and glutamine in the brain increase in parallel; the rate of GABA and aspartic acid accumulation is slower, and for GABA stabilizes on day 14, as does glutamine. In the eye, by day 15, GABA levels are more closely aligned with the aspartic acid content. Finally, throughout embryogenesis serine fluctuations in blood and tissues are in parallel with those of threonine, and different from glycine or alanine which also change in tandem.