Concentrations Of Other Amino Acids Research Articles

Changes of plasma L-arginine levels in spontaneously hypertensive rats under induced hypotension.

Nicardipine, a dihydropyridine type calcium channel blocker, was infused at two flow-rates into spontaneously hypertensive (SH) and control normotensive Wistar-Kyoto (WKY) rats (young, 6-week-old and adult, 23-week-old, n = 5) under pentobarbital anesthesia, to cause hypotension. Mean arterial blood pressure and the concentrations of plasma amino acids and norepinephrine (NE) were measured before infusion and at each step of the infusion. The reduction in blood pressure caused by nicardipine induced a decrease in plasma L-arginine concentration in both young and adult SH rats, this effect being larger in adult rats. There was no significant change in plasma levels of L-arginine in age-matched WKY rats. The concentration of other amino acids did not change in both rat strains. On the contrary, there was an increase in plasma NE concentration in both SH and WKY rats after infusion with nicardipine. Plasma L-arginine concentration showed a good inverse correlation with the logarithm of plasma NE concentration in SH and WKY rats and the correlation was expressed as Y = -alpha log(X) + m (Y, plasma L-arginine concentration (nmol/mL); X, plasma NE concentration (pmol/mL); alpha, a slope; and m, an intercept). alpha, 43.0 and 4.35 for 23-week-old SH and WKY rats, respectively, and 17.0 and 4.0 for 6-week-old SH and WKY rats, respectively. The present data together with previous data suggest a direct noradrenergic stimulation of the synthesis of nitric oxide (NO) from L-arginine. The findings also indicate an impairment of the L-arginine metabolism or pools in SH rats compared with WKY rats. The deficiency of L-arginine increases with the age of SH rats and could be related to the development and maintenance of hypertension due to inefficient production of NO.

GC-MS analysis of diaminopimelic acid stereoisomers and amino acid enantiomers in rumen bacteria.

The amounts and the configuration of the stereoisomers of 2,6-diaminopimelic acid (Dap) and the enantiomeric content of other amino acids were determined in five individual species (Fibrobacter succinogenes, Streptococcus bovis, Selenomonas ruminantium, Prevotella ruminicola and Anaerovibrio lipolytica) of rumen bacteria, and in samples of mixed rumen bacteria isolated from sheep. The separation and quantification of the Dap stereoisomers was achieved by gas chromatography (GC) of trifluoroacetyl 2-propyl esters on a Chirasil-L-Val fused silica column, and detection was achieved by selected ion monitoring mass spectrometry (SIM-MS). No isomers of Dap were detected in S. bovis and P. ruminicola, two of the bacterial isolates. LL- and DD-Dap were not detected in any of the bacterial samples. As only the meso-isomer of Dap was detected in these microorganisms, it was quantified by adding LL-Dap as an internal standard before the bacteria were acid-hydrolyzed. Amounts of between 4.8 and 12.0 mg meso-Dap per gram of bacterial dry matter (DM) were determined. The presence in the rumen bacteria of free amino acid enantiomers, extractable with 70% aqueous ethanol, were determined by GC-SIM-MS; the D-amino acids were predominantly Ala, Asp and Glu, but there was considerable variation between the species.

Ruminal Escape and Apparent Degradation of Amino Acids Administered Intraruminally in Mixtures to Cows

The apparent ruminal degradation and escape of amino acids (AA) administered in 9 different mixtures of essential AA and 8 different mixtures of nonessential AA were studied using two cows fitted with ruminal cannulas. The 600-mmol AA mixtures, which were administered intraruminally using polyethylene glycol as a liquid marker, contained equal amounts of two, four, or eight AA. The amounts of each of the AA in the mixtures were 300, 150, and 75 mmol, respectively. Ruminal degradation and escape were compared with values previously reported for AA administered individually. Across doses, the mean rate of initial degradation (degradation during the 1st h after administration) of essential AA was 26% when the AA were administered in mixtures and 45% when the AA were administered individually. For nonessential AA, the corresponding values were 34 and 54%. Across doses, mean ruminal escape during the first 8h after essential AA administration was 22% when the AA were administered in mixtures and 16% when the AA were administered individually. For nonessential AA, the corresponding values were 13 and 11%. After intraruminal administration of AA, both individually and in mixtures, significant negative correlations were found between rates of degradation during the 1st h and ruminal escape during an 8-h period. Some AA mixtures caused a net increase in the concentration of other AA in ruminal fluid 1h after administration. Twelve of the mixtures that did not contain Ala caused a considerable net increase in the concentration of this AA, and 3 AA mixtures containing Arg and Ala caused a marked net increase in the concentration of Trp.

Effect of serine and ethanolamine administration on phospholipid-related compounds and neurotransmitter amino acids in the rabbit hippocampus.

The report concerns mechanisms for the increase of extracellular levels of ethanolamine and phosphoethanolamine in CNS regions, such as the hippocampus, in transient brain ischemia, hypoglycemia, seizures, etc. L-Serine (2.5-10 mM), D-serine (10 mM), or ethanolamine (10 mM) was administered for 20 min via a microdialysis tubing to the hippocampus of unanesthetized rabbits. The concentrations of primary amines were determined in the dialysates. When levels were elevated 10-100 times in the extracellular fluid, L-serine caused a dose-dependent increase of the concentration of extracellular ethanolamine. Ethanolamine caused a corresponding, although somewhat smaller, increase in serine levels. Furthermore, L-serine also induced an increased concentration of phosphoethanolamine that was delayed in time relative to the peak of ethanolamine. D-Serine was as effective as L-serine in raising ethanolamine levels but had no effect on phosphoethanolamine. Ethanolamine, but not L-serine, also increased extracellular glutamate/aspartate levels in an MK-801-dependent fashion. A similar effect, but delayed in time, was observed with D-serine. These effects were inhibited by MK-801. The concentrations of other amino acids were not significantly affected. The characteristics of the effects are suggestive of base exchange reactions between serine and ethanolamine and between ethanolamine and serine glycerophospholipids, respectively, in neuronal plasma membranes.

Unusually high concentration of free glycine in the midgut content of the silkworm, Bombyx mori, and other lepidopteran larvae

Abstract In the course of investigating the digestion and the absorption of dietary protein by the silkworm, Bombyx mori, reared on an artificial diet, we found the existence of an unusually high concentration of free glycine in the midgut content compared with other amino acids. To test whether this free glycine is from diet or from the silkworm itself, silkworm larvae were fed a diet without a protein source for 1 day and the free amino acids in the midgut content were then analyzed. Unexpectedly, the concentration of free glycine in the midgut content was still high (8.98 μmoles/g midgut content). In contrast, the concentrations of other amino acids were very low, and none of them exceeded 1 20 that of glycine. The concentration of free glycine was high in the anterior half of the midgut, and it decreased toward the posterior region. Free glycine was virtually undetected in the feces. To examine if this phenomenon has any generality, the same experiments were repeated with the sweet potato hornworm, Agrius convolvuli, and the rice armyworm, Pseudaletia separata. A phenomenon similar to that in the silkworm was observed in Agrius convolvuli, but in Pseudaletia separata, no amino acid, including glycine, had a high concentration. We also found that an unusually high concentration of free glycine exists in the digestive juice of Bombyx mori. These results suggest that free glycine is secreted into the intestinal lumen and that the free glycine might have some unknown biological role.

Quantitative changes of amino acid distributions in the rat vestibular nuclear complex after unilateral vestibular ganglionectomy.

Changes of amino acid concentrations in the vestibular nuclear complex (VNC) during lesion-induced vestibular compensation were studied in rats after unilateral vestibular ganglionectomy. Distributions of 12 amino acids within the VNC were measured at 2,4,7, and 30 days after surgery, using microdissection of freeze-dried brain sections and HPLC. Glutamate decreased on the lesioned side in nearly all VNC regions. Changes were fully developed 2 days after lesion and persisted through 30 days. In some regions, glutamate decreased also on the unlesioned side, especially at longer survival times, so that bilateral asymmetries became reduced. Aspartate changes were similar to those of glutamate on either side. Lesion-induced glutamine asymmetry was usually opposite to that of glutamate. Although GABA concentration decreased at early survival times, it recovered at later times and sometimes increased in dorsal parts of lateral and medial nuclei. Taurine changes were similar to those of GABA in most regions. Glycine change was primarily limited to a bilateral decrease in the dorsal part of the lateral vestibular nucleus. Concentrations of other amino acids were much lower, but some showed postlesion changes.

Accumulation of extracellular glutamate by inhibition of its uptake is not sufficient for inducing neuronal damage: an in vivo microdialysis study.

It is well documented that neurons exposed to high concentrations of excitatory amino acids, such as glutamate and aspartate, degenerate and die. The clearance of these amino acids from the synaptic cleft depends mainly on their transport by high-affinity sodium-dependent carriers. Using microdialysis in vivo and HPLC analysis, we have studied the effect of the administration of inhibitors of the glutamate transporter (L-trans-pyrrolidine-2,4-dicarboxylate and dihydrokainate) on the extracellular concentration of endogenous amino acids in the rat striatum. In addition, we have analyzed whether the changes observed in the concentration of glutamate and aspartate were injurious to striatal cells. Neuronal damage was assessed by biochemical determination of choline acetyltransferase and glutamate decarboxylase activities, 7 days after the microdialysis procedure. In other experiments, pyrrolidine dicarboxylate and dihydrokainate, as well as two other inhibitors of the glutamate carrier, DL-threo-beta-hydroxyaspartate and L-aspartate-beta-hydroxamate, were microinjected into the striatum, and neuronal damage was assessed, both biochemically and histologically, 7 or 14 days after the injection. Dihydrokainate and pyrrolidine dicarboxylate produced a similar remarkable increase in the concentration of extracellular aspartate and glutamate. However, the former induced also notable elevations in the concentration of other amino acids. Clear neuronal damage was observed only after dihydrokainate administration, which was partially prevented by intraperitoneal injection of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate or by intrastriatal coinjection of 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline. No cell damage was observed with the other three glutamate carrier inhibitors used. It is concluded that an increased extracellular glutamate level in vivo due to dysfunction of its transporter is not sufficient for inducing neuronal damage. The neurotoxic effects of dihydrokainate could be explained by direct activation of glutamate postsynaptic receptors, an effect not shared by the other inhibitors used.

Overnight branched-chain amino acid infusion causes sustained suppression of muscle proteolysis

Short-term (3 to 4 hours) infusion of branched-chain amino acids (BCAA) has been shown to suppress muscle protein breakdown. Whether these effects are sustained with chronic elevations of BCAA is not known. In the present study, we examined the effect of an overnight (16-hour) systemic BCAA infusion on whole-body and skeletal muscle amino acid metabolism, as assessed by simultaneously measured 3H-phenylalanine and 14C-leucine kinetics in eight normal volunteers; 10 overnight-fasted subjects studied during a 4-hour saline infusion served as controls. Overnight BCAA infusion increased plasma BCAA concentrations by fivefold to eightfold, and this was associated with a 20% to 60% decline in arterial concentrations of other amino acids. For Phe, this decline was mediated by a reduction in the systemic rate of appearance ([R a] 0.38 ± 0.03 v 0.60 ± 0.01 μmol/kg/min for BCAA and saline, respectively, P < .001). Endogenous Leu R a, calculated more indirectly as the difference between the total Leu R a and the unlabeled Leu infusion rate, did not differ between groups. In the forearm, overnight BCAA infusion resulted in a diminished net release of Phe (−3 ± 2 v −18 ± 4 [saline] nmol/min/100 mL, P < .02), and BCAA balance became markedly positive (751 ± 93 v −75 ± 30, P < .001). The diminished net forearm Phe release was accounted for by a decrease in local Phe R a ( P < .02). As with the systemic endogenous Leu R a, forearm Leu R a was not reproducibly affected by infused BCAA. These findings suggest a need for caution in the application of amino acid tracer kinetic methods when tracer and unlabeled tracee are infused simultaneously. In conclusion, overnight BCAA infusion caused a sustained decline in most plasma amino acids and in net forearm release of Phe, effects attributable to a sustained suppression of whole-body and muscle proteolysis.

Transport of metal micronutrients in the phloem of castor bean (Ricinus communis) seedlings

The metal micronutrients (MN) copper, iron, manganese, and zinc are transported via the phloem in the course of remobilization and circulation. The extent of these processes and transport species are still largely unknown. The Ricinus seedling was used to study the transport of these metal micronutrients as well as their interactions with the plant‐endogenous chelator nicotianamine (NA) by daily measurements of the concentrations in the seedling parts and in the sieve tube sap obtained from a cut at the hypocotyl hook.The concentrations of these micronutrients in the phloem exudate decreased slightly from day 4 to day 8 of seedling development. Maximum values at day 4 were 65 μM for Zn, 63 μM for Fe, 27 μM for Cu, and 12 μM for Mn. The phloem transport rates reached maxima of 0.12 nmol cm−2h−1 for Zn and Fe at days 6 and 7, corresponding to the maximum exudation rates. The magnitude of these transport rates were in agreement with the net translocation rates estimated by analyses of the concentrations in the individual seedling parts.The NA content of the seedlings increased from day 0 (seed before sowing) until day 8, from 16 nmol to 474 nmol, which corresponds to an average net synthesis rate of about 100 nmol day−1 between the days 4 and 8. The NA:MN ratio was constant at 0.5 in the seedlings within this period. The NA concentrations and the sum of the concentrations of all four micronutrients in the sieve tube sap showed a constant ratio of 1.25 over the entire experimental period. Thus, both complex partners were subject to a cotransport in the phloem.Removal of the supplying endosperm led to a decrease in MN and NA concentrations in the sieve tube sap to about 80% while an average excess of NA of 1.1 was maintained. Since the concentrations of other amino acids, also possible chelators of metal micronutrients, fall to about 10% after removal of the endosperm, their role seems to be negligible as vehicles of MN transport in the phloem. Thus it is suggested that the divalent micronutrients considered in this study are loaded and maybe transported as NA complexes.

Amino acids, serotonin, and 5-hydroxyindoleacetic acid following foot shock in rats

Concentrations of tryptophan, serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in brain and plasma, as well as plasma amino acid composition, were measured after 1-h foot shock. Stress induced a rise in both plasma and brain 5-HIAA, whereas 5-HT concentration was found to be increased only in plasma. A prominent rise in brain tryptophan was observed, whereas in plasma, foot shock caused a significant increase only in tryptophan level. Concentrations of other amino acids were found to be either decreased or unchanged. Ratio of tryptophan to the other long-chain neutral amino acids increased significantly following foot shock. It is possible that stress-related changes in 5-HT turnover are due to increased plasma tryptophan, in turn causing a rise in brain tryprophan, necessary to cope with enhanced 5-HT metabolism, reflected as a rise in 5-HIAA levels.

Relations between carbon and nitrogen during growth of Nannochloropsis oculata (Droop) Hibberd under continuous illumination.

Growth of the marine eustigmatophyte Nannochloropsis oculata (Droop) Hibberd was Followed through two periods of batch growth from stationary phase until cessation of net C-fixation. Growth continued for two generations after exhaustion of the N-source (100μM NH4 + ), with an increase in the cell C/N mass ratio from 6 to 28. N-deprived cells had a larger mean volume (130%) than N-replete cells. Intracellular concentrations of carotenoids and Chla correlated with cell-N until exhaustion of the N-source, when Chla ml-1 of culture declined significantly. The contribution of intracellular amino-N to cell-N was less than 3% throughout exponential and stationary phases. The major intracellular amino acids were glutamate (Glu), glutamine (Gln) and alanine; concentrations of tyrosine (on a population basis) increased steadily during N-deprivation. The intracellular concentrations of other amino acids showed fluctuations corresponding with changes in growth rate (e.g. arginine) or cell-N (e.g. glycine). The intracellular ratio of Gln/Glu reached a peak of more than 26 within 3 h of inoculation of stationary phase cells into fresh medium, before falling to around 0.6 during exponential growth, and then remained below 0.1 after NH4 - exhaustion. Of the extracellular amino acids, concentrations of alanine and serine remained relatively constant throughout, while those of glycine, glutamate and of total dissolved free amino acids increased during exponential and early post-exponential phases, before levelling off at 1.4μM amino-N. The behaviour of Nannochloropsis oculata is contrasted with the growth and physiology of Isochrysis galbana.

Protein synthesis in ovine muscle and skin: Sequential measurements with three different amino acids based on the large-dose procedure

1. 1. Protein synthesis has been determined in biopsies from ovine skin and muscle by sequential use of three [ 13C] amino acids, valine leucine and phenylalanine, as large-dose injections. 2. 2. Leucine and phenylalanine increased plasma insulin concentrations within 40 min of injection. 3. 3. All three amino acids decreased the plasma concentrations of other amino acids. 4. 4. Intracellular free amino acids in muscle decreased while those in skin increased. 5. 5. The fractional rates of protein synthesis were similar, regardless of which amino acid was used, although the rates for muscle were significantly less than for skin (2.1 vs 11.0%/day, P < 0.001).

Nitrogen Pools in Taproots of Medicago sativa L. After Defoliation

Summary Alfalfa ( Medicago sativa L.) accumulates organic reserves in taproots that are thought to be used as substrates for newly developing shoots after defoliation. Two experiments were conducted to determine if specific N pools in taproot tissues undergo depletion and reaccumulation following defoliation. In Exp. 1, bark tissues of taproots of ‹Hi-Phy› alfalfa had higher concentrations of total N, soluble NH 2 -N and buffer-soluble protein than did wood tissues. Concentrations of these N pools declined in both tissues after defoliation and then reaccumulated after 21 d of regrowth. In Exp. 2, two genotypes differed in concentration of N-containing pools, although trends following defoliation of both genotypes were similar to those observed in Exp. 1. ASP + ASN were the most prevalent of the amino acids found in bark and wood tissues, together comprising approximately 50% of the total amino acid pool. Concentration of the ASP + ASN pool declined markedly in roots following defoliation, while concentrations of other amino acids (LEU, ILE, TYR, and PHE) increased. Characterization of buffer-soluble proteins using SDS-PAGE indicated that specific proteins with molecular masses of 15 and 19 kDa were depleted, especially in bark tissues, as soluble protein concentrations declined. The depletion of specific amino acids and certain buffer-soluble proteins from taproots during regrowth of defoliated alfalfa suggests that these N-pools may be utilized as a source of N during foliar regrowth after defoliation.

Changes in plasma amino acid patterns and wool growth in response to abomasal injections of amino acids during late pregnancy and early lactation

Provision of sulfur-containing amino acids into the abomasum has increased wool production in non-reproducing sheep and, on the basis of such studies, they have generally been considered as the primary limiting nutrients for wool growth. The specific amino acid needs of reproducing ewes were investigated in the current study. Three groups of pregnant ewes were fitted with temporary abomasal fistulae. For the last 3-4 weeks of pregnancy and the first 3 weeks of lactation, solutions containing sodium hydroxide (as a carrier) or methionine or a mixture of valine, arginine, lysine and threonine (VALT) were injected into the abomasum twice per day. The injection of methionine did not increase protein deposition during pregnancy; this was indicated by the failure of the treatment to lower the concentration of other amino acids in plasma, or increase liveweight, lamb birth weight or wool growth. Responses in early lactation were different with the methionine injected sheep having a lower concentration of free lysine, valine, alanine and serine in plasma, indicating an increased rate of protein deposition, and a faster growth rate in the ewes. Injections of VALT caused a decrease in the concentration of cystine and methionine in plasma and depressed wool growth and tensile strength. Theresults indicate that a lack of methionine was not limiting protein deposition during late pregnancy, but may have been during early lactation. Valine, arginine, lysine and threonine were not the primary limiting amino acids in late pregnancy or early lactation.

Growth, photosynthesis, respiration, and intracellular free amino acid profiles in the unicellular alga Cyanidium caldarium. Effect of nutrient limitation and resupply

Growth, intrácellular free amino acid pools and photosynthetic and respiratory activities in nutrient sufficient cells and in N‐ K‐ and P‐limited cells of Cyanidium caldarium (Tilden) Geitler, and responses to nutrient resupply were investigated. Addition of ammonium to N‐limited cells and of phosphate to P‐limited cells resulted in a stimulation of dark respiration and in a decrease in photosynthetic oxygen evolution. Addition of K to K‐limited cells had no effect on rates of photosynthesis and respiration. Nutrient limited cells and sufficient cells exhibited different free amino acid profiles. Upon resupply of ammonium to N‐limited cells levels of glutamine, citrulline, arginine, alanine, and serine increased. Also the levels of δ‐aminolevulinic acid (δ‐ALA) and putrescine increased notably. On adding phosphate to P‐limited cells the level of glutamate decreased significantly whereas the level of alanine increased and the concentrations of other amino acids remained unaffected. On adding potassium to K‐limited cells there was an increase in glutamate and citrulline concentrations, and a decrease in putrescine concentration, whereas concentrations of arginine and alanine remained at the very high levels observed already before addition. Resuspension of N‐ and K‐limited cells in a complete growth only after 25‐30h. In P‐limited cells resumption of growth in complete medium occurred progressively and reached the maximum rate 30h later. P‐, K‐ and N‐ limited cells resuspended into sufficient media showed different rates of ammonium and phosphate assimilation. The pattern of recovery from nutrient limitation is discussed according to the cellular role fulfilled by the nutrient which was growth rate‐limiting.

Amino acid pools in nutrient limited Cyanidium caldarium and responses to resupply

Amino acid pools in Cyanidium caldarium (Tilden) Geitler, growing under conditions of sufficiency of nutrients (sufficient cells), or under conditions of nitrogen, potassium or phosphorus limitation (N-, K- or P-limited cells), and responses upon nutrient resupply were investigated. Glutamate was the dominant amino acid in sufficient cells [11.2 μmol ml −1 packed cell volume (pcv)], in N-limited cells (7.71 μmol ml −1 pcv) and in P-limited cells (7.46 μmol ml −1 pcv), whereas in K-limited cells the dominant amino acid was alanine (8.83 μmol ml −1 pcv). Other amino acids detected occurring at significantly high concentrations were: citrulline, alanine, aspartate, glutamine and δ-aminolevulinic acid in sufficient cells, alanine in N-limited cells; alanine, citrulline, serine, arginine and asparagine in P-limited cells; glutamate, arginine, glutamine, citrulline, asparagine, serine, aspartate and putrescine in K-limited cells. On adding NH 4 + to N-limited cells the level of glutamate decreased and then increased to the starting value; there occurred an increase in the level of glutamine, aspartate, citrulline, arginine, alanine, serine, as well as of δ-ALA and putrescine. Resupply of Pi to P-limited cells caused a significant decrease of glutamate and a concomitant increase of alanine, but was without efrect on the concentration of other amino acids. On adding K + to K-limited cells there was an increase of glutamate and citrulline, and a decrease of putrescine, whereas arginine and alanine remained unvaried at the very high level occurring before addition.

Thermogenic actions of tryptophan in the rat are mediated independently of 5-HT

Serotonin (5-HT) has been implicated in the central control of energy balance, via inhibition of food intake and stimulation of thermogenesis. Its rate of synthesis in brain is dependent on the availability of its precursor amino acid, tryptophan. The objective of the present study was therefore to investigate the thermogenic actions of tryptophan and to determine whether these actions are mediated by 5-HT. Central or peripheral injections of 5-HT (i.c.v.; 0.5–40μg), 5-hydroxytryptophan (5-HTP) (i.c.v.; 20μg) or tryptophan (i.p.; 20 mg/kg, i.c.v.; 12–60 μg) significantly increased resting oxygen consumption (uc|dot|V O2 by approximately 15–20%) in conscious rats, without apparent effects on physical activity. Small increases (5–7%) in uc|dot|V O2 were also observed following peripheral injections of aspartate or glycine (20 mg/kg) but not taurine, whilst central injection of tyrosine or leucine (15–18 μg) significantly increased uc|dot|V o2 by 15%. We have previously reported that the thermogenic and anorexic actions of 5-HT are mediated by corticotropin-releasing factor (CRF) 16. In the present study, the thermogenic actions of 5-HTP, like those of 5-HT, were significantly reduced by pretreatment (5 min before) with the CRF antagonist α-helical CRF 9–41 (25 μg, i.c.v.) or a polyclonal antibody to CRF. However, the thermogenic actions of tryptophan were not significantly modified by pretreatment with either the 5-HT antagonist, methylsergide (20 μg, i.c.v.) or with the CRF antagonist or antibody and thus appear to act through different mechanisms to 5-HT. Despite the well-documented effects of tryptophan on serotonergic systems, tryptophan administration (i.c.v.) did not significantly affect the concentration of either 5-HTP, 5-HT or its metabolite 5-HIAA within the cerebrospinal fluid or in the whole hypothalamus, measured 1 h post-injection. Similarly, no changes in the concentrations of other amino acids were observed either in the plasma or whole hypothalamus. In summary, central thermogenic actions of tryptophan are described which appear to be independent of 5-HT.

Effects of Dietary Protein Sources on Performance and Plasma Amino Acid Concentration of Broilers.

Preceding to a series of experiment to determine the amino acid requirement of broilers, the effect of quality and quantity of dietary protein sources on the performance and concentration of plasma amino acid was studied. To the basal diet mainly consisted of corn, fish meal, soybean meal or whole egg protein was added as a main protein source to contain 0 and 25%, 5 and 40%, or 5 and 20% of diet. The two diets containing same protein sources were mixed to obtain diets containing 6 levels of crude protein (CP) arithmetically. Four-day old male broiler chicks were fed ad libitum experimental diets and water. On the 10th day, the body weights and feed consumptions were recorded and blood samples were taken to determine the plasma amino acid concentration. The maximum body weight gains were obtained at 16.5, 21.9 and 14.5% in dietary CP levels, and the minimum feed conversion ratios were obtained at 16.5, 18.8 and 15.5% in dietary CP levels for fish meal, soybean meal and whole egg protein, respectively. Several amino acid contents of diets which achieved the maximum body weight gains and the minimum feed conversion ratios were calculated to be lower than the NRC requirements in all diets, e.g. arginine, lysine, sulfur containing amino acid and tryptophan in fish meal diet, sulfur containing amino acid in soybean meal diet and arginine, lysine, sulfur containing amino acid, threonine and tryptophan in whole egg protein diet. The response pattern of plasma amino acid concentrations to the dietary CP levels were classified into three types. The concentrations of histidine and phenylalanine were not affected by kind and levels of protein sources. The concentrations of other amino acids remained low and then increased linearly with increasing the corresponding dietary amino acids. The concentrations of alanine, aspartic acid, glycine and glutamic acid reached plateaus at high protein levels. It was left as a subject to be discussed in future whether a break point of each amino acid agrees with the real requirement of amino acid.

Beneficial Effect of Intravenous Taurine Infusion on Electroretinographic Disorder in Taurine Deficient Rats

We investigated the effect of intravenous taurine infusion on the electroretinogram (ERG) of taurine-deficient rats produced by treatment with guanidinoethyl sulfonate (GES), a taurine transport inhibitor. Mother rats were fed a taurine-free diet and given drinking water containing 1% GES from 2 weeks of gestation to weaning. The same feeding conditions were applied to male offspring after weaning. Both ERG measurement and continuous infusion of taurine at a dose of 10, 30 or 100 mg/animal/day were performed for 3 weeks from 7 to 10 weeks of age. GES-treatment reduced a- and b-wave amplitudes to 50% of the control levels and also increased b-wave latencies. Intravenous infusion of taurine improved these ERG abnormalities in a dose-dependent manner. Taurine concentrations in plasma, eyes and brain were also decreased by treatment with GES, and dose-dependent recovery was observed after infusion with taurine, although the concentrations of other amino acids were not affected by GES-treatment and infusion of taurine. Observations of morphological changes revealed that the retinal damage in GES-treated animals was decreased by taurine infusion. These results indicate that the changes in ERG and retinal structure observed in taurine deficiency are improved by intravenous infusion of taurine.

Growth of the Maize Primary Root at Low Water Potentials

Seedlings of maize (Zea mays L. cv WF9 x Mo 17) growing at low water potentials in vermiculite contained greatly increased proline concentrations in the primary root growth zone. Proline levels were particularly high toward the apex, where elongation rates have been shown to be completely maintained over a wide range of water potentials. Proline concentration increased even in quite mild treatments and reached 120 millimolal in the apical millimeter of roots growing at a water potential of -1.6 megapascal. This accounted for almost half of the osmotic adjustment in this region. Increases in concentration of other amino acids and glycinebetaine were comparatively small. We have assessed the relative contributions of increased rates of proline deposition and decreased tissue volume expansion to the increases in proline concentration. Proline content profiles were combined with published growth velocity distributions to calculate net proline deposition rate profiles using the continuity equation. At low water potential, proline deposition per unit length increased by up to 10-fold in the apical region of the growth zone compared to roots at high water potential. This response accounted for most of the increase in proline concentration in this region. The results suggest that osmotic adjustment due to increased proline deposition plays an important role in the maintenance of root elongation at low water potentials.