Elevation of transamination of branched chain amino acids in brain in acute ammonia toxicity

The activity levels of leucine, isoleucine and valine aminotransferases were determined in various cerebral regions, liver and muscle of rats injected with a large dose of ammonium acetate and were compared with those of normal animals. In brain the activity levels of both leucine and isoleucine aminotransferases were elevated in both preconvulsive and convulsive states. Valine aminotransferase activity was suppressed in brain stem and corpus striatum and was elevated in cerebellum and hippocampus in preconvulsive states. During convulsions its activity was suppressed in cerebral cortex and hippocampus. Under these conditions, there was a suppression of both leucine and valine aminotransferases in muscle. In liver, however, the activities of these enzymes were elevated. The results suggested that the glutamate required for glutamine formation in hyperammonaemic states in brain might be obtained from branched chain amino acids, especially leucine and isoleucine.     

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.     

Studies concerning the specificity of the effect of leucine on the turnover of proteins in muscles of control and diabetic rats.

The protein anabolic effect of branched chain amino acids was studied in isolated quarter diaphragms of rats. Protein synthesis was estimated by measuring tyrosine incorporation into muscle proteins in vitro. Tyrosine release during incubation with cycloheximide served as an index of protein degradation. In muscles from normal rats the addition of 0.5 mM leucine stimulated protein synthesis 36--38% (P less than 0.01), while equimolar isoleucine or valine, singly or in combination were ineffective. The three branched chain amino acids together stimulated no more than leucine alone. The product of leucine transamination, alpha-keto-isocaproate, did not stmino norborane-2-carboxylic acid (a leucine analogue) were ineffective. Leucine and isoleucine stimulated protein synthesis in muscles from diabetic rats.Leucine, isoleucine, valine and the norbornane amino acid but not alpha-ketoisocaproate or beta-hydroxybutyrate decreased the concentration of free tyrosine in tissues during incubation with cycloheximide; tyrosine release into the medium did not decrease significantly. Leucine caused a small decrease in total tyrosine release, (measured as the sum of free tyrosine in tissues and media), suggesting inhibition of protein degradation. The data suggest that leucine may be rate limiting for protein synthesis in muscles. The branched chain amino acids may exert a restraining effect on muscle protein catabolism during prolonged fasting and diabetes.     

β-Adrenergic Effects on Plasma and Brain Large Neutral Amino Acids Are Unaltered by Chronic Administration of Antidepressants

Effects of isoproterenol (3 mg kg-1, i.p. for 60 min) and salbutamol (3, 10 mg kg-1, i.p. for 60 min) on large neutral amino acid concentrations in rat plasma and brain were assessed. Phenylalanine, leucine, isoleucine, and valine were measured by gas chromatography with electron-capture detection; tyrosine and tryptophan were measured by HPLC with electrochemical detection. These drugs induced increases in brain tryptophan, tyrosine, phenylalanine, and valine and decreases in plasma tryptophan, tyrosine, leucine, isoleucine, and valine. Effects of salbutamol (3 mg kg-1, i.p. for 60 min) were assessed following chronic administration of phenelzine sulfate and desipramine.HCl (each drug 10 mg kg-1 per day, s.c. via Alzet 2ML4 osmotic minipumps for 28 days). There were no effects of these antidepressants on basal levels of large neutral amino acids in brain and plasma. In both brain and plasma, salbutamol-induced changes in large neutral amino acids were unaffected by these antidepressants. The results indicate that beta-adrenoceptor-regulated availability of plasma and brain large neutral amino acids is unaffected by chronic administration of tricyclic or monoamine oxidase inhibitor antidepressants.     

The effects of sodium arsenate on the free amino acid levels in erythrocytes and plasma in rats.

The effects of arsenate on the levels of free amino acids in rat plasma and red blood cells have been investigated. The biggest changes occur in the branched-chain amino acids valine, isoleucine and leucine which are markedly decreased. The levels of several other amino-acids also change. The effects on the amino acids are not due to a change in the food intake caused by dosing with arsenate. This has been shown by comparing the results with those on fasting rats (40 h). Branched-chain amino acids in particular are markedly increased in plasma of fasting rats as opposed to a decrease in arsenate-treated rats.     

The content of free amino acids in plasma of hens of different strains

Summary Free amino acids were estimated in the plasma of Leghorn, Cornish and White Rock hens, bred under identical conditions. It was found that the plasma of Leghorn hens had a lower content of amino acids. The differences were especially pronounced for proline, glutamic acid and glycine. It was established that a lower percentage of valine, leucine and isoleucine was typical of Leghorn hens in comparison with Cornish hens. The obtained results indicate that the level of free amino acids in blood plasma is genetically controlled     

No significant net uptake of branched chain amino acids by the liver of fed-mid pregnant rats

The hepatic balance for valine, leucine and isoleucine has been measured in anaesthetized virgin controls and 9 and 12-day pregnant rats. The liver of non gravid animals show fractional extraction rates of over 11.6% for valine, 17.6% for leucine and 16.8% for isoleucine. Fed mid-pregnant rats do not show either a significant net uptake nor a release of these amino acids. It is proposed that higher intestinal amino acid requirements for protein synthesis during mid pregnancy than before impregnation may be, in part, the cause of a decreased hepatic uptake and, thus, a different role for the liver in the amino acid inter-organ relationships during this period is suggested.     

Nitrogen sparing effect of a branched-chain amino acid infusion during an acute fast in guinea pigs

Thirty male guinea pigs (350–600 g) were fasted for 48–72 hours while receiving lactated Ringers solution through a catheter in the internal jugular vein which had been implanted just before the start of the experiment under halothane anesthesia. Ten of the animals also received leucine, isoleucine, and valine in their infusions at a level approximating their usual daily requirement for these amino acids. Eight of the animals received glucose in their infusion at a level which was isocaloric to the branched-chain amino acid infusion. There was a 37% improvement (p < .01) in nitrogen balance in the animals supplemented with the branched-chain amino acids compared to the completely fasted animals. Nitrogen balance was increased by 27% (p < .05) in the amino acid treated animals relative to the glucose treated group. These results may relate to the specific regulatory role of leucine, isoleucine, and valine on muscle protein turnover. In addition, the preferential oxidation of these amino acids in muscle may be a limiting factor in the overall reutilization of essential amino acids during early fasting.     

Some Effects of Protein Deficiency in Young Growing Pigs. II. Blood Plasma Free Amino Acids

The influence of protein deficiency, rehabilitation and total starvation on the free amino acid levels in the blood plasma of pigs has been investigated. It was found that the concentration of most amino acids was reduced during protein deficiency. The levels of leucine, isoleucine and valine were diminished by the greatest proportion, followed by threonine, tyrosine and citrulline. During the first few weeks of protein deficiency the levels of lysine, histidine and arginine were slightly increased, but later decreased below control values. Concentrations of glycine and alanine were altered in a similar way except that the initial increase was much more pronounced. The concentrations of most of these amino acids returned to control levels after rehabilitation. Total starvation led to an increase in concentration of leucine, isoleucine, valine, threonine and to a smaller extent phenylalanine, lysine, citrulline and arginine. The concentration of glycine, alanine and glutamic acid were very much reduced. The level of urea in the circulation dropped reversibly during protein deficiency and increased very much during total starvation.     

Ethanol impairs tryptophan transport into the brain and depresses serotonin

Alcoholics were found to have decreased plasma levels of tryptophan, the serotonin precursor, and a decreased ratio of tryptophan over amino acids competing for transport into the brain. Studies conducted in the plasma of rats and baboons with carefully controlled alcohol and dietary intake showed a decreased in the ratio of tryptophan over competing amino acids resulting mostly from increases in valine in the rat and in valine, leucine and isoleucine in the baboon. In the rat concomitant decreases in brain tryptophan and serotonin were noted. Central serotonin dificiency may contribute to the depressive states frequently seen in alcoholics.     

Branched-chain amino acids improve glucose metabolism in rats with liver cirrhosis

It is well established that impaired glucose metabolism is a frequent complication in patients with hepatic cirrhosis. We previously showed that leucine, one of the branched-chain amino acids (BCAA), promotes glucose uptake under insulin-free conditions in isolated skeletal muscle from normal rats. The aim of the present study was to evaluate the effects of BCAA on glucose metabolism in a rat model of CCl(4)-induced cirrhosis (CCl(4) rats). Oral glucose tolerance tests were performed on BCAA-treated CCl(4) rats. In the CCl(4) rats, treatment with leucine or isoleucine, but not valine, improved glucose tolerance significantly, with the effect of isoleucine being greater than the effect of leucine. Glucose uptake experiments using isolated soleus muscle from the CCl(4) rats revealed that leucine and isoleucine, but not valine, promoted glucose uptake under insulin-free conditions. To clarify the mechanism of the blood glucose-lowering effects of BCAA, we collected soleus muscles from BCAA-treated CCl(4) rats with or without a glucose load. These samples were used to determine the subcellular location of glucose transporter proteins and glycogen synthase (GS) activity. Oral administration of leucine or isoleucine without a glucose load induced GLUT4 and GLUT1 translocation to the plasma membrane. GS activity was augmented only in leucine-treated rats and was completely inhibited by rapamycin, an inhibitor of mammalian target of rapamycin. In summary, we found that leucine and isoleucine improved glucose metabolism in CCl(4) rats by promoting glucose uptake in skeletal muscle. This effect occurred as a result of upregulation of GLUT4 and GLUT1 and also by mammalian target of rapamycin-dependent activation of GS in skeletal muscle. From these results, we consider that BCAA treatment may have beneficial effects on glucose metabolism in cirrhotic patients.     

Changes in the concentrations of branched chain amino acids in the blood in response to alterations in the composition of a hypocaloric diet.

This report describes an investigation of the effect of an alteration in the amount of protein, carbohydrate and fat in hypocaloric diets on the concentration ratios of valine/(isoleucine + leucine) in the morning fasting blood in healthy men: in some cases the effect of a higher caloric diet was also analysed. During the nutrition periods, each over 10 days, the concentrations of branched chain amino acids and alanine, blood levels of insulin, glucose and free fatty acids and the nitrogen balance were estimated daily. With hypocaloric diets, as well as with hypercaloric diets, supplementation of food protein from 0.6 or 0.8 up to 2.0 g protein per kg body weight (isocalorically) induced a rise of the molar ratios of valine/(isoleucine + leucine) in blood from 0.98 to 1.25 (4600 kJ/d) or 1.06 to 1.45 (14600 kJ/d) respectively. A correlation of molar ratios of valine/(isoleucine + leucine) in the blood and the nitrogen balance could not be established. However, it is suggested that ratios above a limiting value exclude the possibility of a distinct negative nitrogen balance during 7 or 10 days of observation.     

Alanine and glutamine synthesis and release from skeletal muscle. II. The precursor role of amino acids in alanine and glutamine synthesis.

The synthesis and release of alanine and glutamine have been studied in the intact rat epitrochlaris skeletal muscle preparation. Aspartate, cysteine, leucine, valine, methionine, isoleucine, serine, theronine, and glycine increased significantly the formation and release of alanine from muscle. Cysteine, leucine, valine, methionine, isoleucine, tyrosine, lysine, and phenylalanine increased the rate of glutamine synthesis. Only ornithine, arginine, and tryptophan were without effect on the synthesis of either alanine or glutamine. Half-maximal stimulation of alanine and glutamine formation by added amino acids was observed with concentrations ranging between 0.5 and 1.0 mM. Increases in alanine and glutamine formation were not accompanied by changes in pyruvate production or glucose uptake. The progressive decline in alanine and glutamine synthesis noted on prolonged incubation was prevented by the addition of amino acids to the incubation medium. Stimulation of alanine synthesis by added amino acids was unaffected by inhibition of glycolysis with iodoacetate. Inhibition of alanine aminotransferase with aminooxyacetate significantly decreased alanine formation. Pyruvate and ammonium chloride did not increase further the rate of either alanine or glutamine formation above that produced by added amino acids. These data indicate that most amino acids are precursors for alanine and glutamine synthesis in skeletal muscle. A general mechanism is presented for the de novo formation of alanine from amino acids in skeletal muscle, and the importance of proteolysis for the supply of amino acid precursors for alanine and glutamine synthesis is discussed.     

Quantitative study of free amino acids in human eccrine sweat excreted from the forearms of healthy trained and untrained men during exercise

The free amino acids in eccrine sweat collected from the forearms of 20 healthy trained and 20 healthy untrained men during controlled exercise were determined quantitatively using ion exchange column chromatography. Sweat was deproteinized by adding an equal volume of 5% sulphosalicylic acid. The amino acid concentrations showed a constant qualitative pattern in sweat and large individual differences. Essential amino acids, such as isoleucine, leucine, lysine, methionine, phenylalanine, and valine were excreted in relatively small amounts. As compared to the trained men, untrained men showed statistically significantly higher concentrations in sweat for the following amino acids: Alanine, arginine, glycine, histidine, isoleucine, leucine, lysine, ornithine, phenylalanine, serine, taurine, threonine, tyrosine, and valine. No significant differences were found for citrulline, cystine, ethanolamine, and methionine. The comparison of the amino acid excretions in sweat obtained under controlled exercise and in urine showed that the amounts of amino acids excreted in sweat under controlled exercise were comparable to the losses of amino acids in urine.     

Lysosomal pool of free-amino acids

Free (non-protein) amino acids were measured in whole rat liver and in unmodified lysosomes which were prepared from rat liver by the technique of free-flow electrophoresis. Significant intralysosomal pools of threonine, serine, valine, cystine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine and arginine were found. No efflux occurred from rat liver lysosomes in isotonic buffered sucrose at 0°C, but all amino acids showed various degrees of efflux at 20⁰ and 37⁰.     

Glucose and free amino acids in the blood of lampreys (Lampetra fluviatilis L.) and frogs (Rana temporaria L.) under prolonged starvation

The content variation dynamics of glucose and free amino acids in blood plasma was followed for lampreys and frogs from autumn till spring, when the exogenous feeding is switched off. In October, the glucose level is rather high (8-10 mM) in blood plasma of both lampreys and frogs. It falls by 50% during winter and falls to a critically low level (1-2 mM) during spring. The lamprey plasma amino acid levels increase by 74% from November to April and thus reach the lower limit known for mammals. The amount of free amino acids in frog plasma decreases by 40% by spring in comparison with the values in autumn. More intensive proteolysis in lamprey tissues compared with that in frog tissues has been confirmed by quantitatively determining leucine, isoleucine, and valine in the blood of these animals. Besides these three amino acids, alanine, glycine, lysine, threonine and, in certain periods, tyrosine have been found to be quantitatively significant in the plasma of both animals.     

Protein metabolism in the newborn lamb. IV. Consequences of amino acid and lactose ingestion

A study was made on protein metabolism and hormonal changes following birth in newborn lambs fed amino acids alone or in combination with lactose. Eight newborn lambs taken from their mother immediately after birth were fed hourly for 8 h, either with a solution of peptides and free amino acids obtained by mild hydrolysis of whey proteins (4 lambs; diet AP) or with the same solution + lactose (4 lambs; diet APL). L-[4,5-3H] leucine was continuously perfused into a jugular vein for 6 h when the lambs were 2 h 30 min old. Plasma glucose and insulin levels increased after birth in APL lambs whereas they decreased in the AP; these differences were significantly different. Plasma cortisol levels remained unchanged throughout the experiment. Free essential amino acid levels did not vary when lambs were older than 4.5 h; they depended on the corresponding amino acid intakes. Plasma free threonine, valine, isoleucine, leucine, tyrosine and lysine were lower in APL than in AP lambs. The plasma leucine irreversible loss and leucine oxidation were higher in AP than in APL lambs. The plasma flux of leucine from whole body protein breakdown was lower in APL than in AP lambs inasmuch as the plasma flux of dietary leucine may be estimated by the amounts of leucine ingested in both cases. No significant difference was found for the fractional synthesis rates of tissue proteins such as liver, skin, skeletal muscle, lung, brain and whole body. These rates for skin, muscle and whole body were close to those previously measured in colostrum fed lambs. The increase in whole body protein accretion resulting from lactose feeding in combination with amino acids seemed to result from a decreased protein breakdown that could be mediated by the insulin response.     

INCREASE IN LARGE NEUTRAL AMINO ACID TRANSPORT INTO BRAIN BY INSULIN

The administration of oral glucose to fasted rats produced a decline of all large neutral amino acid levels in serum, including that of the free fraction of tryptophan. In addition to this well known effect, it also decreased the brain concentrations of leucine, isoleucine and valine, while increasing those of tryptophan, tyrosine and phenylalanine. The total concentration of large neutral amino acids in serum was decreased by 44%, while it was slightly increased in brain. Analogous results were obtained in 4 rats injected with exogenous insulin. Moreover, the administration of either glucagon or isoproterenol to rats force-fed with glucose produced a decline in total serum tryptophan concentration proportional to that of the rise in FFA, while it increased free serum tryptophan and brain tryptophan levels. It can be concluded that insulin stimulates the transport of large neutral amino acids from blood to brain and that the level of free serum tryptophan also controls the entry of tryptophan into the brain under the influence of insulin.     

Excess Leucine Intake Induces Serine Dehydratase in Rat Liver

We have hypothesized that rat liver serine dehydratase (SDH) is induced in response to the amount of surplus amino acids from dietary protein. In the present study, we found that excess leucine intake strongly induced SDH activity in the liver but not in the kidney of rats. The increase in activity was accompanied by increases in the levels of SDH mRNA. On the other hand, isoleucine and valine had little effect on SDH induction. These results support our hypothesis and suggest that leucine is a signal for SDH induction.     

Excess leucine intake induces serine dehydratase in rat liver

We have hypothesized that rat liver serine dehydratase (SDH) is induced in response to the amount of surplus amino acids from dietary protein. In the present study, we found that excess leucine intake strongly induced SDH activity in the liver but not in the kidney of rats. The increase in activity was accompanied by increases in the levels of SDH mRNA. On the other hand, isoleucine and valine had little effect on SDH induction. These results support our hypothesis and suggest that leucine is a signal for SDH induction.