Biomedical subjects

J H James

Publications and source records attributed to J H James.

At least 73 records · Page 4Linked to original sources

PubMed1986

Inhibited muscle amino acid uptake in sepsis.

Amino acid uptake in vivo was determined in soleus (SOL) muscle, diaphragm, heart, and liver following intravenous injection of [3H]-alpha-amino-isobutyric acid ([3H]-AIB) in rats made septic by cecal ligation and puncture (CLP) and in sham-operated controls. Muscle amino acid transport was also measured in vitro by determining uptake of [3H]-AIB in incubated extensor digitorum longus (EDL) and SOL muscles. Results were expressed as distribution ratio between [3H]-AIB in intracellular and extracellular fluid. AIB uptake in vivo was reduced by 90% in SOL and cardiac muscle and by 45% in diaphragm 16 hours after CLP. In contrast, AIB uptake by liver was almost four times higher in septic than in control animals. AIB uptake in vitro was reduced by 18% in EDL 8 hours after CLP but was not significantly altered in SOL at the same time point. Sixteen hours after CLP, AIB uptake was significantly reduced in both muscles, i.e., by 17% in EDL and by 65% in SOL. When muscles from untreated rats were incubated in the presence of plasma from septic animals (16 hours CLP) or from animals injected with endotoxin (2 mg/kg body weight), AIB uptake was reduced. Addition of endotoxin in vitro (2-200 micrograms/ml) to incubated muscles did not affect AIB uptake. The results suggest that sepsis leads to marked impairment of amino acid transport system A in muscle and that this impairment is mediated by a circulating factor that is not endotoxin. Reduced uptake of amino acids by skeletal muscle during sepsis may divert amino acids to the liver for increased gluconeogenesis and protein synthesis.

Amino Acids↗

PubMed1986

Reduced muscle amino acid uptake in sepsis and the effects in vitro of septic plasma and interleukin-1.

Inhibited amino acid transport in skeletal muscle during sepsis has been demonstrated previously. In the present study we investigated the effects in vitro of plasma from septic animals or fractions of septic plasma that contain solutes with a molecular weight less than 30,000 daltons or less than 2000 to 3000 daltons on amino acid transport in incubated rat soleus (SOL) muscles. The influence of interleukin-1 (IL-1), prostaglandin E2 (PEG2), and the "catabolic" hormones corticosterone, glucagon, and epinephrine on muscle amino acid uptake was also investigated. Amino acid transport was studied with 3H-alpha-aminoisobutyric acid (AIB). Whole-septic plasma and the two low molecular-weight fractions of the septic plasma reduced muscle amino acid uptake by about 20%. IL-1 or PGE2 did not affect amino acid transport. When the catabolic hormones were added individually to incubated SOL muscles, no changes in AIB uptake were noticed. When glucagon or epinephrine was added in combination with corticosterone or when all three hormones were added together, amino acid transport was reduced by 10% to 15%. The results suggest that inhibited muscle amino acid uptake in sepsis is caused by a circulating factor(s) with a molecular weight less than 2000 to 3000 daltons. A synergistic action among the catabolic hormones may be one important factor for reduced muscle amino acid transport in sepsis.

Amino Acids↗

PubMed1985

Behavioral depression after intraventricular infusion of octopamine in rats.

The behavioral and neurochemical effects of four intraventricular infusions of octopamine (3,200 micrograms), tryptophan (800 micrograms), and octopamine plus tryptophan delivered over 6 hours was studied in rats after performing a portacaval anastomosis or a sham operation. After each infusion, each animal was rated for neurologic depression with a 17 point test battery. Although overt coma was not induced, octopamine infusions severely depressed neurologic function. Concentrations of norepinephrine, dopamine, and serotonin in the brain were significantly decreased after the infusion of octopamine. Levels of norepinephrine in the brain were significantly correlated with neurologic status and greater depletion of norepinephrine was associated with greater neurologic depression. These studies demonstrate that infusing large amounts of the trace amine octopamine depresses behavior in the rat and this depression is most closely associated with depletion of stores of norepinephrine in the brain.

Animals↗

PubMed1985

Effects of jejunoileal bypass on food intake, amino acid levels, and indoleamine metabolism in rats.

Adult rats were subjected to either a 90 to 95 percent jejunoileal bypass or a sham operation and were sacrificed 35 days after surgery. Rats with jejunoileal bypass lost 33 percent of their original weight, whereas the sham operated rats gained 14 percent. Food intake per 100 g body weight was significantly increased between postoperative days 14 and 35 in the jejunoileal bypass rats. Levels of tryptophan were significantly reduced in the cortex, hypothalamus, striatum, hippocampus, mesencephalon, diencephalon, pons-oblongata, and cerebellum, whereas serotonin concentrations were lowered in the diencephalon, pons-medulla, and cerebellum in jejunoileal rats compared with control rats. Levels of 5-HIAA were reduced in the hypothalamus, cortex, mesencephalon, and diencephalon. In the plasma of bypassed rats, concentrations of valine, leucine, isoleucine, tryptophan, methionine, threonine, and tyrosine were significantly lower than in the control rats. In the cerebral cortex, levels of phenylalanine, tyrosine, histidine, and glutamine were increased. The results suggest involvement of indoleamine metabolism in disrupted eating after jejunoileal bypass. The elevated brain levels of glutamine, phenylalanine, tyrosine, and histidine resemble similar changes seen after portosystemic shunting in rats.

Amino Acids↗

PubMed1985

Effect of indomethacin on proteolysis in septic muscle.

The effect of indomethacin on protein degradation in skeletal muscle from septic rats was investigated. Sepsis was induced by cecal ligation and puncture (CLP). Control rats were sham-operated. Protein degradation rate was estimated by measuring release of tyrosine from incubated soleus (SOL) and extensor digitorum longus (EDL) muscles. Three experiments were performed. In the first experiment, indomethacin was administered subcutaneously (3 mg/kg) at the time of CLP and again after 3 hours. Control rats received corresponding volumes of solvent. Groups of rats were studied after 8 hours (early sepsis) or 16 hours (late sepsis). In the second experiment, the animals were pretreated 45 minutes before induction of sepsis with indomethacin (3 mg/kg) and again 3 hours after CLP and were studied during early sepsis. In the third experiment, indomethacin was added in vitro (3 microM) to incubated normal or septic muscle or to normal muscle incubated in the presence of plasma from septic animals, and release of prostaglandin E2 (PGE2) by incubated muscle was measured in addition to protein degradation. There was no mortality in early sepsis. Survival rate 16 hours after CLP was 8/16 (50%) in rats receiving control injections and 7/15 (47%) in indomethacin-treated rats (NS). Proteolytic rate in incubated EDL and SOL was increased by 20-25% during early sepsis and by 30-50% during late sepsis. The increased proteolytic rate was not affected by administration of indomethacin, neither in the first nor in the second experiment. When indomethacin was added in vitro, release of PGE2 by septic muscles and by normal muscles incubated in the presence of septic plasma was reduced by about 50%, but the increased proteolytic rate in these muscles was not affected. In normal muscle, neither release of PGE2 nor protein degradation was affected by indomethacin in vitro. The present results do not support a role for prostaglandins in the enhancement of muscle proteolysis during sepsis. Since neither survival rate nor protein breakdown was affected by indomethacin, recent suggestions to use this substance in the treatment of septic patients might be questioned.

Amino Acids↗

PubMed1985

Relationship of brain glutamine and brain neutral amino acid concentrations after portacaval anastomosis in rats.

Evidence from several sources suggest that blood-brain transport of the large neutral amino acids (NAA) is abnormal in animals with a portacaval anastomosis (PCA) and in patients with liver cirrhosis and portal-systemic shunting and encephalopathy, but the underlying mechanisms are unknown. After PCA, the concentration of glutamine (Gln) in brain is markedly increased as a by-product of cerebral ammonia detoxification, and the rate of efflux of Gln from brain is also increased. The following studies were undertaken to clarify the relationships among plasma and brain concentrations of NAA after PCA in rats and to examine the relationship of brain Gln concentration to plasma and brain NAA concentrations. After PCA plasma phenylalanine, tyrosine and histidine were elevated and leucine, isoleucine and valine were lowered. In brain, phenylalanine, tyrosine, histidine and methionine were markedly elevated after PCA and their concentrations in brain far exceeded the concentrations in plasma. Analyses of single, partial and multiple correlations of plasma NAA ratios expressed as plasma competitor function (PCF), brain NAA and brain Gln showed significant correlations between PCF nd brain NAA in shunted rats. A better correlation was found between brain NAA and brain Gln. Correlation coefficients obtained from multiple correlation analysis equalled or exceeded those obtained in the partial correlation or in the single correlation, suggesting that the effects of PCF and brain Gln on brain NAA were separate and additive. Gln was shown to compete with other NAA for blood brain transport by inhibiting brain 14C phenylalanine uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1985

Effect of hyperammonemia and methionine sulfoximine on the kinetic parameters of blood-brain transport of leucine and phenylalanine.

The activity of the blood-brain neutral amino acid transport system is increased in rats infused with ammonium salts or rendered hyperammonemic by a portacaval anastomosis. This effect may be due to a direct action of ammonia or to some metabolic consequence of high ammonia levels, such as increased brain glutamine synthesis. To test these possibilities we evaluated the kinetic parameters of blood-brain transport of leucine and phenylalanine in control rats, in rats after continuous 24 h infusion of ammonium salts (NH4+ = 2.5 mmol X kg-1 X h-1), and in rats treated with methionine sulfoximine, an inhibitor of glutamine synthetase, before infusion of ammonium salts. In ammonia-infused rats without methionine sulfoximine treatment, the KD and Vmax of phenylalanine transport were increased, respectively, about 170% and 80% compared to controls, whereas the Km and Vmax of leucine transport were increased, respectively, about 100% and 200%. Electron microscopy demonstrated marked swelling of astrocytic processes around brain capillaries of ammonia-infused rats; however, capillary permeability to horseradish peroxidase apparently was not increased by ammonia infusion. Administration of methionine sulfoximine before ammonia infusion inhibited glutamine synthesis and prevented the changes in transport of leucine and phenylalanine, but apparently did not reverse the perivascular swelling. These results suggest that the ammonia-induced increase in the activity of transport of large neutral amino acids across the blood-brain barrier requires glutamine synthesis in brain, and is not a direct effect of ammonia.

Ammonia↗

PubMed1985

Methionine sulfoximine prevents the accumulation of large neutral amino acids in brain of portacaval-shunted rats.

Portal-systemic shunting and hyperammonemia lead to an accumulation of the large neutral amino acids in brain and apparently alter transport of neutral amino acids across the blood-brain barrier. It has been proposed that portal-systemic shunting leads to a high brain concentration of glutamine, a product of cerebral ammonia detoxification, and thereby affects the transport of other neutral amino acids across the blood-brain barrier. To test this hypothesis, rats with a portacaval shunt were treated with L-methionine-dl-sulfoximine (MSO), an inhibitor of glutamine synthesis. Treatment with MSO resulted in lower concentrations of the neutral amino acids in brain of portacaval-shunted rats and a higher brain ammonia concentration, compared with untreated shunted rats. These results suggest that the accumulation of neutral amino acids in brain after portacaval shunt depends on the increased synthesis of glutamine in brain.

Amino Acids↗

PubMed1985

Indole amines and amino acids in various brain regions after infusion of branched chain amino acids into hepatectomized rats.

This study was designed to determine regional changes of amino acids and indole amines in the brain and possible interactions between amino acids and indole amines 18 h after hepatectomy in rats. Hepatectomy and glucose infusion alone resulted in a profound increase of most large neutral amino acids (LNAA) in plasma and in the brain except for the branched-chain amino acids (BCAA), which maintained normal or somewhat lower values in plasma. Hepatectomy and infusion of glucose combined with BCAA sharply reduced the plasma and brain amino acid concentrations of other LNAA. Simultaneously the concentrations of serotonin and 5-hydroxyindoleacetic acid were decreased in all brain regions. In both groups of hepatectomized rats there were regional variations of the amino acid and the indole amine concentrations in the brain, but the response to BCAA infusion was generally the same in all brain regions. No difference in survival between the 2 groups could be found.

Amino Acids↗

PubMed1985

Infusion of branched-chain amino acids and ammonium salts in rats with portacaval shunts.

During infusion into rats with a portacaval shunt of either ammonium (NH4+) salts alone or NH4+ salts combined with the three branched-chain amino acids (BCAAs) in equimolar quantities, we assessed neurologic function and measured plasma and brain ammonia and amino acid levels and the brain content of amine neurotransmitters and their metabolites. Survival was lengthened and neurologic function was preserved longer in rats receiving BCAAs. Infusion of BCAAs resulted in lower plasma and brain ammonia concentrations compared with rats receiving NH4+ salts alone. Plasma glutamine and alanine levels were higher in rats receiving BCAAs, suggesting increased ammonia detoxification. Loss of neurologic function, regardless of which solution was infused, eventually occurred and corresponded with decreased brain norepinephrine and increased brain alanine levels. These results suggest that BCAAs can protect against hyperammonemia by stimulating the peripheral detoxification of ammonia.

Amino Acids, Branched-Chain↗

PubMed1984

Effect of ammonia on amino acid uptake by brain microvessels.

NH+4 ions, at a concentration (0.25 mM) similar to that found in the plasma of patients with hepatic encephalopathy, cause, in vitro, a significant stimulation of the uptake by brain microvessels of large neutral amino acids, without any effect on the uptake of alpha-methylaminoisobutyric acid, glutamic acid, or lysine. Such a stimulation occurs essentially through an increase of the maximal transport capacity (Vmax) of the saturable component. It is apparently mediated by the intracellular formation of glutamine, which is then exchanged, through the L-system of transport, for large neutral amino acids such as leucine, phenylalanine, or tyrosine. At higher concentrations (greater than or equal to 0.5 mM), NH+4 ions cause also a decrease of carrier affinity for neutral amino acids, which counteracts the stimulatory effect on their uptake.

2,4-Dinitrophenol↗

PubMed1984

Infusion of branched chain-enriched amino acid solutions in sepsis.

The goal of nutritional support in sepsis is, as in other conditions, to prevent the use of endogenous protein as an energy substrate and, ideally, to promote the synthesis of proteins specifically required in responding to the particular insult or stress at hand. This entails provision of an utilizable fuel, in sufficient quantity, that does not inhibit the use of endogenous nonprotein sources; preservation of the existing protein mass by minimizing skeletal muscle and visceral proteolysis; provision of amino acids in sufficient quantity and in the appropriate proportions such that protein synthesis is optimized. Specifically, this includes the synthesis of those proteins required to maintain hyperdynamic function of the essential organs as well as the hepatic and leukocytic synthesis of proteins required in immunologic defense. This study has assessed one aspect of this goal during the administration of nutrient solutions differing primarily in branched chain amino acid content. We conclude that leucine is fundamental among the branched chain amino acids for reducing skeletal muscle proteolysis. Solutions designed for sepsis or stress should, therefore, contain adequate amounts of this amino acid.

Amino Acids↗

PubMed1984

Methionine sulfoximine prevents the accumulation of large neutral amino acids in brain of hyperammonemic rats.

Accumulation of neutral amino acids in the brain due to altered transport across the blood-brain barrier appears to be a consequence of portal-systemic shunting and hyperammonemia. It has been suggested that high brain concentrations of glutamine, a product of cerebral ammonia detoxification, accelerates the transport of other neutral amino acids from blood to brain. To test this hypothesis, normal rats were infused with ammonium salts with or without pretreatment with L-methionine-dl-sulfoximine (MSO), an inhibitor of glutamine synthesis. Pretreatment with MSO prevented most ammonium salt-induced changes in the concentrations of the neutral amino acids in brain, suggesting that hyperammonemia alters the transport of neutral amino acids across the blood-brain barrier by causing the brain glutamine level to rise.

Amino Acids↗

PubMed1984

Spontaneous motor activity increases after portacaval anastomosis in rats.

Spontaneous motor activity was monitored in rats at various times, up to 14 weeks, after portacaval anastomosis (PCA) or sham operation. Total 24 hour activity scores rose significantly after PCA and remained significantly higher than those of sham operated rats for twelve weeks. After PCA, activity during the twelve hour lighted period was greatly increased, whereas dark period activity was unchanged. Increased activity in the light period was found to be well correlated with the degree of elevation in brain concentrations of tryptophan, tyrosine, phenylalanine and glutamine. These results are consistent with previously reported EEG studies and suggest that motor-activity measurement may facilitate the correlation of biochemical changes with behaviour in rats with portal systemic shunting.

Amino Acids↗

PubMed1983

Brain microvessels take up large neutral amino acids in exchange for glutamine. Cooperative role of Na+-dependent and Na+-independent systems.

Some regulatory aspects of neutral amino acid transport were investigated in isolated brain microvessels, an in vitro model of the blood-brain barrier. Preloading of the microvessels with glutamine stimulated the subsequent uptake of other neutral amino acids by way of the Na+-independent L system, but had no effect on the uptake of either basic or acidic amino acids. Moreover, this stimulation was abolished when the loading step was carried out in the absence of Na+ ions or in the presence of a high concentration of alpha-methylaminoisobutyric acid, indicating that the microvessels were able to concentrate glutamine via the A system of amino acid transport. Since the presence of the A system of neutral amino acid transport has not been detected in studies of blood-brain transport performed in vivo, the A system is probably associated with the antiluminal side of brain microvessels. Our results indicate, therefore, that the concentrative Na+-dependent A system and the exchanging Na+-independent L system can cooperate in the uptake of the large neutral hydrophobic amino acids. Such a cooperation may be relevant in the pathogenesis of some neurological disturbances such as hepatic encephalopathy, in which brain glutamine concentration is unusually high.

Amino Acids↗

PubMed1983

Increased blood-brain transport of tryptophan after portacaval anastomoses in germ-free rats.

Portal-systemic shunting in rats results in altered plasma concentrations of the large neutral amino acids (NAA), and increased blood-brain barrier NAA transport. Bacterial ammonia production in the bowel, especially the colon, is thought to play a major role in the etiology of portal-systemic encephalopathy (PSE). In order to isolate the role of bacteria in PSE, plasma and brain amino acids and ammonia (NH3) were studied in germ-free (GF) rats with portacaval shunts (PCS). Germ-free rats underwent end-to-side portacaval shunt or sham operation under germ-free conditions and were kept in a germ-free isolator under careful bacteriologic control. Similar operations were carried out on conventional animals. Two weeks post-operatively blood-brain transport of the neutral amino acid tryptophan was studied and the animals sacrificed. Plasma NH3 rose after PCS both in GF and in conventional rats. In germ-free and conventional rats with PCS, there was a significant elevation in plasma of the aromatic amino acids and decreased concentrations of the branched-chain amino acids. In the brain, both groups had elevated aromatic amino acids, while the branched-chain amino acids remained normal. The blood-brain transport of tryptophan was elevated in portacaval shunted rats, whether germ-free or conventional. These studies suggest the elevated plasma levels of ammonia and disturbances in plasma and brain amino acids seen after portacaval shunt are not dependent on the presence of gut bacteria.

Amino Acids↗

PubMed1983

Effect of total hepatectomy and administration of branched-chain amino acids on regional norepinephrine, dopamine, and amino acids in rat brain.

In rats after total hepatectomy, the effect of infusing glucose alone or combined with branched-chain amino acids on amino acid concentrations in plasma and cerebral cortex and on catecholamine levels in eight different regions of the brain was studied. Infusion of branched-chain amino acids reduced the accumulation of tryptophan, phenylalanine, and tyrosine in plasma, while in cerebral cortex, the concentrations of phenylalanine and tyrosine were normalized and that of tryptophan was reduced greatly. In rats with hepatectomy and glucose infusion alone, norepinephrine levels were decreased in seven of eight brain regions with the exception of striatum, while dopamine was reduced significantly in striatum only. Infusion of branched-chain amino acids resulted in higher norepinephrine in cortex, mesencephalon, and hypothalamus and higher striatal dopamine 18 hours after hepatectomy. Thus, infusing branched-chain amino acids and reducing the accumulation of various neutral amino acids in brain may partially prevent the loss of norepinephrine from brain after total hepatectomy.

Amino Acids, Branched-Chain↗

PubMed1983

Plasma aminoacid levels across the brain in patients with respiratory failure.

Animal studies and theoretical considerations have suggested that in hypercapnic respiratory failure there is interconversion of glutamic acid to glutamine within the brain, perhaps as part of a local buffering mechanism to minimize hypercapnia-induced cerebral acidosis. Detection of transcerebral arteriovenous differences, positive for glutamic acid and negative for glutamine, would lend support to this hypothesis. We measured arterial and internal jugular venous levels of twenty-three aminoacids in four patients with hypercapnic respiratory failure and in four suitable controls. In patients, arterial as well as venous glutamine levels were elevated proportionally, and there was no demonstrable A-V difference across the brain; arterial and venous glutamic acid levels were the same as controls. All other aminoacid levels, arterial and venous, were normal. These findings confirm the previous observations that in hypercapnic respiratory failure glutamine metabolism is altered, but provide no support for the proposed glutamic acid-glutamine interconversions within the brain.

Amino Acids↗