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D F Evered

Publications and source records attributed to D F Evered.

At least 19 recordsLinked to original sources
PubMed1992

Characteristics of L-citrulline transport across rat small intestine in vitro.

The amino acid L-citrulline is an important intermediate of urea cycle and a key precursor for arginine biosynthesis. We have examined the characteristics of citrulline transport across the everted sacs of the rat small intestine. Our studies suggest that the optimal site of citrulline absorption is middle to lower ileum. It shows active transport, and this transport is predominantly Na+ dependent. Its uptake is significantly inhibited by ouabain, dinitrophenol, sodium azide, and sodium cyanide. Kinetic estimation reveal an apparent substrate concentration at 1/2 maximum velocity of 4.10 +/- 0.86 mM and a Vmax of 18.7 +/- 1.66 mumol/g wet weight tissue/30 min. Analog inhibition studies suggest that citrulline may share the neutral brush border system described for the mucosal brush border membranes of the rabbit jejunum or a system analogous to system ASC described for nonepithelial cells and for basolateral membranes of certain epithelia. In conclusion, the rat small intestine has developed a specific carrier-mediated, Na(+)-dependent pathway for citrulline absorption.

Amino Acids↗
PubMed1985

Transamination pathways influencing L-glutamine and L-glutamate oxidation by rat enterocyte mitochondria and the subcellular localization of L-alanine aminotransferase and L-aspartate aminotransferase.

Using analytical subcellular fractionation techniques, 12% of the total L-alanine aminotransferase activity and 26% of the total L-aspartate aminotransferase activity was localized in enterocyte mitochondria. Alanine and aspartate were products from the oxidation of glutamine and glutamate by enterocyte mitochondria. At low concentrations, malate stimulated aspartate synthesis but was inhibitory at higher concentrations. The malate inhibition of aspartate synthesis, which increased in the presence of pyruvate, was accompanied by an increase in alanine synthesis. With glutamine as substrate in the presence of pyruvate and malate, alanine synthesis was increased by 127% on addition of purified L-alanine aminotransferase, in spite of large amounts of glutamate generated. It was concluded that when pyruvate is available the important route for glutamine or glutamate oxidation by transamination was via L-alanine:2-oxoglutarate aminotransferase and not via L-aspartate:2-oxoglutarate aminotransferase. Results suggested that mitochondria may account for 50% of alanine production from glutamine in the enterocyte despite the relatively low activity of L-alanine aminotransferase therein.

Alanine↗
PubMed1985

Absorption of glutathione from the gastro-intestinal tract.

Transport of the peptide glutathione (GSH) has been studied with the rat small intestine in vitro and the human buccal cavity in vivo. Uptake was found to be sodium-independent in both systems. Saturation kinetics were demonstrated and uptake did not require energy in either system. Transport was inhibited by other small peptides. Carrier-mediated facilitated diffusion was postulated as the mode of transport.

Amino Acids↗
PubMed1984

Preparation of rat enterocyte mitochondria.

Rat enterocyte mitochondria were prepared with respiratory control ratios of 4 or 5 and occasionally 6. When EGTA was excluded from the mitochondrial incubation medium the calculated P/O ratios were high, especially those based on the first addition of ADP. These ratios were lowered by increasing the EGTA concentration from 1 mM to 2 mM in the mitochondrial preparation medium and including 1 mM-EGTA in the incubation medium. The use of EDTA in the enterocyte isolation medium led to the mitochondria requiring added cytochrome c. Substituting EGTA for EDTA abolished this requirement. The mitochondrial fraction consisted of two components, an upper cream-coloured layer rich in DNA and a lower brown-coloured layer poor in DNA. Both components were capable of oxidative phosphorylation with succinate or the glutamate/malate couple as substrates. The mitochondrial yield was assessed by assaying succinate dehydrogenase activity, and the contamination of the mitochondrial fraction by other cell organelles was assessed by assays for appropriate marker enzymes.

Animals↗
PubMed1984

The oxidation of glutamine and glutamate in relation to anion transport in enterocyte mitochondria.

The oxidation of L-glutamate and L-glutamine by enterocyte mitochondria was supported by malate. The stimulation of the rate of oxidation of the two amino acids by small amounts of added malate was 93% and 76% respectively. This could not be accounted for by the oxidation of the small amounts of malate added. Amino-oxyacetate added initially inhibited malate-supported oxidation of L-glutamate by 81% and that of L-glutamine by 38%. The inhibition of L-glutamate oxidation was partially reversed by L-glutamine. The dicarboxylate-carrier inhibitor 2-phenylsuccinate inhibited the malate-supported oxidation of both amino acids, but appeared to be slightly stimulatory to L-glutamine oxidation when added initially. The inhibition of L-glutamate oxidation was reversed by L-glutamine. The mitochondrial uncoupler FCCP (carbonyl cyanide p-trifluoromethoxyphenylhydrazone) inhibited malate-supported oxidation of L-glutamate by 78% when added initially. The oxidation of L-glutamine was completely inhibited. However, the uncoupler stimulated the oxidation of both amino acids when added finally. Pyruvate inhibited aspartate synthesis when either of these amino acids was the main substrate, alanine being synthesized. There was no effect on O2 uptake. Mitochondria did not swell in KCl solution, but swelled rapidly in water. Mitochondrial swelling in potassium phosphate and potassium acetate solutions was activated by valinomycin and to a lesser extent by the further addition of FCCP. With potassium malate, swelling was mainly activated by phosphate. The swelling of enterocyte mitochondria in potassium glutamate was slow. In glutamine solution, mitochondrial swelling was greater and appeared to be enhanced by the initial presence of small amounts of phosphate.

Animals↗
PubMed1983

Absorption of homocitrulline from the gastrointestinal tract.

1. Transport of L-homocitrulline, an amino acid which occurs in milk products, was studied with rat small intestine in vitro and from the human mouth in vivo. Absorption was partially dependent, in both systems, on the presence of sodium ions. 2. Metabolic inhibitors decreased L-homocitrulline uptake across the small intestine. Transport across the intestine did not occur against the concentration gradient but did show saturation kinetics. 3. The barbiturate, amytal, did not inhibit buccal absorption. Saturation kinetics were demonstrated. 4. Experiments were conducted with L-citrulline, or other amino acids, as possible inhibitors of L-homocitrulline transport. Results were compatible with Na+-dependent carrier-mediated uptake across the buccal mucosa. Active transport could be involved with the small intestine assuming that L-homocitrulline has a low affinity for the carrier system.

Absorption↗
PubMed1980

Absorption of nicotinic acid and nicotinamide from rat small intestine in vitro.

Intestinal absorption of nicotinic acid and nicotinamide was studied using everted sacs of rat small intestine. Transport down the concentration gradient showed saturation kinetics at low concentrations and linear kinetics at higher concentrations. Addition of ouabain or omission of sodium ions decreased absorption. Neither compound was absorbed against a concentration gradient. The mode of transport was thought to be carrier-mediated facilitated diffusion at lower concentrations masked by passive diffusion at higher concentrations.

Animals↗
PubMed1979

Absorption of lactulose from mammalian gastrointestinal tract.

1. The disaccharide lactulose (galactosyl-beta-1,4-fructose) was poorly absorbed from rat small intestine in vitro and human mouth in vivo. 2. These results confirm indirect clinical evidence of poor absorption from the intestine. 3. The presence of calcium ions, or absence of sodium ions, had no effect on lactulose absorption from buccal cavity. 4. The presence of ouabain, or absence of Na+, did not increase the absorption of lactulose from small intestine. 5. It is thought that the mode of transport, in both instances, is by passive diffusion with the concentration gradient.

Adult↗
PubMed1979

Absorption of vitamin C from the human buccal cavity.

1. Ascorbic acid was absorbed across the mucosa of the human mouth. 2. Omission of sodium ions from the medium decreased the absorption of ascorbic acid. 3. The presence of D-glucose, or 3-O-methyl-D-glucose, increased the absorption of ascorbic acid but D-fructose had little effect and D-mannitol had no effect. 4. Calcium ions also increased ascorbic acid absorption probably by a secondary effect on "Na+ fluxes. 5. Buccal mucosa was also permeable to dehydroascorbic acid and D-isoascorbic acid.

Absorption↗
PubMed1978

Infrequency of urinary excretion of beta-aminoisobutyric acid by healthy humans.

Urinary beta-aminoisobutyric acid (BAIB) levels were measured by modified ion-exchange chromatography. Daily BAIB levels are reported for a group of apparently healthy individuals, a subject with infective hepatitis and two human genetic variants who were high "excretors" of BAIB. The frequency of high "excretors" of BAIB was found using low-voltage paper electrophoresis. The frequency among 403 male European subjects was 5 (1.2%) and lower than previous estimates in the United Kingdom. The percentage recovery of fed BAIB suggests that Oriental "excretors" may have a different type of genetic lesion from non-Oriental "excretors". The clinical usefulness of urinary BAIB assays and qualitative screening is reviewed.

Adolescent↗