Splanchnic-bed transfers of amino acids in sheep blood and plasma, as monitored through use of a multiple U-13C-labelled amino acid mixture

Gerald Lobley, A Connell, D K Revell, B J Bequette, David Stanley Brown, Alexander Graham Calder

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Abstract

The response in whole-body and splanchnic tissue mass and isotope amino acid transfers in both plasma and blood has been studied in sheep offered 800 g lucerne (Medicago sativa) pellets/d. Amino acid mass transfers were quantified over a 4 h period, by arterio-venous procedures, across the portal-drained viscera (PDV) and liver on day 5 of an intravenous infusion of either vehicle or the methylated products, choline (0.5 g/d) plus creatine (1.0 g/d). Isotopic movements were monitored over the same period during a 10 h infusion of a mixture of U-13C-labelled amino acids obtained from hydrolysis of labelled algal cells. Sixteen amino acids were monitored by gas chromatography-mass spectrometry, with thirteen of these analysed within a single chromatographic analysis. Except for methionine, which is discussed in a previous paper, no significant effects of choline plus creatine infusion were observed on any of the variables reported. Whole-body protein irreversible-loss rates ranged from 158 to 245 g/d for the essential amino acids, based on the relative enrichments (dilution of the U-13C molecules by those unlabelled) of free amino acids in arterial plasma, and 206-519 g/d, when blood free amino acid relative enrichments were used for the calculations. Closer agreement was obtained between lysine, threonine, phenylalanine and the branched-chain amino acids. Plasma relative enrichments always exceeded those in blood (P <0.001), possibly due to hydrolysis of peptides or degradation of protein within the erythrocyte or slow equilibration between plasma and the erythrocyte. Net absorbed amino acids across the PDV were carried predominantly in the plasma. Little evidence was obtained of any major and general involvement of the erythrocytes in the transport of free amino acids from the liver. Net isotope movements also supported these findings. Estimates of protein synthesis rates across the PDV tissues from [U-13C] leucine kinetics showed good agreement with previous values obtained with single-labelled leucine. Variable rates were obtained between the essential amino acids, probably due to different intracellular dilutions. Isotope dilution across the liver was small and could be attributed predominantly to uni-directional transfer from extracellular sources into the hepatocytes and this probably dominates the turnover of the intracellular hepatic amino acid pools.
Original languageEnglish
Pages (from-to)217-35
Number of pages19
JournalBritish Journal of Nutrition
Volume75
Issue number2
Publication statusPublished - 1 Feb 1996

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Viscera
Sheep
Amino Acids
Isotopes
Essential Amino Acids
Medicago sativa
Creatine
Erythrocytes
Liver
Choline
Leucine
Hydrolysis
Branched Chain Amino Acids
Threonine
Phenylalanine
Intravenous Infusions
Methionine
Gas Chromatography-Mass Spectrometry
Proteolysis
Lysine

Keywords

  • Amino Acids
  • Animals
  • Biological Transport
  • Carbon Isotopes
  • Choline
  • Creatine
  • Erythrocytes
  • Liver
  • Male
  • Plasma
  • Sheep
  • Splanchnic Circulation

Cite this

Splanchnic-bed transfers of amino acids in sheep blood and plasma, as monitored through use of a multiple U-13C-labelled amino acid mixture. / Lobley, Gerald; Connell, A; Revell, D K; Bequette, B J; Brown, David Stanley; Calder, Alexander Graham.

In: British Journal of Nutrition, Vol. 75, No. 2, 01.02.1996, p. 217-35.

Research output: Contribution to journalArticle

Lobley, Gerald ; Connell, A ; Revell, D K ; Bequette, B J ; Brown, David Stanley ; Calder, Alexander Graham. / Splanchnic-bed transfers of amino acids in sheep blood and plasma, as monitored through use of a multiple U-13C-labelled amino acid mixture. In: British Journal of Nutrition. 1996 ; Vol. 75, No. 2. pp. 217-35.
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AU - Brown, David Stanley

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N2 - The response in whole-body and splanchnic tissue mass and isotope amino acid transfers in both plasma and blood has been studied in sheep offered 800 g lucerne (Medicago sativa) pellets/d. Amino acid mass transfers were quantified over a 4 h period, by arterio-venous procedures, across the portal-drained viscera (PDV) and liver on day 5 of an intravenous infusion of either vehicle or the methylated products, choline (0.5 g/d) plus creatine (1.0 g/d). Isotopic movements were monitored over the same period during a 10 h infusion of a mixture of U-13C-labelled amino acids obtained from hydrolysis of labelled algal cells. Sixteen amino acids were monitored by gas chromatography-mass spectrometry, with thirteen of these analysed within a single chromatographic analysis. Except for methionine, which is discussed in a previous paper, no significant effects of choline plus creatine infusion were observed on any of the variables reported. Whole-body protein irreversible-loss rates ranged from 158 to 245 g/d for the essential amino acids, based on the relative enrichments (dilution of the U-13C molecules by those unlabelled) of free amino acids in arterial plasma, and 206-519 g/d, when blood free amino acid relative enrichments were used for the calculations. Closer agreement was obtained between lysine, threonine, phenylalanine and the branched-chain amino acids. Plasma relative enrichments always exceeded those in blood (P <0.001), possibly due to hydrolysis of peptides or degradation of protein within the erythrocyte or slow equilibration between plasma and the erythrocyte. Net absorbed amino acids across the PDV were carried predominantly in the plasma. Little evidence was obtained of any major and general involvement of the erythrocytes in the transport of free amino acids from the liver. Net isotope movements also supported these findings. Estimates of protein synthesis rates across the PDV tissues from [U-13C] leucine kinetics showed good agreement with previous values obtained with single-labelled leucine. Variable rates were obtained between the essential amino acids, probably due to different intracellular dilutions. Isotope dilution across the liver was small and could be attributed predominantly to uni-directional transfer from extracellular sources into the hepatocytes and this probably dominates the turnover of the intracellular hepatic amino acid pools.

AB - The response in whole-body and splanchnic tissue mass and isotope amino acid transfers in both plasma and blood has been studied in sheep offered 800 g lucerne (Medicago sativa) pellets/d. Amino acid mass transfers were quantified over a 4 h period, by arterio-venous procedures, across the portal-drained viscera (PDV) and liver on day 5 of an intravenous infusion of either vehicle or the methylated products, choline (0.5 g/d) plus creatine (1.0 g/d). Isotopic movements were monitored over the same period during a 10 h infusion of a mixture of U-13C-labelled amino acids obtained from hydrolysis of labelled algal cells. Sixteen amino acids were monitored by gas chromatography-mass spectrometry, with thirteen of these analysed within a single chromatographic analysis. Except for methionine, which is discussed in a previous paper, no significant effects of choline plus creatine infusion were observed on any of the variables reported. Whole-body protein irreversible-loss rates ranged from 158 to 245 g/d for the essential amino acids, based on the relative enrichments (dilution of the U-13C molecules by those unlabelled) of free amino acids in arterial plasma, and 206-519 g/d, when blood free amino acid relative enrichments were used for the calculations. Closer agreement was obtained between lysine, threonine, phenylalanine and the branched-chain amino acids. Plasma relative enrichments always exceeded those in blood (P <0.001), possibly due to hydrolysis of peptides or degradation of protein within the erythrocyte or slow equilibration between plasma and the erythrocyte. Net absorbed amino acids across the PDV were carried predominantly in the plasma. Little evidence was obtained of any major and general involvement of the erythrocytes in the transport of free amino acids from the liver. Net isotope movements also supported these findings. Estimates of protein synthesis rates across the PDV tissues from [U-13C] leucine kinetics showed good agreement with previous values obtained with single-labelled leucine. Variable rates were obtained between the essential amino acids, probably due to different intracellular dilutions. Isotope dilution across the liver was small and could be attributed predominantly to uni-directional transfer from extracellular sources into the hepatocytes and this probably dominates the turnover of the intracellular hepatic amino acid pools.

KW - Amino Acids

KW - Animals

KW - Biological Transport

KW - Carbon Isotopes

KW - Choline

KW - Creatine

KW - Erythrocytes

KW - Liver

KW - Male

KW - Plasma

KW - Sheep

KW - Splanchnic Circulation

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SP - 217

EP - 235

JO - British Journal of Nutrition

JF - British Journal of Nutrition

SN - 0007-1145

IS - 2

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