Hepatic response to increased exogenous supply of plasma amino acids by infusion into the mesenteric vein of Holstein-Friesian cows in late gestation

D Wray-Cahen, J A Metcalf, F R C Backwell, B J Bequette, David Stanley Brown, J D Sutton, Gerald Lobley

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

The hepatic responses of late gestation, dry dairy cows to acute (6 h) infusions of an amino acid (AA) mixture (Synthamin; 0.0, 1.1, 2.2, 4.4, 8.8 and 17.6 mmol/min) into the mesenteric vein were determined. Neither blood how nor O-2 consumption across the portal-drained viscera (PDV) and liver was significantly altered by infusion. Similarly, there were no effects on net absorption, or hepatic removal, of acetate, propionate, butyrate or NH3. Glucose PDV appearance was unchanged but hepatic glucose production increased (P = 0.032) by 0.2 mmol/min per mmol/min of AA infused. Additional extraction of alanine, glycine (both infused) and glutamine (not infused) by the liver was sufficient to account for most of the extra C required for glucose synthesis. The N that would be liberated from these glucogenic AA would also account for a large proportion of the increase in urea-N produced in response to the AA infusion. This supports the concept of a correlation between gluconeogenesis and ureagenesis. Furthermore, the amide-N liberated from the extracted glutamine would contribute up to 0.17 of hepatic NH3 flux and assist in balancing N inputs into the carbamoyl phosphate and arginosuccinate entry points of the ornithine cycle. Rates of fractional extraction of the various AA by the Liver were best fitted by linear equations, indicating that even at the highest rates of administration (approximately twice maximal physiological absorption) the transport systems were not saturated. Hepatic fractional extractions of infused essential AA were highest for methionine (0.83) and phenylalanine (0.87) with the lowest proportion removed observed for valine (0.25), leucine (0.30), lysine (0.31) and isoleucine (0.49). For the non-essential AA, the highest apparent fractional extractions were for glycine (0.73), arginine (0.79) and tyrosine (0.63) followed by alanine (0.54), proline (0.47) and serine (0.37). Hepatic removal of AA-N exceeded the increase in urea-N formation such that, at the highest rate of infusion, approximately 10 mmol/min of the extracted AA was apparently available for hepatic anabolism, more than is required to account for assumed increases in liver mass and export protein synthesis. Similarly, the amount of AA available for peripheral tissue protein gain, when assessed against phenylalanine supply as the limitation, would be the equivalent of a maximum of 0.5 g protein retained/min (6 mmol AA-N/min). This would provide sufficient AA for replenishment of peripheral (muscle) protein stores plus support of the placenta and fetus.

Original languageEnglish
Pages (from-to)913-930
Number of pages18
JournalBritish Journal of Nutrition
Volume78
Issue number6
DOIs
Publication statusPublished - Dec 1997

Keywords

  • amino acids
  • urea
  • liver
  • cattle
  • portal-drained viscera
  • splanchic-bed
  • metabolism
  • sheep
  • transport
  • protein
  • blood
  • interconversions
  • nutrition

Cite this

Hepatic response to increased exogenous supply of plasma amino acids by infusion into the mesenteric vein of Holstein-Friesian cows in late gestation. / Wray-Cahen, D ; Metcalf, J A ; Backwell, F R C ; Bequette, B J ; Brown, David Stanley; Sutton, J D ; Lobley, Gerald.

In: British Journal of Nutrition, Vol. 78, No. 6, 12.1997, p. 913-930.

Research output: Contribution to journalArticle

Wray-Cahen, D ; Metcalf, J A ; Backwell, F R C ; Bequette, B J ; Brown, David Stanley ; Sutton, J D ; Lobley, Gerald. / Hepatic response to increased exogenous supply of plasma amino acids by infusion into the mesenteric vein of Holstein-Friesian cows in late gestation. In: British Journal of Nutrition. 1997 ; Vol. 78, No. 6. pp. 913-930.
@article{10d88f5a8bbd4ebda56c38285993ea9c,
title = "Hepatic response to increased exogenous supply of plasma amino acids by infusion into the mesenteric vein of Holstein-Friesian cows in late gestation",
abstract = "The hepatic responses of late gestation, dry dairy cows to acute (6 h) infusions of an amino acid (AA) mixture (Synthamin; 0.0, 1.1, 2.2, 4.4, 8.8 and 17.6 mmol/min) into the mesenteric vein were determined. Neither blood how nor O-2 consumption across the portal-drained viscera (PDV) and liver was significantly altered by infusion. Similarly, there were no effects on net absorption, or hepatic removal, of acetate, propionate, butyrate or NH3. Glucose PDV appearance was unchanged but hepatic glucose production increased (P = 0.032) by 0.2 mmol/min per mmol/min of AA infused. Additional extraction of alanine, glycine (both infused) and glutamine (not infused) by the liver was sufficient to account for most of the extra C required for glucose synthesis. The N that would be liberated from these glucogenic AA would also account for a large proportion of the increase in urea-N produced in response to the AA infusion. This supports the concept of a correlation between gluconeogenesis and ureagenesis. Furthermore, the amide-N liberated from the extracted glutamine would contribute up to 0.17 of hepatic NH3 flux and assist in balancing N inputs into the carbamoyl phosphate and arginosuccinate entry points of the ornithine cycle. Rates of fractional extraction of the various AA by the Liver were best fitted by linear equations, indicating that even at the highest rates of administration (approximately twice maximal physiological absorption) the transport systems were not saturated. Hepatic fractional extractions of infused essential AA were highest for methionine (0.83) and phenylalanine (0.87) with the lowest proportion removed observed for valine (0.25), leucine (0.30), lysine (0.31) and isoleucine (0.49). For the non-essential AA, the highest apparent fractional extractions were for glycine (0.73), arginine (0.79) and tyrosine (0.63) followed by alanine (0.54), proline (0.47) and serine (0.37). Hepatic removal of AA-N exceeded the increase in urea-N formation such that, at the highest rate of infusion, approximately 10 mmol/min of the extracted AA was apparently available for hepatic anabolism, more than is required to account for assumed increases in liver mass and export protein synthesis. Similarly, the amount of AA available for peripheral tissue protein gain, when assessed against phenylalanine supply as the limitation, would be the equivalent of a maximum of 0.5 g protein retained/min (6 mmol AA-N/min). This would provide sufficient AA for replenishment of peripheral (muscle) protein stores plus support of the placenta and fetus.",
keywords = "amino acids, urea, liver, cattle, portal-drained viscera, splanchic-bed, metabolism, sheep, transport, protein, blood, interconversions, nutrition",
author = "D Wray-Cahen and Metcalf, {J A} and Backwell, {F R C} and Bequette, {B J} and Brown, {David Stanley} and Sutton, {J D} and Gerald Lobley",
year = "1997",
month = "12",
doi = "10.1079/BJN19970209",
language = "English",
volume = "78",
pages = "913--930",
journal = "British Journal of Nutrition",
issn = "0007-1145",
publisher = "Cambridge Univ. Press.",
number = "6",

}

TY - JOUR

T1 - Hepatic response to increased exogenous supply of plasma amino acids by infusion into the mesenteric vein of Holstein-Friesian cows in late gestation

AU - Wray-Cahen, D

AU - Metcalf, J A

AU - Backwell, F R C

AU - Bequette, B J

AU - Brown, David Stanley

AU - Sutton, J D

AU - Lobley, Gerald

PY - 1997/12

Y1 - 1997/12

N2 - The hepatic responses of late gestation, dry dairy cows to acute (6 h) infusions of an amino acid (AA) mixture (Synthamin; 0.0, 1.1, 2.2, 4.4, 8.8 and 17.6 mmol/min) into the mesenteric vein were determined. Neither blood how nor O-2 consumption across the portal-drained viscera (PDV) and liver was significantly altered by infusion. Similarly, there were no effects on net absorption, or hepatic removal, of acetate, propionate, butyrate or NH3. Glucose PDV appearance was unchanged but hepatic glucose production increased (P = 0.032) by 0.2 mmol/min per mmol/min of AA infused. Additional extraction of alanine, glycine (both infused) and glutamine (not infused) by the liver was sufficient to account for most of the extra C required for glucose synthesis. The N that would be liberated from these glucogenic AA would also account for a large proportion of the increase in urea-N produced in response to the AA infusion. This supports the concept of a correlation between gluconeogenesis and ureagenesis. Furthermore, the amide-N liberated from the extracted glutamine would contribute up to 0.17 of hepatic NH3 flux and assist in balancing N inputs into the carbamoyl phosphate and arginosuccinate entry points of the ornithine cycle. Rates of fractional extraction of the various AA by the Liver were best fitted by linear equations, indicating that even at the highest rates of administration (approximately twice maximal physiological absorption) the transport systems were not saturated. Hepatic fractional extractions of infused essential AA were highest for methionine (0.83) and phenylalanine (0.87) with the lowest proportion removed observed for valine (0.25), leucine (0.30), lysine (0.31) and isoleucine (0.49). For the non-essential AA, the highest apparent fractional extractions were for glycine (0.73), arginine (0.79) and tyrosine (0.63) followed by alanine (0.54), proline (0.47) and serine (0.37). Hepatic removal of AA-N exceeded the increase in urea-N formation such that, at the highest rate of infusion, approximately 10 mmol/min of the extracted AA was apparently available for hepatic anabolism, more than is required to account for assumed increases in liver mass and export protein synthesis. Similarly, the amount of AA available for peripheral tissue protein gain, when assessed against phenylalanine supply as the limitation, would be the equivalent of a maximum of 0.5 g protein retained/min (6 mmol AA-N/min). This would provide sufficient AA for replenishment of peripheral (muscle) protein stores plus support of the placenta and fetus.

AB - The hepatic responses of late gestation, dry dairy cows to acute (6 h) infusions of an amino acid (AA) mixture (Synthamin; 0.0, 1.1, 2.2, 4.4, 8.8 and 17.6 mmol/min) into the mesenteric vein were determined. Neither blood how nor O-2 consumption across the portal-drained viscera (PDV) and liver was significantly altered by infusion. Similarly, there were no effects on net absorption, or hepatic removal, of acetate, propionate, butyrate or NH3. Glucose PDV appearance was unchanged but hepatic glucose production increased (P = 0.032) by 0.2 mmol/min per mmol/min of AA infused. Additional extraction of alanine, glycine (both infused) and glutamine (not infused) by the liver was sufficient to account for most of the extra C required for glucose synthesis. The N that would be liberated from these glucogenic AA would also account for a large proportion of the increase in urea-N produced in response to the AA infusion. This supports the concept of a correlation between gluconeogenesis and ureagenesis. Furthermore, the amide-N liberated from the extracted glutamine would contribute up to 0.17 of hepatic NH3 flux and assist in balancing N inputs into the carbamoyl phosphate and arginosuccinate entry points of the ornithine cycle. Rates of fractional extraction of the various AA by the Liver were best fitted by linear equations, indicating that even at the highest rates of administration (approximately twice maximal physiological absorption) the transport systems were not saturated. Hepatic fractional extractions of infused essential AA were highest for methionine (0.83) and phenylalanine (0.87) with the lowest proportion removed observed for valine (0.25), leucine (0.30), lysine (0.31) and isoleucine (0.49). For the non-essential AA, the highest apparent fractional extractions were for glycine (0.73), arginine (0.79) and tyrosine (0.63) followed by alanine (0.54), proline (0.47) and serine (0.37). Hepatic removal of AA-N exceeded the increase in urea-N formation such that, at the highest rate of infusion, approximately 10 mmol/min of the extracted AA was apparently available for hepatic anabolism, more than is required to account for assumed increases in liver mass and export protein synthesis. Similarly, the amount of AA available for peripheral tissue protein gain, when assessed against phenylalanine supply as the limitation, would be the equivalent of a maximum of 0.5 g protein retained/min (6 mmol AA-N/min). This would provide sufficient AA for replenishment of peripheral (muscle) protein stores plus support of the placenta and fetus.

KW - amino acids

KW - urea

KW - liver

KW - cattle

KW - portal-drained viscera

KW - splanchic-bed

KW - metabolism

KW - sheep

KW - transport

KW - protein

KW - blood

KW - interconversions

KW - nutrition

U2 - 10.1079/BJN19970209

DO - 10.1079/BJN19970209

M3 - Article

VL - 78

SP - 913

EP - 930

JO - British Journal of Nutrition

JF - British Journal of Nutrition

SN - 0007-1145

IS - 6

ER -