An isotope dilution model for partitioning phenylalanine and tyrosine uptake by the mammary gland of lactating dairy cows.
An isotope dilution model for partitioning phenylalanine and tyrosine uptake by the mammary gland of the lactating dairy cow is constructed and solved in the steady state. The model contains four intracellular and four extracellular pools and conservation of mass principles are applied to generate the fundamental equations describing the behaviour of the system. The experimental measurements required for model solution are milk secretion and plasma flow rate across the gland in combination with phenylalanine and tyrosine concentrations and plateau isotopic enrichments in arterial and venous plasma and free and protein bound milk during a constant infusion of [1-(13)C]phenylalanine and [2,3,5,6-(2)H]tyrosine tracer. If assumptions are made, model solution enables determination of steady state flows for phenylalanine and tyrosine inflow to the gland, outflow from it and bypass, and flows representing the synthesis and degradation of constitutive protein and phenylalanine hydroxylation. The model is effective in providing information about the fates of phenylalanine and tyrosine in the mammary gland and could be used as part of a more complex system describing amino acid metabolism in the whole ruminant.
Animal Science Research Group, School of Agriculture, Policy and Development, University of Reading, Whiteknights, Reading RG6 6AR, UK. Electronic address: l.a.crompton@reading.ac.uk.
L A
LA
Crompton
Centre for Nutrition Modelling, Department of Animal & Poultry Science, University of Guelph, Ontario, Canada, N1G 2W1. Electronic address: jfrance@uoguelph.ca.
J
J
France
Animal Science Research Group, School of Agriculture, Policy and Development, University of Reading, Whiteknights, Reading RG6 6AR, UK. Electronic address: c.k.reynolds@reading.ac.uk.
C K
CK
Reynolds
Animal Science Research Group, School of Agriculture, Policy and Development, University of Reading, Whiteknights, Reading RG6 6AR, UK. Electronic address: j.a.n.mills@reading.ac.uk.
J A N
JA
Mills
Department of Dairy Science, Virginia Tech, 2080 Litton Reaves, Blacksburg, VA 24061, USA. Electronic address: mhanigan@vt.edu.
M D
MD
Hanigan
Centre for Nutrition Modelling, Department of Animal & Poultry Science, University of Guelph, Ontario, Canada, N1G 2W1; Wageningen Institute of Animal Sciences, Animal Nutrition Group, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands. Electronic address: jellis@uoguelph.ca.
J L
JL
Ellis
Wageningen UR Livestock Research, 8219 PH Lelystad, The Netherlands. Electronic address: andre.bannink@wur.nl.
A
A
Bannink
Department of Animal & Avian Sciences, University of Maryland, College Park, MD 20742, USA. Electronic address: bbequett@umd.edu.
B J
BJ
Bequette
Wageningen Institute of Animal Sciences, Animal Nutrition Group, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands. Electronic address: jan.dijkstra@wur.nl.
J
J
Dijkstra
D000818:Animals; D002417:Cattle / Q000378:metabolism; D003612:Dairying; D005260:Female; D007774:Lactation / Q000378:metabolism*; D008321:Mammary Glands, Animal / Q000378:metabolism*; D008892:Milk / Q000378:metabolism; D008962:Models, Theoretical; D010649:Phenylalanine / Q000493:pharmacokinetics*; D011865:Radioisotope Dilution Technique; D014443:Tyrosine / Q000493:pharmacokinetics*
D014443:Tyrosine; D010649:Phenylalanine
Isotope dilution; Kinetic model; Mammary gland; Phenylalanine; Tyrosine