Vascular Sources of Phenylalanine, Tyrosine, Lysine, and Methionine for Casein Synthesis in Lactating Goats

The contribution to casein biosynthesis of peptides derived from blood was examined in late lactation goats (254 to 295 d in milk). Ratios of mammary uptake of free amino acids (AA) in blood to output of AA in milk protein and ratios of the enrichments of Phe, Tyr, Met, and Lys at isotopic plateau i...

Full description

Saved in:
Bibliographic Details
Published in:Journal of dairy science 1999-02, Vol.82 (2), p.362-377
Main Authors: Bequette, B.J., Backwell, F.R.C., Kyle, C.E., Calder, A.G., Buchan, V., Crompton, L.A., France, J., Macrae, J.C.
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
biosynthesis
blood flow
blood plasma
blood protein
Carbon Isotopes
casein
casein synthesis
Caseins - biosynthesis
Deuterium
Female
Fundamental and applied biological sciences. Psychology
goat milk
goats
Goats - blood
Hormone metabolism and regulation
Hydroxylation
infusion
isotope labeling
Kinetics
Lactation
lactation stage
lysine
Lysine - blood
Lysine - metabolism
mammary gland
mammary glands
Mammary Glands, Animal - metabolism
methionine
Methionine - blood
Methionine - metabolism
milk composition
milk yield
peptides
phenylalanine
Phenylalanine - blood
Phenylalanine - metabolism
Pregnancy. Parturition. Lactation
tyrosine
Tyrosine - blood
Tyrosine - metabolism
uptake
Vertebrates: reproduction
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The contribution to casein biosynthesis of peptides derived from blood was examined in late lactation goats (254 to 295 d in milk). Ratios of mammary uptake of free amino acids (AA) in blood to output of AA in milk protein and ratios of the enrichments of Phe, Tyr, Met, and Lys at isotopic plateau in secreted milk casein to the free AA in arterial and mammary vein blood were monitored during the last 5h of a 30-h continuous i.v. infusion of [1-13 C]Phe, [2H4]Tyr, [5-13CH,3]Met, and [2-15N]Lys on two occasions: before (control) and on d 6 of an i.v. infusion of Phe (6 g/d). During the control, uptakes of free Phe and Met were less than their output in milk. This result was comparable with the labeling kinetic results, suggesting that vascular peptides contributed 5 to 11% of Phe and 8 to 18% of Met. Free Tyr and Lys uptakes during the control were sufficient for milk output; however, the labeling kinetics indicated that 13 to 25% of the Tyr and 4 to 13% of the Lys were derived from peptides. Infusion of Phe increased the uptake of free AA but reduced the contribution of peptides toward Phe (0 to 3%) and Tyr (8 to 14%) supply for casein synthesis. Whole body hydroxylation of Phe to Tyr increased from 10 to 18% with the infusion of Phe; within the mammary gland, this conversion was lower (3 to 5%). Results suggest that the mammary utilization of peptides containing Phe and Tyr appears to depend on the supply of free AA in blood.
ISSN:0022-0302
1525-3198
DOI:10.3168/jds.S0022-0302(99)75243-4