A MODEL FOR QUANTIFYING THE CONTRIBUTION OF EXTRACELLULARLY-DERIVED PEPTIDES TO MILK PROTEIN SYNTHESIS IN THE RUMINANT MAMMARY GLAND

Abstract A model based on the dual-labelled tracer technique of Backwell and co-workers is proposed which allows detailed resolution of isotope dilution data that can be generated by this technique, provided these data are supplemented with appropriate arterio-venous difference and blood flow measurements. The proposed model is constructed and solved in the steady state. Model solution permits, if assumptions are made, calculation of the uptake of an amino acid Y from the arterial blood supply in both peptide-bound and free form, oxidation of Y , export of Y into the venous drainage, and synthesis and degradation of milk protein and constitutive tissue protein within the gland. The model provides a means of evaluating the role of amino acids of peptide origin in milk and constitutive protein synthesis in the mammary gland of the lactating ruminant.