Abstract #430
Section: Lactation Biology
Session: Lactation Biology II
Format: Oral
Day/Time: Tuesday 9:30 AM–9:45 AM
Location: Wekiwa 3/4
Session: Lactation Biology II
Format: Oral
Day/Time: Tuesday 9:30 AM–9:45 AM
Location: Wekiwa 3/4
# 430
Glucose activates translation factors in muscle but not in mammary glands of lactating dairy cows when essential amino acids are in excess supply.
Kelly Nichols*1, Michelle Carson2, Julie J. M. Kim1, John A. Metcalf2, John P. Cant1, John Doelman2,1, 1Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada, 2Nutreco Canada Agresearch, Guelph, ON, Canada.
Key Words: protein synthesis, mammary, muscle
Glucose activates translation factors in muscle but not in mammary glands of lactating dairy cows when essential amino acids are in excess supply.
Kelly Nichols*1, Michelle Carson2, Julie J. M. Kim1, John A. Metcalf2, John P. Cant1, John Doelman2,1, 1Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada, 2Nutreco Canada Agresearch, Guelph, ON, Canada.
To determine how glucose modulates protein synthesis when essential amino acids (EAA) are supplied in excess, 5 early-lactation Holstein cows (78 ± 13 DIM) were abomasally infused for 5 d with EAA and glucose in a 5 × 5 Latin square design, and abundances and phosphorylation states of ribosomal S6 kinase 1 (S6K1), eukaryotic initiation factor 4E binding protein-1 (4EBP1) and eukaryotic initiation factor 2α (eIF2α) in mammary tissue and longissimus dorsi were assayed. Treatments were saline, 844 g/d EAA in the profile of casein, 1126 g/d EAA, 844 g/d EAA + 1000 g/d glucose, or 1126 g/d EAA + 1000 g/d glucose. Cows were fed a diet containing 6.96 MJ/kg NEL and 12% crude protein. Measurements were subjected to ANOVA using PROC MIXED in SAS, where cow was a random effect. While no differences were observed between levels of EAA, compared with saline, infusion of EAA increased arterial concentrations of EAA 3- to 4-fold (P < 0.01), increased mammary uptake of EAA from plasma 66% (P < 0.01), and led to 256 g/d higher milk protein yield (P < 0.01). The addition of glucose to EAA infusions decreased Ile, Leu and Val concentrations by 29% (P < 0.01), but did not affect mammary uptake of any amino acids (P > 0.40) or milk protein yield (P = 0.32). Infusion of EAA increased the mammary abundance of S6K1 (P = 0.01) and tended to increase phosphorylated S6K1 abundance (P = 0.09), indicating activation of mRNA translation. Infusion of glucose tended to increase the mammary abundance of phosphorylated eIF2α (P = 0.09) and decrease the total abundance of eIF2α (P = 0.07), both of which are inhibitory to mRNA translation. In muscle tissue, EAA infusion increased the phosphorylation state of 4EBP1 (P = 0.02), which is stimulatory to mRNA translation. When glucose was added, the phosphorylation state of 4EBP1 increased (P = 0.11), and total S6K1 abundance tended to increase (P = 0.11). Thus, EAA activated regulators of mRNA translation in both mammary glands and skeletal muscle, while the addition of glucose activated pathways of mRNA translation in muscle tissue but not in the mammary glands.
Key Words: protein synthesis, mammary, muscle
