Mammary mTOR activity during intravenous glucose infusions into lactating dairy cows
The effects of glucose on milk protein yield and mammary mTOR activity were studied in eight multiparous early lactation Holstein cows fed a TMR with 40% NDF content. Treatments were jugular infusions of either physiological saline (SAL) or approximately 900 g/d glucose (GLC) in a cross over design for two 6 d periods during which blood, milk and mammary tissue were sampled. GLC infusion increased plasma insulin but did not significantly increase plasma glucose and only tended to increase milk protein yields. NEAA and BCAA plasma concentrations significantly increased and decreased, respectively, with GLC treatments. Furthermore, reduction of the phosphorylation state of mTOR signalling protein 4EBP1, as well as reduction of total and phosphorylated S6K1 abundances resulted from the infusion of GLC. The expected increase in milk protein synthesis due to glucose infusion was not observed, presumably because protein synthesis was stimulated in muscle tissue rather than the mammary glands.