Adsa Logo White Adsa Title White

Elucidating the effects of branched-chain amino acid availability on lactose synthesis rates using mammary tissue slices and isotope-labeled glucose.

J. V. V. Silva

Events

06-24-2020

Join J. V. V. Silva on this page for a live text chat!
6:00 PM - 8:00 PM GMT

Abstract:

W107
Elucidating the effects of branched-chain amino acid availability on lactose synthesis rates using mammary tissue slices and isotope-labeled glucose.
J. V. V. Silva*1, L. Showman2, H. K. J. P. Wickramasinghe1, N. Stepanchenko1, M. J. O. Hidalgo1, M. A. Perera2, J. A. D. R. N. Appuhamy1. 1Department of Animal Science, Iowa State University Ames IA, 2W. M. Keck Metabolomics Research Laboratory, Iowa State University Ames IA.

A meta-analysis revealed even though branched-chain amino acid (BCAA) supplementation tended to increase milk yield, plasma leucine (Leu) concentration was negatively related to lactose yield in lactating dairy cows. The objective of this study was to investigate the effects of extracellular BCAA availability on lactose synthesis rates using bovine mammary tissue slices (MTS) and stable isotope-labeled glucose. Mammary tissue slices (119 � 21 mg) were obtained from 3 lactating Holstein cows slaughtered on 3 separate days. Cows were free of mastitis and in late lactattion. The MTS were incubated in 1) medium with all essential amino acids at physiological concentrations (+EAA), 2) +EAA supplemented with Leu at 10 � the physiological concentration (2.0 mM, +LEU), 3) +EAA deprived of all BCAA (-BCAA), and 4) +EAA deprived only of Leu (-LEU) for 3.0 h (t = 3.0). All media contained [13C2]-glucose at 3.15 mM as the sole source of glucose (100% extracellular [13C2] enrichment). Homogenates of cultured tissue slices were subjected to a gas chromatography-mass spectrometry analysis to determine [13C2] enrichment in intracellular precursors (ICE) and single moiety-labeled lactose (LCE). The ICE and LCE were then used to calculate fractional synthesis rate of lactose [FSR, %/h = (LCE � 100)/ (ICE � t)]. Treatment effects on ICE, LCE, and FSR were analyzed with a mixed-effect model including fixed effect of treatment and random effect of cow using the MIXED procedure of SAS. Intracellular precursor enrichment was similar among treatments at 82 � 2% (P = 0.840). Mean LCE was 12.0 � 1.1% across treatments. The LCE of —BCAA (P = 0.023) and —LEU (P = 0.080) were lower than that of +LEU. Mean FSR was 5.0 � 0.7%/h across treatments. Fractional lactose synthesis rates of —BCAA tended to be lower than that of +LEU (5.8 vs. 4.4%/h, P = 0.062). Overall, extracellular availability of total BCAA or only Leu appeared to favorably affect lactose synthesis rates in bovine mammary tissues. The MTS together with stable isotope-labeled glucose could provide a good model for studying how lactose synthesis rates are regulated.

Keywords: leucine, lactose synthesis, bovine mammary.