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Amino Acids

, Volume 45, Issue 3, pp 531–541 | Cite as

Hormonal regulation of leucine catabolism in mammary epithelial cells

  • Jian LeiEmail author
  • Dingyuan Feng
  • Yongliang Zhang
  • Sudath Dahanayaka
  • Xilong Li
  • Kang Yao
  • Junjun Wang
  • Zhenlong Wu
  • Zhaolai Dai
  • Guoyao WuEmail author
Original Article

Abstract

Branched-chain amino acids (BCAA) are actively taken up and catabolized by the mammary gland during lactation for syntheses of glutamate, glutamine and aspartate. Available evidence shows that the onset of lactation is associated with increases in circulating levels of cortisol, prolactin and glucagon, but decreases in insulin and growth hormone. This study determined the effects of physiological concentrations of these hormones on the catabolism of leucine (a representative BCAA) in bovine mammary epithelial cells. Cells were incubated at 37 °C for 2 h in Krebs buffer containing 3 mM d-glucose, 0.5 mM l-leucine, l-[1-14C]leucine or l-[U-14C]leucine, and 0–50 μU/mL insulin, 0–20 ng/mL growth hormone 0–200 ng/mL prolactin, 0–150 nM cortisol or 0–300 pg/mL glucagon. Increasing extracellular concentrations of insulin did not affect leucine transamination or oxidative decarboxylation, but decreased the rate of oxidation of leucine carbons 2–6. Elevated levels of growth hormone dose dependently inhibited leucine catabolism, α-ketoisocaproate (KIC) production and the syntheses of glutamate plus glutamine. In contrast, cortisol and glucagon increased leucine transamination, leucine oxidative decarboxylation, KIC production, the oxidation of leucine 2–6 carbons and the syntheses of glutamate plus glutamine. Prolactin did not affect leucine catabolism in the cells. The changes in leucine degradation were consistent with alterations in abundances of BCAA transaminase and phosphorylated levels of branched-chain α-ketoacid dehydrogenase. Reductions in insulin and growth hormone but increases in cortisol and glucagon with lactation act in concert to stimulate BCAA catabolism for glutamate and glutamine syntheses. These coordinated changes in hormones may facilitate milk production in lactating mammals.

Keywords

Insulin Growth hormone Cortisol Prolactin Glucagon Lactation Leucine 

Abbreviations

BCAA

Branched-chain amino acids

BCAT

Branched-chain amino acid transferase

BCKA

Branched-chain α-ketoacids

BCKAD

Branched-chain α-ketoacid dehydrogenase

HEPES

4-(2-hydroxyethyl)-1-Piperazineethanesulfonic acid

KIC

α-Ketoisocaproate

Notes

Acknowledgments

Jian Lei was supported by a Postgraduate Scholarship from South China Agricultural University. Work in the authors’ laboratories was supported by the National Natural Science Foundation of China grants (#31172217 and 30901041), the Thousand-People Talent Program at China Agricultural University, Chinese Universities Scientific Funds (#2012RC024), China Agricultural University postdoctoral funds, National Research Initiative Competitive Grants (#2008-35206-18764 and 2008-35203-19120) from the USDA National Institute of Food and Agriculture, Texas AgriLife Research Hatch Project (#H-8200) and American Heart Association (#10GRNT4480020). We thank Dr. Susan Hutson and Dr. Christopher Lynch for the kind provision of BCAT and BCKAD E1α antibodies, respectively.

Conflict of interest

The authors declare that they have no conflict of interest.

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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Jian Lei
    • 1
    • 2
    Email author
  • Dingyuan Feng
    • 1
  • Yongliang Zhang
    • 1
  • Sudath Dahanayaka
    • 2
  • Xilong Li
    • 2
  • Kang Yao
    • 2
  • Junjun Wang
    • 2
    • 3
  • Zhenlong Wu
    • 3
  • Zhaolai Dai
    • 3
  • Guoyao Wu
    • 1
    • 2
    • 3
    Email author
  1. 1.College of Animal ScienceSouth China Agricultural UniversityGuangzhouPeople’s Republic of China
  2. 2.Department of Animal Science and Faculty of NutritionTexas A&M UniversityCollege StationUSA
  3. 3.State Key Laboratory of Animal NutritionChina Agricultural UniversityBeijingChina

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