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1 Baylor College of Medicine
* To whom correspondence should be addressed. E-mail: tdavis{at}bcm.tmc.edu.
Chronic treatment of growing pigs with porcine somatotropin (pST) promotes protein synthesis and doubles postprandial levels of insulin, a hormone that stimulates translation initiation. This study aimed to determine whether the pST induced increase in skeletal muscle protein synthesis was mediated through an insulin-induced stimulation of translation initiation. After 7-10 days of pST (150 µg kg-1 d-1) or control saline treatment, pancreatic-glucose-amino acid clamps were performed in overnight fasted pigs to reproduce 1) fasted (5 µU ml-1), 2) fed control (25 µU ml-1), and 3) fed-pST-treated (50 µU ml-1) insulin levels, while glucose and amino acids were maintained at baseline fasting levels. Fractional protein synthesis rates and indices of translation initiation were examined in skeletal muscle. Effectiveness of pST treatment was confirmed by reduced urea nitrogen and elevated insulin like growth factor-1 levels in plasma. Skeletal muscle protein synthesis was independently increased by both insulin and pST. Insulin increased the phosphorylation of protein kinase B and the downstream effectors of the mammalian target of rapamycin, ribosomal protein S6 kinase and eukaryotic initiation factor (eIF) 4E binding protein-1 (4E-BP1). Further, insulin reduced inactive 4E BP1eIF4E complex association and increased active eIF4EeIF4G complex formation, indicating enhanced eIF4F complex assembly. However, pST treatment did not alter translation initiation factor activation. We conclude that the pST-induced stimulation of skeletal muscle protein synthesis in growing pigs is independent of the insulin-associated activation of translation initiation.
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F. A. Wilson, A. Suryawan, R. A. Orellana, H. V. Nguyen, A. S. Jeyapalan, M. C. Gazzaneo, and T. A. Davis Fed levels of amino acids are required for the somatotropin-induced increase in muscle protein synthesis Am J Physiol Endocrinol Metab, October 1, 2008; 295(4): E876 - E883. [Abstract] [Full Text] [PDF] |
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