|Thivierge, M. Carole - UNIV LAVAL ST FOY QUEBEC|
|Bush, Jill - BAYLOR COLL OF MEDICINE|
|Nguyen, Hanh - BAYLOR COLL OF MEDICINE|
|Orellana, Rene - BAYLOR COLL OF MEDICINE|
Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 16, 2005
Publication Date: June 1, 2005
Citation: Thivierge, M.C., Bush, J.A., Suryawan, A., Nguyen, H.V., Orellana, R.A., Burrin, D.G., Jahoor, F., Davis, T.A. 2005. Whole-body and hindlimb protein breakdown are differentially altered by feeding in neonatal piglets. Journal of Nutrition. 135(6):1430-1437. Interpretive Summary: A new born animal has a high growth rate which is characterized by increased protein production and lower protein degradation in skeletal muscle in response to a meal. Since there is little information about the effects of feeding and fasting on protein degradation, we studied protein breakdown in whole-body and leg muscle of 10- and 28-day-old piglets. We used radioactive amino acids (builing blocks of protein) as markers for muscle protein breakdown analysis. Feeding reduced whole-body protein degradation, but increased leg muscle protein degradation, suggesting that tissues other than leg muscle are involved in the reduction of whole-body protein degradation. Fasting resulted in mobilization of amino acids from whole-body protein but not leg muscle protein. These responses were unaffected by age.
Technical Abstract: The high rate of muscle protein accretion in neonates is sustained by the marked increase in muscle protein synthesis in response to feeding. Little is known about the role of proteolysis in the regulation of protein accretion in response to feeding during the neonatal period. To determine the feeding-induced response of protein breakdown at the whole-body level and in the hindlimb of neonates, 10- and 28-d-old piglets that had been food deprived overnight were infused (7 h) with [1-13C]phenylalanine and [ring-2H4]tyrosine during an initial food deprivation period (3 h), followed by a feeding period (4 h). During feeding, endogenous flux of phenylalanine decreased (P < 0.01) in both the whole body and the hindlimb. Feeding reduced (P < 0.01) whole-body proteolysis but increased hindlimb proteolysis (P = 0.04), suggesting that tissues other than the hindlimb are involved in the reduction in whole-body proteolysis during feeding. Overnight food deprivation resulted in a net mobilization of phenylalanine from whole-body proteins (P < 0.01) but not hindlimb proteins. These responses were unaffected by age. The results suggest that the hindlimb requires a continuous supply of free amino acids to sustain the high rate of muscle protein turnover in neonates and that adaptive mechanisms provide free amino acids to sustain skeletal muscle protein accretion in early postnatal life when the amino acid supply is limited.