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1 Department of Surgery, School of Osteopathic Medicine, University of Medicine and Dentistry of New Jersey, Stratford, New Jersey 08084; and 2 Department of Medicine and the General Clinical Research Center, Temple University Health Sciences Center, Philadelphia, Pennsylvania 19140
Bed rest is associated with a loss of
protein from the weight-bearing muscle. The objectives of this
study are to determine whether increasing dietary branched-chain amino
acids (BCAAs) during bed rest improves the anabolic response after bed
rest. The study consisted of a 1-day ambulatory period, 14 days of bed rest, and a 4-day recovery period. During bed rest, dietary intake was
supplemented with either 30 mmol/day each of glycine, serine, and
alanine (group 1) or with 30 mmol/day each of the
three BCAAs (group 2). Whole body protein synthesis was
determined with U-15N-labeled amino acids, muscle, and
selected plasma protein synthesis with
L-[2H5]phenylalanine. Total
glucose production and gluconeogenesis from alanine were determined
with L-[U-13C3]alanine and
[6,6-2H2]glucose. During bed rest, nitrogen
(N) retention was greater with BCAA feeding (56 ± 6 vs. 26 ± 12 mg
N · kg
1 · day1,
P < 0.05). There was no effect of BCAA supplementation
on either whole body, muscle, or plasma protein synthesis or the rate
of 3-MeH excretion. Muscle tissue free amino acid concentrations were
increased during bed rest with BCAA (0.214 ± 0.066 vs. 0.088 ± 0.12 nmol/mg protein, P < 0.05). Total glucose
production and gluconeogenesis from alanine were unchanged with bed
rest but were significantly reduced (P < 0.05) with
the BCAA group in the recovery phase. In conclusion, the improved N
retention during bed rest is due, at least in part, to accretion of
amino acids in the tissue free amino acid pools. The amount accreted is
not enough to impact protein kinetics in the recovery phase but does improve N retention by providing additional essential amino acids in
the early recovery phase.
nitrogen balance; protein loss
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