AJP - Endocrinology and Metabolism, Vol 272, Issue 1 E36-E44, Copyright © 1997 by American Physiological Society
Maintaining muscle protein anabolism after a metabolic stress: role of dextrose vs. amino acid availability
M. J. Borel, P. E. Williams, K. Jabbour, J. C. Hibbard and P. J. Flakoll
Department of Surgery, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
The effect of chronic hypocaloric parenteral infusions of amino acids (AA)
vs. dextrose (D) on protein homeostasis after a generalized metabolic
stress was examined. Multicatheterized mongrel dogs were metabolically
challenged by a 4-day fast and then administered a 4-day intravenous
infusion of saline (S, n = 8), D (n = 8), or isocaloric AA (n = 7).
Although nitrogen balance (g.kg.1.day-1) was similarly negative with S
(-0.37 +/- 0.05), D (-0.28 +/- 0.03), and AA (-0.37 +/- 0.04) during the
fasting period, it was less negative (P < or = 0.05) with AA (-0.06 +/-
0.04) than with D (-0.20 +/- 0.03) or S (-0.23 +/- 0.04) during nutrient
infusion. AA resulted in net hindlimb uptake and D in net hindlimb release
of essential AA (570 +/- 261 vs. -248 +/- 59 nmol.kg-1.min-1). Whereas S
and D infusions led to net hindlimb muscle protein loss (-37 +/- 24 and -89
+/- 33 micrograms.kg-1.min-1, respectively, P < or = 0.05 vs. AA),
parenteral AA resulted in net deposition (169 +/- 62 micrograms.kg-1.min-1)
as measured using L-[ring-2H5]phenylalanine. Thus hypocaloric parenteral D
infusion after a metabolic stress does not favor nitrogen conservation,
because net whole body nitrogen loss, skeletal muscle protein catabolism,
and hindlimb AA release were not blunted compared with S infusion.
Conversely, hypocaloric AA infusion preserves whole body and muscle protein
stores.
