MAINTAINING MUSCLE PROTEIN ANABOLISM AFTER A METABOLIC STRESS - ROLE OF DEXTROSE VS AMINO-ACID AVAILABILITY

The effect of chronic hypocaloric parenteral infusions of amino acids (AA) vs. dextrose (D) on protein homeostasis after a generalized metab olic stress was examined. Multicatheterized mongrel dogs were metaboli cally challenged by a 4-day fast and then administered a 4-day intrave nous infusion of saline (S, n = 8), D (n = 8), or isocaloric AA (n = 7 ). Although nitrogen balance (g . kg(-1) . day(-1)) was similarly nega tive with S (-0.37 +/- 0.05), D (-0.28 +/- 0.03), and AA (-0.31 +/- 0. 04) during the fasting period, it was less negative (P less than or eq ual to 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 hindli mb uptake and D in net hindlimb release of essential AA (570 +/- 261 v s. -248 +/- 59 nmol . kg(-1) . min(-1)). Whereas S and D infusions led to net hindlimb muscle protein loss (-37 +/- 24 and -89 +/- 33 mu g . kg(-1) . min(-1), respectively, P less than or equal to 0.05 vs. AA), parenteral AA resulted in net deposition (169 +/- 62 mu g . kg(-)1 . min(-1)) as measured using L-[ring-H-2(5)]phenylalanine. Thus hypocalo ric parenteral D infusion after a metabolic stress does not favor nitr ogen conservation, because net whole body nitrogen loss, skeletal musc le protein catabolism, and hindlimb AA release were not blunted compar ed with S infusion. Conversely, hypocaloric AA infusion preserves whol e body and muscle protein stores.