Nonessential amino acids are not necessary to stimulate net muscle proteinsynthesis in healthy volunteers

The present study was performed to test the hypothesis that orally administ ered essential amino acids, in combination with carbohydrate, will stimulat e net muscle protein synthesis in resting human muscle in vivo. Four volunt eers ingested 500 mt of a solution containing 13.4 g of essential amino aci ds and 35 g sucrose (EAA). Blood samples were taken from femoral arterial a nd venous catheters over a 2-hour period following the ingestion of EAA to measure arteriovenous concentrations of amino acids across the muscle. Two muscle biopsies were taken during the study, one before administration of t he drink and one approximately 2 hours after consumption of EAA. Serum insu lin increased from normal physiologic levels at baseline (9.2 +/- 0.8 mu U/ mL) and peaked (48 +/- 7.1 mu U/mL) 30 minutes after EAA ingestion. Arteria l essential amino acid concentrations increased approximately 100 to 400% a bove basal levels between 10 a,ld 30 minutes following drink ingestion. Net nitrogen (N) balance changed from negative (-495 +/- 128 nmol/mL) prior to consumption of EAA to a peak positive value (416 +/- 140 nmol/mL) within I O minutes of ingestion of the drink. EAA resulted in an, estimated positive net N uptake of 307.3 mg N above basal levels over the 2-hour period Muscl e amino acid concentrations were similar prior to and 2 hours following ing estion of EAA. We conclude that ingestion of a solution composed of carbohy drates to stimulate insulin release and a small amount of essential amino a cids to increase amino acid availability for protein synthesis is an effect ive stimulator of muscle protein anabolism. (C) Elsevier Science Inc. 1999. All rights reserved.