Alanine and Glutamine Release from the Human Forearm: Effects of Glucose Administration

Abstract

The effect of glucose infusion alone (175 mg/kg bolus dose followed by 4 mg/min/kg for 70 min) and in combination with forearm exercise on the exchange of glucose, alanine, glutamine and other metabolites and amino acids across forearm muscle was studied in 6 healthy individuals after an overnight fast. Arterial and deep venous blood was sampled and a mercury strain gauge plethysmograph was used to measure forearm blood flow. Total body energy expenditure and net glucose and fat oxidation were assessed by indirect calorimetry. During short-term administration of glucose, glutamine becomes the main amino acid released by muscle, carrying as much as 5 times more nitrogen out of muscle than alanine. The suppression of the release of alanine is paralleled by a decreased release of lactate and pyruvate and is consistent with both the activation of the pyruvate dehydrongase complex and diversion of glucose carbon to glycogen. Most of the glucose taken up by forearm muscle appears to be converted to glycogen. During exercise there appears to be breakdown of glycogen, increased availability of lactate and pyruvate and increased release of alanine. Glutamine continues to be released at a high rate during exercise.