Influence of amino acid administration on whole-body leucine kinetics and resting metabolic rate in postabsorptive normal subjects

Abstract

1. We have investigated the effect of an amino acid mixture (Varnin 14; 57.4 ±10.2 μmol h−1 kg−1) on whole-body leucine kinetics, calculated by a steady-state reciprocal pool model, and resting metabolic rate in eight postabsorptive normal subjects. 2. Vamin 14 infusion increased whole-body leucine flux (P < 0.001), leucine employed for protein synthesis (P < 0.001), leucine oxidation (P < 0.001), metabolic clearance rate of α-ketoisocaproic acid (P < 0.05) and levels of all three branched-chain amino acids (P < 0.001) compared with the basal situation. In contrast, whole-body proteolysis was reduced (P < 0.05). 3. Resting metabolic rate was increased during Vamin 14 infusion (P < 0.05) and was positively correlated with whole-body protein synthesis (n = 16, r = 0.6342, P < 0.01; y = 0.605x + 173.7), as was the change in metabolic rate with the change in protein synthesis (n = 8, r = 0.772, P < 0.05; y = 0.493x − 10.85). 4. Overall, Vamin 14 infusion was associated with increased blood glucose (P < 0.001), although the observed increase in plasma glucagon (t = 2.012) and plasma insulin (t = 1.683) failed to reach statistical significance. 5. These data lend a measure of support to the hypothesis that the apparent increase in whole-body protein synthesis in insulin-dependent diabetic (type I) subjects during insulin withdrawal may be substrate related.