Effect of Amino Acid Infusion on Central Thermoregulatory Control in Humans

Background: Administration of protein or amino acids enhances thermogenesis, presumably by stimulating oxidative metabolism. However, hyperthermia results even when thermoregulatory responses are intact, suggesting that amino acids also alter central thermoregulatory control. Therefore, the authors tested the hypothesis that amino acid infusion increases the thermoregulatory set point.

Methods: Nine male volunteers each participated on 4 study days in randomized order: (1) intravenous amino acids infused at 4 kJ middle dot] kg-1 middle dot] h-1 for 2.5 h combined with skin-surface warming, (2) amino acid infusion combined with cutaneous cooling, (3) saline infusion combined with skin-surface warming, and (4) saline infusion combined with cutaneous cooling.

Results: Amino acid infusion increased resting core temperature by 0.3 +/- 0.1degrees]C (mean +/- SD) and oxygen consumption by 18 +/- 12%. Furthermore, amino acid infusion increased the calculated core temperature threshold (triggering core temperature at a designated mean skin temperature of 34degrees]C) for active cutaneous vasodilation by 0.3 +/- 0.3degrees]C, for sweating by 0.2 +/- 0.2degrees]C, for thermoregulatory vasoconstriction by 0.3 +/- 0.3degrees]C, and for thermogenesis by 0.4 +/- 0.5degrees]C. Amino acid infusion did not alter the incremental response intensity (i.e., gain) of thermoregulatory defenses.