PURPOSE: Amino-acid (AA) infusions promote thermogenesis and prevent perioperative hypothermia, but the mechanism of action is unknown. We sought to verify the hypothesis that AA infusions stimulate the release of metabolic hormones during surgery and increase energy expenditure, resulting in thermogenesis.METHODS: Twenty-four patients were randomly assigned to receive AA (4 kJ x kg(-1) x h(-1)) or saline, which was infused for 2 h during off-pump coronary artery bypass surgery (OPCABS). Arterial adrenaline, thyroid hormone, insulin, and leptin levels were determined at five defined times during surgery. Oxygen consumption was measured 3 h after the start of infusion.RESULTS: AA infusion maintained the body core temperature during OPCABS. This effect was accompanied by an increase in oxygen consumption, which depended on increased heart rate. AA infusion prominently stimulated the secretion of insulin and leptin; the insulin level increased rapidly within 2 h after the start of infusion, whereas leptin levels increased gradually over a 6-h period after the start of infusion.CONCLUSION: AA infusion significantly increased body core temperature and oxygen consumption during surgery. Given the release of insulin and leptin in response to AA infusion, it is likely that these hormonal signaling pathways may, in part, have contributed to the thermogenic response that occurred during the surgery.
Aged Amino Acids