Intravenous administration of amino acids during anesthesia stimulates muscle protein synthesis and heat accumulation in the body

The aim of this study was to determine the contribution of protein synthesis to the prevention of anesthesia‐induced hypothermia by intravenous administration of an amino acid (AA) mixture. We examined changes in intraperitoneal temperature (Tcore), rates of protein synthesis (Ks) and the phosphorylation states of translation initiation regulators and their upstream signaling components in skeletal muscle of conscious (Nor) and propofol‐anesthetized (Ane) rats after intravenous administration of a balanced AA mixture or saline (Sal). Compared with Sal administration, AA markedly attenuated the decrease in the Tcore of rats during anesthesia, while Tcore in the Nor‐AA group became slightly elevated during treatment. Stimulation of muscle protein synthesis resulting from AA administration was observed in each case, but Ks in the Ane‐AA group remained lower than in the Nor‐Sal group. Administration of AA during anesthesia significantly increased plasma insulin to levels approximately 6‐fold greater than the Nor‐AA group and enhanced phosphorylation of 4E‐BP1, S6K1, PKB and mTOR, relative to all other groups and treatments. These results suggest that AA administration during anesthesia stimulates muscle protein synthesis via insulin‐mTOR–dependent activation of translation initiation regulators caused by markedly elevated insulin and thereby facilitates thermal accumulation in the body.