The effect of glutamine on protein balance and amino acid flux across arm and leg tissues in healthy volunteers

Background. Glutamine is important in nitrogen transportation and the physiological control of acid–base regulation. In addition, it has been assumed that glutamine regulates protein balance in skeletal muscles based on findings in both experimental and clinical studies. However, little information on glutamine and its effect on protein dynamics in normal individuals is available. Therefore, the aim of this study was to evaluate whether glutamine improves protein balance and uptake of various indispensable amino acids across peripheral tissue in healthy individuals. Material and methods. Standard primed constant infusions of L ‐ring‐²H₅]phenylalanine and ring 3,3‐²H₂]tyrosine (2 μmol kg^?1 h^?1) were performed after overnight fast in five healthy male volunteers before and during infusions of a standard and a glutamine/tyrosine enriched amino acid solution. Flux measurements of amino acids (AA) including 3‐methylhistidine, glucose, lactate and free fatty acids (FFA) were performed across arm and leg tissues. Results. Infusion of the standard AA solution (0·2 g N kg^?1 day^?1) increased the net uptake of individual amino acids, but provision of the enriched solution (0·4 g N kg^?1 day^?1) with increased amounts of glutamine and tyrosine seemed to compete unfavourably with the net uptake of other key amino acids as methionine and phenylalanine, which are indispensable in muscles for protein synthesis. Increased flux of amino acids across peripheral tissues did not influence on flux of glucose, free fatty acid and lactate. Conclusions. Glutamine provision did neither stimulate protein synthesis nor attenuate breakdown of either globular or myofibrillar proteins in skeletal muscles of healthy volunteers.