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 physi ological control of acid-base regulation. In addition, it has been assumed that glutamine regulates protein balance in skeletal muscles based on findi ngs in both experimental and clinical studies. However, little information on glutamine and its effect on protein dynamics in normal individuals is av ailable. Therefore, the aim of this study was to evaluate whether glutamine improves protein balance and uptake of various indispensable amino acids a cross peripheral tissue in healthy individuals. Material and methods. Standard primed constant infusions of L- [ring-H-2(5) ]phenylalanine and [ring 1,3-H-2(2)]tyrosine (2 mu mol kg(-1) h(-1)) were p erformed after overnight fast in five healthy male volunteers before and du ring infusions of a standard and a glutamine/tyrosine enriched amino acid s olution. 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 gN kg(-1) day(-1)) incre ased the net uptake of individual amino acids, but provision of the enriche d 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 a mino acids as methionine and phenylalanine, which are indispensable in musc les for protein synthesis. Increased Aux of amino acids across peripheral t issues did not influence on flux of glucose, free fatty acid and lactate. Conclusions. Glutamine provision did neither stimulate protein synthesis no r attenuate breakdown of either globular or myofibrillar proteins in skelet al muscles of healthy volunteers.