Production of glutamine and utilization of glutamate by rat subcutaneous adipose tissue in vivo.

Information about adipose tissue amino acid metabolism is limited, with most data derived from studies in vitro. The purpose of this study was to further characterize the role of adipose tissue in glutamine metabolism in the rat in vivo. The extracellular concentrations of glutamine, glutamate, alanine, and ammonia were measured in the rat inguinal fat pad using a microdialysis sampling technique. A calibration method was used to accurately assess the extracellular levels of metabolites, and a comparison of these concentrations with those in arterial blood allowed determination of the net flux of each compound. The adipose tissue-arterial blood concentration differences were 122 +/- 19, 54 +/- 37, -61 +/- 21, and -28 +/- 13 microM for glutamine, alanine, glutamate, and ammonia, respectively, indicating a production of glutamine and an uptake of glutamate by subcutaneous adipose tissue. The magnitude of glutamine production suggests that adipose tissue may play a significant role in whole body glutamine homeostasis.