Glutamine and glucose metabolism in rat splenocytes and mesenteric lymph node lymphocytes

The metabolism of glutamine (2 mM) and glucose (5 mM) was studied in splenocytes and mesenteric lymph node lymphocytes of Wistar-Furth rats to assess their relative importance as energy substrates. The major products from glutamine were ammonia, glutamate, aspartate, and CO2, whereas those from glucose were lactate, pyruvate, and CO2 in cells from both lymphoid organs. The individual rates of glutamine and glucose metabolism were decreased in the presence of both substrates, compared with the rates when present separately. The rates of glucose and some (but not all) aspects of glutamine metabolism were higher (P less than 0.01) in splenocytes than in mesenteric lymphocytes. In cells from both lymphoid organs, glutamine and glucose could potentially contribute almost equal amounts of ATP in the presence of both substrates. Glutamine and glucose individually were able to provide sufficient amounts of ATP to maintain its concentrations in the cells throughout a 2-h incubation period at the same levels as with both substrates present. We also found that splenocyte concentration (3.3-100 x 10(6) cells/ml) in the incubations is an important determinant of rates of metabolite formation from glutamine when expressed per 10(6) cells. We conclude that glucose is not the only quantitatively significant energy substrate or even the major one for lymphocytes, because glutamine at near-physiological concentration can be readily utilized by these cells.