The effect of glutamine on the activity of the NADPH oxidase complex from rat neutrophils was investigated. Superoxide anion (O(2)(-)) production was assessed: (1) by scintillation counting by using lucigenin, and (2) by reduction of cytochrome c over 10 min. The effects of glutamine and PMA on the expression of the NADPH oxidase components p22( phox ), gp91( phox ) and p47( phox ) were also determined. Glutamine at 1 and 2 mM increased O(2)(-) generation in the presence of PMA by 100% and 74% respectively, in neutrophils maintained previously for 3 h in medium deprived of this amino acid. DON (6-diazo-5-oxo-L-norleucine), an inhibitor of phosphate-dependent glutaminase and thus of glutamine metabolism, caused a significant decrease in O(2)(-) production by neutrophils stimulated with PMA both in the absence (44%) and in the presence (66%) of glutamine. PMA markedly increased the expression of gp91( phox ), p22( phox ) and p47( phox ) mRNAs. Glutamine (2 mM) increased the expression of these three proteins both in the absence and in the presence of PMA. We postulate that glutamine leads to O(2)(-) production in neutrophils, probably via the generation of ATP and regulation of the expression of components of NADPH oxidase.