We have evaluated the role of prostaglandin E(2) (PGE(2)) in the synthesis of nitric oxide (NO) by the activation of the inducible form of nitric oxide synthase (NOS) in the murine macrophage cell line, J774, stimulated with different doses of lipopolysaccharide (LPS). The stimulation of the J774 line with suboptimal doses of LPS (0.1 mu g/mL) caused a production of endogenous PGE(2) that was capable of stimulating NOS activity inducing an increase in the NO synthesis, as attested by the fact that cyclooxygenase enzyme inhibitor, indomethacin, significantly reduced NO secretion. On the contrary, a higher dose of LPS (I mu g/mL) produced high levels of PGE(2) that reduced the levels of NOS and, subsequently, NO production. Experiments carried out with exogenous PGE(2) indicated that concentrations between 1 and 10 ng/mL are able to stimulate the expression of NOS and the release of NO, while higher concentrations (>50 ng/mL) are inhibitory. Furthermore, our data indicate that there is a network of interaction which involves NO, PGE(2), and tumor necrosis factor. High levels of PGE(2) inhibited TNF alpha secretion, which in turn could exert inhibitory effects on NO synthesis.492105115