Induction of a macrophage-like nitric oxide synthase in cultured rat aortic endothelial cells. IL-1 beta-mediated induction regulated by tumor necrosis factor-alpha and IFN-gamma

We investigated the effects of murine rTNF-alpha, human rIL-1 beta, and rat rIFN-gamma in various concentrations and/or combinations on inducible nitric oxide (NO) production in primary cultures of rat aortic endothelial cells. Northern blot analysis of total RNA from induced and control cultures using the cloned mouse macrophage gene of inducible NO synthase as probe as well as polymerase chain reaction using a specific primer sequence gave a positive signal for activated cells only. A RNA approximately 4.4 kb of length similar to the inducible form of NO synthase in macrophages was labeled. The concentration of nitrite as a stable reaction product of NO in culture supernatants was determined 24 h after incubation with the various cytokines. IL-1 beta alone (40 to 1000 U/ml) induced formation of increasing amounts of nitrite with increasing concentrations of IL-1 beta present. Neither TNF-alpha alone (10 to 2000 U/ml) nor IFN-gamma alone 25 to 500 U/ml) showed significant effects on nitrite production. Simultaneous incubation with low concentrations of TNF-alpha (< or = 100 U/ml) and IL-1 beta abrogated the induction effect of IL-1 beta. Conversely, addition of high concentrations of TNF-alpha (> or = 500 U/ml) led to near maximal levels of nitrite formation even at lowest IL-1 beta concentrations (40 U/ml). In addition, simultaneous incubation of endothelial cells with IFN-gamma plus IL-1 beta and/or TNF-alpha led to near maximal NO production of endothelial cells, even at lowest IFN-gamma concentrations (25 U/ml). We hypothesize that the regulating effect of TNF-alpha may in vivo help to prevent local inflammatory responses from spreading to intact sites.