Simultaneous generation of nitric oxide and superoxide by inflammatory cells in rats

It has recently been shown that peroxynitrite anion is a powerful oxidant that can initiate lipid peroxidation. As this oxidant is the product of the reaction between nitric oxide and superoxide, we have studied whether cells isolated from an inflammatory exudate can release both radicals simultaneously under physiological conditions. The carrageenin-induced granuloma model in rats was used. Cells from the inflammatory pouch were stimulated with opsonized zymosan in the absence or in the presence of exogenous image-arginine. Nitric oxide production without exogenous image-arginine was detectable after 15 min (0.29 nmol NO2−) and increased with time (1.65 nmol NO2− at 4 h). When nitrite released from cells was expressed as a rate a burst was shown in the first few minutes. Between 0 and 15 min, cells produced NO2− at the following rates: 20 pmol NO2−/1 × 106 cells/min without exogenous image-arginine and 83 pmol NO2−/1 × 106 cells/min with exogenous image-arginine. Production was further stimulated with opsonized zymosan (92 pmol NO2−/1 × 106 cells/min), and inhibited by L-NMMA and L-NIO. The production of superoxide increased for up to 2 h and then stabilized. A significant increase in nitrite was observed in the presence of SOD, whereas L-NIO increased superoxide generation. These results suggest that peroxynitrite anion may be formed by inflammatory cells.