Fig. 4. The nitrotyrosine concentration was determined in whole lung homogenates of 96 rats as an index of protein nitrosylation and peroxynitrite generation. Eight rats were examined in each group. Six pairs of lung were excised and exposed to a nitric oxide donor (SIN-1) ex vivo for 1 h and then homogenized and used as internal positive controls. Exposure to 80 ppm nitric oxide in 90% oxygen results in significant increases in the nitrotyrosine concentrations that are similar to those in SIN-1–positive controls. Data are expressed as the mean ± SD, and asterisks indicate significant differences.