Figure 4.

Accumulation of nitrite in the incubation medium of NPE cells exposed to L-arginine (a) or SNP (b). NPE cells were incubated with or without (control) test compounds for 20 min and then the concentration of nitrite was measured in the incubation medium. Nitrite concentration (μM) was shown as the mean±s.e.m. of 12 independent measurements at each concentration of L-arginine and 12–16 measurements at each concentration of SNP. Statistical comparisons were made by analysis of variance followed by the Bonferroni post hoc multiple comparison tests. ^***and ^≠≠≠indicate significant differences from the control values and from values for the preceeding concentration of each drug at P<0.001, respectively.