Endothelium-independent relaxation of aorta segments from 11-13 weeks old apoE-/- mice exposed to carbon black by i.t. instillation. The response is expressed as the % relaxation of the precontraction tension produced by PGF2α. Each point on the curve represents the cumulative response at each concentration of sodium nitroprusside (SNP). The data are expressed as the mean and SEM (see graph for n-values).