Endothelium-dependent vasorelaxation 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 prostaglandin F2α. Each point on the curves represents the cumulative response at each concentration of acetylcholine (ACh). The data are expressed as the mean and SEM (see graph for n-values). * denotes a significant effect on Emax compared to the control group (P < 0.05, ANOVA with unequal variance between groups).