Graphs showing impaired endothelium-dependent relaxation in response to acetylcholine (ACh) in mesenteric resistance arteries of female but not male apoE-/- mice fed a regular chow diet. The values are means ± SEM. **p < 0.01 compared with wild-type (C57) mice. Reproduced with permission from Arruda et al.  (right panel) and from Cola et al.  (left panel).