CBS deficiency promotes endothelial dysfunction. Dilatation of cerebral arterioles to (A) acetylcholine or (B) nitroprusside was measured in 20-week-old mice (n = 10-16 mice per group). Values are mean ± SEM; *P < .05, and **P < .001 compared with Cbs^+/+ and Tg-I278T Cbs^+/+ mice at the same dose of acetylcholine.