NO-induced vasodilation (via SPR) was impaired in mesenteric arterioles following intravenous injection (A, n = 8–12) and gastric gavage (B, n = 8–10) of CeO2 NP. *p ≤ 0.05 versus control, †p ≤ 0.05 versus low dose CeO2 NP (50 µg for intravenous injection and 100 µg for gastric gavage), ‡p ≤ 0.05 versus middle dose CeO2 NP (100 µg for intravenous injection and 300 µg for gastric gavage), ^p ≤ 0.05 versus high dose CeO2 NP (900 µg for intravenous injection and 600 µg for gastric gavage). The brackets indicate differences in the overall slope of the determination.