A, Peripheral blood was collected from Reversa mice 12 and 8 days before Mttp inactivation as well as 16 days after reversal of hypercholesterolemia, and assayed for NOx as described in Materials and Methods. B, NOx levels were also determined in plasma from atheroregressing Reversa mice sacrificed 70 days after Mttp inactivation that were treated with either saline or AMD3100, or received Tie2-GFP+ bone marrow EPCs. C and D, 3-mm wide rings were prepared from aortas removed from atherosclerosis-prone (−pI-pC) and atheroregressing mice that received EPC treatment (+pI-pC, EPC+). Acetylcholine (ACh)- or sodium nitroprusside (SNP)-specific vascular relaxation was determined.