NOS3 and endothelial dysfunction: Endothelial dysfunction was evident as early as 6 hr after unilateral ureteral obstruction (UUO) on the basis of an 85% reduction of NOS3 protein levels compared to sham operated controls, followed by a partial recovery of NOS3 expression, although NOS3 levels remained below normal for the entire 7 days following UUO (Fig 1A&B).