title: Vitamin C improves endothelium-dependent vasodilation in forearm resistance vessels of humans with hypercholesterolemia.
abstract: BACKGROUND
  Endothelium-dependent vasodilation is impaired in humans with hypercholesterolemia. Oxidative degradation of endothelium-derived nitric oxide plays a major role in endothelial dysfunction in animal models of hypercholesterolemia. To assess whether this mechanism is relevant to humans, we studied the effect of vitamin C, an antioxidant, on vasodilator function in forearm resistance vessels of patients with hypercholesterolemia.
  
  
  RESULTS
  We studied 11 hypercholesterolemic and 12 healthy control subjects. Forearm blood flow was determined by venous occlusion plethysmography. Endothelium-dependent vasodilation was assessed by intra-arterial infusion of methacholine (0.3 to 10 micrograms/min). Endothelium-independent vasodilation was measured by intra-arterial infusion of nitroprusside (0.3 to 10 micrograms/min) and verapamil (10 to 300 micrograms/min). Forearm blood flow dose-response curves were determined for each drug before and during coadministration of vitamin C (24 mg/min). In hypercholesterolemic subjects, endothelium-dependent vasodilation to methacholine was augmented by coinfusion of vitamin C (P = .001); in contrast, endothelium-independent vasodilation to nitroprusside and verapamil were not affected by coinfusion of vitamin C (P = .8 and P = .3, respectively). In control subjects, vitamin C administration did not alter endothelium-dependent vasodilation (P = .2).
  
  
  CONCLUSIONS
  We conclude that vitamin C improves endothelium-dependent vasodilation in the forearm resistance vessels of patients with hypercholesterolemia. These findings suggest that nitric oxide degradation by oxygen-derived free radicals contributes to abnormal vascular reactivity in hypercholesterolemic humans.
authors.affiliation: Vascular Medicine and Atherosclerosis Unit, Brigham and Women's Hospital, Boston, MA 02115, USA.
authors.forename: H H
authors.initials: HH
authors.lastname: Ting
authors.forename: F K
authors.initials: FK
authors.lastname: Timimi
authors.forename: E A
authors.initials: EA
authors.lastname: Haley
authors.forename: M A
authors.initials: MA
authors.lastname: Roddy
authors.forename: P
authors.initials: P
authors.lastname: Ganz
authors.forename: M A
authors.initials: MA
authors.lastname: Creager
mesh_terms: D000328:Adult; D001205:Ascorbic Acid / Q000627:therapeutic use*; D004730:Endothelium, Vascular / Q000503:physiopathology*; D005260:Female; D005542:Forearm / Q000098:blood supply*; D006801:Humans; D006937:Hypercholesterolemia / Q000188:drug therapy* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D014677:Pharmaceutical Vehicles / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects; D014655:Vascular Resistance; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D014677:Pharmaceutical Vehicles; D001205:Ascorbic Acid