title: Daily low-dose folic acid supplementation does not prevent nitroglycerin-induced nitric oxide synthase dysfunction and tolerance: a human in vivo study.
abstract: BACKGROUND
  Continuous treatment with nitroglycerin (GTN) causes tolerance and endothelial dysfunction, both of which may involve endothelial nitric oxide synthase (eNOS) dysfunction. eNOS dysfunction may be linked to depletion of tetrahydrobiopterin, and folic acid may be involved in the regeneration of this cofactor. It has been demonstrated that 10 mg⁄day folic acid supplementation prevents the development of GTN tolerance and GTN-induced endothelial dysfunction. However, the efficacy of daily lower-dose folic acid supplementation for preventing these phenomena has not been investigated.
  
  
  OBJECTIVE
  To determine the effect of 1 mg⁄day folic acid supplementation on responses to sustained GTN therapy.
  
  
  RESULTS
  On visit 1, 20 healthy male volunteers were randomly assigned to receive either oral folic acid (1 mg⁄day) or placebo for one week in a double- blind study. All subjects also received continuous transdermal GTN (0.6 mg⁄h). On visit 2, forearm blood flow was measured using venous occlusion strain-gauge plethysmography in response to incremental intra-arterial infusions of acetylcholine, N-monomethyl-L-arginine and GTN. Subjects in both groups displayed significantly decreased responses to acetylcholine and N-monomethyl-L-arginine infusions compared with a control group that received no treatment. Responses to GTN were also significantly diminished in both groups (P<0.05 for all).
  
  
  CONCLUSIONS
  The present data demonstrate that daily supplementation with 1 mg folic acid does not prevent the development of GTN-induced eNOS dysfunction or tolerance.
authors.affiliation: Division of Cardiology, Department of Medicine, Mount Sinai and University Health Network Hospitals, University of Toronto, Toronto, Ontario.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: DiFabio
authors.forename: Tommaso
authors.initials: T
authors.lastname: Gori
authors.forename: George
authors.initials: G
authors.lastname: Thomas
authors.forename: Sean
authors.initials: S
authors.lastname: Jedrzkiewicz
authors.forename: John D
authors.initials: JD
authors.lastname: Parker
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D004311:Double-Blind Method; D004730:Endothelium, Vascular / Q000187:drug effects / Q000201:enzymology / Q000503:physiopathology*; D005492:Folic Acid / Q000008:administration & dosage / Q000494:pharmacology*; D005542:Forearm / Q000098:blood supply; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007271:Injections, Intradermal; D008297:Male; D052250:Nitric Oxide Synthase Type III / Q000187:drug effects / Q000378:metabolism*; D005996:Nitroglycerin / Q000008:administration & dosage / Q000009:adverse effects*; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000009:adverse effects*; D014803:Vitamin B Complex / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D014665:Vasodilator Agents; D014803:Vitamin B Complex; D005492:Folic Acid; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III; D005996:Nitroglycerin