title: Therapy with nitroglycerin increases coronary vasoconstriction in response to acetylcholine.
abstract: OBJECTIVE
  The purpose of this study was to investigate whether therapy with nitroglycerin (GTN) would lead to abnormal coronary artery responses to the endothelium-dependent vasodilator acetylcholine.
  
  
  BACKGROUND
  Nitroglycerin therapy is associated with specific biochemical changes in the vasculature that may lead to increased vascular sensitivity to vasoconstrictors.
  
  
  METHODS
  Patients were randomized to continuous transdermal GTN, 0.6 mg/h (n = 8), or no therapy (n = 7), for 5 days prior to a diagnostic catheterization. Patients had similar risk factors for endothelial dysfunction. Quantitative angiography was performed in the morning to measure the mean luminal diameter of the left anterior descending coronary artery (LAD) in response to intracoronary acetylcholine (peak concentration, 10(-4) mol/liter). The transdermal preparation was removed from the GTN group, and 3 h later experimental procedures were repeated.
  
  
  RESULTS
  In the morning, the GTN group experienced greater coronary constriction in response to acetylcholine infusion than those not receiving GTN (-19.6+/-4.2 vs. -3.8+/-3.0%; p = 0.01). Three hours later, the GTN group continued to display greater constriction to acetylcholine (-24.1+/-5.9%) as compared to the non-GTN group (-1.8+/-4.8%). When the morning and afternoon responses to acetylcholine were compared, the increase in coronary constriction in the GTN group was greater than the change observed in the non-GTN group (p < 0.05).
  
  
  CONCLUSIONS
  This study demonstrates that therapy with GTN causes abnormal coronary vasomotor responses to the endothelium-dependent vasodilator acetylcholine, changes that were persistent for up to 3 hours after GTN discontinuation. This nitrate-associated vasomotor dysfunction has implications with respect to the development of nitrate tolerance and the potential for adverse events during nitrate withdrawal.
authors.affiliation: Department of Medicine, Mount Sinai Hospital, University of Toronto, Ontario, Canada.
authors.forename: P R
authors.initials: PR
authors.lastname: Caramori
authors.forename: A G
authors.initials: AG
authors.lastname: Adelman
authors.forename: E R
authors.initials: ER
authors.lastname: Azevedo
authors.forename: G E
authors.initials: GE
authors.lastname: Newton
authors.forename: A B
authors.initials: AB
authors.lastname: Parker
authors.forename: J D
authors.initials: JD
authors.lastname: Parker
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000328:Adult; D000368:Aged; D003331:Coronary Vessels / Q000187:drug effects* / Q000502:physiology*; D004730:Endothelium, Vascular / Q000187:drug effects; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D005996:Nitroglycerin / Q000494:pharmacology* / Q000627:therapeutic use; D014661:Vasoconstriction / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology* / Q000627:therapeutic use
chemical_list: D014665:Vasodilator Agents; D005996:Nitroglycerin; D000109:Acetylcholine