title: Preventive effects of carvedilol on nitrate tolerance--a randomized, double-blind, placebo-controlled comparative study between carvedilol and arotinolol.
abstract: OBJECTIVE
  This study was designed to compare the preventive efect of nitrate tolerance between carvedilol with antioxidant properties and arotinolol without antioxidant properties.
  
  
  BACKGROUND
  The attenuation of cyclic guanosine monophosphate (cGMP) production due to inactivation of guanylate cyclase by increased superoxide has been reported as a mechanism of nitrate tolerance. Carvedilol has been known to combine alpha- and beta-blockade with antioxidant properties.
  
  
  METHODS
  To evaluate the preventive effect of nitrate tolerance, 24 patients with untreated hypertension were randomized to receive either carvedilol (10 mg twice a day [carvedilol group, n=8]), arotinolol (10 mg twice a day [arotinolol group, n=8]), or placebo (placebo group, n=8). Vasodilatory response to nitroglycerin (NTG) was assessed with forearm plethysmography by measuring the change in forearm blood flow (FBF) before and 5 min after sublingual administration of 0.3 mg NTG, and at the same time blood samples were taken from veins on the opposite side to measure platelet cGMP. Plethysmography and blood sampling were obtained serially at baseline (day 0), 3 days after carvedilol, arotinolol or placebo administration (day 3) and 3 days after application of a 20 mg/24 h NTG tape concomitantly with carvedilol, arotinolol or placebo (day 6).
  
  
  RESULTS
  There was no significant difference in the response of FBF (%FBF) and cGMP (%cGMP) to sublingual administration of NTG on days 0 and 3 among the three groups. On day 6, %FBF and %cGMP were significantly lower in the arotinolol group and the placebo group than days 0 and 3, but these parameters in the carvedilol group were maintained.
  
  
  CONCLUSIONS
  The results indicated that carvedilol with antioxidant properties may prevent the development of nitrate tolerance during continuous therapy with NTG compared with arotinolol without antioxidant properties.
authors.affiliation: Department of Cardiology, KINU Medical Association Hospital, Mitsukaido, Ibaraki, Japan. wata-h@xa2.so-net.ne.jp
authors.forename: H
authors.initials: H
authors.lastname: Watanabe
authors.forename: M
authors.initials: M
authors.lastname: Kakihana
authors.forename: S
authors.initials: S
authors.lastname: Ohtsuka
authors.forename: Y
authors.initials: Y
authors.lastname: Sugishita
mesh_terms: D018674:Adrenergic Antagonists / Q000627:therapeutic use*; D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity / Q000187:drug effects; D001792:Blood Platelets / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects; D002227:Carbazoles / Q000627:therapeutic use*; D000077261:Carvedilol; D006152:Cyclic GMP / Q000096:biosynthesis / Q000097:blood; D004311:Double-Blind Method; D004342:Drug Hypersensitivity / Q000097:blood / Q000209:etiology / Q000517:prevention & control*; D004359:Drug Therapy, Combination; D005260:Female; D005500:Follow-Up Studies; D005542:Forearm / Q000098:blood supply; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006973:Hypertension / Q000097:blood / Q000188:drug therapy; D008297:Male; D008875:Middle Aged; D005996:Nitroglycerin / Q000009:adverse effects*; D011412:Propanolamines / Q000627:therapeutic use*; D014665:Vasodilator Agents / Q000009:adverse effects*
chemical_list: D018674:Adrenergic Antagonists; D002227:Carbazoles; D011412:Propanolamines; D014665:Vasodilator Agents; D000077261:Carvedilol; C024523:arotinolol; D005996:Nitroglycerin; D006152:Cyclic GMP