title: Nitroglycerin tolerance in human vessels: evidence for impaired nitroglycerin bioconversion.
abstract: BACKGROUND
  The basis for progressive attenuation of the effects of organic nitrates during long-term therapy (nitrate tolerance) remains controversial; proposed mechanisms include impaired nitrate bioconversion resulting in decreased release of nitric oxide (NO) from nitrates and/or increased NO clearance through a reaction with incrementally generated superoxide (O(2)(-)).
  
  
  RESULTS
  Patients undergoing elective coronary artery bypass were randomized to receive 24 hours of intravenously infused nitroglycerin (NTG; nitrate group) or no nitrate therapy (control group). Discarded segments of the internal mammary artery and saphenous vein were used to examine (1) vascular responsiveness to NTG, sodium nitroprusside, and the calcium ionophore A23187; (2) bioconversion of NTG to 1,2- and 1,3-glyceryl dinitrate; and (3) the generation of O(2)(-). Responses to NTG were reduced 3- to 5-fold in vessels from the nitrate group compared with control vessels (P:<0. 01 for both types of segments), whereas responses to sodium nitroprusside and A23187 were unchanged. Tissue content of 1, 2-glyceryl dinitrate was lower (P:=0.012) in the saphenous veins from the nitrate group than in those from the control group. O(2)(-) generation was greater (P:<0.01) in internal mammary artery samples from the nitrate group than in those from the control group. However, incremental O(2)(-) generation induced by an inhibitor of superoxide dismutase did not affect NTG responses.
  
  
  CONCLUSIONS
  NTG tolerance in patients with coronary artery disease is nitrate-specific and is associated with evidence of impaired NTG bioconversion. Tolerance was associated with incremental O(2)(-) generation, but short-term elevation of O(2)(-) did not affect NTG responsiveness, suggesting increased NO clearance by O(2)(-) has a minimal contribution to tolerance.
authors: Department of Cardiology, The Queen Elizabeth Hospital, North Western Adelaide Health Service, University of Adelaide, Royal Adelaide Hospital, Adelaide, Australia.
authors: P R
authors: PR
authors: Sage
authors: I S
authors: IS
authors: de la Lande
authors: I
authors: I
authors: Stafford
authors: C L
authors: CL
authors: Bennett
authors: G
authors: G
authors: Phillipov
authors: J
authors: J
authors: Stubberfield
authors: J D
authors: JD
authors: Horowitz
mesh_terms: D001808:Blood Vessels / Q000187:drug effects* / Q000378:metabolism; D003327:Coronary Disease / Q000188:drug therapy / Q000378:metabolism / Q000601:surgery; D004361:Drug Tolerance; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008323:Mammary Arteries / Q000187:drug effects / Q000378:metabolism; D008875:Middle Aged; D009569:Nitric Oxide / Q000378:metabolism; D005996:Nitroglycerin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D012501:Saphenous Vein / Q000187:drug effects / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism
chemical_list: D013481:Superoxides; C014509:dinitroglycerol; D009569:Nitric Oxide; D005996:Nitroglycerin