title: Organic nitrate tolerance is induced by degradation of some cytochrome P450 isoforms.
abstract: The mechanism of nitrate tolerance is poorly defined. We studied the rat P450 (CYP)-catalyzed conversion of organic nitrate to nitric oxide (NO) by purified CYP isoforms and the relationship between P450 expression and nitrate tolerance following continuous infusion of organic nitrates in rats. CYP1A2 effectively formed NO from isosorbide dinitrate and nitroglycerine (NTG). The hypotensive effect of an NTG bolus injection was abolished in rats which had been previously given a continuous 48 h infusion of NTG. Nitrate tolerance was reversible to control levels 2 days after cessation of the continuous infusion. At 48 h after infusion, NTG-induced NO generation of the vessels increased in acetone (a P450 inducer)-pretreated rats, and nitrite and nitrate levels were markedly greater than in normal rats. The appearance and disappearance of P450 isoforms paralleled the conversion of organic nitrates to NO as assessed by immunohistochemistry and Western blotting. Our observations indicate that nitrate tolerance is in large part the result of decreased P450 expression and activity. Interventions that maintain or increase P450 activity may be a useful strategy to provide sustained relief from ischemic conditions in humans.
authors.affiliation: Department of Pathological Research, Graduate School of Medicine and Dentistry, Okayama University, Shikatacho, Okayama, Japan. yukiko@med.osaka-cu.ac.jp
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Minamiyama
authors.forename: Shigekazu
authors.initials: S
authors.lastname: Takemura
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nishino
authors.forename: Shigeru
authors.initials: S
authors.lastname: Okada
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019388:Cytochrome P-450 CYP1A2 / Q000737:chemistry*; D006801:Humans; D007150:Immunohistochemistry; D007548:Isosorbide Dinitrate / Q000494:pharmacology; D008297:Male; D009566:Nitrates / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D005996:Nitroglycerin / Q000494:pharmacology; D020033:Protein Isoforms; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D009566:Nitrates; D020033:Protein Isoforms; D014665:Vasodilator Agents; D009569:Nitric Oxide; D019388:Cytochrome P-450 CYP1A2; D005996:Nitroglycerin; D007548:Isosorbide Dinitrate