title: Roles of superoxide, peroxynitrite, and protein kinase C in the development of tolerance to nitroglycerin.
abstract: A current hypothesis states that tolerance to nitroglycerin (GTN) involves increased formation of superoxide (O2*-). Studies showing that inhibitors of protein kinase C (PKC) prevent tolerance to GTN suggest the involvement of PKC activation, which can also increase O2*-. We examined the roles of O2*-, peroxynitrite (ONOO-), and PKC activation in GTN tolerance. Pre-exposure of rat aortic rings to GTN (5 x 10(-4) M) for 2 h caused tolerance to the vasodilating effect of GTN, as evidenced by a substantial rightward shift of GTN concentration-relaxation curves. This shift was reduced by treatment of the rings with the antioxidants uric acid, vitamin C, or tempol or the PKC inhibitor chelerythrine. We also found that O2*- generation via xanthine/xanthine oxidase in the bath induced tolerance to GTN. However, responses to nitroprusside were not affected. In vivo tolerance produced in rats by 3-day i.v. infusion of GTN was also almost completely prevented by coinfusion of tempol. In bovine aortic endothelial cells (EC), addition of GTN produced a marked increase in tyrosine nitrosylation, indicating increased ONOO- formation. This action was blocked by prior treatment with uric acid, superoxide dismutase, NG-nitro-L-arginine methyl ester, or chelerythrine. We also demonstrated that GTN translocates the alpha- and epsilonPKC isoforms in EC. However, PKCzeta was not affected by GTN treatment. In conclusion, tolerance to GTN involves enhanced production of O2*- and ONOO- and activation of NO synthase. Furthermore, sustained activation of alpha- and epsilonPKC isozymes in EC by GTN may play a role in development of tolerance.
authors.affiliation: Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta, Georgia 30912, USA.
authors.forename: G
authors.initials: G
authors.lastname: Abou-Mohamed
authors.forename: J A
authors.initials: JA
authors.lastname: Johnson
authors.forename: L
authors.initials: L
authors.lastname: Jin
authors.forename: A B
authors.initials: AB
authors.lastname: El-Remessy
authors.forename: K
authors.initials: K
authors.lastname: Do
authors.forename: W H
authors.initials: WH
authors.lastname: Kaesemeyer
authors.forename: R B
authors.initials: RB
authors.lastname: Caldwell
authors.forename: R W
authors.initials: RW
authors.lastname: Caldwell
mesh_terms: D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism; D004361:Drug Tolerance; D004789:Enzyme Activation; D005996:Nitroglycerin / Q000009:adverse effects*; D030421:Peroxynitrous Acid / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013481:Superoxides / Q000378:metabolism*
chemical_list: D013481:Superoxides; D030421:Peroxynitrous Acid; D011493:Protein Kinase C; D005996:Nitroglycerin; D006152:Cyclic GMP