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 × 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 O 2.- 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, N G-nitro-L-arginine methyl ester, or chelerythrine. We also demonstrated that GTN translocates the α-and εPKC isoforms in EC. However, PKCζ 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 α- and εPKC isozymes in EC by GTN may play a role in development of tolerance.
|Original language||English (US)|
|Number of pages||11|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - Jan 2004|
ASJC Scopus subject areas
- Molecular Medicine