Abstract
Anti-ischemic therapy with organic nitrates is complicated by tolerance. Induction of tolerance is incompletely understood and likely multifactorial. Recently, increased production of reactive oxygen species (ROS) has been investigated, but it has not been clear if this is a direct consequence of the organic nitrate on the vessel or anin vivo adaptation to the drugs. To examine the possibility that nitrates could directly stimulate vascular ROS production, we compared the development of nitrate tolerance with the formation of ROS induced by pentaerithrityltetranitrate (PETN) or nitroglycerin (GTN) in vitro in porcine smooth muscle cells, endothelial cells, washed ex vivo platelets and whole blood. By examining cGMP formation, it was found that 24-hr treatment with GTN but not PETN induced significant nitrate tolerance, which was prevented by parallel treatment with Vit C. Incubation of vascular cells acutely with 0.5 mM GTN doubled the rate of ROS generation, whereas PETN had no such effect. The rate of ROS (peroxynitrite and O2—˙) formation detected by specific spin traps in tolerant smooth muscle cells, treated for 24 hr with 0.01 mM GTN, was substantially higher (30.5 nM/min) than in control cells acutely treated with 0.5 mM GTN (25 nM/min). In contrast to PETN, GTN induces nitrate tolerance and also increases the formation of ROS both in vascular cells and in whole blood. ROS formation is minimally stimulated by PETN comparable to data obtained in Vit C-suppressed GTN tolerance. ROS formation induced by organic nitrates seems to be a key factor in the development of nitrate tolerance.
Footnotes
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Send reprint requests to: Prof. Dr. Eberhard Bassenge, Institute of Applied Physiology, Hermann-Herder-Str. 7, D-79104 Freiburg, Germany. E-mail: angphys{at}ruf.uni-freiburg.de
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↵1 This study was supported by the German Heart Foundation (Deutsche Herzstiftung, Frankfurt/Main, Germany) and through a scholarship from the German Academic Exchange Service (Deutscher Akademischer Austausch- dienst, Bonn, Germany) (S.D.).
- Abbreviations:
- CP
- 3-carboxy-proxyl
- CP-H
- 1-hydroxy-3-carboxy-pyrrolidine
- DMPO
- 5,5-dimethyl-1-pyrroline-N-oxide
- DMPO-OH
- 2-hydroxy-5,5-dimethylpyrrolidine-N-oxyl
- ESR
- electron spin resonance
- EC
- endothelial cells
- NO
- nitric oxide
- GTN
- nitroglycerin
- O2—˙
- superoxide radical
- PETN
- pentaerithrityltetranitrate
- ROS
- reactive oxygen species
- SMC
- smooth muscle cells
- SOD
- erythrocyte superoxide dismutase
- TMIO
- 3,5,5-trimethyl-imidazole-1-oxide
- TMIO-OH
- 5-hydroxy-2,2,4,-trimethyl-3-imidazoline-1-oxyl
- TEMPONE-H
- 1-hydroxy-2,2,6,6-tetramethyl-4-oxo-piperidine hydrochloride
- TEMPONE
- 2,2,6,6-tetramethyl-4-oxo-piperidinoxyl
- Vit C
- vitamin C
- Received November 17, 1997.
- Accepted April 10, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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