Inhibition of NO-medicate responses by 7-ethoxyresorufin, a substrate and competitive inhibitor of cytochrome P450.
1. The effects of 7-ethoxyresorufin (7-ER), which is a substrate for and competitive inhibitor of cytochrome P450, were studied on responses to nitric oxide (NO), the NO donors sodium nitroprusside (SNP) and glyceryl trinitrate (GTN), acetylcholine-induced endothelium-dependent relaxations of rat and rabbit aortic rings and nitrergic nerve stimulation-induced relaxations of rat anococcygeus muscles. 2. In rat and rabbit aortic rings, 7-ER (2 microM) inhibited the relaxations to acetylcholine in endothelium-intact preparations and the relaxant action of NO in endothelium-denuded preparations. Relaxant responses to SNP and GTN were inhibited by 7-ER in the rat but not rabbit aortic rings. However, the relaxant actions of papaverine and 8-bromo-cyclic GMP were not affected by 7-ER. 3. In rat anococcygeus muscles, 7ER (2 microM) inhibited the relaxant action of NO, but relaxations elicited by nitrergic nerve stimulation were only partly inhibited by a higher concentration of 7-ER (10 microM). 4. After inhibition by 7-ER, superoxide dismutase (100 u ml-1) restored NO-induced relaxations of the rat aortic rings, but not acetylcholine-, SNP or GTN-induced relaxations, and restored NO- and nitrergic nerve stimulation-induced relaxations of anococcygeus muscles. 5. Another cytochrome P450 inhibitor, troleandomycin (10-30 microM), had no effect on NO- or acetylcholine-induced relaxations of rat aortic rings and NO- or nitrergic nerve stimulation-induced relaxations of anococcygeus muscles. However, resorufin, an analogue of 7-ER, inhibited responses to acetylcholine, NO and GTN in rat aortic rings. 6. The results suggest that 7-ER inhibited responses to NO and nitrergic nerve stimulation through generation of superoxide radicals. However, an additional mechanism may be involved in the reduction in acetylcholine-induced response in aortic rings. 7. A 7-ER sensitive P450 system may be involved in the bioactivation of GTN and SNP in rat aortic rings, but not in rabbit aorta or rat anococcygeus muscles.
Li
C G
CG
Department of Medical Laboratory Science, Royal Melbourne Institute of Technology, Victoria, Australia.
Rand
M J
MJ
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000294:innervation; D001120:Arginine / Q000494:pharmacology; D001667:Binding, Competitive; D002374:Catalase / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000294:innervation; D009569:Nitric Oxide / Q000037:antagonists & inhibitors*; D010078:Oxazines / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D013482:Superoxide Dismutase / Q000494:pharmacology; D014217:Troleandomycin / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D010078:Oxazines; D014665:Vasodilator Agents; C016276:8-bromocyclic GMP; D009569:Nitric Oxide; C007649:ethoxyresorufin; C014180:resorufin; D001120:Arginine; D014217:Troleandomycin; D002374:Catalase; D013482:Superoxide Dismutase; D006152:Cyclic GMP; D000109:Acetylcholine