title: N omega-nitro-L-arginine blocks the second phase but not the first phase of the endothelium-dependent relaxations induced by substance P in isolated rings of pig carotid artery.
abstract: Endothelium-dependent relaxations can be evoked by a variety of stimuli, among them substance P (SP), which is found in sensory nerve fibers supplying the adventitia-media junction of most muscular arteries. This study determined the role of endothelium-derived nitric oxide as a mediator of endothelium-dependent relaxations to SP in isolated rings of the pig carotid artery suspended in organ chambers for isometric tension recording. SP (10(-12)-10(-7) M) caused concentration-dependent relaxations of arteries precontracted with norepinephrine (10(-7) M). The relaxations were characterized by a partially transient relaxation (phase 1) and a sustained relaxation of the artery (phase 2). The inhibitor of nitric oxide formation, N omega-nitro-L-arginine (L-NNA) methyl ester caused a gradual increase in tension, the phase I response at 3 x 10(-10) to 3 x 10(-7) M SP was shifted to the right, but the maximal relaxation was comparable in the presence of L-NNA. However, the sustained relaxation after addition of substance P (phase II) was lost and tension in the presence of L-NNA returned to a level above that induced by L-NNA and norepinephrine (10(-9) M). These results suggest that the endothelium-dependent relaxations to SP, particularly the prolonged relaxation (phase II), are due to de novo synthesis of nitric oxide and hence fully abolished by a specific inhibitor.
mesh_terms: D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology; D002339:Carotid Arteries / Q000187:drug effects / Q000502:physiology; D004730:Endothelium, Vascular / Q000502:physiology*; D005260:Female; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000378:metabolism; D019335:Nitroarginine; D009638:Norepinephrine / Q000494:pharmacology; D013373:Substance P / Q000494:pharmacology*; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects
chemical_list: D019335:Nitroarginine; D009569:Nitric Oxide; D013373:Substance P; D001120:Arginine; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine