Nitric oxide synthase activity and non-adrenergic non-cholinergic relaxation in the rat gastric fundus.
1. In the presence of atropine (1 microM) and guanethidine (5 microM), electrical field stimulation (EFS, 120 mA, 1 ms, 0.5-16.0 Hz, trains of 2 min) induced frequency-dependent relaxations of 5-hydroxytryptamine (3 microM)-precontracted longitudinal muscle strips from the rat gastric fundus. 2. L-Citrulline concentrations were measured in the incubation medium of precontracted strips before and after EFS to investigate nitric-oxide (NO) synthase activity and its possible relation to non-adrenergic non-cholinergic (NANC) relaxation. 3. Basal NO synthase activity was reflected by the finding of prestimulation levels of L-citrulline of approximately 30 nM. These levels were unaffected by tetrodotoxin (3 microM) and NG-nitro-D-arginine methyl ester (D-NAME, 100 microM), slightly reduced by a calcium-free medium and halved by NG-nitro-L-arginine methyl ester (L-NAME, 100 microM). 4. EFS evoked significant, frequency-dependent increases in bath levels of L-citrulline at all frequencies tested. The increases evoked by 16-Hz EFS were abolished by tetrodotoxin (3 microM), a calcium-free medium and L-NAME (100 microM) but not by D-NAME (100 microM). 5. L-NAME (0.1 microM-1.0 mM) produced significant reduction of 4-Hz EFS-induced L-citrulline production (100% inhibition at 10 microM), but had less marked effects on basal production (approximately 50% reduction at 100 microM) and 4-Hz EFS-induced NANC relaxation (approximately 50% reduction at 1 mM). 6. L-Arginine (1 mM), but not D-arginine (1 mM), increased basal L-citrulline levels and reversed the inhibitory effect of L-NAME (10 microM). 7. These findings represent clear biochemical evidence of both basal and EFS-stimulated NO synthase activity in the rat gastric fundus.
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Institute of Pharmacology, Catholic University School of Medicine, Rome, Italy.
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D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D002956:Citrulline / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D005748:Gastric Fundus / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D006145:Guanethidine / Q000494:pharmacology; D066298:In Vitro Techniques; D007552:Isotonic Solutions / Q000494:pharmacology; D008297:Male; D019331:NG-Nitroarginine Methyl Ester; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D007552:Isotonic Solutions; C051865:Krebs-Ringer solution; D002956:Citrulline; D012701:Serotonin; D013779:Tetrodotoxin; D001285:Atropine; D001120:Arginine; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester; D006145:Guanethidine