Vascular pro-oxidant effects secondary to the autoxidation of gallic acid in rat aorta.
Gallic acid autoxidation was monitored by absorption spectroscopy and H(2)O(2) production; vascular effects related to the autoxidation process were studied on intact and rubbed aortic rings from WKY rats. Gallic acid autoxidation in an oxygenated physiological salt solution (37 degrees C, pH=7.4) mostly occurred in a 2-h time period. Superoxide anions, H(2)O(2) and gallic acid quinones were produced during gallic acid autoxidation. In rings partially precontracted with phenylephrine, 0.1-3 microM gallic acid induced marked and largely endothelium-dependent contractions, 10-30 microM gallic acid induced endothelium-independent contractions and 0.1-0.3 mM gallic acid induced complete, fast-developing, endothelium-independent relaxations. Superoxide dismutase (SOD) shifted the endothelium-dependent gallic acid contractions to the right, and N(G)-nitro-l-arginine abolished them. Indomethacin suppressed the endothelium-independent gallic acid contractions, and catalase abolished the endothelium-independent contractions and relaxations. Gallic acid (30 microM) inhibited the relaxant effects of acetylcholine and sodium nitroprusside. In rings maximally precontracted with KCl, 0.1-100 microM gallic acid did not modify the tone, whereas 0.3 mM induced complete, slow-developing, endothelium-independent relaxations. Moreover, 0.3 mM gallic acid induced an irreversible impairment of ring reactivity and the release of lactate dehydrogenase. Catalase and N-acetyl cysteine suppressed the deleterious effects induced by gallic acid in the rings.


CONCLUSIONS
(a) gallic acid is rapidly and nonenzymatically oxidized in physiological solutions, generating superoxide anions, H(2)O(2) and quinones; (b) superoxide anions (by destroying NO) and low H(2)O(2) levels (by activating cyclooxygenase) both increase vascular tone; (c) moderate H(2)O(2) levels decrease vascular tone; (d) high H(2)O(2) and quinone levels cause irreversible relaxations due to cellular damage.
Gil-Longo
José
J
Department of Pharmacology, Faculty of Pharmacy, Universidade de Santiago de Compostela, Campus Universitario Sur, E-15782 Santiago de Compostela, Spain. jose.gil.longo@usc.es
González-Vázquez
Cristina
C
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000502:physiology; D002374:Catalase / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000503:physiopathology; D005260:Female; D016166:Free Radical Scavengers / Q000494:pharmacology; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009465:Neuromuscular Agents / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D011809:Quinones / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D011921:Rats, Inbred WKY; D013481:Superoxides / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology
D016861:Cyclooxygenase Inhibitors; D016166:Free Radical Scavengers; D009465:Neuromuscular Agents; D011809:Quinones; D013481:Superoxides; D005707:Gallic Acid; D006861:Hydrogen Peroxide; D002374:Catalase; D000111:Acetylcysteine