title: Role of superoxide anions in the mediation of endothelium-dependent contractions.
abstract: We designed experiments to characterize the role of superoxide anions in the mediation of endothelium-dependent contractions in isolated canine basilar arteries. Rings with and without endothelium were suspended for isometric tension recording in Krebs-Ringer bicarbonate solution bubbled with 94% O2-6% CO2 (37 degrees C, pH 7.4). Radioimmunoassay was used to determine the levels of cyclic GMP and cyclic AMP. Calcium ionophore A23187 (10(-9) to 10(-6) mol/L) caused concentration-dependent contractions. The removal of endothelium abolished the effect of A23187. Contractions to A23187 were reversed into relaxations in the presence of superoxide dismutase (150 U/mL) or the prostaglandin H2/thromboxane A2 receptor antagonist SQ29548 (10(-6) mol/L). NG-nitro-L-arginine methyl ester (3 x 10(-4) mol/L) augmented contractions to A23187. In rings with endothelium, A23187 (3 x 10(-7) mol/L) significantly increased levels of both cyclic AMP and cyclic GMP. Indomethacin (10(-5) mol/L) inhibited stimulatory effects of A23187 on cyclic AMP production. In contrast, indomethacin augmented A23187-induced production of cyclic GMP. Selective augmentation of cyclic GMP production by indomethacin appears to be due to protection of nitric oxide or a closely related molecule released following translocation of calcium into endothelial cells. Our findings suggest that (1) an increased concentration of calcium in endothelial cells may activate both cyclooxygenase and the L-arginine/nitric oxide pathway, (2) arachidonic acid metabolism via cyclooxygenase is a source of superoxide anions, and (3) superoxide anions may be responsible for impairment of balance between relaxing and contracting factors leading to contraction of underlying smooth muscle cells.
authors.affiliation: Department of Anesthesiology, Mayo Clinic, Rochester, MN 55905.
authors.forename: F
authors.initials: F
authors.lastname: Cosentino
authors.forename: J C
authors.initials: JC
authors.lastname: Sill
authors.forename: Z S
authors.initials: ZS
authors.lastname: Katusić
mesh_terms: D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D006152:Cyclic GMP / Q000096:biosynthesis; D004285:Dogs; D004730:Endothelium, Vascular / Q000502:physiology*; D005609:Free Radicals; D066298:In Vitro Techniques; D019331:NG-Nitroarginine Methyl Ester; D011451:Prostaglandin-Endoperoxide Synthases / Q000502:physiology; D013482:Superoxide Dismutase / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism*; D014661:Vasoconstriction
chemical_list: D005609:Free Radicals; D013481:Superoxides; D000001:Calcimycin; D001120:Arginine; D000242:Cyclic AMP; D011451:Prostaglandin-Endoperoxide Synthases; D013482:Superoxide Dismutase; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester