Electron spin resonance detection of hydrogen peroxide as an endothelium-derived hyperpolarizing factor in porcine coronary microvessels.
OBJECTIVE
Endothelium-derived hyperpolarizing factor (EDHF) plays an important role in modulating vascular tone, especially in microvessels, although its nature has yet to be elucidated. This study was designed to examine whether hydrogen peroxide (H2O2) is an EDHF in porcine coronary microvessels with use of an electron spin resonance (ESR) method to directly detect H2O2 production from the endothelium.


RESULTS
Isometric tension and membrane-potential recordings demonstrated that bradykinin and substance P caused EDHF-mediated relaxations and hyperpolarizations of porcine coronary microvessels in the presence of indomethacin and Nomega-nitro-L-arginine. The contribution of H2O2 to the EDHF-mediated responses was demonstrated by the inhibitory effect of catalase and by the relaxing and hyperpolarizing effects of exogenous H2O2. Endothelial production of H2O2 was quantified in bradykinin- or substance P-stimulated intact blood vessels by ESR spectroscopy. Tiron, a superoxide scavenger that facilitates H2O2 formation, enhanced bradykinin-induced production of H2O2, as well as the EDHF-mediated relaxations and hyperpolarizations. By contrast, cytochrome P-450 inhibitors (sulfaphenazole or 17-octadecynoic acid) or a gap junction inhibitor (18alpha-glycyrrhetinic acid) failed to inhibit the EDHF-mediated relaxations. Involvement of endothelium-derived K+ was not evident in experiments with ouabain plus Ba2+ or exogenous K+.


CONCLUSIONS
These results provide ESR evidence that H2O2 is an EDHF in porcine coronary microvessels.
Matoba
Tetsuya
T
Department of Cardiovascular Medicine, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan.
Shimokawa
Hiroaki
H
Morikawa
Keiko
K
Kubota
Hiroshi
H
Kunihiro
Ikuko
I
Urakami-Harasawa
Lemmy
L
Mukai
Yasushi
Y
Hirakawa
Yoji
Y
Akaike
Takaaki
T
Takeshita
Akira
A
D014013:1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001685:Biological Factors / Q000378:metabolism; D001920:Bradykinin / Q000494:pharmacology; D002374:Catalase / Q000494:pharmacology; D003331:Coronary Vessels / Q000187:drug effects / Q000378:metabolism*; D000090762:Cytochrome P-450 CYP2J2; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism*; D016166:Free Radical Scavengers / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000378:metabolism* / Q000494:pharmacology; D007202:Indicators and Reagents / Q000494:pharmacology; D007552:Isotonic Solutions / Q000737:chemistry; D008297:Male; D008833:Microcirculation; D009126:Muscle Relaxation; D010105:Oxygenases / Q000037:antagonists & inhibitors; D011092:Polyethylene Glycols / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D013426:Sulfaphenazole / Q000494:pharmacology; D013482:Superoxide Dismutase / Q000494:pharmacology; D013552:Swine
D001685:Biological Factors; D065607:Cytochrome P-450 Enzyme Inhibitors; D016166:Free Radical Scavengers; D007202:Indicators and Reagents; D007552:Isotonic Solutions; C051865:Krebs-Ringer solution; C067410:endothelium-dependent hyperpolarization factor; D013426:Sulfaphenazole; D011092:Polyethylene Glycols; D014013:1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt; D003577:Cytochrome P-450 Enzyme System; D006861:Hydrogen Peroxide; D002374:Catalase; D010105:Oxygenases; D000090762:Cytochrome P-450 CYP2J2; D013482:Superoxide Dismutase; C063471:polyethylene glycol-superoxide dismutase; D011188:Potassium; D001920:Bradykinin