Akira Takeshita

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. Methods and 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 N&ohgr;-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 (18&agr;-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+. Conclusion—These results provide ESR evidence that H2O2 is an EDHF in porcine coronary microvessels.

Coronary Artery Spasm: Basic Aspects

Coronary artery spasm plays an important role in a wide variety of coronary artery syndromes, not only in variant angina but also in unstable angina, myocardial infarction, and sudden death [1–5]. The prevalence of the spasm is apparently higher in Japanese patients with ischemic heart disease [5] than in Caucasians [6–9] (see Chap. 59). Since coronary artery spasm can be induced by a variety of stimuli with different mechanisms of action (even in the same patient), the occurrence of the spasm appears to be due to the local hyperreactivity of the coronary artery rather than to an enhanced stimulation with a single mechanism of action [10–12]. In order to elucidate the cellular and molecular mechanisms of the spasm, animal models of the spasm have been developed in the authors’ laboratory, the only working models of the spasm to date. In this chapter, recent advances on the cellular and molecular mechanisms of coronary artery spasm in the authors’ models are briefly summarized.

Coronary Artery Spasm: Clinical Aspects

Angina caused by spasm of epicardial coronary arteries has been known as variant angina. By the most strict definition, variant angina is a syndrome in patients having rest angina associated with reversible ST segment elevation on electrocardiogram (ECG) but no evidence of myocardial necrosis as determined by serial ECGs and enzymatic analyses. This peculiar form of angina pectoris was systematically described for the first time by Myron Prinzmetal and colleagues in 1959 [1], based on the observations of 32 patients with rest angina associated with transient ST elevation. Most of the characteristic clinical features that are at present well recognized were reported in the Prinzmetal report. Namely, chest pain typically occurs at night or in the early morning hours and tends to be clustered. Night awakening with chest pain is common. As compared with classic angina, chest pain in variant angina is usually longer in duration and severe in intensity, and frequently associated with autonomic symptoms such as nausea and cold sweats. During the daytime, exercise tolerance is usually preserved.