Impairment by Hypoxia or Hypoxia/Reoxygenation of Nitric Oxide–Mediated Relaxation in Isolated Monkey Coronary Artery: the Role of Intracellular Superoxide

Abstract

Abstract.To investigate the effect of hypoxia or hypoxia/reoxygenation on vascular smooth muscle function, mechanical response of monkey coronary artery without endothelium was studied under normoxia, hypoxia, and hypoxia/reoxygenation. Hypoxia or hypoxia/reoxygenation impaired the relaxation by nitroglycerin or isosorbide dinitrate but not that by 8-bromoguanosine-3′,5′-cyclic monophosphate or isoproterenol. Tempol restored the impaired relaxation by nitroglycerin or isosorbide dinitrate, but superoxide dismutase had no effect. Apocynin, an NADPH oxidase inhibitor, improved the nitroglycerin-induced relaxation under hypoxia, but not under reoxygenation. Under combined treatment of apocynin with oxypurinol (xanthine oxidase inhibitor), rotenone (mitochondria electron transport inhibitor), or both, hypoxic impairment of vasorelaxation was restored more effectively. Similarly, impairment of the nitroglycerin-induced vasorelaxation under hypoxia/ reoxygenation was restored by combined treatment with three inhibitors, apocynin, oxypurinol, and rotenone. Increase in superoxide production under hypoxia tended to be inhibited by apocynin and that under hypoxia/reoxygenation was abolished by combined treatment with three inhibitors. These findings suggest that increased intracellular superoxide production under hypoxia or hypoxia/reoxygenation attenuates vasodilation mediated with a nitric oxide/soluble guanylyl cyclase, but not adenylyl cyclase, signaling pathway. The main source of superoxide production under hypoxia seems to be different from that under reoxygenation: superoxide is produced by NADPH oxidase during hypoxia, whereas it is produced by xanthine oxidase, mitochondria, or both during reoxygenation.[Supplementary Figure: available only at http://dx

Soluble Guanylate Cyclase Redox State Under Hypoxia or Hypoxia/Reoxygenation in Isolated Monkey Coronary Arteries

“…The impairment by hypoxia or by hypoxia/reoxygenation of BAY 41-2272-evoked relaxation in endothelium-denuded monkey coronary arteries observed in the present study was not so severe as that of NO donorsinduced relaxation observed in our previous study (9). Incidentally, this impairment of vasorelaxation in response to NO donors was also prevented by treatment with tempol (9), indicating that the crucial factor underlying the impairment is also superoxide.…”

“…That is, these highly reactive species oxidize the sGC heme moiety from the ferrous (Fe 2+ ) to the ferric (Fe 3+ ) state and subsequently remove the heme from the enzyme, resulting in the increase in the ratio of the oxidized/heme-free form to the reduced form. In the previous study, we have shown that the tissue level of superoxide is increased by hypoxia or by hypoxia/reoxygenation in isolated endotheliumdenuded monkey coronary arteries (9). Consequently, the shift of sGC redox state under hypoxia or under hypoxia/reoxygenation observed in the present study was considered to be due to superoxide and/or its derivatives.…”

“…In the previous study, we have reported that hypoxia or hypoxia/reoxygenation impairs the relaxation by NO donors, but not that by a cGMP analog, through the increase in intracellular superoxide generation in isolated endothelium-denuded monkey coronary arteries (9). However, it was still unclear whether or not this impairment of NO signaling is mediated via a shift of the sGC redox equilibrium towards the NO-insensitive oxidized/ heme-free state.…”

“…The effects of tempol (3 mM), a membrane-permeable superoxide dismutase mimetic, on the response of the strips treated for 10 -30 min were also evaluated. The concentration of tempol was determined based on the previous work (9).…”

“…Accordingly, the performance of coronary artery during hypoxia or hypoxia/ reoxygenation is of great importance in clinical conditions such as angina pectoris and atherosclerosis. Although the tone of the coronary artery is modulated by several endogenous and exogenous substances acting on smooth muscle, this regulation has been reported to be affected in varying degrees in the process of hypoxia/ reoxygenation injury in several animal species, including rat (2, 3), cattle (4,5), swine (3, 5 -8), monkey (9), and human (3). There is a need to better understand the influence of hypoxia or hypoxia/reoxygenation on coronary function in order to establish an effective treatment strategy.…”