Hydrogen peroxide induces endothelium-dependent and -independent coronary arteriolar dilation: role of cyclooxygenase and potassium channels.

Abstract

Hydrogen peroxide, a relatively stable reactive oxygen species, is known to elicit vasodilation, but its underlying mechanism remains elusive. Here, we examined the role of endothelial nitric oxide (NO), prostaglandin, cytochrome P-450-derived metabolites, and smooth muscle potassium channels in coronary arteriolar dilation to abluminal H2O2. Pig subepicardial coronary arterioles (50-100 microm) were isolated and pressurized without flow for in vitro study. Arterioles developed basal tone and dilated dose dependently to H2O2 (1-100 microM). Disruption of th endothelium and inhibition of cyclooxygenase (COX) by indomethacin produced identical attenuation of vasodilation to H2O2. Conversely, the vasodilation to H2O2 was not affected by either the NO synthase inhibitor NG-nitro-l-arginine methyl ester or the cytochrome P-450 enzyme blocker miconazole. Inhibition of the COX-1, but not the COX-2 pathway, attenuated H2O2-induced dilation similarly to indomethacin. The production of prostaglandin E2 (PGE2), but not prostaglandin I2, from coronary arterioles was significantly increased by H2O2. Furthermore, inhibition of PGE2 receptors with AH-6809 attenuated vasodilation to H2O2 similar to that produced by indomethacin. In the absence of a functional endothelium, H2O2-induced dilation was attenuated, in an identical manner, by a depolarizing agent KCl and a calcium-activated potassium (KCa) channel inhibitor iberiotoxin. However, PGE2-induced dilation was not affected by iberiotoxin. The endothelium-independent dilation to H2O2 was also insensitive to the inhibition of guanylyl cyclase, lipoxygenase, ATP-sensitive potassium channels, and inward rectifier potassium channels. These results suggest that H2O2 induces endothelium-dependent vasodilation through COX-1-mediated release of PGE2 and also directly relaxes smooth muscle by hyperpolarization through KCa channel activation.