Investigation of Hydrogen Peroxide/Reactive Oxygen Species-Related Signaling on Vasoactive Responses in Myogenic Resistance Arteries

Abstract

The study focuses on the investigation of H2O2 and reactive oxygen species as a putative contributor to endothelium-derived hyperpolarization in myogenically-active resistance arteries, and its contribution to the responses evoked by established vasoactive agents. In particular, I hypothesize that H2O2 and/or ROS serve as physiologic, vasoactive agents in myogenically-active resistance arteries in normal tissue and/or in arteries exhibiting endothelial dysfunction (i.e. conditions with reduced NO bioavailability). Using a number of different experimental protocols such as lucigenin molecular assays provided the amount of NADPH-oxidase inhibition in the presence of apocynin, ML171 and VAS2870, where pressure myography experiments showed the response of rat cremaster arteries to external hydrogen peroxide, indicating a role for hydrogen peroxide within the vasculature. Pressure myography experiments also showed the arterial response to the different NADPH-oxidase inhibitors in terms of baseline myogenic tone. Application of apocynin (10µM and 100µM) further constricted the vessels, ML171 resulted in a transient relaxation, with a full relaxation seen with exposure to higher concentrations (0.1µM, 0.3µM, 10µM) of VAS2870. Responses to established vasoactive agents were observed in the presence of the NADPH-oxidase inhibitors, showing reduced responses at ~50% NADPH-oxidase inhibition, with enhanced responses at greater NADPH-oxidase inhibition. The study shows that the three structurally diverse NADPH-oxidase inhibitors differentially affect basal myogenic tone at concentrations (~IC50 values) that produce comparable inhibition of vascular NADPH-oxidase activity.