Effects of Pharmacological Inhibitors of NADPH Oxidase on Myogenic Contractility and Evoked Vasoactive Responses in Rat Resistance Arteries.

Dylan J Kendrick,Andrew P Braun,Ramesh C Mishra,Cini Mathew John,Hai-Lei Zhu

doi:10.3389/fphys.2021.752366

Dylan J Kendrick, Andrew P Braun + Show 3 more

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https://doi.org/10.3389/fphys.2021.752366

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Abstract

Reactive oxygen species (ROS), such as superoxide anions and hydrogen peroxide, are reported to contribute to the dynamic regulation of contractility in various arterial preparations, however, the situation in pressurized, myogenically active resistance arteries is much less clear. In the present study, we have utilized established pharmacological inhibitors of NADPH oxidase activity to examine the potential contribution of ROS to intrinsic myogenic contractility in adult Sprague–Dawley rat resistance arteries and responses to vasoactive agents acting via the endothelium (i.e., acetylcholine, SKA-31) or smooth muscle (i.e., sodium nitroprusside, phenylephrine). In cannulated and pressurized cremaster skeletal muscle and middle cerebral arteries, the NOX inhibitors 2-acetylphenothiazine (2-APT) and VAS2870, selective for NOX1 and NOX2, respectively, evoked concentration-dependent inhibition of basal myogenic tone in a reversible and irreversible manner, respectively, whereas the non-selective inhibitor apocynin augmented myogenic contractility. The vasodilatory actions of 2-APT and VAS2870 occurred primarily via the vascular endothelium and smooth muscle, respectively. Functional responses to established endothelium-dependent and –independent vasoactive agents were largely unaltered in the presence of either 2-APT or apocynin. In cremaster arteries from Type 2 Diabetic (T2D) Goto-Kakizaki rats with endothelial dysfunction, treatment with either 2-APT or apocynin did not modify stimulus-evoked vasoactive responses, but did affect basal myogenic tone. These same NOX inhibitors produced robust inhibition of total NADPH oxidase activity in aortic tissue homogenates from control and T2D rats, and NOX isozymes 1, 2 and 4, along with superoxide dismutase 1, were detected by qPCR in cremaster arteries and aorta from both species. Based on the diverse effects that we observed for established, chemically distinct NOX inhibitors, the functional contribution of vascular NADPH oxidase activity to stimulus-evoked vasoactive signaling in myogenically active, small resistance arteries remains unclear.

Highlights

Reactive oxygen species (ROS) can have deleterious effects on cellular activity, but it is apparent that these molecules contribute to cell signaling events (Thannickal and Fanburg, 2000)
The observed sensitivity of myogenically constricted cremaster arteries to H2O2 raised the possibility that H2O2 may serve as an endogenous signaling molecule for vasodilatory stimuli acting on the vascular endothelium and/or smooth muscle
As NADPH oxidase activity represents an important source of superoxide anions used for H2O2 production, we asked whether inhibition of vascular NOX enzymes by the reported pharmacological blockers 2-acetylphenothiazine (2-APT, aka ML171), VAS2870 and apocynin (Selemidis et al, 2008; Altenhöfer et al, 2015) would modify endothelium-dependent vasodilation in myogenically constricted cremaster arteries

Summary

Introduction

Reactive oxygen species (ROS) can have deleterious effects on cellular activity, but it is apparent that these molecules contribute to cell signaling events (Thannickal and Fanburg, 2000). Another prominent source of ROS is the enzymatic activity of NADPH oxidase, which generates superoxide anions that are often considered harmful to cellular function. Superoxide anions interfere with endotheliumdependent dilation by combining with nitric oxide (NO) to form peroxynitrite, a reactive by-product that reduces NO bioavailability and chemically modifies cellular constituents, such as lipids, DNA and proteins, thereby promoting tissue injury (Pacher et al, 2007). Arterial contractility is dynamically governed by both chemical and mechanical signaling, as well as intrinsic processes within the vascular wall that generate myogenic tone (Davis and Hill, 1999; Félétou et al, 2011; Davis, 2012; Vanhoutte et al, 2017). Khavandi et al (2016) have further reported that elevated intraluminal pressure in resistance arteries may stimulate H2O2 production and PKG activation as an intrinsic feedback mechanism to regulate vascular tone

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