The uremic toxin indoxyl sulfate (IS) was reported to be the cause of cardiovascular disease associated with chronic kidney disease. Therefore, we evaluated the direct influences of IS on vascular function, focusing on the superoxide anion (O) and nitric oxide (NO)/soluble guanylate cyclase (sGC) pathways.
Isolated rat thoracic aortas with and without vascular endothelium were incubated with IS for 4 h in a physiological solution. In some experiments, several inhibitors were treated 30 min before the addition of IS. O production was measured by the chemiluminescence method, and the vascular reactivity to different vasorelaxants was examined using organ chamber technique.
1) Experiments using endothelium-intact vascular rings: IS significantly increased O production. The increase was suppressed by addition of the NADPH oxidase inhibitor apocynin, the antioxidant ascorbic acid and the aryl hydrocarbon receptor (AhR) inhibitor CH223191. Furthermore, IS attenuated the acetylcholine (ACh)-induced vasorelaxantion, which was suppressed by addition of the above drugs. 2) Experiments using endothelium-denuded vascular rings: IS significantly increased O production and also attenuated sodium nitroprusside (SNP)-induced vasorelaxation. These influences of IS were normalized only by ascorbic acid addition. On the other hand, IS did not affect the vasorelaxation by the sGC stimulator BAY 41-2272.
This study suggested that IS causes O production in vascular tissues, thereby attenuating ACh- and SNP-induced vasorelaxation, probably through NO inactivation. Furthermore, it is reasonable to consider that IS-promoted O production in the presence of vascular endothelium is through binding to AhR and the activation of NADPH oxidase.

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