The Role of NO and H2O2 in Ach-Induced Dilation of Human Arterioles in the Absence and Presence of Coronary Artery Disease
Authors: Drachuk Kostiantyn , Nishijima Yoshinori , Zhang David 
Published: May 2024

The endothelium regulates vascular tone through the release of various vasodilatory factors such as NO, PGI2, and endothelium-derived hyperpolarizing (EDH) signaling that is more important in resistance arteries and arterioles. Using freshly isolated human arterioles, previous studies indicate that hydrogen peroxide (H2O2), an EDH factor, mediates flow-mediated dilation in patients with coronary artery disease (CAD), whereas NO plays a more prominent role in patients without CAD. However, the mechanisms of receptor agonists (e.g., acetylcholine)-induced dilation remains to be clarified in human arterioles. The objective of this study was to compare the role of NO and H2O2 in acetylcholine (Ach-induced dilation in human adipose arterioles (HAA) from non-CAD and CAD patients. HAA (100-200 μm) dissected from discarded surgical samples of non-CAD and CAD patients, were cannulated onto glass micropipettes and pressurized at 60 mmHg for measurement of diameter changes by using videomicroscopy. Microvessels were incubated with L-NAME (100 μM), an inhibitor of NO synthase, Indomethacin (Indo, 10 μM), an inhibitor of PGI2 synthesis and peg-CAT (500 U/ml), a scavenger of H2O2. To study the dose-dependent response to Ach (log 10-9 – 10-5 M), HAA were preconstricted with endothelin-1 (0.1-0.5 nM). In non-CAD tissues Ach induced potent concentration-dependent dilation (maximal dilation at 10−5 M: 95.6±1.8%). After preincubation with L-NAME, this dilation was partially reduced (maximal dilation at 10−5 M: 77.4±3.1%, P<0.05 vs. control), while the combination of L-NAME and Indo reduced it to the same extent as L-NAME by itself (maximal dilation at 10−5 M: 73.1±7.4%, P<0.05 vs. control). To further determine the role of H2O2 in dilatory response to Ach, we treated HAA with peg-CAT. Incubation of peg-CAT significantly reduced the dilation (maximal dilation at 10−5 M: 74.6±8.1% and 51.3±8.7% in the absence and presence of L-NAME and Indo, P<0.05 vs. control). In HAA obtained from CAD patients, the dilation response to Ach was similar to non-CAD (maximal dilation at 10−5 M: 93.9± 1.8%) and the combination of L-NAME and Indo reduced this dilation to a lesser extent (maximal dilation at 10−5 M: 83.1±3%, P=0.055), compared to non-CAD patients (maximal dilation at 10−5 M: 73.1±7.4%, P<0.05 vs. control). The preincubation with peg-CAT attenuated the dilation only at log -7 M (maximal dilation at 10−7 M: 33.8±9.5%, P<0.05 vs. 54.6±7.5% in control). The large portion of the dilation remaining after the combination of L-NAME and Indo was almost completely abolished in the presence of high K+ concentration (maximal dilation at 10−5 M: 12.9±5.1% P<0.05 vs. control). Together, these results provide new evidence that in non-CAD arterioles both NO and H2O2 play an important role in Ach-induced dilation whereas PGI2 is likely not involved. In CAD arterioles, NO, PGI2 and H2O2 have much less contribution to Ach-induced dilation, while a H2O2-independent EDH signaling plays the major role in the dilatory response. Further studies are required to determine the specific mechanism or factor involved in Ach-induced EDH-dependent dilation in HAA. This work was supported by the National Heart, Lung, and Blood Institute [R01HL096647]. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.