Interestingly, Alectinib nmr these authors suggested that H2O2 generation occurs at the vascular smooth muscle cell plasma membrane rather than in the endothelium [12]. In coronary arterioles from heart failure patients [44,58], flow-induced vasodilation is inhibited by catalase and by inhibitors of potassium channels, providing evidence that H2O2 functions as an EDHF in this vascular bed. Similar observations have been made in other human microvascular beds [32,53,69]. For example, Matoba et al. [53] found that H2O2 is a

primary EDHF in human mesenteric resistance arteries and Phillips et al. [69] observed that H2O2 could replace NO• as the primary vasodilatory agent in microvessels from human visceral fat. Interestingly, Hatoum et al. [32] observed that H2O2 is released by the vascular endothelium of human submucosal intestinal microvessels, but that it does not act as EDHF in these vessels; on the contrary, it produces vasoconstriction LY294002 in denuded vessels. Overall these results indicate that H2O2 functions as an EDHF

in human arterioles; however, the net vasoactive effect of H2O2 may depend on the vascular bed and the health status of the patients being studied [32]. In a recent study of the human cutaneous microcirculation, Medow et al. [57], showed that H2O2 scavenging with Ebselen (Sigma, St. Louis, MO, USA) reduced cutaneous vasodilation to heat in healthy young subjects. These results provide evidence that H2O2 contributes to control of local blood flow in vivo and emphasize the need for further studies to establish the mechanisms of H2O2 generation and action in the

human microcirculation in vivo. Moreover, it would be interesting to use this in vivo model to study the role of H2O2 in regulation of cutaneous blood flow in elderly subjects. Although numerous studies have now implicated a role for H2O2 in regulation of vascular resistance in humans, virtually nothing Clomifene is known regarding the effects of age on H2O2 signaling in the microcirculation of humans. The work of Miura et al. suggests that H2O2 functions as a significant endothelium-dependent vasodilator in coronary arterioles from heart failure patients [57], a disease that is more prevalent in elderly populations. It is possible that H2O2 compensates for a loss of NO•-mediated vasodilation in elderly humans. Alternatively, if dysregulation of H2O2 production/degradation occurs with age, damage to either the endothelium or the vascular smooth muscle could ensue and contribute to age-induced vascular dysfunction. Further studies in human subjects are needed to assess the effects of age on (1) regulation of vascular H2O2 production/scavenging, and (2) H2O2 signaling in both the endothelium and vascular smooth muscle. Although increased oxidative stress in the endothelial cell can result in increased production of ONOO•− (Figure 1), an increase in ONOO•− does not necessarily decrease NO• bioavailability.