Impaired flow-induced dilation of coronary arterioles of dogs fed a low-salt diet: roles of ANG II, PKC, and NAD(P)H oxidase

Abstract

Low-salt (LS) diet has been considered to be beneficial in the prevention and treatment of hypertension; however, it also increases plasma angiotensin (ANG) II and may cause adverse cardiovascular effects, such as endothelial dysfunction. We assessed endothelial function of coronary arterioles and vascular superoxide production, as a function of LS diet. Dogs were fed with LS (0.05% NaCl) or a normal-salt (NS, 0.65% NaCl) diet for 2 wk. There were threefold increases in plasma ANG II, associated with a 60% reduction in flow-induced dilation (FID) in coronary arterioles of LS compared with NS dogs. In vessels of NS dogs, FID was primarily mediated by nitric oxide (NO), as indicated by an eliminated FID by N(ω)-nitro-l-arginine methyl ester (l-NAME). In vessels of LS dogs, however, FID was eliminated. Administration of apocynin, a NAD(P)H oxidase inhibitor, partially restored FID and additional l-NAME eliminated FID. Generation of superoxide, measured with dihydroethidium, was significantly greater in vessels of LS than in NS dogs, which was further increased in response to ANG II or phorbol 12,13-dibutyrate, an agonist of protein kinase C (PKC). The enhanced superoxide was normalized by apocynin, losartan (a blocker of angiotensin type 1 receptor), and chelerythrine chloride (an antagonist of PKC). Western blotting indicated an upregulation of gp91(phox) and p47(phox), associated with increased expression of phosphorylated PKC in vessels of LS dogs. In separate experiments, dogs were fed simultaneously with LS and losartan (LS + Losa) for 2 wk. There was a significant increase in plasma ANG II in LS + Losa dogs, which, however, was associated with normal FID and gp91(phox) expression in coronary arterioles. In conclusion, LS led to endothelial dysfunction, as indicated by an impaired flow-induced dilation caused by decreasing NO bioavailibility, a response that involves angiotensin-induced activation of PKC that, in turn, activates vascular NAD(P)H oxidase to produce superoxide.

Role of homocysteinylation of ACE in endothelial dysfunction of arteries

“…1) and the ANG II signaling pathway (36) in blood vessels as well as abundant expression of ACE (3) in the endothelium provide the biophysiological basis for these interactions. Although the activation of NADPH oxidase by ANG II signaling has been demonstrated to be responsible for exacerbation of vascular oxidative stress in isolated arterioles (15,16), the specific action of local Hcy in promoting ANG II-dependent activation of NADPH oxidase is still unknown. Our studies show that AT 1 R and ACE are active participants in Hcy-driven, superoxide-mediated endothelial dysfunction, as evidenced by the fact that inhibition of vascular ACE and AT 1 R fully prevents the Met/Hcy-induced impairment of SSID and NO release, as well as the NADPH oxidase-dependent production of superoxide (Figs.…”

“…Superoxide production in mesenteric arteries was assessed by using dihydroethidium (DHE) and an HPLC/fluorescence detector-based assay to detect 2-hydroxyethidium (2-EOH), a superoxide-induced oxidative product of DHE (15,55). Isolated mesenteric arteries were incubated in control media and in the presence of 0.3 and 1 mmol/l Met, and Met (1 mmol/l) plus enalapril (100 mol/l, ACE inhibitor), losartan (10 M), or 3-benzyl-7-(2-benzoxazolyl)thio-1,2,3-triazolo(4,5-d)pyrimidine (VAS2870, 5 M, a selective inhibitor of NADPH oxidase; Enzo Life Sciences) for 24 h, respectively.…”

Loss of renal medullary endothelin B receptor function during salt deprivation is regulated by angiotensin II

“…While changes in ET B receptor expression do not account for changes in ET B receptor function, the restoration of ET B receptor function by candesartan may be explained by a variety of potential postreceptor mechanisms related to ET B receptor signaling pathways. ANG II could reduce NO synthase (NOS) activity (42), increase superoxide production (12,18), and stimulate ENaC expression and activity (4,25,28). It is possible that the inhibition of ANG II activity in the kidney by AT 1 blockade could oppose any or all of these effects to reduce ENaC activity, as well as increase the ET B /NOS1 signaling, thus leading to enhancing ET B -dependent natriuresis under these conditions.…”

The NADPH Oxidase Family and its Inhibitors

“…Furthermore, it was shown to attenuate aldosteroneinduced hypertension (Xue et al 2011) and to decrease superoxide anion production in the coronary arteries of low salt-diet dogs where upregulation of gp91phox and p47phox was observed (Huang et al 2010). Moreover, apocynin administration to mice with hereditary hypertension normalized blood pressure, catecholamines, H 2 O 2 , isoprostane, and NO concentration (Gayen et al 2010).…”