Flow- and acetylcholine-induced dilatation in small arteries from rats with renovascular hypertension — effect of tempol treatment
Introduction
Free oxygen radicals have attracted much attention as a contributing factor to the endothelial dysfunction associated with hypertension. One such free radical is superoxide (O2−) which can be generated by the NAD(P)H oxidase system in the vascular wall. Superoxide is degraded to hydrogen peroxide (H2O2) by superoxide dismutase, but may also react with nitric oxide (NO) resulting in the production of peroxynitrite (ONOO−) thus decreasing the bioavailability of NO. A consequence of this would be a reduced NO-dependent vasodilatation (McIntyre et al., 1999).
A short transient pressure increase in isolated arteries is associated with increased superoxide production and diminished flow-mediated dilatation (Huang et al., 1998, Ungvari et al., 2003, Christensen et al., 2007). This abnormality can be corrected by inhibition of the NAD(P)H oxidase with apocynin (Hamilton et al., 2002, Ungvari et al., 2003) and the superoxide dismutase mimetic tempol (Christensen et al., 2007). Also long term high blood pressure in vivo is related to increased vascular superoxide production and alterations in endothelial function. This has been demonstrated in various models of high blood pressure such as the spontaneously hypertensive rat (Zalba et al., 2000) and the DOCA salt sensitive rat model of hypertension (Ghosh et al., 2004). Also rats with renovascular hypertension show impairment of NO-dependent vasodilatation due to superoxide production (Heitzer et al., 1999). Similar abnormalities have been described in patients with essential hypertension (Taddei et al., 1998) as well as renovascular mediated hypertension (Higashi et al., 2002). Also in rats with hypertension due to aortic banding the superoxide generating NAD(P)H oxidase is upregulated (Vaziri and Ni, 2005). Thus, the ubiquitously finding of an activated NAD(P)H system during hypertension suggests this to be due to high blood pressure per se rather than related to the cause of hypertension.
Previous studies have demonstrated that flow-mediated dilatation of mesenteric small arteries from normotensive rats is almost entirely dependent on NO, whereas receptor-mediated dilatation to acetylcholine possess the characteristics of endothelial derived hyperpolarizing factor (EDHF) type and relies on activation of Ca2+-activated potassium channels (Edwards et al., 1998, Thorsgaard et al., 2003). This discrimination between flow- and acetylcholine-induced dilatation also seems to apply to human small arteries (Paniagua et al., 2001, Buus et al., 2000). The different mechanisms for flow- and acetylcholine-induced dilatation allowed us to investigate whether high blood pressure preferentially affects NO-dependent or EDHF-type vasodilatation. In contrast to the mesenteric small arteries, acetylcholine relaxation is NO-mediated in rat coronary small arteries (Symons et al., 2006), and intraluminal measurements of NO concentrations allow direct assessment of NO bioavailability (Simonsen et al., 1999).
Despite the well established role for superoxide as NO scavenger in endothelial dysfunction during high blood pressure conditions, it has not been studied whether receptor- and flow-mediated dilatation is affected in the same vascular preparation under similar experimental conditions. The primary aim of the present study was therefore to investigate to which extent high blood pressure in a rat model of renovascular hypertension influences NO-dependent flow-mediated dilatation or EDHF type acetylcholine-induced dilatation in isolated small arteries. Secondary, we tested whether scavenging of superoxide with tempol selectively affects either type of vasodilatation.
Section snippets
Animal model of hypertension
The investigation conformed to the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health (NIH Publication No. 85–23, revised 1996). Male Sprague–Dawley rats (7–8 weeks, 180–200 g) were obtained from Møllegaard Breeding Center, Skensved, Denmark. The rats were anaesthesized with intraperitoneal midazolam (0.413 mg/kg), fentanyl (0.026 mg/kg) and fluanisone (0.825 mg/kg) and supplied with extra fluanisone if necessary. The right kidney was removed in
Blood pressure measurements
Five and 10 weeks after placement of the clip systolic blood pressure was significantly elevated in one-kidney, one-clip (1K1C) rats compared to sham operated normotensive control rats (Fig. 1A). Tempol treatment from weeks 5 to 10 after placement of the clip lowered systolic blood pressure to the level of the normotensive group, while blood pressure in the group receiving vehicle remained elevated (Fig. 1A). There were no differences in heart rate among the three experimental groups (Fig. 1B)
Discussion
The present study is the first to directly compare NO- and non-NO-dependent dilatation in isolated arteries from hypertensive animals under similar experimental conditions. We confirm the finding from several previous studies that high blood pressure results in impaired flow-mediated vasodilatation (Huang et al., 1998, Ungvari et al., 2003), but also demonstrates that the EDHF type dilatation remains normal. Thus, the main findings of the present study are as follows: (1) Renovascular
Acknowledgements
We thank Helle Zibrandtsen for technical assistance. This study was supported by grants from the Danish Heart Association, the Danish Research Council, and Aarhus University Research Foundation.
References (31)
- et al.
Effect of severe aortic banding above the renal arteries on nitric oxide synthase isotype expression
Kidney Int.
(2001) - et al.
Increased NAD(P)H oxidase-mediated superoxide production in renovascular hypertension: evidence for involvement of protein kinase C
Kidney Int.
(1999) - et al.
Mechanisms of hydroxyl radical-induced contraction of rat aorta
Eur. J. Pharmacol.
(2004) - et al.
Increased NADPH oxidase activity mediates spontaneous aortic tone in genetically hypertensive rats
Eur. J. Pharmacol.
(2006) - et al.
Chronic treatment with a superoxide dismutase mimetic prevents vascular remodeling and progression of hypertension in salt-loaded stroke-prone spontaneously hypertensive rats
Am. J. Hypertens.
(2002) - et al.
Expression of NOX-I, gp91phox, p47phox and P67phox in the aorta segments above and below coarctation
Biochim. Biophys. Acta
(2005) - et al.
Nitric oxide, prostanoid and non-NO, non-prostanoid involvement in acetylcholine relaxation of isolated human small arteries
Br. J. Pharmacol.
(2000) - et al.
High pressure selectively blunts flow-evoked vasodilatation in rat mesenteric small arteries
Br. J. Pharmacol.
(2007) - et al.
Role of angiotensin II and free radicals in blood pressure regulation in a rat model of renal hypertension
Hypertension
(2001) - et al.
Renovascular hypertension impairs formation of endothelium-derived relaxation factors and sensitivity to endothelin-1 in resistance arteries
Br. J. Pharmacol.
(1991)
K+ is an endothelium-derived hyperpolarizing factor in rat arteries
Nature
In vitro perfusion studies of human resistance artery function in essential hypertension
Hypertension
Ca2+-independent activation of the endothelial nitric oxide synthase in response to tyrosine phosphatase inhibitors and fluid shear stress
Circ. Res.
Role of oxidative stress and nitric oxide in the regulation of spontaneous tone in aorta of DOCA-salt hypertensive rats
Br. J. Pharmacol.
NAD(P)H oxidase inhibition improves endothelial function in rat and human blood vessels
Hypertension
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