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Introduction: Age and hypertension are two major determinants of arterial stiffness, as well as endothelial dysfunction. The present study was designed to test whether a chronic reduction of endogenous nitric oxide (NO) produces arterial stiffening close to that observed in old spontaneously hypertensive rats (SHR), and also to study the effect of an acute or a chronic decrease in blood pressure (BP) on aortic distensibility. Methods: BP, aortic stiffness, endothelial dysfunction and remodelling were measured in male adult (20-week-old) SHR, in adult SHR treated with a nonspecific NO synthase inhibitor L-NAME (SHR/L-NAME) for 2 weeks, in adult SHR/L-NAME cotreated with perindopril (1 mg/kg/day) and in old SHR (55-week-old). Age-matched WKY were used as a normotensive group. Results: Aortic endothelial dysfunction, remodelling and stiffening appeared in old SHR. Reduction of NO production in adult SHR caused similar alterations. Acute decreases in BP in SHR/L-NAME did not improve isobaric aortic distensibility but a chronic reduction of BP prevented endothelial dysfunction, aortic remodelling and aortic wall stiffening. Conclusion: NO reduction in adult SHR induces aortic alterations similar to those observed during aging, which supports the major role of NO in the development of arterial stiffening. These aortic alterations can be prevented by angiotensin-converting enzyme inhibitor treatment.

Vayssettes-Courchay C, Ragonnet C, Isabelle M, Verbeuren TJ. Aortic stiffness in vivo in hypertensive rat via echo-tracking: analysis of the pulsatile distension waveform. Am J Physiol Heart Circ Physiol 301: H382-H390, 2011. First published May 20, 2011 doi:10.1152/ajpheart.00094.2011.-Large-artery stiffening is a major risk factor in aging and hypertension. Elevated blood pressure (BP) and vascular wall properties participate in arterial stiffening; we aimed to evaluate their respective role by combining echo-tracking and the spontaneously hypertensive rats (SHR) treated with low doses of a nitric oxide synthase inhibitor, shown to have arterial stiffening. Normotensive [Wistar-Kyoto (WKY)], SHR, and SHR treated for 2 wk with N G -nitro-L-arginine methyl ester (SHRLN) were anesthetized; BP and distension (pulsatile displacement) of the aortic walls with the ArtLab echo-tracking device were measured. Stiffness index increased in SHRLN vs. SHR; compliance, distensibility, and the slopes and area of the distension-pressure loop curve decreased. The pulsatile distension and pressure waveforms were strongly altered in SHRLN. Maximal values were decreased and increased, respectively, and the waveform kinetics also differed. Thus the area under the curve adjusted to heart rate (AUC/ms) was calculated. Acute BP reductions were induced by diltiazem in SHR and SHRLN, to levels similar to those of WKY. In SHR, compliance, distensibility, stiffness index, and the ascending slope of the distension-pressure loop reached the values of WKY, whereas they were only partially improved in SHRLN. Aortic distension (maximal value and AUC/ms) and the area of the distension-pressure loop were improved in SHR, but not in SHRLN. These data confirm the aortic stiffening induced by nitric oxide reduction in SHR. They show that the ArtLab system analyzes aortic stiffness in rats, and that the aortic pulsatile distension waveform is a parameter strongly dependent on the vascular wall properties.hypertension; compliance; distensibility; pulse-wave velocity; nitric oxide; spontaneously hypertensive rats ARTERIAL STIFFENING IS A MAJOR cardiovascular risk factor (6,17,26,27) in hypertension, end-stage renal disease, hypercholesterolemia, obesity, and diabetes (9,12,21,28). It is also an age-dependent alteration of the vascular wall (21) that has been defined as an early vascular aging factor (22). Elevated blood pressure, inflammation, endothelial dysfunction, remodeling, and hypertrophy are closely related factors that lead to organ damage and vascular stiffening. In hypertension, the long-term elevation of blood pressure leads to endothelial damage and vascular wall remodeling. It has also been proposed that remodeling may precede the hypertensive state (30). In hypertensive patients, major therapeutic targets to avoid cardiovascular events are decreases in blood pressure and improvement of the vascular wall protection (6, 21). Up until now, it remains difficult in humans and in animals to separate the causal effects of blood pressure eleva...

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Age and hypertension are major causes of large artery remodeling and stiffening, a cardiovascular risk factor for heart and kidney damage. The aged spontaneously hypertensive rat (SHR) model is recognized for human cardiovascular pathology, but discrepancies appeared in studies of arterial stiffness. We performed experiments using a robust analysis via echo tracking in 20‐week adult (n = 8) and 80‐week‐old SHR (n = 7), with age‐matched normotensive Wistar Kyoto rats (WKY, n = 6;6) at basal and matched levels of blood pressure (BP). After anesthesia with pentobarbital, abdominal aortic diameter and pressure were recorded and BP was decreased by clonidine i.v. At basal BP, aortic pulse distension, compliance, and distensibility (AD) were reduced and stiffness index increased with age and hypertension and further altered with age + hypertension. When BP was adjusted in SHR to that of normotensive rats (130 mmHg), there was no difference between 20‐week‐old SHR and WKY. Importantly, the age effect was maintained in both WKY and SHR and accentuated by hypertension in old rats. At 130 mmHg, with similar pulse pressure in the four groups, AD (kPa−3) = 24.2 ± 1 in 20 weeks WKY, 19.7 ± 1.4 in 20 weeks SHR, 12.4 ± 1.3 in 80 weeks WKY and 6.6 ± 0.6 in 80 weeks SHR; distension = 7.6 ± 0.4%, 6.7 ± 0.6%, 3.7 ± 0.3%, and 1.8 ± 0.2% in the same groups. In conclusion, reduced distensibility, that is, stiffening due to age is clearly shown here in both WKY and SHR as well as a synergistic effect of age and hypertension. This technique will allow new studies on the mechanisms responsible and drug intervention.

The purpose of the present work was to elucidate the mechanisms underlying the endothelium-dependent and endothelium-independent components of the vascular relaxation induced by a water-soluble and ruthenium-based carbon monoxide (CO)-releasing agent, tricarbonylchloro(glycinato)ruthenium(II) (CORM-3). Changes in isometric tension and cyclic guanosine monophosphate (cGMP) production were measured in isolated aortic rings from normotensive Wistar-Kyoto rats. Nitric oxide (NO) generation was assessed in cultured human umbilical vein endothelial cells (HUVEC) by electron spin resonance. In rat aortic rings, CORM-3, but not the inactivated compound, iCORM, induced relaxations. In rings with but not in those without endothelium relaxations were partially inhibited by L-nitro-arginine (L-NA), 1H-(1,2,4)-oxadiazolo(4,2-a)quinoxalin-1-one (ODQ), or hydroxocobalamin, inhibitors of NO-synthase, soluble guanylyl cyclase, and scavenger of NO, respectively. In rings with and without endothelium, deoxyhemoglobin abolished the relaxations. A combination of potassium channel blockers (barium, glibenclamide, and iberiotoxin) blunted the relaxation in rings without endothelium. CORM-3 produced an endothelium-dependent generation of cGMP that was inhibited by L-NA. CORM-3, but not iCORM, inhibited the endothelium-dependent relaxation to acetylcholine without affecting the response to sodium nitroprusside. In HUVEC, CORM-3 produced a concentration-dependent release of NO. Therefore, CORM-3-induced relaxations involve the soluble guanylyl cyclase-independent activation of smooth muscle potassium channels. Additionally, CO can produce concomitantly activation and inhibition of NO synthase, the former being responsible for the endothelium- and cGMP-dependent effect of CORM-3, the latter for the inhibition of acetylcholine-induced endothelium-dependent relaxations.

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BACKGROUND AND PURPOSEThe purpose of the study was to investigate renal endothelium-dependent vasodilatation in a model of severe hypertension associated with kidney injury. EXPERIMENTAL APPROACHChanges in perfusion pressure were measured in isolated, perfused kidneys taken from 18-week-old Wistar-Kyoto rat (WKY), spontaneously hypertensive rats (SHR) and SHR treated for 2 weeks with N w -nitro-L-arginine methyl ester in the drinking water (L-NAME-treated SHR, 6 mg·kg KEY RESULTSAcetylcholine caused similar dose-dependent renal dilatation in the three groups. In vitro administration of indomethacin did not alter the vasodilatation, while the addition of N w -nitro-L-arginine (L-NA) produced a differential inhibition of the vasodilatation, (inhibition in WKY > SHR > L-NAME-treated SHR). Further addition of ODQ, an inhibitor of soluble guanylyl cyclase, abolished the responses to sodium nitroprusside but did not affect the vasodilatation to acetylcholine. However, the addition of TRAM-34 (or charybdotoxin) inhibitors of Ca 2+ -activated K + channels of intermediate conductance (KCa3.1), blocked the vasodilatation to acetylcholine, while apamin, an inhibitor of Ca 2+ -activated K + channels of small conductance (KCa2.3), was ineffective. Dilatation induced by an opener of KCa3.1/KCa2.3 channels, NS-309, was also blocked by TRAM-34, but not by apamin. The magnitude and duration of NS-309-induced vasodilatation and the renal expression of mRNA for KCa3.1, but not KCa2.3, channels followed the same ranking order (WKY < SHR < L-NAME-treated SHR). CONCLUSIONS AND IMPLICATIONSIn SHR kidneys, an EDHF-mediated response, involving activation of KCa3.1 channels, contributed to the mechanism of endothelium-dependent vasodilatation. In kidneys from L-NAME-treated SHR, up-regulation of this pathway fully compensated for the decrease in NO availability. AbbreviationsEDHF, endothelium-derived hyperpolarizing factor; HbNO, iron-nitroxyl-haemoglobin; L-NA, N w -nitro-L-arginine; L-NAME, N w -nitro-L-arginine methyl ester; NS-309, 6-7-dichloro-1 H-indole-2,3-dione 3-oxime; ODQ, 1H-(1,2,4)-oxadiazolo(4,2-a)quinoxalin-1-one; SHR, spontaneously hypertensive rat; TRAM-34, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole; WKY rat, Wistar-Kyoto rat