In vivo Evidence of Arterial Dynamic Properties Alteration in Atherosclerotic Rabbit.

OBJECTIVES: Atherosclerosis severely damages the arterial wall. The aim of this study was to assess in vivo, for the first time, arterial dynamic properties, reactivity, and stiffness in atherosclerotic (ATH) rabbits. METHODS: The rabbits were fed with 0.3% cholesterol diet. Femoral artery (FA) or abdominal aorta (AA) diameter was recorded by echotracking, together with blood pressure. Arterial reactivity after local administration of agents and stiffness were measured as diameter or pulsatile diameter changes. RESULTS: FA dilation induced by acetylcholine was reduced in the function of diet duration (9-65 weeks). With mid-term diet duration (35-45 weeks), the dilation to nitroprusside was greatly reduced; the constriction to norepinephrine was reduced but not that to serotonin, thromboxane agonist, or angiotensin II. After 17- and 28-week diet AA and FA stiffness were increased while distensibility was reduced. Arterial stiffness measured by regional pulse wave velocity was unaltered. We observed that after 28-week diet, FA exhibited a stiffened wall at the plaque level and higher distensibility at the upstream site. DISCUSSION/CONCLUSION: Arterial reactivity and compliance were greatly modified by atherosclerosis, at various degrees dependent on diet duration. ATH rabbit is therefore a suitable model for in vivo investigations of treatments targeting dynamic properties of arterial wall.

Chronic NO Restriction in Hypertensive Rats Increases Abdominal but Not Thoracic Aortic Intrinsic Stiffness via an Augmentation in Profibrotic Materials.

The spontaneously hypertensive rat model with reduced NO synthesis (SHRLN) shares features with aging and hypertension in humans, among other a severe aortic stiffening. The present in vivo study aimed to compare thoracic (TA) and abdominal (AA) aortic stiffness in the SHRLN (treated 5 weeks with L-NAME), SHR, and normotensive Wistar Kyoto (WKY). Dynamic properties of TA and AA were measured in the same rats, using echotracking recording of aortic diameter coupled with blood pressure (BP). Measurements were performed first at operating BP and then after BP reduction in hypertensive rats, thus in isobaric conditions. Histological staining and immunohistochemistry were used for structural analysis at both sites. At operating pressure, BP and pulse pressure (PP) were higher in SHRLN compared with SHR. Stiffness index was also increased and distensibility decreased in both TA and AA in SHRLN. At WKY-matched blood pressure, isobaric AA parameters remained specifically altered in SHRLN, whereas TA recovered to values identical to WKYs. Collagen, fibronectin, α5-selectin, and FAK were increased in SHRLN compared with SHR or WKY. Nevertheless, only the strong accumulations of fibronectin and collagen at the AA site in SHRLN were associated with intrinsic stiffening. In conclusion, we confirm that NO restriction associated with hypertension induces a severe pathological phenotype and shows that L-NAME induced stiffening is more pronounced in AA than in TA as a result of greater fibrosis.

Differential Stiffening between the Abdominal and Thoracic Aorta: Effect of Salt Loading in Stroke-Prone Hypertensive Rats.

Central artery stiffening is recognized as a cardiovascular risk. The effects of hypertension and aging have been shown in human and animal models but the effect of salt is still controversial. We studied the effect of a high-salt diet on aortic stiffness in salt-sensitive spontaneously hypersensitive stroke-prone rats (SHRSP). Distensibility, distension, and ß-stiffness were measured at thoracic and abdominal aortic sites in the same rats, using echotracking recording of the aortic diameter coupled with blood pressure (BP), in SHRSP-salt (5% salted diet, 5 weeks), SHRSP, and normotensive Wistar-Kyoto (WKY) rats. Hemodynamic parameters were measured at BP matched to that of WKY. Histological staining and immunohistochemistry were used for structural analysis. Hemodynamic isobaric parameters in SHRSP did not differ from WKY and only those from the abdominal aorta of SHRSP-salt presented decreased distensibility and increased stiffness compared with WKY and SHRSP. The abdominal and thoracic aortas presented similar thickening, increased fibrosis, and remodeling with no change in collagen content. SHRSP-salt presented a specific increased elastin disarray at the abdominal aorta level but a decrease in elastin content in the thoracic aorta. This study demonstrates the pro-stiffening effect of salt in addition to hypertension; it shows that only the abdominal aorta presents a specific pressure-independent stiffening, in which elastin disarray is likely a key mechanism.

Age and hypertension strongly induce aortic stiffening in rats at basal and matched blood pressure levels.

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.

Chronic reduction of nitric oxide level in adult spontaneously hypertensive rats induces aortic stiffness similar to old spontaneously hypertensive rats.

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.

Aortic stiffness in vivo in hypertensive rat via echo-tracking: analysis of the pulsatile distension waveform.

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.

Role of thromboxane TP and angiotensin AT1 receptors in lipopolysaccharide-induced arterial dysfunction in the rabbit: an in vivo study.

Inflammation plays a major role in pathological conditions leading to cardiovascular events. Administration of lipopolysaccharide to animals decreases arterial blood flow, in contrast to the dilatations that occur in microvessels. The purpose of the present study was to determine whether or not lipopolysaccharide, in vivo, evokes arterial constriction and if so the underlying mechanisms. Rabbits were anaesthetized, blood pressure monitored and femoral artery diameter continuously recorded with an echotracking device. Lipopolysaccharide induced leucopenia, thrombocytopenia, acidosis and a progressive hypotension with a decrease in femoral artery diameter (-30.7+/-2.4% after 3 h) and an increase in arterial rigidity. Three hours after lipopolysaccharide administration, the arterial dilatations to acetylcholine, arachidonic acid and iloprost were inhibited while that to sodium nitroprusside was not altered; the constrictions to norepinephrine, angiotensin II, U46619 (thromboxane analog) and serotonin were not modified. Under control conditions endothelin-1 produced an endothelin ET(B) dependent dilatation, reversed after lipopolysaccharide to an endothelin ETA dependent constriction. The thromboxane TP receptor antagonist S 18886 partially blocked the constriction; the angiotensin AT1 receptor antagonist candesartan prevented it. S 18886 normalized the impaired dilatations to acetylcholine, antagonists of 5-HT-receptors partially restored them while candesartan was ineffective. Antagonists of the endothelin or the histamine receptors had no effect. The present data show that lipopolysaccharide-induced inflammation causes 1) a strong constriction of the femoral artery in which activation of both thromboxane and angiotensin AT1 receptors is involved 2) a reduction of the endothelium-dependent dilatation to acetylcholine attributed to the activation of thromboxane TP receptors.

Cutaneous venous dysfunction studied in vivo in the LPS-treated rabbit: implication of NO in saphenous vein hyporeactivity.

Superficial vein pathology involves both mechanical (hyperpressure and distension) and inflammatory mechanisms. Conflicting results exist about the role of NO in the venous hyporeactivity induced by inflammation. In order to clarify this point, we aimed to investigate the effects of sepsis on cutaneous vein responsiveness in vivo and the possible contributions of constitutive and inducible NOS to the changes of venous contractility. Saphenous vein diameter was recorded by an ultrasonic echo-tracking device in pentobarbital-anaesthetised rabbits. Bacterial lipopolysaccharide (LPS) was administered i.v. at 20 mg/kg/15 min, inducing a progressive fall in mean arterial blood pressure after 2-3 h. The effects of LPS on saphenous vein responsiveness to noradrenaline (2 microg/kg i.v.) were measured simultaneously. In some rabbits, veins were removed for immunochemistry to detect iNOS staining. The venoconstriction to noradrenaline was already significantly reduced at 30 min after LPS (6+/-1% instead of 19+/-1% before LPS) and was completely abolished 3 h after LPS. A reduction of the venoconstriction induced by sumatriptan, a 5-HT(1B/D) agonist, (100 microg/kg, 11+/-1% after saline n=5) was also observed 180 min after LPS infusion (3+/-1%, n=4). The venodilatations induced by acetylcholine or sodium nitroprusside injected locally into the vein were not altered by LPS. When administered 90 min after LPS infusion, the NOS inhibitor L-NAME but not the selective iNOS inhibitor L-NIL (10 mg/kg) induced a recovery of the venoconstriction. Preventive perfusion with L-NAME (10 mg/kg/2 h) reduced the initial hyporeactivity to noradrenaline (30 to 60 min), but accelerated the lethal fall in MAP. L-NIL (10 mg/kg/2 h), to a lesser extent than L-NAME, also reduced the initial hyporeactivity to noradrenaline; in contrast to L-NAME, L-NIL also delayed the complete loss of noradrenaline constriction and improved animal survival. In control animals, neither L-NAME nor L-NIL modified the venoconstriction induced by noradrenaline. iNOS staining was observed in the saphenous vein endothelium after LPS. The experimental model developed in these experiments allows the study of venous responsiveness during sepsis in vivo. Our results show that LPS administration reduces saphenous vein contractility to both adrenergic and serotoninergic constrictor agents. The data suggest that both endothelial and inducible NO are involved in the loss of venous reactivity but these enzymes exert contrasting effects on blood pressure changes.