Preventive and chronic mineralocorticoid receptor antagonism is highly beneficial in obese SHHF rats.

BACKGROUND AND PURPOSE: Mineralocorticoid receptor (MR) activation contributes to heart failure (HF) progression. Its overactivity in obesity is thought to accelerate cardiac remodelling and HF development. Given that MR antagonists (MRA) are beneficial in chronic HF patients, we hypothesized that early MRA treatment may target obesity-related disorders and consequently delay the development of HF. EXPERIMENTAL APPROACH: Twenty spontaneously hypertensive HF dyslipidaemic obese SHHF(cp/cp) rats and 18 non-dyslipidaemic lean SHHF(+/+) controls underwent regular monitoring for their metabolic and cardiovascular phenotypes with or without MRA treatment [eplerenone (eple), 100 mg∙kg(-1) ∙day(-1) ] from 1.5 to 12.5 months of age. KEY RESULTS: Eleven months of eple treatment in obese rats (SHHF(cp/cp) eple) reduced the obesity-related metabolic disorders observed in untreated SHHF(cp/cp) rats by reducing weight gain, triglycerides and total cholesterol levels and by preserving adiponectinaemia. The MRA treatment predominantly preserved diastolic and systolic functions in obese rats by alleviating the eccentric cardiac hypertrophy observed in untreated SHHF(cp/cp) animals and preserving ejection fraction (70 ± 1 vs. 59 ± 1%). The MRA also improved survival independently of these pressure effects. CONCLUSION AND IMPLICATIONS: Early chronic eple treatment resulted in a delay in cardiac remodelling and HF onset in both SHHF(+/+) and SHHF(cp/cp) rats, whereas SHHF(cp/cp) rats further benefited from the MRA treatment through a reduction in their obesity and dyslipidaemia. These findings suggest that preventive MRA therapy may provide greater benefits in obese patients with additional risk factors of developing cardiovascular complications.

Expression of the semicarbazide-sensitive amine oxidase in articular cartilage: its role in terminal differentiation of chondrocytes in rat and human.

OBJECTIVE: Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the oxidation of primary amines into ammonia and reactive species (hydrogen peroxide, aldehydes). It is highly expressed in mammalian tissues, especially in vascular smooth muscle cells and adipocytes, where it plays a role in cell differentiation and glucose transport. The study aims at characterizing the expression and the activity of SSAO in rat and human articular cartilage of the knee, and to investigate its potential role in chondrocyte terminal differentiation. DESIGN: SSAO expression was examined by immunohistochemistry and western blot. Enzyme activity was measured using radiolabeled benzylamine as a substrate. Primary cell cultures of rat chondrocytes were treated for 21 days by a specific SSAO inhibitor, LJP 1586. Terminal chondrocyte differentiation markers were quantified by RT-qPCR. The basal and IL1ß-stimulated glucose transport was monitored by the entrance of (3)[H]2-deoxyglucose in chondrocytes. RESULTS: SSAO was expressed in chondrocytes of rat and human articular cartilage. SSAO expression was significantly enhanced during the hypertrophic differentiation of chondrocytes characterized by an increase in MMP13 and in alkaline phosphatase (ALP) expressions. SSAO inhibition delayed the late stage of chondrocyte differentiation without cell survival alteration and diminished the basal and IL1ß-stimulated glucose transport. Interestingly, SSAO activity was strongly increased in human osteoarthritic cartilage. CONCLUSIONS: SSAO was expressed as an active form in rat and human cartilage. The results suggest the involvement of SSAO in rat chondrocyte terminal differentiation via a modulation of the glucose transport. In man, the increased SSAO activity detected in osteoarthritic patients may trigger hypertrophy and cartilage degeneration.

Disseminated arterial calcification and enhanced myogenic response are associated with abcc6 deficiency in a mouse model of pseudoxanthoma elasticum.

OBJECTIVE: Pseudoxanthoma elasticum is an inherited metabolic disorder resulting from ABCC6 gene mutations. It is characterized by progressive calcification and fragmentation of elastic fibers in the skin, retina, and the arterial wall. Despite calcium accumulation in the arteries of patients with pseudoxanthoma elasticum, functional consequences remain unknown. In the present study, we investigated arterial structure and function in Abcc6(-/-) mice, a model of the human disease. APPROACH AND RESULTS: Arterial calcium accumulation was evaluated using alizarin red stain and atomic absorption spectrometry. Expression of genes involved in osteochondrogenic differentiation was measured by polymerase chain reaction. Elastic arterial properties were evaluated by carotid echotracking. Vascular reactivity was evaluated using wire and pressure myography and remodeling using histomorphometry. Arterial calcium accumulation was 1.5- to 2-fold higher in Abcc6(-/-) than in wild-type mice. Calcium accumulated locally leading to punctuate pattern. Old Abcc6(-/-) arteries expressed markers of both osteogenic (Runx2, osteopontin) and chondrogenic lineage (Sox9, type II collagen). Abcc6(-/-) arteries displayed slight increase in arterial stiffness and vasoconstrictor tone in vitro tended to be higher in response to phenylephrine and thromboxane A2. Pressure-induced (myogenic) tone was significantly higher in Abcc6(-/-) arteries than in wild type. Arterial blood pressure was not significantly changed in Abcc6(-/-), despite higher variability. CONCLUSIONS: Scattered arterial calcium depositions are probably a result of osteochondrogenic transdifferentiation of vascular cells. Lower elasticity and increased myogenic tone without major changes in agonist-dependent contraction evidenced in aged Abcc6(-/-) mice suggest a reduced control of local blood flow, which in turn may alter vascular homeostasis in the long term.

The Nebivolol action on vascular tone is dependent on actin cytoskeleton polymerization and Rho-A activity into ECs and SMCs.

Nitric oxide is implicated in the target action of Nebivolol, a selective ß1 adrenoceptor blocker used in hypertension treatment. As the Nitric Oxide (NO) production and the actin cytoskeleton are linked, the aim of this work was to study the involvement of actin cytoskeleton on mechanism of action of Nebivolol in cultured endothelial cells. We studied the effect of Nebivolol (200 µM) on actin filaments remodeling and its impact on NO production and eNOS activation. Results showed that Nebivolol perturbs actin filaments polymerization, increases NO production and eNOS activity between 30 minutes and 1 h. Stabilization of actin filaments with phalloïdine (50 µM) abolishes Nebivolol effects on eNOS activation and NO production. Furthermore, Rho-kinase activity decreased during the first hour of Nebivolol treatment, then increased after 3 h, while actin filaments repolymerized, eNOS activation and NO production decreased. In SMCs, Nebivolol induced a decrease in the Rho-kinase activity from 1 h until 24 h of incubation. In conclusion, we suggest that Nebivolol induced NO production in Endothelial Cells (ECs) via complementary actions between actin cytoskeleton remodeling inducing eNOS activation and Rho-kinase implication. The effect of Nebivolol on ECs occurs during the first hour, this effect on SMCs seems to be maintained until 24 h, explaining persisted action of Nebivolol observed in vivo.

Telomere length in vascular tissues from patients with atherosclerotic disease.

OBJECTIVES: The present study was aimed at evaluating telomere length in blood and in different vascular tissues with or without atheroma, in 3 groups of subjects: a group of atherosclerotic subjects who underwent surgery (Atherosclerosis-Surgery), a second group of subjects with asymptomatic atherosclerotic carotid plaques but who did not undergo cardiovascular surgery (Atherosclerosis-No surgery), and a third group of subjects without atherosclerotic disease (Controls). The main objective was to determine if there is in vivo regulation of telomere length in situ by atherosclerotic lesions. METHODS: A total of 84 subjects (mean age 69 ± 8 years) were studied. Blood and arterial tissue telomere lengths were determined by Southern blotting. Personal medical history (diabetes, hypertension, cardiovascular disease, dyslipidemia), family medical history, drug intake, and lifestyle were evaluated in the entire population through the use of a questionnaire. RESULTS AND CONCLUSION: Arterial segments which did not develop atherosclerosis such as the saphenous vein and internal mammary artery, had longer telomere length than aortic segments. On the other hand, telomere length was shorter in aortic tissues which presented atherosclerotic lesions compared to corresponding tissues without atherosclerotic lesions. These results also suggest tissue regulation of telomere size by local factors likely related to oxidative stress responses.

Effects of lean and fat mass on bone mineral density and arterial stiffness in elderly men.

SUMMARY: The role of body composition on arterial stiffness and osteoporosis remains unclear, especially in the elderly male population. Our results indicate that elderly men with high lean mass and low fat mass exhibit the best arterial and bone profile with the lowest arterial stiffness and the highest bone mineral density. INTRODUCTION: The aim of this study was to evaluate the influence of fat and lean mass on both arterial stiffness and bone mass density (BMD) in elderly men. METHODS: This study was performed in 169 French males over 60 years old. Aortic stiffness was assessed by carotid/femoral pulse wave velocity (PWV). BMD and body composition were determined with a dual-energy X-ray absorptiometry device in the lumbar spine L1-L4, femoral neck, and total body. RESULTS: Lean mass was positively correlated with the three T scores accounting for 11.6%, 26.6%, and 12.2% of the variability in the lumbar spine L1-L4, femoral neck, and total body BMD T scores, respectively. Fat mass had no effect on BMD. However, fat mass was positively correlated with aortic PWV, accounting for 9.8% of its variability. Lean mass was not a determinant of PWV. Hypertension, diabetes, and dyslipidemia were associated with higher PWV but had no effect on BMD. CONCLUSIONS: In males from a general population over 60 years of age, bone and arterial aging are differently influenced by lean and fat mass. Our results indicate that elderly men with high lean mass and low fat mass exhibit the best arterial and bone profile with the lowest arterial stiffness and the highest BMD.

In vitro impact of physiological shear stress on endothelial cells gene expression profile.

In the vascular system, the shear applied to the vascular wall activates mechano-sensors located on endothelial cells (ECs) leading to a modification in the gene expression profile. We applied laminar shear stress at 1 Pa on ECs for 6 h and measured by quantitative real time PCR the expression modulation of genes implied in inflammation (ICAM-1 and E-selectin), oxidative stress sensing (HO-1) and vascular tone modulation (eNOS). We showed that all these genes are shear stress inducible. ICAM-1 is more up-regulated than E-selectin suggesting different levels of implication in inflammatory responses and different modes of induction (SSRE, cytokine). Laminar shear stress induces an oxidative stress translated into HO-1 up-regulation, and a possible vasodilatation through the induction of eNOS. Our laminar shear stress system opens a novel and interesting frame in the evaluation of the impact on ECs and blood cells of new pharmacological substances injected in the bloodstream.

Potential relation between cytoskeleton reorganization and e-NOS activity in sheared endothelial cells (Effect of rate and time of exposure).

Endothelial cells (ECs) which participate the interface between the blood and the vessel wall undergo morphologic changes in response to shear stress induced by blood flow, liable for the important regulation on physiologic and pathophysiologic function of blood vessels. Shear stress induced changes in cell morphology, begin with elongation in the direction of shearing and end by a reorientation and assembly of F-actin stress fibers. Shear stress is also implicated in many important ECs functions such as: decrease of platelet aggregation, anti-thrombogenic and anti-adhesive effects, inhibition of vascular smooth muscle cell (SMC) proliferation and regulation of their contraction and arterial tonicity, via a regulation of vasodilator and vasoconstrictor secretion molecules such as nitric oxide (NO), endothelin I, prostacyclin and angiotensin II. Besides, many of human diseases such as hypercholesterolemia, diabetes and hypertension, are strongly linked to a disturbance of the production of several vasodilator or vasoconstrictor molecules. The aim of this in-vitro study was to evaluate the potential balance between time and rate effects of shearing in cell shape changes and e-NOS activity. Two unidirectional steady laminar flow rates (1.2 Pa and 2.0 Pa) were applied on EC monolayers, each one for a short and a long period, (6 h and 24 h). Cytoskeleton reorganization was evaluated by actin filaments labelling and observed by confocal microscopy. NO production was evaluated by a colorimetric method using the Griess reagent kit for nitrite determination. Results showed that laminar flow affected cell rearrangement by inducing cytoskeleton reorientation and increased production of NO. Laminar shear rate at 2.0 Pa for 24 h did not upregulate NO release. Whereas at 1.2 Pa for 24 h, NO release increased by 33% compared with the static conditions. Both 1.2 Pa and 2.0 Pa for 6 h increased NO release by 17% and 24% respectively as compared with the static conditions. These observations suggested that stress fiber assembly, which controls EC reorientation and NO production, are dependent on rate and time of shearing. In addition, there appear to be a relation between the cytoskeleton reorganization stage and NO production. These results could promote the parameters to evaluate the more appropriate pattern of shearing, to evaluate a potential pharmacological effect on hypertension disorder decrease.

Disturbance of macro- and microcirculation: relations with pulse pressure and cardiac organ damage.

Whereas large arteries dampen oscillations resulting from intermittent ventricular ejection, small arteries steadily deliver optimal blood flow to various organs as the heart. The transition from pulsatile to steady pressure is influenced by several factors as wave travel, damping, and reflections, which are mainly determined by the impedance mismatch between large vessels and arteriolar bifurcations. The mechanism(s) behind the dampening of pressure wave in the periphery and the links between central and peripheral pulsatile pressure (PP) may determine cardiac damage. Active pathways participate to pulse widening and changes in pulse amplitude in microvessels. Steady and cyclic stresses operate through different transduction mechanisms, the former being focal adhesion kinase and the latter being free radicals and oxidative stress. Independently of mechanics, calcifications and attachment molecules contribute to enhance vessel wall stiffness through changes in collagen cross-links, proteoglycans, integrins, and fibronectin. Enhanced PP transmission may thus occur and precipitate organ damage at each time that autoregulatory mechanisms, normally protecting the heart from vascular injury, are blunted. Such circumstances, observed in old subjects with systolic hypertension and/or Type 2 diabetes mellitus, particularly under high-sodium diet, cause cardiac damage and explain why increased PP and arterial stiffness are significant predictors of morbidity and mortality in the elderly.

5-HT activates vagal afferent cell bodies in vivo: role of 5-HT2 and 5-HT3 receptors.

Occipital artery (OA) injections of 5-HT elicit pronounced reductions in heart rate and mean arterial blood pressure (MAP) in urethane-anesthetized rats by activation of vagal afferent cell bodies in the ipsilateral nodose ganglion. In contrast, internal carotid artery (ICA) and i.v. injections elicit similar cardiovascular responses by activation of peripheral vagal afferent terminals. The aim of this study was to examine the roles of 5-HT3 and 5-HT2 receptors in the 5-HT-induced activation of vagal afferent cell bodies and peripheral afferent terminals in urethane-anesthetized rats. OA, ICA and i.v. injections of 5-HT elicited dose-dependent reductions in heart rate and MAP that were virtually abolished after i.v. administration of the 5-HT3 receptor antagonists, MDL 7222 or ICS 205-930. The responses elicited by the OA injections of 5-HT were markedly diminished after i.v. injection of the 5-HT2 receptor antagonists, xylamidine or ketanserin, whereas the responses elicited by i.v. or ICA injections of 5-HT were not affected. The present findings suggest that (1) 5-HT3 and 5-HT2 receptor antagonists gain ready access to nodose ganglion cells upon i.v. administration, and (2) functional 5-HT3 and 5-HT2 receptors exist on the cell bodies of vagal afferent neurons mediating the cardiovascular responses elicited by OA injections of 5-HT. These findings also support a wealth of evidence that 5-HT3 receptors exist on the peripheral terminals of vagal afferents, and although they do not discount the possibility that 5-HT2 receptors exist on peripheral vagal afferent terminals, it appears that activation of these receptors does not have pronounced effects on 5-HT3 receptor activity on terminals that mediate the hemodynamic responses to 5-HT.

Occipital artery injections of 5-HT may directly activate the cell bodies of vagal and glossopharyngeal afferent cell bodies in the rat.

The primary objective of this study was to determine whether circulating factors gain direct access to and affect the activity of vagal afferent cell bodies in the nodose ganglia and glossopharyngeal afferents cell bodies in the petrosal ganglia, of the rat. We found that the occipital and internal carotid arteries provided the sole blood supply to the nodose ganglia, and that i.v. injections of the tracer, Basic Blue 9, elicited strong cytoplasmic staining in vagal and glossopharyngeal afferent cell bodies that was prevented by prior ligation of the occipital but not the internal carotid arteries. We also found that occipital artery injections of 5-HT elicited pronounced dose-dependent reductions in heart rate and diastolic arterial blood pressure that were (1) virtually abolished after application of the local anesthetic, procaine, to the ipsilateral nodose and petrosal ganglia, (2) markedly attenuated after transection of the ipsilateral vagus between the nodose ganglion and brain and virtually abolished after subsequent transection of the ipsilateral glossopharyngeal nerve between the petrosal ganglion and the brain, (3) augmented after ipsilateral transection of the aortic depressor and carotid sinus nerves, and (4) augmented after transection of all ipsilateral glossopharyngeal and vagal afferent nerves except for vagal cardiopulmonary afferents. These findings suggest that blood-borne 5-HT in the occipital artery gains direct access to and activates the cell bodies of vagal cardiopulmonary afferents of the rat and glossopharyngeal afferents of undetermined modalities.

Effect of chronic heart rate reduction with ivabradine on carotid and aortic structure and function in normotensive and hypertensive rats.

BACKGROUND: A reduction of heart rate (HR) by surgical means or pharmacological agents affects the progression and/or regression of atherosclerotic lesions. Nevertheless, the effect of bradycardia per se on large artery structure and function has never been investigated in rat models of hypertension. METHODS: Four groups of Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) were treated for 28 days either by placebo or by the selective HR-reducing agent ivabradine (8.4 mg/kg/day), a novel compound devoid of inotropic or vasodilating effects and without direct action on the autonomic nervous system. At the end of the follow-up period, intra-arterial blood pressure, carotid pulsatile arterial hemodynamics (echo tracking techniques) and the medial cross-sectional area (MCSA) of the aorta and the carotid artery were determined. RESULTS: In conscious animals, chronic administration of ivabradine significantly reduced HR by 26-30% with no change in tail systolic blood pressure. In anesthetized animals, the decrease in HR and the subsequent increase in the diastolic period were responsible for a decrease in diastolic blood pressure. At the site of the large arteries, ivabradine produced a decrease in the MCSA of the thoracic but not of the abdominal aorta, as well as an increase in pulsatile change of the carotid diameter without change in the isobaric distensibility and MCSA. The changes in pulsatile diameter were significantly larger in WKY rats than in SHRs. CONCLUSION: In normotensive and mainly in SHRs, selective chronic HR reduction by ivabradine is associated with alterations in large arteries involving an aortic antihypertrophic effect.

Mechanical strength of the isolated carotid artery in SHR.

We have previously reported an adaptation of arterial wall elasticity in spontaneously hypertensive rats (SHR) that involves an increase in both fibronectin/alpha5beta1-integrin complexes and smooth-muscle elastic lamellae connections. We examined the mechanical strength (MS) of the carotid artery in relation to its elastic properties, its elastin/collagen content, and the structure of the internal elastic lamina. MS was defined as the in vitro intraluminal pressure and wall stress that produces rupture of the vascular wall. Intact carotid arteries from 3-month-old normotensive rats (Wistar-Kyoto, WKY) and SHR were cannulated on a specially designed device and adjusted to their in situ length. A slowly increasing static pressure was applied until wall rupture occurred to determine the static mechanical behavior and MS. Static elasticity was similar in SHR and WKY, as were the rupture pressure (2740+/-90 versus 2740+/-40 mm Hg) and wall stress at rupture (11.5+/-1.0 versus 12.8+/-0.4 MPa), indicating equivalent MS in both groups. Histological examination showed several wall ruptures and dissociation of lamellar units that did not differ significantly between the 2 groups. Confocal microscopy showed that the size of fenestrations of the internal elastic lamina and the fraction of area occupied by them were reduced 3-fold in SHR. We have demonstrated that static elasticity of the arterial wall and mechanical strength are similar in carotid arteries from SHR and WKY.

Effects of valsartan on mechanical properties of the carotid artery in spontaneously hypertensive rats under high-salt diet.

The aim of this investigation was to evaluate the influence of a high-salt diet (HSD) on the effects of valsartan, an angiotensin II type 1 (AT(1)) receptor antagonist, on carotid arterial stiffness and structure in spontaneous hypertensive rats (SHR). Carotid arterial stiffness was studied in SHR receiving a HSD or a normal-salt diet (NSD) from the 10th to 20th week of age. Within each of the 2 groups, the animals received treatment with either placebo or valsartan (30 mg. kg(-1). d(-1)) administered on the 4th to 20th week of age. Arterial pressure, wall stress, incremental elastic modulus (Einc), medial cross-sectional area, and EIIIA fibronectin isoform were significantly increased in placebo-HSD rats compared with placebo-NSD rats with no change in the ratio of collagen to elastin. Valsartan reduced mean arterial pressure in both NSD and HSD rats but reduced pulse pressure only in NSD rats. In NSD rats, valsartan reduced Einc and medial cross-sectional area. In HSD, valsartan increased Einc and did not modify medial cross-sectional area and fibronectin. In valsartan-treated rats, the ratio of collagen to elastin was greater in HSD than in NSD rats. In conclusion, the effects of AT(1) blockade are greatly influenced by salt intake in SHR. Despite a reduction in mean arterial pressure in HSD rats, AT(1) blockade was not able to prevent the effects of a HSD on pulse pressure, carotid artery stiffness, and hypertrophy.

Mechanical properties and structure of carotid arteries in mice lacking desmin.

OBJECTIVE: Our aim was to determine in desmin homozygous mutant mice the viscoelastic properties, the mechanical strength and the structure of the carotid artery. METHODS: To assess the viscoelastic properties of large arteries, we have performed an in vivo analysis of the diameter-, and distensibility-pressure curves of the common carotid artery (CCA) in homozygous (Des -/-), heterozygous (Des +/-) and wild-type (Des +/+) mice. To evaluate the mechanical strength, we have measured the in vitro intraluminal pressure producing the rupture of the carotid artery wall. The structure analysis of the arterial wall was based on histology and electronic microscopy. RESULTS: A lower distensibility and an increase of arterial wall viscosity were observed in Des -/- compared with Des +/+. Arterial thickness of Des -/- was similar to those of Des +/+, without changes in elastin and collagen contents. Electron microscopy revealed that the perimeter of cellular fingerlike-projections was smaller in Des -/-, indicating that the cells have lost part of their connections to the extracellular matrix. The rupture pressure was significantly lower in Des -/- (1500+/-200 mmHg) compared with Des +/+ (2100+/-80 mmHg) indicating a lower mechanical strength of the vascular wall. No significant difference was found between Des +/- and Des +/+. CONCLUSION: The desmin is essential to maintain proper viscoelastic properties, structure and mechanical strength of the vascular wall.

Angiotensin II type 1 receptor-153A/G and 1166A/C gene polymorphisms and increase in aortic stiffness with age in hypertensive subjects.

OBJECTIVES: Arterial stiffness is associated with excess morbidity and mortality, independently of other cardiovascular risk factors. Age is the main determinant responsible for arterial wall changes leading to arterial stiffening. Environmental and genetic factors may however influence the magnitude of the effects of age on large artery stiffness. DESIGN AND METHODS: The present study assessed whether or not the relationship between age and aortic stiffness was influenced by genetic variants of angiotensinogen (AGT 174T/M, 235M/T), angiotensin converting enzyme (ACE I/D), angiotensin II type 1 receptor (AT1 1166A/C, -153A/G) and aldosterone synthase (CYP11B2 -344T/C). This study was realized in 441 untreated hypertensive subjects of European origin (aged 18-74 years). Aortic stiffness was assessed by carotid-femoral pulse wave velocity (PWV). RESULTS: Carriers of the angiotensin II type 1 receptor -153G allele showed a steeper age/PWV relationship than the AT1 -153AA subjects. The effect of the AT1 -153A/G polymorphism on aortic stiffness became apparent after the age of 55 years. In subjects with the AT1 1166C allele, the relationship age/PWV is shifted upward, indicating higher values of aortic stiffness at any age compared to the AT1 1166AA patients. Carriers of both the AT1 1166C and -153G alleles presented the additive effects of these 2 genotypes on aortic stiffness. Angiotensinogen, ACE and CYP11B2 genotypes did not influence the effects of age on PWV. CONCLUSIONS: AT1 receptor genotypes could influence arterial ageing in hypertensive subjects. These results also show that the association between genotypes and arterial stiffness may manifest itself later in life.

Fenestrations of the carotid internal elastic lamina and structural adaptation in stroke-prone spontaneously hypertensive rats.

Our aim was to determine the structural factors that determine the mechanical adaptation of the carotid arterial wall in stroke-prone hypertensive rats (SHRSP). Distensibility-pressure and elastic modulus-stress curves assessed by in vivo echo-tracking measurements indicated a reduction in arterial stiffness in 13-week-old SHRSP compared with Wistar-Kyoto rats (WKY). Elastin and collagen contents determined biochemically were not different between SHRSP and WKY. Confocal microscopy showed that the mean area of fenestrations and fraction of area occupied by fenestrations of the internal elastic lamina (IEL) were smaller in SHRSP than in WKY, which indicated a reduction in stress-concentration effects within the IEL. Immunohistologic staining of EIIIA fibronectin isoform and total fibronectin (also as determined by Western blot) was greater in SHRSP, which suggested increased cell-matrix interactions. We suggest that these structural modifications of the vascular wall play a synergistic role in the mechanical adaptation to a high level of stress in SHRSP.

Prevention of aortic and cardiac fibrosis by spironolactone in old normotensive rats.

OBJECTIVES: Because the synthesis of aldosterone is mainly modulated by angiotensin II through type I receptor stimulation and because converting enzyme inhibition (CEI) does not modify aortic extracellular matrix in old normotensive rats, the aim of the present study was to determine whether inhibition of aldosterone formation was able to prevent aortic fibrosis in old Sprague-Dawley normotensive rats. BACKGROUND: We have previously shown that long-term aldosterone antagonism prevents the age-related increase in aortic collagen accumulation in young spontaneously hypertensive rats, independent of blood pressure changes. In contrast, we reported that the positive effects of CEI in the prevention of aortic collagen accumulation were related to the inhibition of angiotensin II actions on angiotensin II type I receptors. METHODS: For this purpose, we studied the histomorphometric and stiffness (echo-tracking technique) changes of an eight-week treatment with the aldosterone antagonist spironolactone by comparison with placebo. RESULTS: At the end of treatment, spironolactone in conscious animals did not change intra-arterial blood pressure, aortic and carotid wall thickness, and cardiac weight. Cardiac collagen density and, to a lesser extent, carotid collagen and elastin densities and contents were significantly decreased in association with an increase of carotid distensibility. CONCLUSIONS: These results show that in old normotensive rats, spironolactone can markedly prevent cardiac and, to a lesser extent, arterial fibrosis and improve arterial stiffness, despite a lack of hypotensive effect.

Intrinsic stiffness of the carotid arterial wall material in essential hypertensives.

We have previously shown that the decrease in large artery distensibility observed in patients with essential hypertension (HT group) was primarily due to an increase in distending pressure and not to hypertension-associated structural modifications of the artery, suggesting a functional adaptation of the wall material. To evaluate the elastic properties of the wall material of the common carotid artery, we determined Young's incremental elastic modulus (Einc) in the HT group and in normotensive subjects (NT group) as a function of blood pressure and circumferential wall stress. In 102 HT patients with never-treated essential hypertension and 40 age- and gender-matched NT subjects, the Einc-pressure and Einc-stress curves were calculated from intima-media thickness and from diameter and pressure waveforms, determined with echo tracking and aplanation tonometry, respectively. The "effective" stiffness of the wall material, determined through Einc calculated at mean blood pressure, was significantly higher in the HT than in the NT group. The "intrinsic" stiffness of the wall material, determined through Einc calculated at a common circumferential wall stress, did not differ between the 2 groups. However, when each group (HT and NT) was analyzed according to tertiles of age, the "intrinsic" stiffness of the arterial wall material was increased only in younger HT patients. In middle-aged and older HT patients, the intrinsic mechanical properties of the carotid arterial wall material were unchanged, and the increased stiffness of the common carotid artery in the HT group was due primarily to the increased level of blood pressure. These results also indicate that the deleterious effects of aging and hypertension on "intrinsic" stiffness are not additive.