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.

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.

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.

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.

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.

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.

Association between local pulse pressure, mean blood pressure, and large-artery remodeling.

BACKGROUND: The aim of the present study was to determine the respective influences of local pulse pressure and mean blood pressure on arterial remodeling in humans at 2 arterial sites: a central, predominantly elastic artery (the common carotid artery) and a peripheral muscular artery (the radial artery). METHODS AND RESULTS: Forty-three healthy subjects and 124 never-treated hypertensive patients were included in the study. Intima-media thickness and internal diameter of the carotid and radial arteries were noninvasively determined with high-definition echo-tracking devices. Pulse pressure was measured locally with applanation tonometry. Multivariate regression models including mean blood pressure and local pulse pressure were established in the whole population. Carotid internal diameter and intima-media thickness were strongly influenced (P<0.0001) by carotid pulse pressure but not by mean blood pressure or brachial pulse pressure, independently of age and sex. Radial artery internal diameter was correlated with age but not with mean blood pressure or radial pulse pressure. Radial artery intima-media thickness was correlated with mean blood pressure (P<0.001) but not with radial pulse pressure. CONCLUSIONS: Carotid pulse pressure was a strong independent determinant of carotid artery enlargement and wall thickening, whereas mean blood pressure and brachial pulse pressure were not, indicating the prominent influence of local pulsatile mechanical load on arterial remodeling. These relationships were observed at the site of an elastic artery but not at the site of a muscular artery, suggesting the contribution of cyclic stretching to the pulse pressure-induced arterial remodeling.

Central pulse pressure is a major determinant of ascending aorta dilation in Marfan syndrome.

BACKGROUND: In patients with Marfan syndrome (MFS), brachial pulse pressure (PP) has been recognized as a risk factor for aortic dilatation, leading to aortic dissection, the main cause of premature death. However, the relationships between aortic PP, aortic stiffness, and aortic root dilation have not been investigated. Our main objective was to determine whether central PP, which takes into account wave reflections and aortic stiffness, is a better determinant of ascending aorta diameter than brachial PP in MFS patients. METHODS AND RESULTS: Twenty patients with confirmed MFS and 20 age- and sex-matched control subjects were included in this cross-sectional, noninvasive study. Elastic properties of the abdominal aorta and common carotid, common femoral, and radial arteries were calculated from the pulsatile changes in arterial diameter and pressure. The ascending aorta diameter, measured with conventional echocardiography, was 37% larger in MFS than in control subjects (P<0.001). Arterial distensibility was 38% lower in MFS than in control subjects at the site of the abdominal aorta (P<0.01) but not at other sites (common carotid, common femoral, and radial arteries). Independently of age and body surface area, ascending aorta diameter was positively correlated with carotid PP in MFS (P<0. 01) and negatively in control subjects (P<0.01) but was not correlated with brachial PP and mean blood pressure. CONCLUSIONS: In patients with MFS, local PP, estimated from carotid PP, was a major determinant of ascending aorta diameter, whereas brachial PP was not. Increased arterial stiffness was confined to the aorta.

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.

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.

Hemodynamics of the carotid artery after vasodilation in essential hypertension.

We performed simultaneous noninvasive measurements of common carotid artery and brachial artery hemodynamics in nine normal subjects and 10 subjects with sustained essential hypertension. In hypertensive subjects, brachial artery blood flow and forearm vascular resistance were in the normal range while carotid artery blood flow and carotid artery resistance were decreased and increased, respectively. The most important findings were the changes in the internal caliber of large arteries. Although the brachial and carotid artery diameters of hypertensive subjects were measured for the same level of mean arterial pressure, brachial artery diameter was significantly increased and carotid artery diameter was strictly normal as compared with values found in normal subjects. To assess whether carotid artery circulation could influence the baroreceptor reflex response to arteriolar vasodilation, carotid artery and brachial artery hemodynamics were measured in immediate succession in normotensive and hypertensive subjects before and after oral administration of cadralazine, a dihydralazine derivative. After cadralazine treatment, carotid artery tangential tension decreased in hypertensive subjects, and the changes were significantly correlated to the increase in heart rate. A similar correlation was found in normal subjects, but it was reset toward higher heart rates. These results indicate that the carotid artery does not behave like the brachial artery in response to a chronic increase in blood pressure. This behavior indicates intrinsic alterations of the arterial wall and might be involved in the resetting of the carotid baroreceptor reflex. Carotid artery circulation could play a role in hypertension by modulating the carotid baroreceptor mechanisms involved in the response to drug-induced arteriolar vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Connection of smooth muscle cells to elastic lamellae in aorta of spontaneously hypertensive rats.

We have recently demonstrated that in large arteries of spontaneously hypertensive rats (SHR), there is no increase of stiffness despite the increase in wall thickness, a sign of mechanical adaptation of the arterial wall to the higher level of stress. Because the dense plaques of smooth muscle are a major site of anchorage between the muscle cells and extracellular matrix, we determined by electron microscopy the distribution of dense plaques and their connections to elastic lamellae in the abdominal aorta of 1-year-old SHR and control Wistar rats. In vivo echo-tracking measurement of aortic distensibility and elastic modulus indicates a reduction of arterial stiffness in SHR compared with Wistar rats when they are studied over a common range of blood pressure. The media thickness to body weight ratio was higher in SHR than in Wistar rats. In the media, the percentage of sectional area occupied by extracellular matrix was not different between Wistar rats and SHR. The average number of dense plaques per muscle cell was not different between Wistar rats and SHR. However, the percentage of cell surface occupied by dense plaques was increased in SHR, and the percentage of cell surface connected to the elastic lamellae was twice as high in SHR compared with Wistar rats (9.4+/-1.5% versus 3.8+/-1.1%). These results suggest that the elastin network plays a major role in the mechanical adaptation of the arterial wall in SHR, not through variations of its total amount but through variations of the extent of anchorage to the muscle cells.

Role of sympathetic nerve activity in the generation of vascular nitric oxide in urethane-anesthetized rats.

The aim of the present study was to examine the involvement of the sympathetic nervous system in the generation or release of vascular nitric oxide. In urethane-anesthetized rats, the administration of the novel nitric oxide synthesis inhibitor L-N-nitro arginine (LNA) (0.02 mmol/kg i.v.) increased mean arterial pressure and renal, mesenteric, and hindquarter vascular resistances. The intravenous administration of L-arginine (60 mg/kg plus 12 mg/kg/min i.v.) produced small reductions in arterial pressure and vascular resistances and abolished the hemodynamic effects of LNA. Pretreatment with the ganglion blocking agent chlorisondamine lowered mean arterial pressure and vascular resistances, abolished the LNA-induced pressor and renal vasoconstrictor response, and attenuated the increases in mesenteric and hindquarter resistances. In contrast, the vasodilator hydralazine lowered mean arterial pressure and vascular resistances to levels equivalent to that of ganglionic blockade; however, the subsequent administration of LNA still produced significant increases in arterial pressure and regional vascular resistances. In ganglion-blocked rats in which pressure and vascular resistances were returned to normal levels by infusion of arginine vasopressin or phenylephrine, the pressor and vasoconstrictor effects of LNA were restored. However, phenylephrine was significantly more efficacious and markedly exaggerated the action of LNA. These results suggest that the sympathetic nervous system plays an important role in modulating the synthesis or release of vascular nitric oxide through the effects of 1) normal sympathetic discharge, 2) humoral activation of alpha-adrenergic receptors, and 3) vascular tone per se.

Smooth muscle tone and arterial wall viscosity: an in vivo/in vitro study.

The relationships between steady and pulsatile pressures, smooth muscle tone, and arterial viscoelastic behavior remain a matter of controversy. We previously showed that arterial wall viscosity (AWV) was 3-fold lower in vivo than in vitro and suggested that in vivo active mechanisms could minimize intrinsic AWV to improve the efficiency of heart-vessel coupling energy balance. The aim of the present study was to determine the role of smooth muscle tone on AWV, under various levels of steady and pulsatile pressures, both in vivo and in vitro. AWV of rat abdominal aorta was studied first in vivo after bolus injections of phenylephrine (PE) or sodium nitroprusside (SNP), then in vitro in response to PE or SNP. In vitro, arterial segments were submitted first to steady pressure (0 to 200 mm Hg) by increments of 20 mm Hg, then to increasing levels of pulse pressure (20 to 50 mm Hg) at various mean arterial pressures (75 to 150 mm Hg). AWV was quantified as the area of the pressure/diameter relationship hysteresis, issued from the simultaneous measurements of pressure (Millar micromanometer) and diameter (NIUS echotracking device). In vivo, AWV increased after PE and decreased after SNP, in parallel with pressure changes. In vitro, AWV was not significantly influenced by PE and SNP. After both PE and SNP, AWV increased with pulse pressure but was not influenced by mean arterial pressure. At any given pulse pressure, AWV was higher in vitro than in vivo. The relation between AWV and pulse pressure was significantly steeper in vitro than in vivo. These results show that AWV is strongly influenced by steady and pulsatile mechanical load but not by smooth muscle tone, both in vivo and in vitro. Factors other than sustained smooth muscle activation should be explored to explain the minimization of AWV in vivo compared with intrinsic in vitro values.

Central modulation of baroreceptor reflex response to phenylephrine by dihydropyridines in rats.

The effects of two dihydropyridine derivatives, the calcium channel agonist BAY k 8644 or the antagonist PN 200-110, on the central nervous components of the baroreceptor reflex control of heart rate during activation of baroreceptors by phenylephrine (2 micrograms i.v.) were studied in pentobarbital-anesthetized normotensive (Wistar) rats and spontaneously hypertensive rats (SHR). To rule out an effect on peripheral vessels or on the sinoauricular node (or on both), BAY k 8644 and PN 200-110 were administered intracerebroventricularly (i.c.v.) at doses that did not change blood pressure. Baroreceptor reflex sensitivity was calculated as the slope of the relationship between systolic arterial pressure and heart period. Baroreceptor reflex sensitivity increased with time following the onset of anesthesia. In SHR, injection of BAY k 8644 (3 micrograms/kg i.c.v.) suppressed the time-dependent increase in baroreceptor reflex sensitivity. The inhibitory effect of BAY k 8644 (3 micrograms/kg i.c.v.) on the time-dependent increase in baroreceptor reflex sensitivity was suppressed by pretreatment with PN 200-110 (0.6 microgram/kg i.c.v.) but not with the solvent, indicating that the central effect of BAY k 8644 occurred at the level of specific dihydropyridine binding sites. In addition, the inhibitory effect of BAY k 8644 (3 micrograms/kg i.c.v.) on the time-dependent increase in baroreceptor reflex sensitivity was suppressed by pretreatment with the muscarinic antagonist atropine methylnitrate (80 micrograms/kg i.c.v.) but not with the solvent. In normotensive rats, the time-dependent increase in baroreceptor reflex sensitivity was not significantly altered by BAY k 8644 (3 micrograms/kg i.c.v.).(ABSTRACT TRUNCATED AT 250 WORDS)

Common carotid artery stiffness and patterns of left ventricular hypertrophy in hypertensive patients.

The aim of this study was to determine the relationship between the lumen diameter and function of the common carotid artery, a vessel representative of the capacitance portion of the circulation, and the different patterns of left ventricular hypertrophy in uncomplicated essential hypertensive patients. Carotid luminal diastolic cross-sectional area, distensibility, and compliance were derived from measurements by a high-definition echotracking system. Left ventricular dimensions were from echocardiography. The 86 hypertensive patients included 31 who had never been treated (group 1), 31 in whom treatment had been stopped for at least 2 weeks (group 2), and 24 treated patients (group 3). In multivariate analysis of the population as a whole, the following relations were statistically independent of age, blood pressure, gender, and group: Left ventricular end-diastolic volume index was positively correlated to carotid luminal cross-sectional area (r = .46, P < .0001) and compliance (r = .47, P < .0001); left ventricular mean wall thickness and mass-volume ratio were negatively correlated to distensibility (r = -.68, P < .0001; r = -.46, P < .0001, respectively) and compliance (r = -.40, P < .0001; r = -.37; P < .001, respectively); and left ventricular mass index was positively correlated to luminal cross-sectional area (r = .23, P < .02) and negatively to distensibility (r = -.26, P < .01). These results indicate that geometric and functional changes in the common carotid artery accompany geometric changes in the left ventricle. More specifically, they suggest that a reduction in distensibility paralleled cardiac concentric hypertrophy and remodeling, whereas an increase in arterial volume paralleled increased left ventricular cavity size.

Mechanical stress of the carotid artery at the early phase of spontaneous hypertension in rats.

Common carotid artery (CCA) hypertrophy has long been recognized in the neonatal period of development in spontaneously hypertensive rats (SHR), but the mean circumferential and shear stresses acting on the arterial wall have never been investigated in vivo. We investigated intra-arterial blood pressure in conscious rats, CCA diameter (echotracking techniques), blood flow velocity (pulsed Doppler), wall thickness (histomorphometry), and ganglionic blockade (hexamethonium) in Wistar rats and SHR at 5 and 12 weeks of age. During this interval, weight gain was identical in the strains, whereas the increase in wall thickness and blood pressure was greater in SHR. CCA diameter was identical at week 5 and increased similarly at week 12 in both strains. During ganglionic blockade, a larger diameter was observed in SHR at week 5 for the same BP level, whereas equivalent values were observed at week 12. Blood flow velocity decreased with age but to a significantly greater extent in SHR. Mean circumferential stress and shear stress index were identical in both strains at week 12. However, from weeks 5 to 12, mean circumferential stress increased with age similarly in both strains, whereas the age-related decrease in mean shear stress index was much greater in SHR than Wistar rats. Thus, despite a higher blood pressure, SHR exhibit the same carotid diameter as Wistar rats during early development. Because the kinetics of shear stress are different in both strains, altered flow-dilatation mechanisms, and possibly resulting endothelial dysfunction, may be involved in the diameter changes.

Aortic distensibility and structural changes in sinoaortic-denervated rats.

The purpose of the present study was to determine the effects of chronic sinoaortic denervation on the mechanical properties and composition of the abdominal aorta in Wistar rats. We used a high-resolution echotracking system to determine in situ under physiological conditions of blood flow and arterial wall innervation the aortic diameter-, compliance-, and distensibility-pressure curves in 16-week-old anesthetized rats that had been denervated at 10 weeks of age for 6 weeks (n = 8). Compared with sham-operated rats (n = 8) we observed a marked reduction of baroreflex response and increase in overall mean blood pressure variability as measured by standard deviation and spectral analysis in sinoaortic-denervated rats. Mean blood pressure was not affected by sinoaortic denervation in both conscious and anesthetized rats. Sinoaortic denervation significantly shifted the distensibility-pressure curve toward lower levels of distensibility, indicating a decreased aortic distensibility for a given level of arterial pressure. Sinoaortic denervation produced a significant increase of aortic wall cross-sectional area and collagen content, one of the less-distensible components of the arterial wall. These results suggest that intact arterial baroreceptors are necessary for maintaining normal functional and structural properties of large arteries in rats. The reduction in arterial distensibility in chronic sinoaortic-denervated rats may have resulted from different factors, including the initial hypertensive phase, aortic wall hypertrophy, and increase in collagen content. The changes in aortic wall structure and related reduction in aortic distensibility, in addition to other mechanisms, might have been direct consequences of an increased blood pressure variability.