Aortic Wall Area Research Articles

Aortic plaque regression as determined by magnetic resonance imaging with high-dose and low-dose statin therapy

We sought to compare the effects of high-dose with low-dose simvastatin therapy on aortic plaque morphology using transoesophageal magnetic resonance imaging (TEMRI). Thirty-one patients with established moderate-to-severe atherosclerosis were recruited and randomized to 80 versus 20 mg/day simvastatin therapy. Aortic vessel wall and lumen volumes and areas were measured by TEMRI at baseline and 12 months. Significant differences were observed between the low-dose and high-dose statin therapy in reduction of low-density lipoprotein cholesterol (LDL-c) (10 mg/dl, P = 0.001), total cholesterol (16.2 mg/dl, P < 0.001), vessel wall area (19.0 mm2, P < 0.001) and volume (343.4 mm3, P < 0.001), as well as increase in lumen area (54.4 mm2, P < 0.001) and volume (1038 mm3, P < 0.001). LDL-c lowering was significantly associated with aortic wall area and volume reduction in both groups. High-dose statin leads to greater LDL-c reduction, aortic vessel wall reduction and lumen increase than low-dose statin therapy in patients with at least moderate-documented atherosclerosis.

Trial of new vascular clips for aortic anastomosis in a canine model

We created a new vascular clip designed for aortic surgery. The purposes of this investigation were to examine surgical applicability in a clinically relevant aortic replacement model and to assess biomechanical strength of the clipped anastomosis and serial histologic changes in the clipped anastomotic site. Twenty-one beagles underwent descending thoracic aortic replacement. Distal anastomosis was performed with the new clips, mimicking the cuffed anastomosis technique, and proximal anastomosis was carried out by conventional suture anastomosis. Tissue specimens of the anastomotic sites were harvested at 1, 3, 6, and 12 months postoperatively for examination. There was no significant difference in the time required to carry out clip anastomosis (12.2 +/- 1.3 minutes) and suture anastomosis (13.7 +/- 0.9 minutes; P = .38). Neither type of anastomotic site was disrupted by raising the intraluminal pressure to 280 mm Hg. Microscopically, the areas of aortic wall compressed by vascular clips appeared as hyalinized areas adjacent to surrounding collagen fibers, with no significant infiltration of inflammatory cells. Identical histologic changes were observed at the site of the sutured anastomosis. The media at the clipped anastomosis site was significantly thinner than that at the sutured anastomosis site at 1 month after the operation. However, there was no significant difference in the thickness of the media at 3 months. The new vascular clips were effective in this clinically relevant model, with appropriate biomechanical strength, and the anastomotic sites underwent similar histologic changes to those observed after suture anastomosis.

Systemic cardiovascular disease in uremic rats induced by 1,25(OH)2D3

Vitamin D may contribute to cardiovascular disease in the absence of hypercalcemia in patients with chronic kidney disease. We investigated the effects of long-term (6-week) treatment with 1,25(OH)2D3, at a non-hypercalcemic dosage (0.25 microg/kg per day per orally) in 5/6 nephrectomized rats: (i) vehicle-treated, sham-operated rats; (ii) 1,25(OH)2D3-treated, sham-operated rats; (iii) vehicle-treated, 5/6 nephrectomized rats; and (iv) 1,25(OH)2D3-treated, 5/6 nephrectomized rats. Creatinine clearance after 6 weeks was significantly lower and parathyroid hormone levels were significantly higher in 1,25(OH)2D3-treated uremic rats, compared with uremic controls (P < 0.01). Serum calcium levels, as well as the calcium-phosphorus product, did not differ between both groups. Mean systolic blood pressure in 1,25(OH)2D3-treated animals was significantly increased, compared with vehicle (each P < 0.01). In addition, 1,25(OH)2D3-treated uremic animals showed left ventricular hypertrophy. Diffuse aortic calcification involving the intima and media layer occurred in 1,25(OH)2D3-treated uremic animals, but not in other groups. The mean aortic wall area and lumen area were increased two-fold in 1,25(OH)2D3-treated uremic animals compared with vehicle (P < 0.01), whereas the wall/lumen ratio remained unchanged, indicating fusiform aneurysm formation. Hypertension, left ventricular hypertrophy, aortic calcification, and aneurysm, without hypercalcemia, occurred in 1,25(OH)2D3-treated, 5/6 nephrectomized rats. These data indicate a permissive effect of uremia for cardiovascular damage induced by non-hypercalcemic doses of 1,25(OH)2D3.

Angiotensin II-induced hypertrophy is potentiated in mice overexpressing p22phox in vascular smooth muscle.

Increased reactive oxygen species (ROS) are implicated in several vascular pathologies associated with vascular smooth muscle hypertrophy. In the current studies, we utilized transgenic (Tg) mice (Tg(p22smc)) that overexpress the p22(phox) subunit of NAD(P)H oxidase selectively in smooth muscle. These mice have a twofold increase in aortic p22(phox) expression and H(2)O(2) production and thus provide an excellent in vivo model in which to assess the effects of increased ROS generation on vascular smooth muscle cell (VSMC) function. We tested the hypothesis that overexpression of VSMC p22(phox) potentiates angiotensin II (ANG II)-induced vascular hypertrophy. Male Tg(p22smc) mice and negative littermate controls were infused with either ANG II or saline for 13 days. Baseline blood pressure was not different between control and Tg(p22smc) mice. ANG II significantly increased blood pressure in both groups, with this increase being slightly exacerbated in the Tg(p22smc) mice. Baseline aortic wall thickness and cross-sectional wall area were not different between control and Tg(p22smc) mice. Importantly, the ANG II-induced increase in both parameters was significantly greater in the Tg(p22smc) mice compared with control mice. To confirm that this potentiation of vascular hypertrophy was due to increased ROS levels, additional groups of mice were coinfused with ebselen. This treatment prevented the exacerbation of hypertrophy in Tg(p22smc) mice receiving ANG II. These data suggest that although increased availability of NAD(P)H oxidase-derived ROS is not a sufficient stimulus for hypertrophy, it does potentiate ANG II-induced vascular hypertrophy, making ROS an excellent target for intervention aimed at reducing medial thickening in vivo.

Determination of aortic compliance from magnetic resonance images using an automatic active contour model

The possibility of monitoring changes in aortic elasticity in humans has important applications for clinical trials because it estimates the efficacy of plaque-reducing therapies. The elasticity is usually quantified by compliance measurements. Therefore, the relative temporal change in the vessel cross-sectional area throughout the cardiac cycle has to be determined. In this work we determined and compared the compliance between three magnetic resonance (MR) methods (FLASH, TrueFISP and pulse-wave). Since manual outlining of the aortic wall area is a very time-consuming process and depends on an operator's variability, an algorithm for the automatic segmentation of the artery wall from MR images through the entire heart cycle is presented. The reliable detection of the artery cross-sectional area over the whole heart cycle was possible with a relative error of about 1%. Optimizing the temporal resolution to 60 ms we obtained a relative error in compliance of about 7% from TrueFISP (1.0 × 1.0 × 10 mm3, signal-to-noise ratio (SNR) > 12) and FLASH (0.7 × 0.7 × 10 mm3, SNR > 12) measurements in volunteers. Pulse-wave measurements yielded an error of more than 9%. In a study of ten volunteers, a compliance between C = 3 × 10−5 Pa−1 and C = 8 × 10−5 Pa−1 was determined, depending on age. The results of the TrueFISP and the pulse-wave measurements agreed very well with one another (confidence interval of 1 × 10−5 Pa−1) while the results of the FLASH method more clearly deviated from the TrueFISP and pulse-wave (confidence interval of more than 2 × 10−5 Pa−1).

Characterization of aortic root atherosclerosis in ApoE knockout mice: high-resolution in vivo and ex vivo MRM with histological correlation.

In vivo, cardiac-gated, black-blood, and ex vivo magnetic resonance microscopy (MRM) images of the aortic root, and histopathology data were obtained from 12 transgenic and wild-type (WT) mice. MRM was performed using a black-blood imaging spin-echo sequence with upstream and downstream in-flow saturation pulses to obtain aortic root images in three contrast techniques: proton density-weighted (PDW), T(1)- (T(1)W), and T(2)-weighted (T(2)W). Aortic wall thickness and area were measured and correlated with histopathology data (R > 0.90). Ex vivo lesion components (lipid core, fibrous tissue, and cell tissue) were identified and characterized by differing image contrast in PDW, T(1)W, and T(2)W MRM, and by histopathology. The differences between WT and transgenic mice for maximal wall thickness and area were statistically significant (P < 0.05). This study demonstrates the feasibility of in vivo murine aortic root lesion assessment and ex vivo plaque characterization by MRM.

Role of angiotensin II and free radicals in blood pressure regulation in a rat model of renal hypertension.

One-kidney, 1-clip rats (1K1C) or uninephrectomized controls were treated with either the superoxide dismutase mimetic tempol (0.5 mmol. kg(-1). d(-1)), angiotension type 1 receptor inhibitor losartan (50 mmol. L(-1). kg(-1). d(-1)), or both (n=6 per group) for 2 weeks. At the end of the study, systolic blood pressure (BP) decreased on average by 21% in tempol-treated and 29% in losartan-treated versus untreated 1K1C (217+/-4.4 mm Hg) and was normalized in the losartan plus tempol group. Mean BP also decreased from 159+/-3.7 mm Hg in 1K1C to 93+/-2.8 mm Hg in the losartan plus tempol group. Also, aortic wall area was reduced by 18% in losartan- or tempol-treated 1K1C and by 30% in losartan plus tempol rats compared with untreated 1K1C. Plasma renin activity was increased from 4.8+/-0.3 in untreated 1K1C to 15.9+/-0.9 ng. mL(-1). h(-1) in losartan-treated but not tempol-treated 1K1C. Superoxide generation by the isolated aortic rings assessed by lucigenin chemiluminescence was significantly decreased (by approximately 40%) in all losartan, tempol, and losartan plus tempol groups compared with untreated 1K1C. Nitrotyrosine ELISA in the kidney displayed a significant reduction, from 59+/-13 ng/mg of protein in 1K1C to 12.5+/-5 ng/mg of protein in the losartan plus tempol 1K1C. Western blotting for nNOS in kidney cortex and medulla showed a protein increase in both fractions of 1K1C versus controls and was normalized by losartan plus tempol treatment. Collectively, data show a synergistic effect of losartan and tempol on BP reduction in 1K1C rats. The mechanism may involve reduced superoxide production and nitrotyrosine formation in kidney and decreased kidney neuronal-type NO synthase expression in treated animals. This status in the oxidative balance seems to affect BP in the renal hypertensive rats.

Role of Free Radicals and Angiotensin II in Blood Pressure Regulation in a Renal Model of Hypertension in Rat

P17 One kidney one clip (1K1C) or uninephrectomized controls were treated with either the SOD mimetic tempol (T) (0.5 mmol/kg/day), AT1 receptor inhibitor losartan (L) (50mM/kg/day), or both(L+T) (n=6/group), for 2 weeks. At the end of the study,systolic BP decreased on average by 21% in T- and 29% in L-treated compared to untreated 1K1C (217±4.4 mmHg) and was normalized in the L+T group (123.5±3.3 mmHg). Mean BP also decreased from 130±3.7 mmHg in 1K1C to 83±2.8mmHg in the L+T treated group. The differences were significant (p&lt;0.003) as tested with Bonferroni multiple comparisons test. Also, aortic wall area was reduced by 18% in the L or T treated 1K1C and by 30% in the L+T rats, compared to 1K1C (0.548±0.03 mm2). Plasma renin activity was increased from 4.8±0.3 in 1K1C to 15.9±0.9 ng/ml/h in L - but not T- 1K1C. Superoxide generation by the isolated aortic rings assessed by lucigenin (25μM) chemiluminescence was significantly decreased by ∼40% in all L, T and L+T groups compared to 1K1C controls (1065±200 RLU/mg DNAx10 5 ). The nitrotyrosine ELISA assay in the kidney displayed a significant reduction from 59±13 ng/mg protein in 1K1C to 12.5±5 ng/mg protein in the L+T 1K1C rats. Western blotting for nNOS in the kidney cortex and medulla showed a protein increase in both fractions of 1K1C vs controls and was normalized by the L+T treatment. Collectively, data show a synergistic effect of L and T on the blood pressure reduction in 1K1C rats. The mechanism may involve the reduced superoxide production and decreased kidney nNOS expression in the treated animals. Also, the reduced nitrosylation of the proteins in the kidney might have an important effect on blood pressure regulation.

Development of hypertension in a rat model of diet-induced obesity.

Although obesity is a risk factor for hypertension, the relationship between these 2 conditions is not well understood. Therefore, we examined some parameters of hypertension and cardiovascular disease in a dietary model of obesity. Male Sprague-Dawley rats were provided either a control diet (C) or a diet containing 32% kcal as fat (similar to a Western diet) for 1, 3, or 10 weeks. Rats in the latter group diverged based on body weight gain into obesity-prone (OP) and obesity-resistant (OR) groups. Systolic blood pressure in OP rats was significantly higher after 10 weeks of the diet (149+/-4. 8 mm Hg) compared with both OR and C groups (131+/-3.7 and 129+/-4.5 mm Hg, respectively). The aortic wall area of OP rats was significantly increased, indicating arterial hypertrophy, and a 2-fold increase in plasma renin activity was found in OP rats compared with OR and C rats. The lipid profile showed a significant increase in plasma and VLDL triglycerides of OP versus OR and C groups as early as 3 weeks on the diet. Plasma and LDL-cholesterol levels were increased in the OP group versus the OR and C groups after 3 weeks of the diet, but the difference was blunted after 10 weeks. Lipid peroxidation (thiobarbituric acid-reactive substances) in OP rats was increased 2-fold in LDL and 1.5-fold in aortic wall compared with OR rats, suggesting an increased oxidative stress in these animals. Periodic acid-Schiff staining of the kidney showed mesangial expansion and focal sclerosis that were more prominent in OP rats than in OR rats. The results suggest that hypercholesterolemia, but not hypertriglyceridemia, is linked to the diet; that hypertension and renin-angiotensin system activation are associated with obesity; and that lipid peroxidation and renal damage are the results of both factors.

High-resolution intravascular magnetic resonance imaging: monitoring of plaque formation in heritable hyperlipidemic rabbits.

The individual makeup of atherosclerotic plaque has been identified as a dominant prognostic factor. With the use of an intravascular magnetic resonance (MR) catheter coil, we evaluated the effectiveness of high-resolution MR in the study of the development of atherosclerotic lesions in heritable hyperlipidemic rabbits. Sixteen hyperlipidemic rabbits were investigated at the ages of 6, 12, 24, and 36 months. The aorta was studied with digital subtraction angiography and high-resolution MR with the use of a surface coil and an intravascular coil that consisted of a single-loop copper wire integrated in a 5F balloon catheter. Images were correlated with histological sections regarding wall thickness, plaque area, and plaque components. Digital subtraction angiography revealed no abnormalities in the 6- and 12-month-old rabbits and only mild stenoses in the 24- and 36-month-old rabbits. High-resolution imaging with surface coils resulted in an in-plane resolution of 234x468 microm. Delineation of the vessel wall was not possible in younger rabbits and correlated only poorly with microscopic measurements in the 36-month-old rabbits. Intravascular images achieved an in-plane resolution of 117x156 microm. Increasing thickness of the aortic wall and plaque area was observed with increasing age. In the 24- and 36-month-old animals, calcification could be differentiated from fibrous and fatty tissue on the basis of the T2-fast spin echo images, as confirmed by histological correlation. Atherosclerotic evolution of hyperlipidemic rabbits can be monitored with high-resolution intravascular MR imaging. Image quality is sufficient to determine wall thickness and plaque area and to differentiate plaque components.

Evans' blue dye abolishes endothelium-dependent relaxation of rabbit aortic rings

Dear Editors, Anitschkow [1] observed that areas of rabbit aortic wall downstream of branch points are prone to diet-induced disease and also show an enhanced uptake of circulating trypan blue dye. Numerous subsequent studies using trypan blue or, more commonly, its isomer Evans’ blue dye (EBD) have confirmed for a range of species, ages and diets that these dyes accumulate preferentially downstream of branch points. Studies employing other tracers, however, have only found this pattern in immature vessels [2–5]; in mature vessels, elevated transport occurs upstream of branches [6,7]. We have recently demonstrated that the adult pattern of uptake reverts to the juvenile one in mature rabbit aortas perfused with an inhibitor of NO synthesis [8]. Consequently, the lack of an age-related reversal in the pattern of EBD uptake near branches could be explained if the dye, like methylene blue, inhibits the release or action of NO. To investigate this possibility, we have examined the effect of EBD on NO-mediated relaxation of aortic rings. Three female New Zealand White (NZW) rabbits aged 99–100 days (2.72–2.75 kg) were heparinised (1000 USP units, Sigma) and anaesthetised with pentobarbital (240 mg Sagatal, Rhone Merieux) via the marginal ear vein. In each animal, the abdomen was opened along the midline, the phrenic arteries were clamped, the diaphragm was cut away and the sternum was split along its length. Descending thoracic aortas were gently excised and placed in Holman’s buffer (120 mM NaCl, 5 mM KCl, 2.5 mM CaCl2, 1.3 mM NaH2PO4, 25 mM NaHCO3, 10 mM sucrose, 11.1 mM D-glucose; pH 7.4) equilibrated with 95% O2 and 5% CO2. At least 6 rings 2–3 mm wide were cut from each vessel, two being de-endothelialised by abrasion with a matchstick. The aortic rings were suspended on isometric force transducers (Harvard Apparatus) in Student tissue water baths (Harvard Apparatus) containing 50 ml of the same buffer at 37°C. They were tensioned to 2 g for 1 h before being constricted by addition of 1 mM phenylephrine (L-phenylephrine hydrochloride, Sigma). This dose was used because a preliminary series of experiments [9] using other NZW rabbits had shown that it gives approximately 50% of the maximum phenylephrine-induced constriction and therefore allows the demonstration of further constriction as well as relaxation. Representative chart recorder traces for the constriction and for the changes described below are shown in Fig. 1. After 5 min, by which time a steady force was being generated, 10 mM indomethacin (Calbiochem-Novabiochem) was added to avoid effects mediated by cyclo-oxygenase products in subsequent interventions. After a further 5 min, 1 mM acetylcholine (Sigma) was added to stimulate the release of endotheliumderived relaxing factor. The preliminary experiments [9] had shown this to be the lowest concentration giving maximal relaxation of rings preconstricted with 1 mM * Corresponding author. Tel.: +44 1734 875123 ext. 7053; fax: +44 1734 310180; e-mail P.D.Weinberg@reading.ac.uk

Longitudinal effect of captopril on aortic and arteriolar development in normotensive rats

Normotensive rats were chronically given 100 mg.kg-1.day-1 of captopril in their drinking water beginning 1 day before uninephrectomy. Mean blood pressure was significantly decreased 4 (17%) and 8 (18%) wk later in treated rats vs. age-matched controls. When histological techniques were used, a marked reduction of medial-intimal area of the abdominal aorta was found in treated rats at 4 (24%) and 8 (15%) wk without significant change in internal diameter. Cremaster arteriolar dimensions were measured by intravital microscopy after topical application of 10(-3) M adenosine. Structural diameter reductions occurred in large arterioles starting at 4 wk in treated rats and in small arterioles at 8 wk. Despite a significant increase in wall-to-lumen ratio of some large and small arterioles in treated rats, the wall cross-sectional area of these vessels was significantly decreased by captopril. Measured by stereological techniques, small arteriolar density decreased 17% at 4 wk and 13% at 8 wk in treated rats. Although decreased blood pressure may contribute to smaller aortic cross-sectional wall area, the effect of captopril was probably the major cause for smaller arteriolar lumens, reduced arteriolar cross-sectional wall areas, and arteriolar rarefaction.

Captopril reduces aortic and microvascular growth in hypertensive and normotensive rats.

This experiment was designed to investigate the effect of converting enzyme inhibition on functional and structural vascular alterations in one-kidney, one clip hypertensive rats and in normotensive rats. Starting 1 day before surgery, 100 mg/kg/day captopril was given chronically to half of the hypertensive and normotensive groups in their drinking water. With use of intravital microscopy in the cremaster muscle, arteriolar dimensions were measured 4 weeks later, both before and after topical application of 10(-3) M adenosine. Mean blood pressure was 124 +/- 4 mm Hg in control rats and 103 +/- 5 mm Hg in captopril-treated control rats (p less than 0.05). Mean blood pressure was significantly elevated to 183 +/- 5 mm Hg in captopril-treated one-kidney, one clip hypertensive rats and 193 +/- 5 mm Hg in one-kidney, one clip hypertensive rats. With use of histological techniques, a marked reduction of medial-intimal area of the abdominal aorta was found in captopril-treated control rats (24%), and hypertrophy of the aortic wall in one-kidney, one clip hypertensive rats was decreased 26% by captopril. Structural diameter reductions occurred in large arterioles of the captopril-treated control and hypertensive groups and the nontreated hypertensive group. In spite of a significant increase in wall-to-lumen ratio of first-order arterioles in all captopril-treated rats, captopril decreased cross-sectional wall area of these vessels 37% in hypertensive and 20% in control rats, respectively. Measured by stereological techniques, small arteriolar density decreased 30% in captopril-treated hypertensive rats and 17% in captopril-treated control rats. Therefore, smaller arteriolar lumens, decreased aortic and arteriolar cross-sectional wall area, and arteriolar rarefaction after converting enzyme inhibition, in spite of rising or falling blood pressure, are evidence that vascular growth was inhibited in vivo.

動脈壁内のいわゆる“クリアランス”について

The insudation of blood plasma components into the intima is one of the most important atherogenic factors. But, the accumulation of blood components would not occur when the intimal fluid transportation (“clearance”) is satisfactory enough to carry them away.We examine microscopically the declining of intimal clearance with aging about non-sclerotic areas of human aortic wall by Berlin-blue production after infusion of ferric citrate solution.The infusion of fluid was much easier and more uniform in the younger aortas than in older cases, and it was washed away by perfusing of saline solution. But in older cases, blue dye remained distinctly in the intima.It was noted that the clearance mechanism of human aortic wall declined steadily with aging even in the non-sclerotic “normal” areas.