Chronic angiotensin II AT1 receptor blockade increases cerebral cortical microvessel density

Thromboxane-induced cerebral microvascular rarefaction predicts depressive symptom emergence in metabolic disease

Previous studies have suggested that the loss of microvessel density in the peripheral circulation with evolving metabolic disease severity represents a significant contributor to impaired skeletal muscle oxygenation and fatigue-resistance. Based on this and our recent work, we hypothesized that cerebral microvascular rarefaction was initiated from the increased prooxidant and proinflammatory environment with metabolic disease and is predictive of the severity of the emergence of depressive symptoms in obese Zucker rats (OZRs). In male OZR, cerebrovascular rarefaction followed the emergence of elevated oxidant and inflammatory environments characterized by increased vascular production of thromboxane A2 (TxA2). The subsequent emergence of depressive symptoms in OZR was associated with the timing and severity of the rarefaction. Chronic intervention with antioxidant (TEMPOL) or anti-inflammation (pentoxifylline) therapy blunted the severity of rarefaction and depressive symptoms, although the effectiveness was limited. Blockade of TxA2 production (dazmegrel) or action (SQ-29548) resulted in a stronger therapeutic effect, suggesting that vascular production and action represent a significant contributor to rarefaction and the emergence of depressive symptoms with chronic metabolic disease (although other pathways clearly contribute as well). A de novo biosimulation of cerebrovascular oxygenation in the face of progressive rarefaction demonstrates the increased probability of generating hypoxic regions within the microvascular networks, which could contribute to impaired neuronal metabolism and the emergence of depressive symptoms. The results of the present study also implicate the potential importance of aggressive prodromic intervention in reducing the severity of chronic complications arising from metabolic disease.NEW & NOTEWORTHY With clinical studies linking vascular disease risk to depressive symptom emergence, we used obese Zucker rats, a model of chronic metabolic disease, to identify potential mechanistic links between these two negative outcomes. Depressive symptom severity correlated with the extent of cerebrovascular rarefaction, after increased vascular oxidant stress/inflammation and TxA2 production. Anti-TxA2 interventions prevasculopathy blunted rarefaction and depressive symptoms, while biosimulation indicated that cerebrovascular rarefaction increased hypoxia within capillary networks as a potential contributing mechanism.

Application of a novel index for understanding vascular health following pharmacological intervention in a pre-clinical model of metabolic disease

While a thorough understanding of microvascular function in health and how it becomes compromised with progression of disease risk is critical for developing effective therapeutic interventions, our ability to accurately assess the beneficial impact of pharmacological interventions to improve outcomes is vital. Here we introduce a novel Vascular Health Index (VHI) that allows for simultaneous assessment of changes to vascular reactivity/endothelial function, vascular wall mechanics and microvessel density within cerebral and skeletal muscle vascular networks with progression of metabolic disease in obese Zucker rats (OZR); under control conditions and following pharmacological interventions of clinical relevance. Outcomes are compared to "healthy" conditions in lean Zucker rats. We detail the calculation of vascular health index, full assessments of validity, and describe progressive changes to vascular health index over the development of metabolic disease in obese Zucker rats. Further, we detail the improvement to cerebral and skeletal muscle vascular health index following chronic treatment of obese Zucker rats with anti-hypertensive (15%-52% for skeletal muscle vascular health index; 12%-48% for cerebral vascular health index; p < 0.05 for both), anti-dyslipidemic (13%-48% for skeletal muscle vascular health index; p < 0.05), anti-diabetic (12%-32% for cerebral vascular health index; p < 0.05) and anti-oxidant/inflammation (41%-64% for skeletal muscle vascular health index; 29%-42% for cerebral vascular health index; p < 0.05 for both) drugs. The results present the effectiveness of mechanistically diverse interventions to improve cerebral or skeletal muscle vascular health index in obese Zucker rats and provide insight into the superiority of some pharmacological agents despite similar effectiveness in terms of impact on intended targets. In addition, we demonstrate the utility of including a wider, more integrative approach to the study of microvasculopathy under settings of elevated disease risk and following pharmacological intervention. A major benefit of integrating vascular health index is an increased understanding of the development, timing and efficacy of interventions through greater insight into integrated microvascular function in combination with individual, higher resolution metrics.

A novel vascular health index: Using data analytics and population health to facilitate mechanistic modeling of microvascular status

The study of vascular function across conditions has been an intensive area of investigation for many years. While these efforts have revealed many factors contributing to vascular health, challenges remain for integrating results across research groups, animal models, and experimental conditions to understand integrated vascular function. As such, the insights attained in clinical/population research from linking datasets, have not been fully realized in the basic sciences, thus frustrating advanced analytics and complex modeling. To achieve comparable advances, we must address the conceptual challenge of defining/measuring integrated vascular function and the technical challenge of combining data across conditions, models, and groups. Here, we describe an approach to establish and validate a composite metric of vascular function by comparing parameters of vascular function in metabolic disease (the obese Zucker rat) to the same parameters in age-matched, "healthy" conditions, resulting in a common outcome measure which we term the vascular health index (VHI). VHI allows for the integration of datasets, thus expanding sample size and permitting advanced modeling to gain insight into the development of peripheral and cerebral vascular dysfunction. Markers of vascular reactivity, vascular wall mechanics, and microvascular network density are integrated in the VHI. We provide a detailed presentation of the development of the VHI and provide multiple measures to assess face, content, criterion, and discriminant validity of the metric. Our results demonstrate how the VHI captures multiple indices of dysfunction in the skeletal muscle and cerebral vasculature with metabolic disease and provide context for an integrated understanding of vascular health under challenged conditions.

Perfusion of Brain Preautonomic Areas in Hypertension: Compensatory Absence of Capillary Rarefaction and Protective Effects of Exercise Training

Remodeling of capillary rarefaction and deleterious arteries are characteristic hallmarks of hypertension that are partially corrected by exercise training. In addition, experimental evidence showed capillary rarefaction within the brain cortex and reduced cerebral blood flow. There is no information on hypertension- and exercise-induced effects on capillary profile and function within preautonomic nuclei. We sought now to evaluate the effects of hypertension and exercise training (T) on the capillary network within hypothalamic paraventricular (PVN) and solitary tract (NTS) nuclei, and on the remodeling of brain arteries. Age-matched spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY), submitted to moderate T or kept sedentary (S) for three months, were chronically cannulated for hemodynamic recordings at rest. Rats were anesthetized for i.v. administration of fluorescein isothiocyanate (FITC)-dextran (capillary volume/density measurements) or 4% paraformaldehyde perfusion (basilar, middle, and posterior arteries' morphometry) followed by brain harvesting and processing. Other groups of conscious rats had carotid blood flow (CBF, ultrasound flowmeter) acquired simultaneously with hemodynamic recordings at rest and exercise. SHR-S exhibited elevated pressure and heart rate, reduced CBF, increased wall/lumen ratio of arteries, but no capillary rarefaction within the PVN and NTS. T improved performance gain and caused resting bradycardia in both groups; reduction of pressure and sympathetic vasomotor activity and normalization of the wall/lumen ratio were only observed in SHR-T. T groups responded with marked PVN and NTS capillary angiogenesis and augmented CBF during exercise; to avoid overperfusion at rest, reduced basal CBF was observed only in WKY-T. Data indicated that the absence of SHR-S capillary rarefaction and the intense SHR-T angiogenesis within autonomic areas associated with correction of deleterious arteries' remodeling are essential adjustments to hypertension and exercise training, respectively. These adaptive responses maintain adequate baseline perfusion in SHR-S and SHR-T preautonomic nuclei, augmenting it in exercised rats when a well-coordinated autonomic control is required.

Genomics and Inflammation in Cardiovascular Disease

Chronic cardiovascular diseases are associated with inflammatory responses within the blood vessels and end organs. The origin of this inflammation has not been certain, and neither is its relationship to disease clear. There is a need to determine whether this association is causal or coincidental to the processes leading to cardiovascular disease. These processes are themselves complex: many cardiovascular diseases arise in conjunction with the presence of sustained elevation of blood pressure. Inflammatory processes have been linked to hypertension, and causality has been suggested. Evidence of causality poses the difficult challenge of linking the integrated and multifaceted biology of blood pressure regulation with vascular function and complex elements of immune system function. These include both, innate and adaptive immunity, as well as interactions between the host immune system and the omnipresent microorganisms that are encountered in the environment and that colonize and exist in commensal relationship with the host. Progress has been made in this task and has drawn on experimental approaches in animals, much of which have focused on hypertension occurring with prolonged infusion of angiotensin II. These laboratory studies are complemented by studies that seek to inform disease mechanism by examining the genomic basis of heritable disease susceptibility in human populations. In this realm too, evidence has emerged that implicates genetic variation affecting immunity in disease pathogenesis. In this article, we survey the genetic and genomic evidence linking high blood pressure and its end-organ injuries to immune system function and examine evidence that genomic factors can influence disease risk. © 2021 American Physiological Society. Compr Physiol 11:1-22, 2021.

Constitutive accessibility of circulating proteins to hippocampal neurons in physiologically normal rats

INTRODUCTION

Although the hippocampus (HIP) is thought impermeable to blood-borne proteins because of the integrity of the blood-brain barrier (BBB), it was recently suggested to be susceptible to hydrophilic hormones. The present study determined the accessibility of blood-borne signal molecules such as hormones to hippocampal neurons in physiologically normal rats.

METHODS

As a probe for accessibility, Evans blue dye (EB) that rapidly binds to albumin (Alb), which is impermeable to the BBB, was injected intravenously. To increase the vascular permeability of the BBB, a daily single administration of angiotensin II (Ang II) was applied intravenously for seven consecutive days.

RESULTS

Fifteen minutes after the injection of EB, histological observation revealed that a number of neurons had entrapped and accumulated EB into their cell bodies in the hippocampal dentate gyrus in all rats. Of these, relatively large oval neurons (>15 µm) in the hilus and molecular layer showed parvalbumin immunopositivity, indicating they are GABAergic interneurons. The population of EB-accumulating neurons (approximately 10 µm) were localized in the inner margin of the granule cell layer, suggesting they were granule cells. However, the number of EB-positive neurons did not change in rats treated with Ang II compared with vehicle injection.

CONCLUSIONS

These findings suggest an intriguing possibility that blood-derived proteins such as hormones have access to hippocampal neurons constitutively in the absence of stimuli that increase the vascular permeability of the BBB in a physiologically normal state.

Beneficial Pleiotropic Antidepressive Effects of Cardiovascular Disease Risk Factor Interventions in the Metabolic Syndrome

BACKGROUND

Although the increased prevalence and severity of clinical depression and elevated cardiovascular disease risk represent 2 vexing public health issues, the growing awareness of their combined presentation compounds the challenge. The obese Zucker rat, a model of the metabolic syndrome, spontaneously develops significant depressive symptoms in parallel with the progression of the metabolic syndrome and, thus, represents a compelling model for study. The primary objective was to assess the impact on both cardiovascular outcomes, specifically vascular structure and function, and depressive symptoms in obese Zucker rats after aggressive treatment for cardiovascular disease risk factors with long-term exercise or targeted pharmacological interventions.

METHODS AND RESULTS

We chronically treated obese Zucker rats with clinically relevant interventions against cardiovascular disease risk factors to determine impacts on vascular outcomes and depressive symptom severity. While most of the interventions (chronic exercise, anti-hypertensive, the interventions (long-term exercise, antihypertensive, antidyslipidemia, and antidiabetic) were differentially effective at improving vascular outcomes, only those that also resulted in a significant improvement to oxidant stress, inflammation, arachidonic acid metabolism (prostacyclin versus thromboxane A2), and their associated sequelae were effective at also blunting depressive symptom severity. Using multivariable analyses, discrimination between the effectiveness of treatment groups to maintain behavioral outcomes appeared to be dependent on breaking the cycle of inflammation and oxidant stress, with the associated outcomes of improving endothelial metabolism and both cerebral and peripheral vascular structure and function.

CONCLUSIONS

This initial study provides a compelling framework from which to further interrogate the links between cardiovascular disease risk factors and depressive symptoms and suggests mechanistic links and potentially effective avenues for intervention.

Regulation of skeletal muscle capillary growth in exercise and disease

Capillaries, which are the smallest and most abundant type of blood vessel, form the primary site of gas, nutrient, and waste transfer between the vascular and tissue compartments. Skeletal muscle exhibits the capacity to generate new capillaries (angiogenesis) as an adaptation to exercise training, thus ensuring that the heightened metabolic demand of the active muscle is matched by an improved capacity for distribution of gases, nutrients, and waste products. This review summarizes the current understanding of the regulation of skeletal muscle capillary growth. The multi-step process of angiogenesis is coordinated through the integration of a diverse array of signals associated with hypoxic, metabolic, hemodynamic, and mechanical stresses within the active muscle. The contributions of metabolic and mechanical factors to the modulation of key pro- and anti-angiogenic molecules are discussed within the context of responses to a single aerobic exercise bout and short-term and long-term training. Finally, the paradoxical lack of angiogenesis in peripheral artery disease and diabetes and the implications for disease progression and muscle health are discussed. Future studies that emphasize an integrated analysis of the mechanisms that control skeletal muscle capillary growth will enable development of targeted exercise programs that effectively promote angiogenesis in healthy individuals and in patient populations.

Cerebral Cortical Microvascular Rarefaction in Metabolic Syndrome is Dependent on Insulin Resistance and Loss of Nitric Oxide Bioavailability

OBJECTIVE

Chronic presentation of the MS is associated with an increased likelihood for stroke and poor stroke outcomes following occlusive cerebrovascular events. However, the physiological mechanisms contributing to compromised outcomes remain unclear, and the degree of cerebral cortical MVD may represent a central determinant of stroke outcomes.

METHODS

This study used the OZR model of MS and clinically relevant, chronic interventions to determine the impact on cerebral cortical microvascular rarefaction via immunohistochemistry with a parallel determination of cerebrovascular function to identify putative mechanistic contributors.

RESULTS

OZR exhibited a progressive rarefaction (to ~80% control MVD) of the cortical microvascular networks vs. lean Zucker rats. Chronic treatment with antihypertensive agents (captopril/hydralazine) had limited effectiveness in blunting rarefaction, although treatments improving glycemic control (metformin/rosiglitazone) were superior, maintaining ~94% control MVD. Chronic treatment with the antioxidant TEMPOL severely blunted rarefaction in OZR, although this ameliorative effect was prevented by concurrent NOS inhibition.

CONCLUSIONS

Further analyses revealed that the maintenance of glycemic control and vascular NO bioavailability were stronger predictors of cerebral cortical MVD in OZR than was prevention of hypertension, and this may have implications for chronic treatment of CVD risk under stroke-prone conditions.

Sequential Therapy with Minocycline and Candesartan Improves Long-Term Recovery After Experimental Stroke

Minocycline and candesartan have both shown promise as candidate therapeutics in ischemic stroke, with multiple, and somewhat contrasting, molecular mechanisms. Minocycline is an anti-inflammatory, antioxidant, and anti-apoptotic agent and a known inhibitor of matrix metalloproteinases (MMPs). Yet, minocycline exerts antiangiogenic effects both in vivo and in vitro. Candesartan promotes angiogenesis and activates MMPs. Aligning these therapies with the dynamic processes of injury and repair after ischemia is likely to improve success of treatment. In this study, we hypothesize that opposing actions of minocycline and candesartan on angiogenesis, when administered simultaneously, will reduce the benefit of candesartan treatment. Therefore, we propose a sequential combination treatment regimen to yield a better outcome and preserve the proangiogenic potential of candesartan. In vitro angiogenesis was assessed using human brain endothelial cells. In vivo, Wistar rats subjected to 90-min middle cerebral artery occlusion (MCAO) were randomized into four groups: saline, candesartan, minocycline, and sequential combination of minocycline and candesartan. Neurobehavioral tests were performed 1, 3, 7, and 14 days after stroke. Brain tissue was collected on day 14 for assessment of infarct size and vascular density. Minocycline, when added simultaneously, decreased the proangiogenic effect of candesartan treatment in vitro. Sequential treatment, however, preserved the proangiogenic potential of candesartan both in vivo and in vitro, improved neurobehavioral outcome, and reduced infarct size. Sequential combination therapy with minocycline and candesartan improves long-term recovery and maintains candesartan's proangiogenic potential.

Cerebral small-resistance artery structure and cerebral blood flow in normotensive subjects and hypertensive patients

INTRODUCTION

The aim of this study was to prospectively investigate whether the structure of cerebral small-resistance arteries is related to cerebral perfusion parameters as measured with dynamic susceptibility-weighted contrast magnetic resonance imaging (DSC-MRI) in a selected cohort of hypertensive and normotensive patients.

METHODS

Ten hypertensive and 10 normotensive patients were included in the study. All patients underwent neurosurgical intervention for an intracranial tumor and were investigated with DSC-MRI at 1.5 T. Cerebral small-resistance arteries were dissected from a small portion of morphologically normal cerebral tissue and mounted on an isometric myograph for the measurement of the media-to-lumen (M/L) ratio. A quantitative assessment of cerebral blood flow (CBF) and volume (CBV) was performed with a region-of-interest approach. Correlation coefficients were calculated for normally distributed variables. The institutional review board approved the study, and informed consent was obtained from all patients.

RESULTS

Compared with normotensive subjects, hypertensive patients had significantly lower regional CBF (mL/100 g/min) in the cortical grey matter (55.63 ± 1.90 vs 58.37 ± 2.19, p < 0.05), basal ganglia (53.34 ± 4.39 vs 58.22. ± 4.33, p < 0.05), thalami (50.65 ± 3.23 vs 57.56 ± 4.45, p < 0.01), subcortical white matter (19.32 ± 2.54 vs 22.24 ± 1.9, p < 0.05), greater M/L ratio (0.099 ± 0.013 vs 0.085 ± 0.012, p < 0.05), and lower microvessel density (1.66 ± 0.67 vs 2.52 ± 1.28, p < 0.05). A statistically significant negative correlation was observed between M/L ratio of cerebral arteries and CBF in the cortical grey matter (r = -0.516, p < 0.05), basal ganglia (r = -0.521, p < 0.05), thalami (r = -0.527 p < 0.05), and subcortical white matter (r = -0.612, p < 0.01).

CONCLUSION

Our results indicate that microvascular structure might play a role in controlling CBF, with possible clinical consequences.

Candesartan induces a prolonged proangiogenic effect and augments endothelium-mediated neuroprotection after oxygen and glucose deprivation: role of vascular endothelial growth factors A and B

Angiogenesis is a key component of recovery after stroke. Angiotensin II receptor blocker (ARB) treatment improves neurobehavioral outcome and is associated with enhanced angiogenesis after stroke. The purpose of this study is to investigate the temporal pattern of the ARB proangiogenic effect in the ischemic brain and its association with vascular endothelial growth factors VEGF-A and VEGF-B. Wistar rats were exposed to 90-minute middle cerebral artery occlusion and treated with candesartan (1 mg/kg) at reperfusion. The proangiogenic potential of the cerebrospinal fluid was determined at 8, 24, 48, and 72 hours using an in vitro Matrigel tube formation assay. In addition, the expression of VEGF-A and VEGF-B was measured in brain homogenates using Western blotting at the same time points. A single candesartan dose induced a prolonged proangiogenic effect and a prolonged upregulation of VEGF-A and VEGF-B in vivo. In the ischemic hemisphere, candesartan treatment was associated with stabilization of hypoxia-inducible factor-1α and preservation of angiopoietin-1. The effect of ARB treatment on endothelial cells was studied in vitro. Our results identified brain endothelial cells as one target for the action of ARBs and a source of the upregulated VEGF-A and VEGF-B, which exerted an autocrine angiogenic response, in addition to a paracrine neuroprotective effect. Taken together, this study highlights the potential usefulness of augmenting the endogenous restorative capacity of the brain through the administration of ARBs.

Angiotensin receptor blockade has protective effects on the poststenotic porcine kidney

Angiotensin converting enzyme inhibitors (ACEI)/ angiotensin-II receptor blockers (ARBs) may induce an acute decrease of glomerular filtration rate (GFR) in the stenotic kidney in renal artery stenosis, but most patients tolerate these drugs well. We hypothesized that ACEI/ARBs stabilize stenotic kidney function during prolonged treatment by conferring protective effects. We tested this in control domestic pigs and pigs with renal artery stenosis untreated or treated with valsartan, or triple therapy (7 pigs in each group) for 4 weeks starting 6 weeks after stenosis induction. Renal function, oxygenation, tubular function, and microcirculation were assessed by multi-detector computed tomography (CT), blood-oxygen-level-dependent magnetic-resonance imaging, and micro-CT. Valsartan and triple therapy decreased blood pressure similarly, however, valsartan did not change the GFR of the stenotic kidney compared to renal artery stenosis and was similar to triple therapy. Both valsartan and triple therapy stimulated microvascular density, and improved tubular function. Valsartan also caused a greater increase of angiogenic factors and a decrease in oxidative stress, which were related to higher cortical perfusion and tubular response than triple therapy. Thus, valsartan did not decrease stenotic kidney GFR, but improved cortical perfusion and microcirculation. These beneficial effects may partly offset the hemodynamic GFR reduction in renal artery stenosis and preserve kidney function.

Blockade of the renin-angiotensin system improves cerebral microcirculatory perfusion in diabetic hypertensive rats

We examined the functional and structural microcirculatory alterations in the brain, skeletal muscle and myocardium of non-diabetic spontaneously hypertensive rats (SHR) and diabetic SHR (D-SHR), as well as the effects of long-term treatment with the angiotensin AT1-receptor antagonist olmesartan and the angiotensin-converting enzyme inhibitor enalapril. Diabetes was experimentally induced by a combination of a high-fat diet with a single low dose of streptozotocin (35 mg/kg, intraperitoneal injection). D-SHR were orally administered with olmesartan (5 mg/kg/day), enalapril (10 mg/kg/day) or vehicle for 28 days, and compared with vehicle-treated non-diabetic SHR or normotensive non-diabetic Wistar-Kyoto rats. The cerebral and skeletal muscle functional capillary density of pentobarbital-anesthetized rats was assessed using intravital fluorescence videomicroscopy. Chronic treatment with olmesartan or enalapril significantly lowered blood pressure and reversed brain functional capillary rarefaction. Brain oxidative stress was reduced to non-diabetic control levels in animals treated with olmesartan or enalapril. Histochemical analysis of the structural capillary density showed that both olmesartan and enalapril increased the capillary-to-fiber ratio in skeletal muscle and the capillary-to-fiber volume density in the left ventricle. Olmesartan and enalapril also prevented collagen deposition and the increase in cardiomyocyte diameter in the left ventricle. Our results suggest that the association between hypertension and diabetes results in microvascular alterations in the brain, skeletal muscle and myocardium that can be prevented by chronic blockade of the renin-angiotensin system.

Angiotensin receptor blockers and angiogenesis: clinical and experimental evidence

Angiotensin II type 1 receptor antagonists [ARBs (angiotensin receptor blockers)] are indicated for BP (blood pressure)-lowering, renal protection and cardioprotection in patients unable to tolerate ACEIs (angiotensin-converting enzyme inhibitors). A recent meta-analysis revealed an association between ARBs and tumour development, possibly due to enhancement of angiogenesis. However, published evidence is conflicting on the effects of ARBs on angiogenesis or the expansion of the existing vascular network. ARBs have been shown to exert primarily anti-angiogenic effects in basic science studies of cancer, retinopathy, peripheral artery disease and some models of cardiovascular disease. In animal and cellular models of myocardial infarction and stroke, however, ARB administration has been associated with robust increases in vascular density and improved recovery. The aim of the present review is to examine the angiogenic effects of ARBs in animal and cellular models of relevant disease states, including proposed molecular mechanisms of action of ARBs and the clinical consequences of ARB use.

An automatic algorithm for the segmentation and morphological analysis of microvessels in immunostained histological tumour sections

A fully automatic segmentation and morphological analysis algorithm for the analysis of microvessels from CD31 immunostained histological tumour sections is presented. Development of the algorithm exploited the distinctive hues of stained vascular endothelial cells, cell nuclei and background, to provide the seeds for a 'region-growing' method for object segmentation in the 3D hue, saturation, value (HSV) colour model. The segmented objects, identified as microvessels by CD31 immunostaining, were post-processed with three morphological tasks: joining separate objects that were likely to belong to a single vessel, closing objects that had a narrow gap around their periphery, and splitting objects with multiple lumina into individual vessels. The automatic segmentation was validated against a hand-segmented set of 44 images from three different SW1222 human colorectal carcinomas xenografted into mice. 96.3 ± 0.9% of pixels were found to be correctly classified. Automated segmentation was carried out on a further 53 images from three histologically distinct mouse fibrosarcomas (MFs) for morphological comparison with the SW1222 tumours. Four morphometric measurements were calculated for each segmented vessel: vascular area (VA), ratio of lumen area to vascular area (lu/VA), eccentricity (e), and roundness (ro). In addition, the total vascular area relative to tumour tissue area (rVA) was calculated. lu/VA, e and ro were found to be significantly smaller in MF tumours than in SW1222 tumours (p < 0.05; unpaired t-test). The algorithm is available through the website http://www.caiman.org.uk where images can be uploaded, processed and sent back to users. The output from CAIMAN consists of the original image with boundaries of segmented vessels overlaid, the calculated parameters and a Matlab file, which contains the segmentation that the user can use to derive further results.

Pleiotropic effects of angiotensin receptor blockers: addressing comorbidities by optimizing hypertension therapy

The efficacy of angiotensin receptor blockers (ARBs) in the management of hypertension is well established. Whether these agents induce pleiotropic effects that promote the amelioration of vascular disorders independent of blood pressure reduction remains controversial. This review examines preclinical and clinical data that highlight a potentially important role for ARBs in several common vascular disorders, including cardiovascular, cerebrovascular, renal, and metabolic disorders. The preponderance of evidence suggests that some of the benefits derived from ARBs might improve outcomes in these disorders by actions that extend beyond blood pressure reduction. This review also identifies some potentially important differences in the mechanism of action between ARBs and angiotensin-converting enzyme inhibitors that may have clinical significance in the management of vascular diseases.

Divergent effects of losartan and metoprolol on cardiac remodeling, c-kit+ cells, proliferation and apoptosis in the left ventricle after myocardial infarction

There is strong evidence for the use of angiotensin converting enzyme inhibitors and beta-blockers to reduce morbidity and mortality in patients with myocardial infarction (MI), whereas the effect of angiotensin receptor blockers is less clear. We evaluated the effects of an angiotensin receptor blocker losartan and a beta-blocker metoprolol on left ventricular (LV) remodeling, c-kit+ cells, proliferation, fibrosis, apoptosis, and angiogenesis using a model of coronary ligation in rats. Metoprolol treatment for 2 weeks improved LV systolic function. In contrast, losartan triggered deleterious structural remodeling and functional deterioration of LV systolic function, ejection fraction being 41% and fractional shortening 47% lower in losartan group than in controls 2 weeks after MI. The number of c-kit+ cells as well as expression of Ki-67 was increased by metoprolol. Losartan-induced thinning of the anterior wall and ventricular dilation were associated with increased apoptosis and fibrosis, while losartan had no effect on the expression of c-kit or Ki-67. Metoprolol or losartan had no effect on microvessel density. These results demonstrate that beta-blocker treatment attenuated adverse remodeling via c-kit+ cells and proliferation, whereas angiotensin receptor blocker-induced worsening of LV systolic function was associated with increased apoptosis and fibrosis in the peri-infarct region.

Prior use of angiotensin-converting enzyme inhibitors does not affect outcome in patients with intracerebral hemorrhage

BACKGROUND AND OBJECTIVES

Angiotensin-converting enzyme inhibitors (ACEI) exert protective effects in patients with stroke but their effects remain unknown in patients with intracerebral hemorrhage (ICH).

METHODS

We recruited consecutive patients with acute ICH and analysed pre-admission demographic variables and drug therapy as well as clinical and radiological parameters. Functional and neurological outcomes were determined with the modified Rankin score (mRS) and the NIH Stroke Scale (NIHSS) score administered 90 days after ICH.

RESULTS

Three hundred and ninety-nine patients were included over 6 years with a mortality rate of 47.3%. Before ICH, 130 patients (32.6%) used ACEI. ACEI-treated patients more often had vascular co-morbidities and were more frequently treated with anti-platelets. Admission NIHSS scores were significantly higher in ACEI-treated patients but 90 days NIHSS scores were not. Improvement from baseline NIHSS scores was significantly larger in ACEI-treated patients. Pre-ICH use of ACEI was not associated with lower mortality or better functional outcome on univariate analysis. On multivariable logistic regression analysis, controlling for possible confounding variables, ACEI use was not associated with increased chances for good outcome and failed to show an influence on mortality.

DISCUSSION

In conclusion, our study does not support a possible neuroprotective effect for ACEI use prior to the occurrence of ICH.

Ischemia-induced brain damage is enhanced in human renin and angiotensinogen double-transgenic mice

To investigate the role of brain angiotensin II (ANG II) in the pathogenesis of injury following ischemic stroke, mice overexpressing renin and angiotensinogen (R+A+) and their wild-type control animals (R-A-) were used for experimental ischemia studies. Focal brain ischemia was induced by middle cerebral artery occlusion (MCAO). The severity of ischemic injury was determined by measuring neurological deficits and histological damage at 24 and 48 h after MCAO, respectively. To exclude the influence of blood pressure and local collateral blood flow, brain slices were used for oxygen and glucose deprivation (OGD) studies. The severity of OGD-induced damage was determined by measuring indicators of tissue swelling and cell death, the intensity of the intrinsic optical signal (IOS), and the number of propidium iodide (PI) staining cells, respectively. Results showed 1) R+A+ mice showed higher neurological deficit score (3.8 +/- 0.5 and 2.5 +/- 0.3 for R+A+ and R-A-, respectively, P < 0.01) and larger infarct volume (22.2 +/- 1.6% and 14.1 +/- 1.2% for R+A+ and R-A-, respectively, P < 0.01); 2) The R+A+ brain slices showed more severe tissue swelling and cell death in the cortex (IOS: 140 +/- 6% and 114 +/- 10%; PI: 139 +/- 20 cells/field and 39 +/- 9 cells/field for R+A+ and R-A-, respectively, P < 0.01); 3) treatment with losartan (20 micromol/l) abolished OGD-induced exaggeration of cell injury seen in R+A+ mice. The data indicate that activation of ANG II/AT(1) signaling is harmful to brain exposed to ischemia.

Introgression of Brown Norway chromosome 13 improves visual spatial memory in the Dahl S rat

The present study was conducted in an effort to evaluate whether chromosomal substitution can repair impaired exploration learning and memory. It has previously been observed that Dahl salt-sensitive (SS) rodents exhibit impaired cognitive function along with abnormal physiological responses to muscle stimulation. Introgression of Brown Norway chromosome (13(BN)) has been found to restore normal physiological processes in SS animals. However, the effect of chromosomal substitution on cognitive performance has not been explored. It was hypothesized that 13(BN) also rescues cognitive impairments in these animals. Visual spatial learning and cognitive flexibility were evaluated using the Morris water maze (MWM) and the T-maze. This manipulation is effective in rescuing impaired task acquisition, but not perseveration observed in the SS animal. These animals may represent a natural animal model in which to isolate genetic information responsible for learning and memory function.

Altered structure of small cerebral arteries in patients with essential hypertension

OBJECTIVE

Structural alterations in the microcirculation may be considered an important mechanism of organ damage. An increased media-to-lumen ratio of subcutaneous small resistance arteries has been demonstrated to predict the development of cardiocerebrovascular events in hypertensive patients. Alterations in the structure of small cerebral arteries have been demonstrated in animal models of experimental or genetic hypertension. However, no evaluation with reliable techniques has ever been performed in humans.

DESIGN AND METHODS

Twenty-eight participants were included in the present study: they were 13 hypertensive patients and 15 normotensive individuals. All participants underwent a neurosurgical intervention for benign or malign tumors. A small portion of morphologically normal cerebral tissue was excised from surgical samples and examined. Cerebral small resistance arteries (relaxed diameter around 200 mum) were dissected and mounted on an isometric and isobaric myograph, and the tunica media to internal lumen ratio was measured. In addition, cerebral cortical microvessel density (MVD) was also evaluated. The tissue was sectioned and stained for CD31, and MVD was measured with an automated image analyzer (percentage of area stained). Blood pressure values were evaluated, before surgical intervention, by standard sphygmomanometry.

RESULTS

M/L was significantly greater and MVD significantly lower in hypertensive patients than that in normotensive individuals. No difference between groups in collagen content or mechanical properties of cerebral small arteries was observed.

CONCLUSION

Our results indicate that structural alterations of small cerebral vessels are present in hypertensive patients compared with normotensive individuals, similar to those previously observed in subcutaneous small arteries.

Acute Limb Ischemia Caused by Femoral Arterial Line Induces Remote Liver Injury in a Rabbit Model of Liver Ischemia/Reperfusion Injury

Femoral arterial lines are used for continuous monitoring of arterial blood pressure in experimental studies. However, placement of a catheter in the femoral artery could produce acute limb ischemia with associated systemic effects. The aim of this study was to investigate the effect of femoral arterial line insertion on liver function, in a rabbit liver lobar ischemia-reperfusion (I/R) model. Four groups of animals (n = 6 each) were studied: groups 1 and 2 (sham) underwent laparotomy but no liver ischemia. In groups 3 and 4 (I/R), liver lobar ischemia was induced for 60 minutes followed by 7 hours of reperfusion. In groups 1 and 3, the arterial line was placed in the femoral artery whereas in groups 2 and 4 in the ear artery. Liver function was assessed by serum alanine aminotransferase (ALT) activity, bile flow, plasma lactate levels, and histology. Results are expressed as mean ± SEM. Alanine aminotransferase activity and lactate levels were significantly higher in the I/R femoral line group compared with the I/R ear line group at 7 hours postreperfusion. Bile production was significantly lower (75 ± 9.6 vs 112 ± 10 μL/min per 100 g liver weight). Histopathology showed more extensive hepatocellular necrosis and neutrophil accumulation in the I/R femoral line group compared with I/R ear line group. The sham femoral group showed liver injury, which was more marked than the ear line group (all P < .05). In conclusion, femoral artery cannulation induces remote liver injury. The use of femoral arterial lines should be avoided in experimental studies concerning liver function.

Angiogenesis after cerebral ischemia

Though the vascular system of the adult brain is extremely stable under normal baseline conditions, endothelial cells start to proliferate in response to brain ischemia. The induction of angiogenesis, primarily in the ischemic boundary zone, enhances oxygen and nutrient supply to the affected tissue. Additionally, the generation of new blood vessels facilitates highly coupled neurorestorative processes including neurogenesis and synaptogenesis which in turn lead to improved functional recovery. To take advantage of angiogenesis as a therapeutic concept for stroke treatment, the knowledge of the precise molecular mechanisms is mandatory. Especially, since a couple of growth factors involved in post-ischemic angiogenesis may have detrimental adverse effects in the brain by increasing vascular permeability. This article summarizes the knowledge of molecular mechanisms of angiogenesis following cerebral ischemia. Finally, experimental pharmacological and cellular approaches to stimulate and enhance post-ischemic angiogenesis are discussed.

Effects of thyroidectomy, T4, and DITPA replacement on brain blood vessel density in adult rats

In hypothyroid patients, altered microvascular structure and function may affect mood and cognitive function. We hypothesized that adult male hypothyroid rats will have significantly lower forebrain blood vessel densities (BVD) than euthyroid rats and that treatment with 3,5-diiothyroprionic acid (DITPA) (a thyroid hormone analog) or thyroxine (T4) will normalize BVDs. The euthyroid group received no thyroidectomy or treatment. The other three groups received thyroidectomies and pellets. The hypothyroid group received a placebo pellet, the DITPA group received an 80-mg DITPA-containing pellet, and the T4group received a 5.2-mg T4slow-release pellet for 6 wk. Body weights, cardiac function, and body temperatures were measured. A monoclonal antiplatelet endothelial cell adhesion antibody was used to visualize blood vessels. The euthyroid group averaged body weights of 548 ± 54 g, while the hypothyroid group averaged a body weight of 332 ± 19 g ( P value < 0.001). Relative to the euthyroid group, the DITPA-treated group was significantly lighter ( P value < 0.05), while the T4-treated group was comparable in body weight to the euthyroid group. The same trends were seen with body temperature and cardiac function with the largest difference between the euthyroid and hypothyroid groups. BVD in the euthyroid group was 147 ± 12 blood vessels/mm2and in hypothyroid group 69 ± 5 blood vessels/mm2( P = 0.013) but similar among the euthyroid, DITPA, and T4groups. These results show that hypothyroidism decreased BVD in adult rat forebrain regions. Moreover, DITPA and T4were efficacious in preventing effects of hypothyroidism on cardiac function and BVD.

Angiotensin II is a critical mediator of prazosin-induced angiogenesis in skeletal muscle

OBJECTIVE

The purpose of this study was to determine whether a high-salt diet modulates physiological angiogenesis in skeletal muscle by altering angiotensin II (ANGII) and vascular endothelial growth factor (VEGF) levels.

METHODS

Sprague-Dawley rats were placed on a control diet (0.4% NaCl by weight) or high-salt diet (4.0% NaCl) prior to treatment with the vasodilator prazosin in the drinking water. In addition, a group of animals fed high salt were infused intravenously with ANGII at a low dose to prevent ANGII suppression by high salt, and a group of rats fed control diet were treated with the angiotensin II type I (AT(1)) receptor blocker losartan and prazosin.

RESULTS

Prazosin induced significant angiogenesis in the tibialis anterior muscle after 1 week of treatment. High-salt-fed rats demonstrated a complete inhibition of this angiogenic response. Maintenance of ANGII levels restored prazosin-induced angiogenesis in animals fed a high-salt diet. In addition, losartan treatment blocked prazosin-induced angiogenesis in animals on a control diet. Western blot analysis indicated that prazosin-induced angiogenesis was independent of changes in muscle levels of VEGF.

CONCLUSIONS

This study demonstrates an inhibitory effect of high salt intake on prazosin-induced angiogenesis. Further, these results indicate that ANGII acting through the AT(1) receptor is a critical pathway in this model of angiogenesis.