Why are strokes related to hypertension? Classic studies and hypotheses revisited

Effects of calcium channel blockers on perioperative ischemic events in hypertensive patients with intracranial aneurysms undergoing neurointervention

BACKGROUND

Although calcium channel blockers (CCBs) are useful in stroke prevention, their specific role in preventing stroke in hypertensive patients with intracranial aneurysms undergoing endovascular stent placement remains unclear.

METHODS

We retrospectively examined 458 hypertensive patients with intracranial aneurysms who underwent stent treatment, drawn from a larger multicenter cohort comprising 1326 patients across eight centers. Patients were dichotomized into two groups according to use of a CCB. Propensity score matching (PSM) was performed to balance group differences in patient and aneurysm characteristics. We conducted a comparison of patient and aneurysm characteristics, ischemic complications, and clinical outcomes between the two groups.

RESULTS

The CCB and non-CCB groups comprised 279 and 179 patients, respectively. PSM resulted in 165 matched pairs. After PSM, the incidence of ischemic events within 1 month of the procedure (4.2% vs 10.9%; P=0.022) and proportion of patients with modified Rankin Scale score >2 at last follow-up (1.5% vs 7.8%; P=0.013) were significantly lower in the CCB group. Among patients treated with combination therapy, inclusion of a CCB was associated with a lower incidence of ischemic events (1.5% vs 13.3%; P=0.345), but the difference was not statistically significant after correction.

CONCLUSIONS

CCB use in hypertensive patients undergoing endovascular stenting for treatment of intracranial aneurysms is associated with a lower incidence of ischemic events and a lower incidence of unfavorable neurological outcomes, especially when used in combination therapy.

Association between short-term air pollution exposure and traumatic intracranial hemorrhage: pilot evidence from Taiwan

Introduction

The detrimental effects of air pollution on the brain are well established. However, few studies have examined the effect of air pollution on traumatic brain injury (TBI). This pilot study evaluated the association between short-term air pollution exposure and traumatic intracranial hemorrhage (TIH).

Methods

Hospital data of patients with TBI following road traffic accidents were retrospectively collected from the electronic medical records at five trauma centers in Taiwan between 1 January and 31 December 2017. TIH was employed as an outcome measure. All road accident locations were geocoded, and air quality data were collected from the nearest monitoring stations. Air pollutants were entered into five multivariable models. A sensitivity analysis was performed on patients who are vulnerable to suffering TBI after road accidents, including motorcyclists, bicyclists, and pedestrians.

Results

Among 730 patients with TBI, 327 had TIH. The ages of ≥65 [odds ratio (OR), 3.24; 95% confidence interval (CI), 1.85-5.70], 45-64 (OR, 2.61; 95% CI, 1.64-4.15), and 25-44 (OR, 1.79; 95% CI, 1.13-2.84) years were identified as significant risk factors in the multivariable analysis. In the best-fit multivariable model, exposure to higher concentrations of particulate matter ≤ 2.5 μm in aerodynamic diameter (PM_2.5) was associated with an elevated TIH risk (OR, 1.50; 95% CI, 1.17-1.94). The concentration of nitrogen oxides (NO_X) did not increase the risk of TIH (OR, 0.45; 95% CI, 0.32-0.61). After categorizing the air pollution concentration according to quartile, the trend tests in the multivariate model showed that the concentrations of PM_2.5 and NO_X were significant (p = 0.017 and p < 0.001, respectively). There was a negative borderline significant association between temperature and TIH risk (OR, 0.75; 95% CI, 0.56-1.00, p = 0.05). Notably, the single-vehicle crash was a significant risk factor (OR, 2.11; 95% CI, 1.30-3.42) for TIH.

Discussion

High PM_2.5 concentrations and low temperatures are risk factors for TIH in patients with TBI. High NO_X concentrations are associated with a lower TIH risk.

Brain Bioenergetics in Chronic Hypertension: Risk Factor for Acute Ischemic Stroke

Chronic hypertension is one of the key modifiable risk factors for acute ischemic stroke, also contributing to determine greater neurological deficits and worse functional outcome when an acute cerebrovascular event would occur. A tight relationship exists between cerebrovascular autoregulation, neuronal activity and brain bioenergetics. In chronic hypertension, progressive adaptations of these processes occur as an attempt to cope with the demanding necessity of brain functions, creating a new steady-state homeostatic condition. However, these adaptive modifications are insufficient to grant an adequate response to possible pathological perturbations of the established fragile hemodynamic and metabolic homeostasis. In this narrative review, we will discuss the main mechanisms by which alterations in brain bioenergetics and mitochondrial function in chronic hypertension could lead to increased risk of acute ischemic stroke, stressing the interconnections between hemodynamic factors (i.e. cerebral autoregulation and neurovascular coupling) and metabolic processes. Both experimental and clinical pieces of evidence will be discussed. Moreover, the potential role of mitochondrial dysfunction in determining, or at least sustaining, the pathogenesis and progression of chronic neurogenic hypertension will be considered. In the perspective of novel therapeutic strategies aiming at improving brain bioenergetics, we propose some determinant factors to consider in future studies focused on the cause-effect relationships between chronic hypertension and brain bioenergetic abnormalities (and vice versa), so to help translational research in this so-far unfilled gap.

Arterial hypertension and cerebral hemodynamics: impact of head-down tilt on cerebral blood flow (arterial spin-labeling-MRI) in healthy and hypertensive patients

OBJECTIVE

Hypertension affects cerebrovascular autoregulation and increases the risk of cerebrovascular events and dementia. Notably, it is associated with cerebrovascular remodeling and lower resting cerebral blood flow (CBF). We wanted to determine, using arterial spin-labeling-MRI, the impact of a head-down tilt (HDT) dynamic maneuver on CBF in hypertensive patients.

METHODS

The current prospective study measured 36 patients' CBFs (18 normotensive individuals; 18 hypertensive patients) on 1.5T arterial spin-labeling-MRI in the supine position and after 4 min at -15° HDT. We reconstructed CBF maps of left and right subcortical nuclear gray matter, cortical gray matter and white matter (16 structures) to explore cerebrovascular autoregulation modification under dynamic conditions.

RESULTS

Normotensive and hypertensive participants had no significant CBF differences in the supine position. After HDT, CBF mean variations (CBF-mVs) across all structures declined (mean -5.8%) for the whole population (n = 36), with -6.6 and -7.6% decreases, respectively, in white matter and gray matter (P < 0.001). Left and right accumbens nuclei had the largest changes (-9.6 and -9.2%, respectively; P < 0.001). No CBF-mV difference (0/16) was found in hypertensive patients after HDT, whereas normotensive participants' CBF-mVs changed significantly in four structures (left and right accumbens, putamen and left caudate nucleus) and gray matter. Hypertensive patients exhibited fewer CBF-mVs in left caudate nuclei (P = 0.039) and cortical gray matter (P = 0.013). Among hypertensive patients, people with diabetes had smaller CBF-mVs than people without diabetes.

CONCLUSION

Our results highlight the significantly different CBF reactions to HDT of normotensive and hypertensive participants. They support the hypothesis that hypertension is responsible for deficient cerebrovascular autoregulation.

Re-thinking the Etiological Framework of Neurodegeneration

Neurodegenerative diseases are among the leading causes of disability and death worldwide. The disease-related socioeconomic burden is expected to increase with the steadily increasing life expectancy. In spite of decades of clinical and basic research, most strategies designed to manage degenerative brain diseases are palliative. This is not surprising as neurodegeneration progresses "silently" for decades before symptoms are noticed. Importantly, conceptual models with heuristic value used to study neurodegeneration have been constructed retrospectively, based on signs and symptoms already present in affected patients; a circumstance that may confound causes and consequences. Hence, innovative, paradigm-shifting views of the etiology of these diseases are necessary to enable their timely prevention and treatment. Here, we outline four alternative views, not mutually exclusive, on different etiological paths toward neurodegeneration. First, we propose neurodegeneration as being a secondary outcome of a primary cardiovascular cause with vascular pathology disrupting the vital homeostatic interactions between the vasculature and the brain, resulting in cognitive impairment, dementia, and cerebrovascular events such as stroke. Second, we suggest that the persistence of senescent cells in neuronal circuits may favor, together with systemic metabolic diseases, neurodegeneration to occur. Third, we argue that neurodegeneration may start in response to altered body and brain trophic interactions established via the hardwire that connects peripheral targets with central neuronal structures or by means of extracellular vesicle (EV)-mediated communication. Lastly, we elaborate on how lifespan body dysbiosis may be linked to the origin of neurodegeneration. We highlight the existence of bacterial products that modulate the gut-brain axis causing neuroinflammation and neuronal dysfunction. As a concluding section, we end by recommending research avenues to investigate these etiological paths in the future. We think that this requires an integrated, interdisciplinary conceptual research approach based on the investigation of the multimodal aspects of physiology and pathophysiology. It involves utilizing proper conceptual models, experimental animal units, and identifying currently unused opportunities derived from human data. Overall, the proposed etiological paths and experimental recommendations will be important guidelines for future cross-discipline research to overcome the translational roadblock and to develop causative treatments for neurodegenerative diseases.

Relationship between cognitive function and regulation of cerebral blood flow

Ageing is the primary risk factor for cognitive deterioration. Given that the cerebral blood flow (CBF) or regulation of cerebral circulation is attenuated in the elderly, it could be expected that ageing-induced cognitive deterioration may be affected by a decrease in CBF as a result of brain ischemia and energy depletion. CBF regulation associated with cerebral metabolism thus likely plays an important role in the preservation of cognitive function. However, in some specific conditions (e.g. during exercise), change in CBF does not synchronize with that of cerebral metabolism. Our recent study demonstrated that cognitive function was more strongly affected by changes in cerebral metabolism than by changes in CBF during exercise. Therefore, it remains unclear how an alteration in CBF or its regulation affects cognitive function. In this review, I summarize current knowledge on previous investigations providing the possibility of an interaction between regulation of CBF or cerebral metabolism and cognitive function.

Protective effect of telmisartan on neurovascular unit and inflammasome in stroke-resistant spontaneously hypertensive rats

OBJECTIVES

Hypertension is a crucial risk factor for both stroke and dementia, including Alzheimer's disease (AD). We inspected the effect of telmisartan on the neurovascular unit (NVU) and related inflammatory responses in spontaneously hypertensive rat stroke resistant (SHR-SR) by observing the components of NVU such as N-acetyl glucosamine oligomer (NAGO), collagen IV, astrocytes, and matrix metalloproteinase-9 (MMP-9), as well as inflammasome NOD-like receptors family protein 3 (NLRP3).

METHODS

In the present study, we examined the effect of a highly selective angiotensin type 1 (AT-1) antagonist of angiotensin 2 receptor with high lipid solubility, telmisartan, on NVU and related inflammatory responses in SHR-SR with a low dose (0.3 mg/kg/day) only for improving metabolic syndrome, and a high dose (3 mg/kg/day) for improving both metabolic syndrome and SHR-SR hypertension.

RESULTS

Compared to normotensive Wistar rats, long-lasting hypertension in SHR-SR disrupted NVU by changing immunohistological components such as NAGO, collagen IV, astrocytes, and MMP-9. SHR-SR also strongly induced AD-related inflammasome NLRP3 in neuronal cells with age. However, such NVU disruption and inflammasome activation were greatly improved with dose-dependent telmisartan treatments.

DISCUSSION

These results suggest that telmisartan comprehensively protected the NVU components by reducing inflammatory reactions relative to AD in hypertensive rats, which could also preclude the risk of AD under hypertension.

The Impact of Left Ventricular Hypertrophy and Diastolic Dysfunction on Outcome in Intracerebral Hemorrhage Patients

Background

The objective of this study was to determine the prevalence of LVH and DD in patients presenting with supratentorial deep ICH and to determine if the presence of LVH or DD was an independent predictor of initial ICH volume, hematoma expansion, or poor outcome.

Methods

A cross-sectional study was performed on ICH patients who presented from 7/2008 to 12/2010. Cases were excluded if ICH was traumatic, lobar, infratentorial, secondary to elevated international normalized ratio, suspicious for underlying structural malformation, or where surgical evacuation was performed. Logistic and linear regressions were used to assess the ability of LVH to predict ICH imaging characteristics and patient outcomes.

Results

After adjusting for use of hemostatic agents, LVH was not a significant independent predictor of initial ICH volume (P = 0.344) or 33% volume expansion (P = 0.378). After adjusting for age, infectious complications, and use of hemostatic agents, LVH was not a significant independent predictor of poor functional outcome (P = 0.778). Similar results were seen for DD.

Conclusion

In our sample, patients with deep ICH and LVH were more likely to develop IVH, but LVH was not a significant independent predictor of initial ICH volume, hematoma expansion, or poor short-term outcome.

Associations of outdoor air pollution with hemorrhagic stroke mortality

OBJECTIVE

Evidence linking short-term exposure to outdoor air pollution with hemorrhagic stroke is inconsistent.

METHODS

We evaluated the associations between outdoor air pollution and specific types of stroke in Tokyo, Japan, from April 2003 to December 2008. We obtained daily counts of stroke mortality (n = 41,440) and concentrations of nitrogen dioxide as well as particles less than 2.5 μm in diameter. Time-series analysis was employed.

RESULTS

Although same-day air pollutants were positively associated with ischemic stroke and intracerebral hemorrhage mortality, both air pollutants were more strongly associated with subarachnoid hemorrhage mortality: rate ratio was 1.041 (95% confidence interval: 1.011-1.072) for each 10 μg/m3 increase in the previous-day particles less than 2.5 μm.

CONCLUSIONS

This study suggests that short-term exposure to outdoor air pollution increases the risks of hemorrhagic stroke mortality as well as ischemic stroke mortality.

Cytochrome P450 eicosanoids and cerebral vascular function

The eicosanoids 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs), which are generated from the metabolism of arachidonic acid by cytochrome P450 (CYP) enzymes, possess a wide array of biological actions, including the regulation of blood flow to organs. 20-HETE and EETs are generated in various cell types in the brain and cerebral blood vessels, and contribute significantly to cerebral blood flow autoregulation and the coupling of regional brain blood flow to neuronal activity (neurovascular coupling). Investigations are beginning to unravel the molecular and cellular mechanisms by which these CYP eicosanoids regulate cerebral vascular function and the changes that occur in pathological states. Intriguingly, 20-HETE and the soluble epoxide hydrolase (sEH) enzyme that regulates EET levels have been explored as molecular therapeutic targets for cerebral vascular diseases. Inhibition of 20-HETE, or increasing EET levels by inhibiting the sEH enzyme, decreases cerebral damage following stroke. The improved outcome following cerebral ischaemia is a consequence of improving cerebral vascular structure or function and protecting neurons from cell death. Thus, the CYP eicosanoids are key regulators of cerebral vascular function and novel therapeutic targets for cardiovascular diseases and neurological disorders.

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.

Circadian Variation in Stroke Onset: Identical Temporal Pattern in Ischemic and Hemorrhagic Events

Stroke is the culmination of a heterogeneous group of cerebrovascular diseases that is manifested as ischemia or hemorrhage of one or more blood vessels of the brain. The occurrence of many acute cardiovascular events--such as myocardial infarction, sudden cardiac death, pulmonary embolism, critical limb ischemia, and aortic aneurysm rupture--exhibits prominent 24 h patterning, with a major morning peak and secondary early evening peak. The incidence of stroke exhibits the same 24 h pattern. Although ischemic and hemorrhagic strokes are different entities and are characterized by different pathophysiological mechanisms, they share an identical double-peak 24 h pattern. A constellation of endogenous circadian rhythms and exogenous cyclic factors are involved. The staging of the circadian rhythms in vascular tone, coagulative balance, and blood pressure plus temporal patterns in posture, physical activity, emotional stress, and medication effects play central and/or triggering roles. Features of the circadian rhythm of blood pressure, in terms of their chronic and acute effects on cerebral vessels, and of coagulation are especially important. Clinical medicine has been most concerned with the prevention of stroke in the morning, when population-based studies show it is of greatest risk during the 24 h; however, improved protection of at-risk patients against stroke in the early evening, the second most vulnerable time of cerebrovascular accidents, has received relatively little attention thus far.

Sex-specific differences in cerebral arterial myogenic tone in hypertensive and normotensive rats

Cerebral blood flow (CBF) is maintained constant despite changes in systemic blood pressure (BP) through multiple mechanisms of autoregulation such as vascular myogenic reactivity. Our aim was to determine myogenic characteristics of cannulated middle cerebral arteries (MCA) in male and female stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto rats (WKY) at 12 wk of age under pressurised no-flow conditions. MCA pressure-diameter relationships (20–200 mmHg) were constructed in active (with calcium) and passive (without calcium) conditions, and myogenic and mechanical properties were determined. Myogenic reactivity in WKY ( P < 0.05) and SHRSP ( P < 0.05) males was impaired compared with their female counterparts. Comparison of SHRSP with WKY in males revealed similar myogenic reactivity, but in females SHRSP exhibited augmented myogenic reactivity ( P < 0.05). In both sexes, myogenic tone yielded at lower pressure in SHRSP compared with WKY vessels (120–140 vs. 140–180 mmHg). Stress-strain relationships and elastic moduli in WKY rats showed that vessels were stiffer in females than in males. Conversely, in SHRSP, male vessels were stiffer than female vessels. Comparison of strains in males indicated that stiffness was increased in SHRSP compared with WKY vessels, whereas the converse was observed in females. These findings demonstrate that MCA myogenic and distensibility characteristics exhibit significant sex- and strain-dependent differences. Inappropriate myogenic adaptation and augmented vascular stiffness, particularly in male SHRSP, are potential limiting factors in blood flow autoregulation and may increase the predisposition for stroke-related cerebrovascular events.

Neurovascular coupling in the normal brain and in hypertension, stroke, and Alzheimer disease

The brain is critically dependent on a continuous supply of blood to function. Therefore, the cerebral vasculature is endowed with neurovascular control mechanisms that assure that the blood supply of the brain is commensurate to the energy needs of its cellular constituents. The regulation of cerebral blood flow (CBF) during brain activity involves the coordinated interaction of neurons, glia, and vascular cells. Thus, whereas neurons and glia generate the signals initiating the vasodilation, endothelial cells, pericytes, and smooth muscle cells act in concert to transduce these signals into carefully orchestrated vascular changes that lead to CBF increases focused to the activated area and temporally linked to the period of activation. Neurovascular coupling is disrupted in pathological conditions, such as hypertension, Alzheimer disease, and ischemic stroke. Consequently, CBF is no longer matched to the metabolic requirements of the tissue. This cerebrovascular dysregulation is mediated in large part by the deleterious action of reactive oxygen species on cerebral blood vessels. A major source of cerebral vascular radicals in models of hypertension and Alzheimer disease is the enzyme NADPH oxidase. These findings, collectively, highlight the importance of neurovascular coupling to the health of the normal brain and suggest a therapeutic target for improving brain function in pathologies associated with cerebrovascular dysfunction.

Association of blunted nocturnal blood pressure dip with intracerebral hemorrhage

OBJECTIVES

Nondipping pattern of nocturnal blood pressure is associated with silent ischemic cerebrovascular lesions and lacunar infarctions. In this case-control study, we aimed to evaluate the association of diurnal blood pressure variation with the occurrence of intracerebral hemorrhage.

METHODS

Ambulatory blood pressure monitoring was performed at 21-28 days after ictus in 78 first-ever unselective consecutive patients with intracerebral hemorrhage and in 80 age-adjusted and sex-adjusted controls who were referred to the hypertension center of our institution. The degree of nocturnal blood pressure dip was calculated as [(mean daytime values-mean night-time values)/mean daytime values]x100. Nondippers were defined as patients who exhibited a <10% nocturnal dip in systolic blood pressure. Logistic regression models were constructed to assess the association of nondipping status with intracerebral hemorrhage after adjusting for potential confounders (cardiovascular risk factors, office and ambulatory blood pressure levels).

RESULTS

Prevalence of nondipping was significantly greater among cases than among controls (74.4% vs. 43.8%, P<0.001). Nondipping status was independently (P=0.033) associated with intracerebral hemorrhage (OR: 2.326, 95% CI: 1.068-5.050) in a multiple variable logistic regression model that adjusted for baseline characteristics, cardiovascular risk factors, office and ambulatory blood pressure variables. The magnitude of the nocturnal systolic blood pressure dipping was inversely related to the risk of intracerebral bleeding; the odds ratio for intracerebral hemorrhage associated with every 1% decrease in nocturnal systolic blood pressure dip was 1.143 (95% CI: 1.058-1.235, P=0.001).

CONCLUSIONS

Given the previous reports that nondipping contributes to the risk of cerebral infarction, our results indicate that blunted nocturnal blood pressure dip may be also associated with the occurrence of intracerebral hemorrhage.

Lipoprotein-associated phospholipase A2 is an independent marker for coronary endothelial dysfunction in humans

OBJECTIVE

The purpose of the current study was to determine whether lipoprotein-associated phospholipase A2 (Lp-PLA2) is associated with coronary endothelial dysfunction and is a predictor of endothelial dysfunction in humans.

METHODS AND RESULTS

Patients (172) with no significant coronary artery disease (<30% stenosis) undergoing assessment of coronary endothelial function were studied. Endothelial function was assessed by the change in coronary blood flow and coronary artery diameter in response to intracoronary acetylcholine. Plasma concentrations of Lp-PLA2 were measured, and patients were divided into tertiles. Patients in tertiles 2 and 3 had a significantly lower change in coronary blood flow (63.8+/-73.2 and 32.0+/-71.7 versus 78.4+/-73.2%; P<0.001) and greater epicardial coronary artery vasoconstriction (-14.1+/-14.7 and -23.3+/-25.1 versus -9.5+/-15.2% mean diameter change; P<0.001) in response to acetylcholine. Patients with coronary endothelial dysfunction had significantly higher serum concentrations of Lp-PLA2 than those with normal endothelial function (246.2+/-71.6 versus 209+/-56.7 ng/mL; P=0.001). The odds ratio for coronary endothelial dysfunction in patients with Lp-PLA2 in the highest tertile was 3.3 (95% CI, 1.6 to 6.6).

CONCLUSIONS

Lp-PLA2 is independently associated with coronary artery endothelial dysfunction and is a strong predictor of endothelial dysfunction in humans.

Relative contribution of Rho kinase and protein kinase C to myogenic tone in rat cerebral arteries in hypertension

Arterial smooth muscle constriction in response to pressure, i.e., myogenic tone, may involve calcium-dependent and calcium-sensitization mechanisms. Calcium sensitization in vascular smooth muscle is regulated by kinases such as PKC and Rho kinase, and activity of these kinases is known to be altered in cardiovascular disorders. In the present study, we evaluated the relative contribution of PKC and Rho kinase to myogenic tone in cerebral arteries in hypertension. Myogenic tone and arterial wall calcium in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were measured simultaneously, and the effect of PKC and Rho kinase inhibitors on myogenic tone was evaluated. SHR arteries showed significantly greater myogenic tone than WKY arteries. Pressure/wall tension-arterial wall calcium curves showed a hyperbolic relation in WKY rats, but the curves for SHR arteries were parabolic. Myogenic tone was decreased by the Rho kinase inhibitors Y-27632 and HA-1077, with a significantly greater effect in SHR than in WKY arteries. Reduction in myogenic tone produced by the PKC inhibitor bisindolylmaleimide I in WKY and SHR arteries was significantly less than that produced by Rho kinase inhibition. The pressure-dependent increase in myogenic tone was significantly decreased by Y-27632, and the decrease was markedly greater than that produced by bisindolylmaleimide I in SHR arteries. In WKY arteries, the pressure-dependent increase in myogenic tone was decreased to a similar extent by Y-27632 and bisindolylmaleimide I. These results suggest greater myogenic tone with increased calcium sensitization in SHR arteries, largely because of Rho kinase activation, with a minor contribution of PKC activation.

Common carotid artery intima-media thickness for the risk assessment of lacunar infarction versus intracerebral haemorrhage

BACKGROUND AND PURPOSE

Arterial hypertension is the major risk factor for intracerebral haemorrhage (ICH) and lacunar infarction (LI) and both types of cerebral lesions originate from pathology of the same deep perforating small arteries. We aimed to evaluate the relationship between vascular risk factors including common carotid artery intima-media thickness (CCA-IMT) with LI versus ICH.

METHODS

We prospectively collected data from 159 first ever stroke patients (67 cases with ICH and 92 cases with LI) with documented history of hypertension. All subjects underwent B-mode ultrasonographic measurements of the CCA-IMT. Logistic regression modelling was used to determine the factors (established vascular risk factors, severity and duration of hypertension, concomitant medications and CCA-IMT) that may significantly differentiate LI from ICH.

RESULTS

Patients with LI had significantly (p=0.002) larger CCA-IMT values (0.926 mm, 95% CI: 0.881-0.971) than subjects with ICH (0.815 mm, 95% CI: 0.762-0.868) even after adjusting for baseline characteristics and cardiovascular medications. The multivariate logistic regression procedure selected CCA-IMT, diabetes mellitus and hypercholesterolaemia as the only independent factors able to discriminate between LI and ICH. The risk for LI versus ICH increased continuously with increasing CCA-IMT. For each increment of 0.1 mm in CCA-IMT the probability of suffering from LI versus ICH increased by 36.6% (95 % CI: 13%-65.2%, p=0.001) even after adjustment for cardiovascular risk factors.

CONCLUSIONS

Increased CCA-IMT values are a factor favouring LI over ICH in hypertensive patients. The measurement of CCA-IMT may be a useful non-invasive diagnostic tool for the risk assessment of LI with respect to ICH in such patients.

Endothelial function and dysfunction. Part II: Association with cardiovascular risk factors and diseases. A statement by the Working Group on Endothelins and Endothelial Factors of the European Society of Hypertension*

Dysfunction of the vascular endothelium is a hallmark of most conditions that are associated with atherosclerosis and is therefore held to be an early feature in atherogenesis. However, the mechanisms by which endothelial dysfunction occurs in smoking, dyslipidaemia, hyperhomocysteinaemia, diabetes mellitus, arterial hypertension, cerebrovascular diseases, coronary artery disease and heart failure are complex and heterogeneous. Recent data indicate that endothelial dysfunction is often associated with erectile dysfunction, which can precede and predict cardiovascular disease in men. This paper will provide a concise overview of the mechanisms causing endothelial dysfunction in the different cardiovascular risk factors and disease conditions, and of the impact of the intervention measures and treatments.

The role of the renin–angiotensin system in malignant vascular injury affecting the systemic and cerebral circulations

Malignant hypertension is a rare but serious syndrome complicating 1% of essential hypertension and causing neurological, renal and cardiac complications. Despite improved anti-hypertensive medication, the incidence of this condition fails to decline. In the first part of this review, we discuss transgenic rat models of malignant hypertension, generated by over-expressing renin, to illustrate the role of the renin-angiotensin system in the development of systemic hypertensive vascular remodelling and hypertension. In the second part, we focus on the cerebrovascular response to hypertension and discuss new data using a conditional, transgenic model of malignant hypertension, the inducible hypertensive rat (IHR). Cerebral infarction associates strongly with hypertension in man and the mechanisms by which hypertension predisposes to different types of stroke remains poorly understood. Rats have similar cerebrovascular anatomy and structure to humans and as such provide a good experimental tool. To date, such models lack controllability and blood-pressure matched controls. Using the IHR, we have manipulated dietary salt and water intake to generate a novel, controllable stroke phenotype. Hypertensive small-vessel stroke develops over a predictable time period, permitting the study of developing cerebrovascular lesions. Systemic end-organ injury and hypertension are not affected. Dissociation of the systemic and central vascular responses in this way, will allow for comparative study of animals with equivalent hypertension, genetic background and systemic features of hypertension with or without stroke.

Isolation of a chromosome 1 region affecting blood pressure and vascular disease traits in the stroke-prone rat model

Recently, a genome-wide screen has shown a major quantitative trait locus (QTL) for a stroke-associated phenotype on rat chromosome 1 (RNO1) independent of QTL for blood pressure (BP) in the stroke-prone spontaneously hypertensive rat (SHRSP) of a Heidelberg colony. However, it remains to be elucidated whether these observations reflect the existence of different genes predisposing to each of the disorders. To address this issue, we performed comprehensive approaches in a Japanese colony, Izm, as follows. First, we undertook genome-wide searches in F1(SHRSP/IzmxWKY/Izm)xSHRSP/Izm back-cross (n=63) to pursue a causal relation between hypertension and stroke. Although the strongest linkage to BP (LOD score of 3.4) was identified on RNO1, its relevance to stroke was not supported in the F1 back-cross studied. Second, we also investigated linkage to BP in F2 progeny (n=175) involving the stroke-resistant (or normal) spontaneously hypertensive rat (SHR). In F2 studies of SHR/Izm, this locus did not appear to constitute a principal BP QTL. Third, we constructed congenic animals with detailed phenotype characterization. Transfer of a chromosomal fragment between markers Klk1 and D1Rat116 from WKY/Izm onto the SHRSP/Izm background lowered systolic BP by 20 to 80 mm Hg, prevented development of apparent stroke, and exaggerated impaired glucose tolerance. In conclusion, we have successfully isolated an RNO1 region affecting BP, stroke, and glucose tolerance in SHRSP/Izm-derived congenic rats. The size of the introgressed region is large, but our novel congenic strain should help delineate complex, genetic impairments underlying BP and associated vascular disease phenotypes.

Angiotensin II attenuates functional hyperemia in the mouse somatosensory cortex

We investigated whether angiotensin II (ANG II), a peptide that plays a central role in the genesis of hypertension, alters the coupling between synaptic activity and cerebral blood flow (CBF), a critical homeostatic mechanism that assures adequate cerebral perfusion to active brain regions. The somatosensory cortex was activated by stroking the facial whiskers in anesthetized C57BL/6J mice while local CBF was recorded by laser-Doppler flowmetry. Intravenous ANG II infusion (0.25 mug.kg-1.min-1) increased mean arterial pressure (MAP) from 82 +/- 2 to 102 +/- 3 mmHg (P < 0.05) without affecting resting CBF (P > 0.05). ANG II attenuated the CBF increase produced by whisker stimulation by 65% (P < 0.05) but did not affect the response to hypercapnia or to neocortical application of the nitric oxide donor S-nitroso-N-acetyl penicillamine (P > 0.05). The effect of ANG II on functional hyperemia persisted if the elevation in MAP was offset by controlled hemorrhage or prevented by topical application of the peptide to the activated cortex. ANG II did not reduce the amplitude of the P1 wave of the field potentials evoked by whisker stimulation (P > 0.05). Infusion of phenylephrine increased MAP (P > 0.05 from ANG II) but did not alter the functional hyperemic response (P > 0.05). The data suggest that ANG II alters the coupling between CBF and neural activity. The mechanisms of the effect are not related to the elevation in MAP and/or to inhibition of the synaptic activity evoked by whisker stimulation. The imbalance between CBF and neural activity induced by ANG II may alter the homeostasis of the neuronal microenvironment and contribute to brain dysfunction during ANG II-induced hypertension.

Coronary endothelial dysfunction is associated with an increased risk of cerebrovascular events

BACKGROUND

Stroke, mainly attributable to atherothrombotic disease, represents a leading cause of disability and death in the Western world. Endothelial dysfunction, which is considered a key factor in atherogenesis, is associated with an increased risk of cardiovascular events. However, the magnitude of the association between coronary endothelial dysfunction (CED) and cerebrovascular events is unknown. This study was performed to investigate the association between CED and cerebrovascular events.

METHODS AND RESULTS

We studied 503 patients without obstructive coronary artery disease (CAD) who underwent coronary endothelial function testing by intracoronary acetylcholine infusion. Patients were divided according to the presence (n=305) or absence (n=198) of CED, and medical records were examined for the occurrence of ischemic or hemorrhagic stroke or transient ischemic attack either before (prevalent) or after (incident) coronary endothelial function testing. Among the study population, a total of 25 cerebrovascular events were documented, 22 in patients with CED (15 prevalent) and 3 in patients without (all prevalent) (P=0.008). Multivariable logistic regression, which included traditional cerebrovascular disease-related risk factors, identified the presence of CED as the single strongest factor associated with cerebrovascular events (OR, 4.32; 95% CI, 1.26 to 14.83). Kaplan-Meier analysis indicated that patients with CED had a significantly higher cumulative cerebrovascular event rate than those without (P=0.04).

CONCLUSIONS

Presence of CED in patients without obstructive CAD is independently associated with an increased risk of cerebrovascular events. Thus, detection of this early stage of atherosclerosis may provide important information to identify patients who benefit from aggressive preventive strategies.

Strokes and their relationship to hypertension

PURPOSE OF REVIEW

There is rapidly growing appreciation that stroke morbidity and the risk of an ischaemic stroke becoming haemorrhagic can be influenced by new information about prophylaxis, rapid diagnosis and treatment.

RECENT FINDINGS

Strokes are strongly associated with hypertension mainly because hypertension is strongly associated with atheromatous deposits blocking or narrowing brain arteries, predisposing to local clot formation. Atheroma and its ischaemic consequences may damage cerebral arterioles and the brain tissue they supply. Cerebral infarcts are more common than spontaneous cerebral haemorrhages. High blood pressure itself cannot directly rupture cerebral blood vessels because their small size protects them and intracerebral haemorrhage usually follows previous ischaemic vascular damage. It is obvious that lowering blood pressure would reduce the risk and extent of bleeding into the brain once a break in an arteriolar wall has occurred, but it is not clear why lowering blood pressure should protect against cerebral infarction. One might expect that slowing down the rate of cerebral blood flow would give more time for local clots to form. It seems most likely that induced hypotension protects against ischaemic strokes by preventing pressure- or ischaemia-induced arteriolar spasm and by advantageous vasodilation of some of the more ischaemic territories. Added protection can be provided by coenzyme-A reductase inhibitors (statins), but probably not by antioxidants.

SUMMARY

Lowering blood pressure strongly protects against ischaemic and haemorrhagic stroke. Recent work shows that more accurate and faster diagnosis of stroke pathology is urgently needed, so that appropriate treatment (e.g. with tissue plasminogen activators) can be started before local bleeding has occurred.