Structure Of Cerebral Arterioles Research Articles

Abstract 70: Eplerenone Increases Dilation and the Diameter of Cerebral Penetrating Arterioles in Rats with Sustained Hypertension

Hypertension is linked to dementia in humans, as well as remodeling and dysfunction in large cerebral arteries. The effects of hypertension on cerebral microvessels, such as penetrating arterioles (PenA), are still unknown. These arterioles are the bottlenecks bridging the pial circulation to the deep parenchymal microcirculation, and they are vital for neurovascular coupling and functional hyperemia. Mineralocorticoid receptor (MR) antagonism reverses hypertension-induced changes in large cerebral arteries. Thus, we hypothesized that MR antagonism will improve PenA dilation and structure in adult rats with sustained hypertension. Twelve-week-old male stroke-prone spontaneously hypertensive rats (SHRSP) were treated with the MR antagonist eplerenone (EPL, 100mg/kg/day) or placebo for 6 weeks. PenA function and structure were studied by pressure myography. Data are means±SEM at 60mmHg intralumenal pressure, placebo vs EPL. Myogenic tone generation was not different between groups (%myogenic tone: 40.3±2.3 vs 41.3±2.0). PenA diameter after tone was higher in EPL (42.47±1.5 vs 49.21±2.4μm, p=0.02, t-test). Dilation of PenA to nifedipine (calcium channel blocker) was improved after EPL treatment, as evidenced by an increase in diameter change (10μM nifedipine: 13.44±1.94 vs 18.44±2.39μm, p<0.01, Two-way ANOVA) and PenA diameter (10μM nifedipine: 58.01±2.28 vs 68.58±3.74μm, p<0.01, Two-way ANOVA). PenA passive structure was improved in SHRSP+EPL, as evidenced by an increase in PenA diameter (65.67±1.17 vs 81.00±5.11, p<0.01, Two-way ANOVA) and lumen diameter (55.17±1.8 vs 73.00±5.00, p<0.01, Two-way ANOVA), and a reduction in the wall-to-lumen ratio (0.10±0.01 vs 0.07±0.01, p<0.01, Two-way ANOVA). PenA stiffness was increased after EPL (β-coefficient: 10.91±0.93 vs 14.84±1.83, p=0.03, t-test), but distensibility was unchanged (24.45±3.20 vs 21.88±2.68). These data suggest that MR antagonism improves the structure of cerebral arterioles and their responsiveness to calcium channel blockade in adult rats with sustained hypertension. These improvements have the potential to reduce the risk of developing vascular cognitive impairments and dementia in chronically hypertensive subjects.

Nox2 Deficiency Prevents Hypertension-Induced Vascular Dysfunction and Hypertrophy in Cerebral Arterioles

Oxidative stress is involved in many hypertension-related vascular diseases in the brain, including stroke and dementia. Thus, we examined the role of genetic deficiency of NADPH oxidase subunit Nox2 in the function and structure of cerebral arterioles during hypertension. Arterial pressure was increased in right-sided cerebral arterioles with transverse aortic banding for 4 weeks in 8-week-old wild-type (WT) and Nox2-deficient (-/y) mice. Mice were given NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg) or vehicle to drink. We measured the reactivity in cerebral arterioles through open cranial window in anesthetized mice and wall cross-sectional area and superoxide levels ex vivo. Aortic constriction increased systolic and pulse pressures in right-sided carotid arteries in all groups of mice. Ethidium fluorescence showed increased superoxide in right-sided cerebral arterioles in WT, but not in Nox2-/y mice. Dilation to acetylcholine, but not sodium nitroprusside, was reduced, and cross-sectional areas were increased in the right-sided arterioles in WT, but were unchanged in Nox2-/y mice. L-NAME reduced dilation to acetylcholine but did not result in hypertrophy in right-sided arterioles of Nox2-/y mice. In conclusion, hypertension-induced superoxide production derived from Nox2-containing NADPH oxidase promotes hypertrophy and causes endothelial dysfunction in cerebral arterioles, possibly involving interaction with nitric oxide.

Oxidative Stress, Vascular Remodeling, and Vascular Inflammation in Hypertension

Hypertension is a major public health problem worldwide, affecting over 50 million individuals in the United States alone. The modern history of hypertension begins with the understanding of the cardiovascular system with the work of the physician William Harvey (1578–1657), who described the circulation of blood in his book De Motu Cordis. The English clergyman Stephen Hales made the first published measurement of blood pressure in 1733. Frederick Akbar Mahomed (1849–1884) made the first report of elevated blood pressure in a person without evidence of kidney disease. However, hypertension as a clinical entity came into being in 1896 with the invention of the cuff-based sphygmomanometer by Scipione Riva-Rocci. This apparatus has allowed the measurement of the blood pressure into the clinic. In 1905, Nikolai Korotkoff improved the technique by describing the Korotkoff sounds that are heard when the artery is auscultated with a stethoscope while the sphygmomanometer cuff is deflated. The concept of essential hypertension (“hypertonic essential”) was introduced in 1925 by the physiologist Otto Frank to describe elevated blood pressure for which no cause could be found. Over the several decades, increasing evidence accumulated from actuarial reports and longitudinal studies, such as the Framingham Heart Study. In the actuality, the term “inflammation” is used in the context of cardiovascular disease as a catchall referring to nonspecific phenomena, such as elevation of C-reactive protein. Most clinicians and investigators find this vague and difficult to understand. In this issue, we will attempt to address some of these puzzling questions. In this way, several authors write on oxidative stress in the pathophysiology of target organ damage. G. Csanyi and P. J. Pagano postulated that peptides mimicking the Nox4 B-loop and regions C-terminus on inhibit Nox4 activity and their findings suggest that Nox4 exists in a tightly assembled and active conformation which, unlike other Noxes, cannot be disrupted by conventional means. R. O. Maranon et al. demonstrated, in nonischemic 5/6 nephrectomized rat (NefR), a model of chronic kidney disease, that tempol improves NO-contents and basal tone, without decrease MAP, indicating that oxidative stress could be implicated early and independently to hypertension, in the vascular alterations. B. P. Campagnaro et al. proposed that the non-hemodynamic effects of angiotensin II are important for the damage observed in the two-kidney, one-clip (2K1C) renovascular hypertension model and demonstrated that 2K1C hypertensive mice have an elevated lymphocyte count, while undifferentiated bone marrow mononuclear cells counts were diminished. N. Arias et al. describe mechanisms associated with inflammation and oxidative stress in the brain. N. Arias et al., in their study, examined the differential contribution of these leading factors to the oxidative metabolism of diverse brain limbic system regions frequently involved in memory process by histochemical labelling of cytochrome oxidase (COx). S.-L. Chan and G. L. Baumbach examined the role of genetic deficiency of NAD(P)H-oxidase subunit Nox2 in the function and structure of cerebral arterioles during hypertension and concluded that hypertension-induced superoxide production derived from Nox2-containing NADPH oxidase promotes hypertrophy and causes endothelial dysfunction in cerebral arterioles, possibly involving interaction with nitric oxide. On the other hand, J. Alvarez-Camacho et al. describe the pathophysiologic link between the metabolic syndrome, obesity, hypertension, and adipokines at experimental and clinical level. J. Alvarez-Camacho et al. addresse topics related to modern aspects in the pathophysiology of hypertension such as the role of inflammation, environment, epigenetics, and adiponectin in hypertension, and Y. Mendizabal et al. discuss the central role of hypertension and vascular inflammation in metabolic syndrome and the role of sympathetic tone. Subsequently, they examine the link between endothelial dysfunction and insulin resistance. Finally, animal models used in the study of vascular function of metabolic syndrome are reviewed, in particular, the Zucker fatty rat and the spontaneously hypertensive obese rat (SHROB). N. F. Renna et al. conducted a review of the mechanisms involved in the physiopathological vascular changes, adaptive and maladaptive, called vascular remodeling and the involvement of inflammatory mechanisms. Finally, D. M. Babbitt et al. performed their analysis on a clinical protocol that demonstrated that aerobic exercise training might be a viable, nonpharmacological method to improve inflammation status and endothelial function and thereby contribute to risk reduction for cardiovascular disease in African Americans. In conclusion, the observed elevation in inflammatory parameters in subjects who subsequently go on to develop hypertension is particularly relevant and creates options for potential primary prevention strategies. A number of therapeutic agents have been identified which are able to influence this inflammatory process and positively influence cardiovascular outcomes. Nicolas Federico Renna

Protecting the Brain With eNOS

See related article, pages 1132–1140 Nitric oxide (NO) plays a major role in both vascular and neural biology in health and disease. This concept is exemplified when one examines the role of NO in the brain and the cerebral circulation. NO is a potent vasodilator, and blood vessels in the brain are normally exposed to NO from 2 major sources—endothelium and neurons. Acting as a messenger molecule, NO mediates the majority of endothelium-dependent responses in the brain.1 The source of this NO is the endothelial isoform of NO synthase (eNOS). This prominent role for NO has been observed in a variety of blood vessels from multiple species including humans.1–3 Through this signaling mechanism, NO influences resting vascular tone and mediates responses to varied stimuli, including endothelium-dependent agonists and increases in blood flow (Figure).1,4,5 In addition, eNOS inhibits vasoconstrictor responses and cerebral vasospasm6–8 and can affect permeability of cerebral endothelium, the blood-brain barrier (Figure).9 eNOS normally inhibits cerebral vascular growth or hypertrophy (Figure),10 a structural change that can have functional consequences by impairing of maximal vasodilator capacity. Impairment of NO-mediated signaling is a key underlying mechanism of vascular dysfunction in diverse forms of disease and aging.1,11–13 Impairment of these eNOS-dependent mechanisms in the presence of cardiovascular risk factors may contribute to …

Editorial Comment: eNOS: Can We Exploit the Good?

HomeStrokeVol. 36, No. 1Editorial Comment: eNOS: Can We Exploit the Good? Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBEditorial Comment: eNOS: Can We Exploit the Good? Frank M. Faraci, PhD Frank M. FaraciFrank M. Faraci Departments of Internal Medicine and Pharmacology, Cardiovascular Center, University of Iowa Carver College of Medicine, Iowa City, Iowa Search for more papers by this author Originally published1 Jan 2005https://doi.org/10.1161/01.str.0000152179.37900.8dStroke. 2005;36:160–161One of the major functions of vascular endothelium is to regulate tone of underlying smooth muscle. This function is mediated in large part by release of diverse endothelium-derived relaxing factors (EDRFs).1,2 A major EDRF that regulates both cerebral vascular function and structure is nitric oxide (NO) produced by the endothelial isoform of NO synthase (eNOS).1,3 Most studies indicate that NO is the predominant EDRF in the cerebral circulation.1 Although dozens of studies in animal models support this view, it is important to recall that NO is also a major EDRF in both large arteries and microvessels in the human brain.1,4In the present study by Sorenson et al,5 the investigators examined effects of gene transfer of a mutant form of eNOS (S1179DeNOS) that is constitutively active (ie, active in the absence of agonist induced stimulation) on vascular function in human pial arteries obtained at the time of surgery. Because eNOS has many beneficial effects within the vessel wall, it was of interest to examine effects of expression of S1179DeNOS on vascular function.Expression of S1179DeNOS increased basal levels of cyclic GMP, a key second messenger in relation to NO-mediated signaling, and reduced responses to an endothelium-dependent agonist and an NO donor. Reduced responses to NO in vessels that express S1179DeNOS probably reflects a compensatory response within vascular muscle because of increase basal levels of NO.Reduced responses to NO in these experiments did not appear to be mediated by oxidative stress as a scavenger of the free radical superoxide had no effect on impaired responses. This observation is important as increased activity of eNOS could potentially deplete enzyme substrate (l-arginine) or cofactors (ie, tetrahydrobiopterin), resulting in ‘uncoupling’ of eNOS and production of superoxide rather than NO.The use of viral-mediated gene transfer of NOS isoforms to study the impact of NO on the vasculature is a relatively recent experimental approach. The strategy allows testing of basic biology of the vasculature but is also attractive as it may lay the framework, or at least establish proof-of-principle, for future therapeutic applications using viral vectors. To my knowledge, only two studies have used adenoviral vectors to express any gene in human cerebral arteries.6,7 The present work suggests that gene transfer of a constitutively active form of eNOS alters vascular function in these arteries. Because the vector used appears to increase basal levels of NO without increasing superoxide levels, it may have beneficial effects in models of cerebral vascular disease. This latter possibility remains to be tested.References1 Faraci FM, Heistad DD. Regulation of the cerebral circulation: role of endothelium. Physiological Reviews. 1998; 78: 53–97.CrossrefMedlineGoogle Scholar2 Bryan RM, You J, Golding EM, Marrelli SP. Endothelium-derived hyperpolarizing factor: a cousin to nitric oxide and prostacyclin. Anesthesiology. (In press).Google Scholar3 Baumbach GL, Sigmund CD, Faraci FM. Structure of cerebral arterioles in mice deficient in expression of the gene for endothelial NO synthase. Circulation Res. 2004; 95: 822–829.LinkGoogle Scholar4 Elhusseiny A, Hamel E. Muscarinic –but not nicotinic –acetylcholine receptors mediate a nitric oxide-dependent dilation in brain cortical arterioles: a possible role for the M5 receptor subtype. J Cerebral Blood Flow Metabol. 2000; 20: 298–305.CrossrefMedlineGoogle Scholar5 Sorenson J, Santhanam AVR, Smith LA, Akiyama M, Sessa WC, Katusic ZS. Expression and function of recombinant S1179D endothelial nitric oxide synthase in human pial arteries. Stroke. 2005; 36: 158–160.LinkGoogle Scholar6 Khurana VG, Smith LA, Weiler DA, Springett MJ, Parisi JE, Meyer FB, Marsh WR, O’Brien T, Katusic ZS. Adenovirus-mediated gene transfer to human cerebral arteries. J Cerebral Blood Flow Metabol. 2000; 20: 1360–1371.CrossrefMedlineGoogle Scholar7 Gunnett CA, Lund DD, Howard MA, Chu Y, Faraci FM, Heistad DD. Gene transfer of inducible nitric oxide synthase impairs relaxation in human and rabbit cerebral arteries. Stroke. 2002; 33: 2292–2296.LinkGoogle Scholar Previous Back to top Next FiguresReferencesRelatedDetails January 2005Vol 36, Issue 1 Advertisement Article InformationMetrics https://doi.org/10.1161/01.str.0000152179.37900.8dPMID: 15618450 Originally publishedJanuary 1, 2005 PDF download Advertisement

Structure of cerebral arterioles in mice deficient in expression of the gene for endothelial nitric oxide synthase.

We examined effects of pharmacological inhibition of nitric oxide synthase (NOS) and genetic deficiency of the endothelial isoform of NOS (eNOS) on structure and mechanics of cerebral arterioles. We measured pressure, diameter, and cross-sectional area (CSA) of the vessel wall (histologically) in maximally dilated cerebral arterioles in mice that were untreated or treated for 3 months with the NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME; 10 mg/kg per day in drinking water). Treatment with L-NAME increased systemic arterial mean pressure (SAP; 143+/-4 versus 121+/-4 mm Hg, P<0.05) and CSA (437+/-27 versus 310+/-34 microm2, P<0.05). These findings suggest that hypertension induced in mice by NOS inhibition is accompanied by hypertrophy of cerebral arterioles. To determine the role of the eNOS isoform in regulation of cerebral vascular growth, we examined mice with targeted disruption of one (heterozygous) or both (homozygous) genes encoding eNOS. Wild-type littermates served as controls. SAP and CSA were significantly increased in homozygous (SAP, 141+/-5 versus 122+/-3 mm Hg in wild-type mice, P<0.05; CSA, 410+/-18 versus 306+/-15 microm2 in wild-type mice, P<0.05), but not in heterozygous (SAP, 135+/-4 mm Hg; CSA, 316+/-32 microm2) eNOS-deficient mice. Carotid ligation normalized cerebral arteriolar pulse pressure did not prevent increases in CSA in homozygous eNOS-deficient mice. Thus, cerebral arterioles undergo hypertrophy in homozygous eNOS-deficient mice, even in the absence of increases in arteriolar pulse pressure. These findings suggest that eNOS plays a major role in regulation of cerebral vascular growth.

Effects of chronic nitric oxide synthase inhibition on cerebral arterioles in Wistar-Kyoto rats.

Cerebral arterioles in stroke-prone spontaneously hypertensive rats (SHRSP), but not in Sprague-Dawley rats with hypertension induced by nitric oxide (NO) synthase inhibition, undergo inward remodeling. The goal of this study was to determine whether development of vascular inward remodeling may depend on genetic factors. We examined effects of NO synthase inhibition on the structure of cerebral arterioles in Wistar-Kyoto rats (WKY), a rat strain genetically distinct from Sprague-Dawley. Pressure (servonull), diameter (cranial window) and cross-sectional area of the vessel wall (CSA, histologically) were measured in maximally dilated (EDTA) cerebral arterioles in WKY, untreated (n = 8) or treated for 3 months with the NO synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) (10 mg/kg per day, n = 10) in the drinking water, and in untreated SHRSP (n = 7). Treatment with L-NAME in WKY increased mean cerebral arteriolar pressure (69 +/- 7 versus 47 +/- 7 mmHg, P < 0.05) and pulse pressure (30 +/- 3 versus 17 +/- 1 mmHg, P < 0.05) to levels significantly lower than in SHRSP (98 +/- 5 and 35 +/- 1 mmHg respectively, P < 0.05). CSA was significantly greater in L-NAME-treated WKY and SHRSP than in untreated WKY (1692 +/- 50 and 1525 +/- 98 microm respectively, versus 1224 +/- 85, P < 0.05). External diameter was significantly less in L-NAME-treated WKY than in untreated WKY (119 +/- 5 versus 135 +/- 4 microm, P < 0.05) but significantly greater than in SHRSP (98 +/- 1 microm, P < 0.05). Cerebral arterioles undergo hypertrophy and remodeling in WKY with L-NAME-induced hypertension. These findings suggest that genetic factors present in WKY and SHRSP may play a role in the development of vascular inward remodeling during chronic hypertension in rats.

Hyperhomocysteinemia, Oxidative Stress, and Cerebral Vascular Dysfunction

An elevated circulating concentration of the sulfur-containing amino acid homocysteine, hyperhomocysteinemia, produces complex changes within the blood vessel wall. In the peripheral circulation, these changes include oxidative stress, proinflammatory effects such as expression of tumor necrosis factor-α and inducible nitric oxide (NO) synthase (iNOS), and endothelial dysfunction.1–6 Hyperhomocysteinemia-induced oxidative stress may occur as a result of decreased expression and/or activity of key antioxidant enzymes as well as increased enzymatic generation of superoxide anion (the precursor for multiple reactive oxygen and reactive nitrogen species).2,4 Do hyperhomocysteinemia-induced changes occur in the cerebral circulation and why are they potentially important? Hyperhomocysteinemia is a an emerging risk factor for carotid artery disease (atherosclerosis) and stroke and is associated with Alzheimer’s disease and vascular dementia.7–11 It was not until relatively recently, however, that experimental studies began to define the impact of hyperhomocysteinemia on cerebral vascular biology and the molecular mechanisms that account for these changes. This work has been facilitated by the development of mouse models with genetic alterations in different components of the homocysteine metabolic pathway (see below). Early work in the cerebral microcirculation observed that acute local administration of a very high concentration of homocysteine (1 mmol/L) in the presence of exogenous Cu2+ produced superoxide-mediated reductions in resting cerebral blood flow (CBF) as well as attenuation of endothelium-dependent and NO-mediated responses.12 Our group was among the first to show that mild chronic hyperhomocysteinemia produces endothelial dysfunction in the carotid artery.1,13 Moderate hyperhomocysteinemia, induced by acute methionine loading, …

Drug-induced changes in mechanics and structure of cerebral arterioles

Cerebral arterioles in stroke-prone spontaneously hypertensive rats (SHRSP) undergo remodeling with a reduction in external diameter, paradoxically becoming more distensible, despite hypertrophy of the vessel wall. Two concepts have been proposed. (1) Remodeling of cerebral arterioles is an important mechanism, in addition to hypertrophy, of encroachment on the vascular lumen in SHRSP. (2) Increases in arteriolar distensibility partly compensate cerebral arterioles for other factors, such as hypertrophy and remodeling, which reduce the dilator capacity of these arterioles in chronic hypertension. Recently, we have studied the effects of reducing blood pressure by drug treatment or carotid clipping on hypertrophy and remodeling of cerebral arterioles in SHRSP. Our findings suggest that (1) pulse pressure may be a more important stimulus than mean pressure for hypertrophy of cerebral blood vessels and (2) remodeling of cerebral arterioles may occur independently of hypertrophy. Treatment that effectively prevents vascular hypertrophy during chronic hypertension may not be effective in preventing remodeling, and may therefore fail to restore cerebral vascular function to normal.