Early narrowed afferent arteriole is a contributor to the development of hypertension

Vascular remodelling in cardiovascular diseases: hypertension, oxidation, and inflammation

Optimal vascular structure and function are essential for maintaining the physiological functions of the cardiovascular system. Vascular remodelling involves changes in vessel structure, including its size, shape, cellular and molecular composition. These changes result from multiple risk factors and may be compensatory adaptations to sustain blood vessel function. They occur in diverse cardiovascular pathologies, from hypertension to heart failure and atherosclerosis. Dynamic changes in the endothelium, fibroblasts, smooth muscle cells, pericytes or other vascular wall cells underlie remodelling. In addition, immune cells, including macrophages and lymphocytes, may infiltrate vessels and initiate inflammatory signalling. They contribute to a dynamic interplay between cell proliferation, apoptosis, migration, inflammation, and extracellular matrix reorganisation, all critical mechanisms of vascular remodelling. Molecular pathways underlying these processes include growth factors (e.g., vascular endothelial growth factor and platelet-derived growth factor), inflammatory cytokines (e.g., interleukin-1β and tumour necrosis factor-α), reactive oxygen species, and signalling pathways, such as Rho/ROCK, MAPK, and TGF-β/Smad, related to nitric oxide and superoxide biology. MicroRNAs and long noncoding RNAs are crucial epigenetic regulators of gene expression in vascular remodelling. We evaluate these pathways for potential therapeutic targeting from a clinical translational perspective. In summary, vascular remodelling, a coordinated modification of vascular structure and function, is crucial in cardiovascular disease pathology.

Specialized Pro-Resolving Lipid Mediators: New Therapeutic Approaches for Vascular Remodeling

Vascular remodeling is a typical feature of vascular diseases, such as atherosclerosis, aneurysms or restenosis. Excessive inflammation is a key mechanism underlying vascular remodeling via the modulation of vascular fibrosis, phenotype and function. Recent evidence suggests that not only augmented inflammation but unresolved inflammation might also contribute to different aspects of vascular diseases. Resolution of inflammation is mediated by a family of specialized pro-resolving mediators (SPMs) that limit immune cell infiltration and initiate tissue repair mechanisms. SPMs (lipoxins, resolvins, protectins, maresins) are generated from essential polyunsaturated fatty acids. Synthases and receptors for SPMs were initially described in immune cells, but they are also present in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs), where they regulate processes important for vascular physiology, such as EC activation and VSMC phenotype. Evidence from genetic models targeting SPM pathways and pharmacological supplementation with SPMs have demonstrated that these mediators may play a protective role against the development of vascular remodeling in atherosclerosis, aneurysms and restenosis. This review focuses on the latest advances in understanding the role of SPMs in vascular cells and their therapeutic effects in the vascular remodeling associated with different cardiovascular diseases.

Changes in retinal vascular diameters in senior and geriatric cats in association with variation in systemic blood pressure

OBJECTIVES

Early diagnosis of arterial hypertension is essential to prevent target organ damage. In humans, retinal arteriolar narrowing predicts hypertension. This blinded prospective observational study investigated the retinal vessel diameters in senior and geriatric cats of varying systolic blood pressure (SBP) status and evaluated retinal vascular changes in hypertensive cats after treatment.

METHODS

Cats with a median age of 14 years (range 9.1-22 years) were categorised into five groups: group 1, healthy normotensive (SBP <140 mmHg; n = 40) cats; group 2, pre-hypertensive (SBP 140-160 mmHg; n = 14) cats; group 3, cats with chronic kidney disease (CKD) and normotensive (n = 26); group 4, cats with CKD and pre-hypertensive (n = 13); and group 5, hypertensive cats (SBP >160 mmHg, n = 15). Colour fundus images (Optibrand ClearView) were assessed for hypertensive lesions. Retinal vascular diameters and bifurcation angles were annotated and calculated using the Vascular Assessment and Measurement Platform for Images of the Retina annotation tool (VAMPIRE-AT). When available, measurements were obtained at 3 and 6 months after amlodipine besylate treatment.

RESULTS

Ten hypertensive cats had retinal lesions, most commonly intraretinal haemorrhages and retinal exudates. Arteriole and venule diameters decreased significantly with increasing age (-0.17 ± 0.05 pixels/year [P = 0.0004]; -0.19 ± 0.05 pixels/year). Adjusted means ± SEM for arteriole and venule diameter (pixels) were 6.3 ± 0.2 and 8.9 ± 0.2 (group 1); 7.6 ± 0.3 and 10.1 ± 0.4 (group 2); 6.9 ± 0.2 and 9.5 ± 0.3 (group 3); 7.4 ± 0.3 and 10.0 ± 0.4 (group 4); and 7.0 ± 0.3 and 9.8 ± 0.4 (group 5). Group 1 arteriole and venule diameters were significantly lower than those of groups 2 and 4. Group 2 arteriole bifurcation angle was significantly narrower than those of groups 1 and 3. Post-treatment, vessel diameters decreased significantly at 3 and 6 months in seven hypertensive cats.

CONCLUSIONS AND RELEVANCE

Increased age was associated with reduced vascular diameters. Longitudinal studies are required to assess if vessel diameters are a risk indicator for hypertension in cats.

Pancreatic Microcirculation Profiles in the Progression of Hypertension in Spontaneously Hypertensive Rats

BACKGROUND

Emerging evidence indicates that the pancreas serves as a major source of degrading protease activities and that uncontrolled proteolytic receptor cleavage occurs under hypertensive conditions, which leading to systemic dysfunction and end-organic damage. However, changes in pancreatic microcirculation profiles during the progression of hypertension remain unknown.

METHODS

Pancreatic microcirculatory blood distribution patterns and microvascular vasomotion of spontaneously hypertensive rats (SHRs) and normotensive control Wistar Kyoto rats at 5, 8, 13, and 18 weeks of age were determined. Wavelet transform analysis was performed to convert pancreatic microhemodynamic signals into time-frequency domains and construct 3-dimensional spectral scalograms. The amplitudes of characteristic oscillators including endothelial, neurogenic, myogenic, respiratory, and cardiac oscillators were compared among groups. Plasma nitrite/nitrate levels were measured using a Griess reaction. Additionally, endothelin-1, malondialdehyde, superoxide dismutase, and interleukin-6 levels were determined by enzyme-linked immunosorbent assay.

RESULTS

SHRs exhibited a reduced blood distribution pattern with progressively decreased average blood perfusion, amplitude, and frequency of microvascular vasomotion. Wavelet transform spectral analysis revealed significantly reduced amplitudes of endothelial oscillators from 8- to 18-week-old SHRs. Additionally, the blood microcirculatory chemistry complements explained the microhemodynamic profiles partially, as demonstrated by an increase in plasma nitrite/nitrate, endothelin-1, malondialdehyde, and interleukin-6 levels and a decreased superoxide dismutase level in SHRs.

CONCLUSIONS

Pancreatic microcirculation profiles are abnormal in the progression of hypertension in SHRs, including a disarranged blood distribution pattern, impaired microvascular vasomotion, and reduced amplitudes of endothelial oscillators.

Reactive oxygen species in renal vascular function

Reactive oxygen species (ROS) are produced by the aerobic metabolism. The imbalance between production of ROS and antioxidant defence in any cell compartment is associated with cell damage and may play an important role in the pathogenesis of renal disease. NADPH oxidase (NOX) family is the major ROS source in the vasculature and modulates renal perfusion. Upregulation of Ang II and adenosine activates NOX via AT1R and A1R in renal microvessels, leading to superoxide production. Oxidative stress in the kidney prompts renal vascular remodelling and increases preglomerular resistance. These are key elements in hypertension, acute and chronic kidney injury, as well as diabetic nephropathy. Renal afferent arterioles (Af), the primary resistance vessel in the kidney, fine tune renal hemodynamics and impact on blood pressure. Vice versa, ROS increase hypertension and diabetes, resulting in upregulation of Af vasoconstriction, enhancement of myogenic responses and change of tubuloglomerular feedback (TGF), which further promotes hypertension and diabetic nephropathy. In the following, we highlight oxidative stress in the function and dysfunction of renal hemodynamics. The renal microcirculatory alterations brought about by ROS importantly contribute to the pathophysiology of kidney injury, hypertension and diabetes.

Relationship between subtle urinary albumin excretion and risk of incident hypertension: modification by glomerular filtration rate

It has been reported that an increase in urinary albumin excretion (UAE) within the normal range could be a risk factor for incident hypertension. However, it remains unclear how the subtle increases in UAE and renal function interact in the development of hypertension. We examined the modification of UAE as a risk factor for incident hypertension by glomerular filtration rate (GFR) in the Japanese population. We prospectively followed 1281 normotensive individuals from Watari town (34.3% men; mean age, 58.0±12.3 years old) whose UAE was <30 mg g⁻¹· Cr. Hypertension was diagnosed as a systolic blood pressure (BP)⩾140 mm Hg and/or a diastolic BP⩾90 mm Hg, or antihypertensive medication use. The relationship between sex-specific quartiles of UAE and incident hypertension was examined with Cox proportional hazard analysis. During a mean follow-up of 3.7 years, 315 individuals developed hypertension. Multivariate Cox proportional hazard analysis revealed that a subtle increase in UAE was a risk factor for incident hypertension, but there was a significant interaction between UAE and estimated GFR (eGFR) (P=0.018). The risk of incident hypertension dose dependently increased in the highest eGFR quartile (⩾90 ml min⁻¹ per 1.73 m²). Decline in renal function alone increased the risk of incident hypertension but the increased risk with a subtle increase in UAE became smaller and less clear in the lower eGFR quartiles. The present data suggest that UAE as a risk factor for incident hypertension is largely dependent on eGFR levels.

Persistent effect of treatment with candesartan cilexetil on blood pressure in spontaneously hypertensive rats

We have investigated whether the angiotensin II type-1 (AT1) receptor antagonist, candesartan cilexetil, has a persistent effect on blood pressure even after withdrawal of treatment, as has been shown consistently for angiotensin-converting enzyme inhibitors (ACE-1). Spontaneously hypertensive rats (SHR) were divided into four groups (n=16 per group) and treated with candesartan cilexetil (high-dose: 5 mg/kg/day; middle-dose: 1 mg/kg/day; low-dose: 0.5 mg/kg/day) or control from age four weeks to 20 weeks. Normotensive Wistar-Kyoto rats (WKY) were also investigated. The drug was given in the drinking water, the concentration adjusted for water consumption and rat weight. Blood pressure (BP) was measured regularly by the indirect tail-cuff method during the treatment period and after treatment, from age 20 weeks to 32 weeks.

At age 20 weeks, candesartan treatment had caused a slight reduction in body weight, an increase in water consumption and a reduction in heart rate. During treatment, candesartan caused a dose-dependent reduction in BP. After withdrawal of treatment, BP increased but remained lower than that of untreated control SHR for the medium- and high-dose groups throughout the follow-up period, the reduction being 8—11% at the end of follow-up. At age 32 weeks, there was no significant difference between the three candesartan-treated groups.

We conclude that treatment with the AT1-receptor antagonist candesartan has a modest persistent effect on BP after withdrawal of treatment.

NADPH oxidases and vascular remodeling in cardiovascular diseases

Reactive oxygen species (ROS) are key signaling molecules that regulate vascular function and structure in physiological conditions. A misbalance between the production and detoxification of ROS increases oxidative stress that is involved in the vascular remodeling associated with cardiovascular diseases such as hypertension by affecting inflammation, hypertrophy, migration, growth/apoptosis and extracellular matrix protein turnover. The major and more specific source of ROS in the cardiovascular system is the NADPH oxidase (NOX) family of enzymes composed of seven members (NOX1-5, DUOX 1/2). Vascular cells express several NOXs being NOX-1 and NOX-4 the most abundant NOXs present in vascular smooth muscle cells. This review focuses on specific aspects of NOX-1 and NOX-4 isoforms including information on regulation, function and their role in vascular remodeling. In order to obtain a more integrated view about the role of the different NOX isoforms in different types of vascular remodeling, we discuss the available literature not only on hypertension but also in atherosclerosis, restenosis and aortic dilation.

Renal Haemodynamics are not Related to Genotypes in Offspring of Parents with Essential Hypertension

Introduction. The pathogenesis of essential hypertension (EH) has a major genetic component and is associated with renal abnormalities. Normotensive offspring of hypertensive parents are likely to develop EH and are a suitable population for identifying possible relations between genetic and renal abnormalities.

Methods. We investigated if renin-angiotensin-aldosterone system associated genotypes (angiotensinogen [M235T] and ACE [I/D]) are related to blood pressure (BP), renal haemodynamics and sodium excretion in sex and age-matched (18—35 years) healthy Caucasian offspring of either two parents with EH (n=101, EH-offspring) or two normotensive parents (n=50, controls). The alpha-adducin polymorphism (G460W) was also investigated.

Results. Compared to controls, BP, heart rate, renal vascular resistance (RVR) and urinary sodium excretion were, respectively, 5%, 7%, 15% and 20% higher in EH-offspring. In controls, the TT-genotype of the M235T angiotensinogen polymorphism was associated with higher BP and higher plasma angiotensinogen. By contrast, in EHoffspring the TT-genotype was associated with lower BP and unchanged plasma angiotensinogen. Plasma angiotensinogen correlated positively with BP in EH-offspring, with a similar tendency (p=0.08) in controls. The distributions of the three candidate polymorphisms were similar in EH-offspring and controls. There were no associations between any of the polymorphisms and any of the renal parameters measured.

Conclusion. The markedly greater RVR, proportionally larger than the greater BP, supports a role for RVR in the pathogenesis of EH. The lack of association between the candidate polymorphisms and the investigated parameters, even in this homogenous and for hypertension strongly predisposed group, suggests that the polymorphisms investigated do not play important roles in the pathogenesis of hypertension.

Remodeling of Afferent Arterioles From Mice With Oxidative Stress Does Not Account for Increased Contractility but Does Limit Excessive Wall Stress

Because superoxide dismutase (SOD) knockout enhances arteriolar remodeling and contractility, we hypothesized that remodeling enhances contractility. In the isolated and perfused renal afferent arterioles from SOD wild type (+/+) and gene-deleted mice, contractility was assessed from reductions in luminal diameter with perfusion pressure from 40 to 80 mm Hg (myogenic responses) or angiotensin II (10(-6) mol/L), remodeling from media:lumen area ratio, superoxide (O2 (·-)) and hydrogen peroxide (H2O2) from fluorescence microscopy, and wall stress from wall tension/wall thickness. Compared with +/+ strains, arterioles from SOD1-/-, SOD2+/-, and SOD3-/- mice developed significantly (P<0.05) more O2 (·-) with perfusion pressure and angiotensin II and significantly increased myogenic responses (SOD1-/-: -20.7±2.2% versus -12.7±1.6%; SOD2+/-: -7.4±1.3% versus -12.6±1.4%; and SOD3-/-: -9.1±1.9% versus -15.8±2.2%) and angiotensin II contractions and ≈2-fold increased media:lumen ratios. Media:lumen ratios correlated with myogenic responses (r(2) =0.23; P<0.01), angiotensin II contractions (r(2)=0.57; P<0.0001), and active wall tension (r(2) =0.19; P<0.01), but not with active wall stress (r(2)=0.08; NS). Differences in myogenic responses among SOD3 mice were abolished by bath addition of SOD and were increased 3 days after inducing SOD3 knockout (-26.9±1.7% versus -20.1±0.7%; P<0.05), despite unchanged media:lumen ratios (2.01±0.09 versus 2.02±0.03; NS). We conclude that cytosolic, mitochondrial, or extracellular O2 (·-) enhance afferent arteriolar contractility and remodeling. Although remodeling does not enhance contractility, it does prevent the potentially damaging effects of increased wall stress.

Pubertal administration of antiserum against nerve growth factor regresses renal vascular remodeling in spontaneously hypertensive rats

To investigate the role of nerve growth factor (NGF) in the development of hypertensive renal vascular remodeling, antiserum against NGF (anti-NGF) or vehicle was injected at 3 weeks of age in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats (n = 9 for each treatment in each strain). Flow-pressure (F-P) and pressure-glomerular filtration rate (P-GFR) relationships at vasodilated perfused kidneys were determined at 10 weeks of age. In the vehicle rats, blood pressure, renal noradrenaline content, the gradient of F-P (minimal vascular resistance at pre- and post-glomerular vasculature) and the X-intercept of P-GFR (preglomerular : postglomerular vascular resistance ratio) were greater in SHR than in WKY rats, although the gradient of P-GFR (glomerular filtration capacity) did not differ significantly between the strains. Blood pressure and renal noradrenaline content were lower in SHR receiving anti-NGF than in SHR receiving vehicle, although such difference was not observed in WKY rats. The gradient of F-P was less but the gradient of P-GFR was greater in SHR receiving anti-NGF compared with SHR receiving vehicle, although the similar differences did not occur in WKY rats. Blood pressure and renal noradrenaline content remained greater in SHR treated with anti-NGF compared with WKY rats treated with vehicle; however, the gradient of F-P did not differ significantly between them. Contrary, anti-NGF did not affect the X-intercept of P-GFR in either strain. In conclusion, NGF could contribute to the genesis of renal vascular remodeling, at least in part, through modification of renal sympathetic activity and blood pressure in SHR.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Microcirculatory marker for the prediction of renal end points: a prospective cohort study in patients with chronic kidney disease stage 2 to 4

Retinal arteriolar narrowing reflects aging, hypertension, chronic kidney disease (CKD), and other vascular processes. We examined the predictive value of retinal arteriolar narrowing alone and in combination with albuminuria on renal disease progression in CKD. A white CKD stage 2 to 4 cohort of 164 men and women (60.8±13.8 years) underwent retinal photography and determination of albuminuria. The calibers of all retinal arterioles were measured after digital conversion of the photographs. Cases of incident renal end points defined as 50% renal function loss and start of renal replacement therapy were identified and validated by case record reviews. Over an average period of 1410 (range, 106-1606) days, 25 patients with CKD had incident renal end points. Kaplan-Meier analysis revealed that patients with CKD within the tertile of narrowest arterioles had more renal end points (log-rank P<0.001). Cox regression analysis confirmed this before (β=1.183±0.411) and after adjusting for age and baseline renal function (β=1.204±0.416). With respect to renal end points, a significant interaction was present between narrow arterioles and albuminuria. The relative risk for renal end points of narrow arterioles was 3.7 (1.7-8.4), of albuminuria was 5.4 (2.5-12.0), and of combined narrow arterioles and albuminuria was 16.2 (4.6-57.2). Hence retinal arteriolar narrowing is related to incident renal end points. Narrow arterioles and albuminuria reveal a synergistic predictive value. The findings support a leading role of the microvasculature in the pathogenesis of renal disease progression. They also suggest that retinal photography in combination with albuminuria determination may be useful for risk stratification with respect to renal disease progression in patients with CKD stage 2 to 4.

Serum cystatin C, creatinine-based estimated glomerular filtration rate, and the risk of incident hypertension in middle-aged men

BACKGROUND

The aim of this study was to examine the predictive value of serum cystatin C (CysC) and that of creatinine-based estimated glomerular filtration rate (eGFRCreat) for the risk of incident hypertension in a middle-aged male population.

METHODS

Serum CysC levels were measured in 904 nonhypertensive, Japanese male subjects (mean age = 44±6 years) who received an annual general health examination in a company. Serum creatinine levels were simultaneously measured, and eGFRCreat was calculated. Subjects were followed-up for a maximum period of 4 years, and annual blood pressure measurements were recorded.

RESULTS

During the follow-up period, 124 subjects developed hypertension, defined as systolic/diastolic blood pressure ≥140/90 mmHg or use of antihypertensive medications. In the Kaplan-Meier analysis, both the third quintile of CysC and that of eGFRCreat showed the lowest 4-year cumulative incident rate of hypertension. The multiadjusted hazard ratio for incident hypertension was significantly increased in the highest quintile of CysC compared with the third quintile (2.60; 95% confidence interval (CI) = 1.41-4.77; P = 0.002), as well as compared with the lowest 4 quintiles combined (1.89; 95% CI = 1.26-2.84; P = 0.002). However, eGFRCreat did not show significant hazard ratios for incident hypertension in any of the adjusted models.

CONCLUSIONS

Elevated serum CysC levels could predict the risk of incident hypertension in this study population with a maximum follow-up period of 4 years. In contrast, eGFRCreat did not show predictive value for the risk of incident hypertension.

Oxidative stress in hypertension: role of the kidney

SIGNIFICANCE

Renal oxidative stress can be a cause, a consequence, or more often a potentiating factor for hypertension. Increased reactive oxygen species (ROS) in the kidney have been reported in multiple models of hypertension and related to renal vasoconstriction and alterations of renal function. Nicotinamide adenine dinucleotide phosphate oxidase is the central source of ROS in the hypertensive kidney, but a defective antioxidant system also can contribute.

RECENT ADVANCES

Superoxide has been identified as the principal ROS implicated for vascular and tubular dysfunction, but hydrogen peroxide (H2O2) has been implicated in diminishing preglomerular vascular reactivity, and promoting medullary blood flow and pressure natriuresis in hypertensive animals.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Increased renal ROS have been implicated in renal vasoconstriction, renin release, activation of renal afferent nerves, augmented contraction, and myogenic responses of afferent arterioles, enhanced tubuloglomerular feedback, dysfunction of glomerular cells, and proteinuria. Inhibition of ROS with antioxidants, superoxide dismutase mimetics, or blockers of the renin-angiotensin-aldosterone system or genetic deletion of one of the components of the signaling cascade often attenuates or delays the onset of hypertension and preserves the renal structure and function. Novel approaches are required to dampen the renal oxidative stress pathways to reduced O2(-•) rather than H2O2 selectivity and/or to enhance the endogenous antioxidant pathways to susceptible subjects to prevent the development and renal-damaging effects of hypertension.

Curved and folded micropatterns in 3D cell culture and tissue engineering

Cells live in a highly curved and folded micropatterned environment within the human body. Hence, there is a need to develop engineering paradigms to replicate these microenvironments in order to investigate the behavior of cells in vitro, as well as to develop bioartificial organs for tissue engineering and regenerative medicine. In this chapter, we first motivate the need for such micropatterns based on anatomical considerations and then survey methods that can be utilized to generate curved and folded micropatterns of relevance to 3D cell culture and tissue engineering. The methods surveyed can broadly be divided into two classes: top-down approaches inspired by conventional 2D microfabrication and bottom-up approaches most notably in the self-assembly of thin patterned films. These methods provide proof of concept that the high resolution, precise and reproducible patterning of cell and matrix microenvironments in anatomically relevant curved and folded geometries is possible. A specific protocol is presented to create curved and folded hydrogel micropatterns.

Retinal microvasculature as a model to study the manifestations of hypertension

The retinal vasculature allows direct noninvasive visualization of the body's mircrovasculature. Because the retina and other end organs (brain and kidney) share similar anatomical features and physiological properties, the retinal vessels offer a unique and easily accessible window to study the health and disease of the human microcirculation. Advanced retinal vascular imaging technologies have been developed to allow a more objective and precise assessment of retinal vascular changes. The changes in the retinal vasculature associated with hypertension can be broadly divided into 3 groups: (1) classic retinal vascular changes in response to blood pressure (referred to as hypertensive retinopathy signs), (2) changes in retinal vascular caliber, and (3) changes in more global geometrical patterns of the retina. In this review, we summarize the current understanding of the relationship between retinal vascular changes and blood pressure, the evidence for the retinal vasculature as a biological model to study the manifestation and early pathogenic correlates of hypertension, the latest advances in retinal vascular imaging technologies, and the future opportunities and challenges of retinal vascular imaging. We suggest that further development of retinal vascular analyses and standardized measurement protocols, evaluation of the clinical use of retinal vascular imaging in assessing cardiovascular risk prediction, and using retinal vascular imaging to test antihypertensive treatments will allow the translation of retinal vascular imaging as a tool to improve the diagnosis, prognosis, and management of hypertension in clinical practice.

Influence of arterial hypertension on colonic healing in rats

PURPOSE

Evaluation of colonic healing in spontaneously hypertensive rats.

METHODS

Fifty male, young and inbred rats were used. Twenty-five Wistar Kyoto rats (WKY) as control and twenty-five spontaneously hypertensive rats (SHR) as an experimental group. Colotomy and bowel suture at 2.5 cm from the peritoneal reflection were performed. All animals were allocated randomly into sub-groups for review at the third, seventh and fourteenth days after surgery. We evaluated the concentration of angiotensin II, the burst pressure, epithelialization, the organization of the tunics of the bowel wall, inflammatory response and collagen deposition.

RESULTS

The burst pressure, epithelialization, organization of the tunics and collagen deposition was not significant between groups. The inflammatory reaction was more intense in the control group on the third postoperative day (p=0.023) as the experimental group on the remaining time.

CONCLUSION

Systemic arterial hypertension in rats did not influence significantly the healing process of colonic anastomoses.

The dietary phase 2 protein inducer sulforaphane can normalize the kidney epigenome and improve blood pressure in hypertensive rats

BACKGROUND

Our previous studies have shown that broccoli sprouts high in the glucosinolate glucoraphanin decreases renal and vascular oxidative stress and inflammation as well as blood pressure in spontaneously hypertensive stroke-prone (SHRSP) rats. The objective of this study was to determine whether the metabolite of glucoraphanin, sulforaphane, was responsible for this improved blood pressure and whether this is associated with normalization of renal methylated DNA.

METHODS

Sulforaphane was given by gavage to SHRSP and Sprague Dawley (SD) rats over 4 months and blood pressure measured under anesthesia just before euthanasia. Renovascular morphology was determined by histology and methylated deoxycytosine levels analyzed using high-performance liquid chromatography.

RESULTS

Mean arterial pressure was 20% higher in vehicle-treated SHRSP when compared to SD. Sulforaphane administration to SHRSP improved blood pressure and lowered this difference to 11%. Vehicle-treated SHRSP had significantly increased wall:lumen ratios in renal arteries, increased numbers of vascular smooth muscle cells (VSMCs), increased renal protein nitration, and decreased (11%) renal DNA methylation compared to SD. Sulforaphane administration to SHRSP significantly lowered arterial wall:lumen ratio by 35%, reduced the number of VSMCs, reduced the level of protein nitration, and increased methylated deoxycytosine levels by 14%.

CONCLUSIONS

Sulforaphane administration rectified pathological abnormalities in SHRSP kidneys and significantly improved blood pressure. This was associated with normalization of global kidney DNA methylation suggesting that DNA methylation could be associated with hypertension.

p47(phox) is required for afferent arteriolar contractile responses to angiotensin II and perfusion pressure in mice

Myogenic and angiotensin contractions of afferent arterioles generate reactive oxygen species. Resistance vessels express neutrophil oxidase-2 and -4. Angiotensin II activates p47(phox)/neutrophil oxidase-2, whereas it downregulates NOX-4. Therefore, we tested the hypothesis that p47(phox) enhances afferent arteriolar angiotensin contractions. Angiotensin II infusion in p47(phox) +/+ but not -/- mice increased renal cortical NADPH oxidase activity (7±1-12±1 [P<0.01] versus 5±1-7±1 10(3) · RLU · min(-1) · μg protein(-1) [P value not significant]), mean arterial pressure (77±2-91±2 [P<0.005] versus 74±2-77±1 mm Hg [P value not significant]), and renal vascular resistance (7.5±0.4-10.1±0.7 [P<0.01] versus 7.9±0.4-8.3±0.4 mm Hg/mL · min(-1) · gram kidney weight(-1) [P value not significant]). Afferent arterioles from p47(phox) -/- mice had a lesser myogenic response (3.1±0.4 versus 1.4±0.2 dynes · cm(-1) · mm Hg(-1); P<0.02) and a lesser (P<0.05) contraction to 10(-6) M angiotensin II (diameter change +/+: 9.3±0.2-3.4±0.6 μm versus -/-: 9.9±0.6-7.5±0.4 μm). Angiotensin and increased perfusion pressure generated significantly (P<0.05) more reactive oxygen species in p47(phox) +/+ than -/- arterioles. Angiotensin II infusion increased the maximum responsiveness of afferent arterioles from p47(phox) +/+ mice to 10(-6) M angiotensin II yet decreased the response in p47(phox) -/- mice. The angiotensin infusion increased the sensitivity to angiotensin II only in p47(phox) +/+ mice. We conclude that p47(phox) is required to enhance renal NADPH oxidase activity and basal afferent arteriolar myogenic and angiotensin II contractions and to switch afferent arteriolar tachyphylaxis to sensitization to angiotensin during a prolonged angiotensin infusion. These effects likely contribute to hypertension and renal vasoconstriction during infusion of angiotensin II.

Changes in angiotensin receptors expression play a pivotal role in the renal damage observed in spontaneously hypertensive rats

The renal renin-angiotensin system plays a central role in the development of hypertension. The aim of this work was to verify the expression of angiotensin II receptors AT1R and AT2R in the microsomal fraction of renal cortex and correlate this with the development of hypertension and renal damage in spontaneously hypertensive rats (SHR) using Wistar-Kyoto rats (WKY) as controls. AT1R expression increased (126%) and AT2R expression decreased (66%) in 4-wk-old SHR; AT2 expression decreased in 14-wk-old SHR (61%) compared with respective age-matched WKY. These modifications were correlated to the increase in protein kinase C activity and decrease in protein kinase A activity. Four-week-old SHR showed large accumulations of macrophages in kidney glomerulus and the tubulointerstitial area, dense cortical collagen deposition, and arterial proliferative changes in the walls of arterioles and medium-sized vessels. Similar modifications were also observed in 14-wk-old SHR. Four-week-old SHR treated with losartan (30 mg·kg−1·day−1) or hydralazine (15 and 30 mg·kg−1·day−1) by gavage for 10 wk did not develop hypertension. The decrease in AT2R expression and renal damage observed in SHR remained even after treatment with hydralazine. On the other hand, losartan treatment prevented the modifications observed in 14-wk-old SHR, indicating that renal injuries are caused specifically by AT1 rather than an increase in blood pressure. Our results indicate that the imbalance in AT1R and AT2R expression is associated with an inflammatory process that contributes to renal injury in adult SHR and to the development of hypertension.

Retinal vessel diameters and risk of hypertension: the Multiethnic Study of Atherosclerosis

OBJECTIVE

To describe the prospective relationship of retinal vessel diameters with risk of hypertension in a multiethnic population-based cohort.

METHODS

The Multi-Ethnic Study of Atherosclerosis is a population-based study of subclinical cardiovascular disease among white, African-American, Hispanic, and Chinese American adults aged 45-84 years. Retinal vessel diameters were measured using a standardized imaging software at the second examination (considered baseline in this analysis) and summarized as the central retinal artery/vein equivalent. Presence of retinopathy and retinal focal arteriolar narrowing and arteriovenous nicking was assessed by trained graders. Incidence of hypertension was defined among participants at risk as systolic blood pressure at least 140 mmHg, diastolic blood pressure at least 90 mmHg, or use of an antihypertensive medication.

RESULTS

Of the initial 6237 participants at baseline, 2583 were at risk of hypertension. After 3.2 +/- 0.5 years of follow-up, 448 (17.3%) participants developed hypertension. After adjusting for age, sex, race/ethnicity, the average of mean arterial blood pressure in the first and second examination, and other vascular risk factors, persons with narrower retinal arteriolar diameter and wider venular diameter at baseline were more likely to develop hypertension [odds ratio per SD decrease in central retinal artery equivalent 1.20, 95% confidence intervals 1.02, 1.42; and odds ratio per SD increase in central retinal vein equivalent 1.18, 95% confidence interval 1.02, 1.37]. Persons with focal arteriolar narrowing were also more likely to develop hypertension (odds ratio 1.80, 95% confidence interval 1.09, 2.97).

CONCLUSION

Findings from this multiethnic population confirm that narrower retinal arteriolar diameter and wider venular diameter are associated with the development of hypertension independent of traditional risk factors.

End-organ dysfunction and cardiovascular outcomes: the role of the microcirculation

Risk factors for cardiovascular disease mediate their effects by altering the structure and function of wall and endothelial components of arterial blood vessels. A pathological change in the microcirculation plays a pivotal role in promoting end-organ dysfunction that not only predisposes to further organ damage, but also increases the risk for future macrovascular events. The microcirculation is recognized as the site where the earliest manifestations of cardiovascular disease, especially inflammatory responses, occur that may play a pivotal role in driving the atherosclerotic process in conduit vessels. Furthermore, the vast surface area of the endothelium compared with conduit vessels means that the vascular effects of endothelial dysfunction or activation will be most apparent in this section of the vasculature. Current techniques providing indices of vascular health focus on large arteries without providing insight into the structure and function of small vessels. Techniques capable of detecting microvascular damage and monitoring the response to therapeutic interventions, especially in vulnerable target organs of interest, may improve risk stratification and represent a valuable surrogate for future cardiovascular outcome.

Capillary rarefaction in treated and untreated hypertensive subjects

This study aimed to determine if capillary rarefaction is detectable and associated with endothelial dysfunction in persons with mild systolic blood pressure (SBP) elevation. Capillary density and endothelial function were quantified for 150 nondiabetic participants, grouped by blood pressure (BP) as normotensive, untreated high BP, and treated high BP. Structural capillary rarefaction measures were not different between the three groups. Functional capillary rarefaction measures were significantly lower in both high BP groups compared to normotensives, and correlated inversely with endothelial function. The study findings indicate that the hypertensive vascular pathologic process is already underway at modest levels of blood pressure elevation.

Retinal Vascular Imaging

The microcirculation is relatively inaccessible to direct visualization and investigation. Recent methods have been developed which use advanced retinal photographic imaging techniques and computer-assisted image analysis to characterize, measure and quantify subtle variations and abnormalities in the retinal vasculature. These quantitative and qualitative assessments demonstrate a close association of retinal vascular signs to both clinical and subclinical cerebrovascular, cardiovascular and metabolic outcomes. Retinal vascular imaging may thus offer potential as a noninvasive research tool to probe the role and pathophysiology of the microvasculature, and as a cardiovascular risk prediction tool. Key areas where retinal vascular imaging has contributed to increased understanding of microvascular pathology and major areas of current and new research are discussed in this review.

The long-term relation among retinal arteriolar narrowing, blood pressure, and incident severe hypertension

The authors assessed associations between retinal vascular signs and incident severe hypertension in an older population-based cohort. At baseline (1992-1994), 3,654 residents aged 49-97 years living in the Blue Mountains area west of Sydney, Australia, were examined; respectively, 2,335 (75.1%) and 1,952 (76%) survivors were reexamined 5 and 10 years later. Retinal arteriolar and venular calibers were measured, and average central retinal artery and central retinal vein equivalents for that eye were estimated. Severe hypertension was defined by previous diagnosis of hypertension plus antihypertensive medication use or by systolic blood pressure > or =160 mmHg and/or diastolic blood pressure > or =100 mmHg at examinations. Of the 1,424 participants at risk, 618 developed severe hypertension over 10 years (cumulative incidence = 47.7%, 95% confidence interval: 44.9, 50.5). Participants who subsequently developed severe hypertension had significantly narrower mean central retinal artery equivalents than those who did not (187.0 vs. 191.9 mum, p < 0.0001). After adjusting for age, sex, body mass index, smoking, mean arterial blood pressure, and plasma glucose and triglyceride levels, baseline narrowing central retinal artery equivalent was associated with increased risk of severe hypertension (per standard deviation reduction, odds ratio = 1.1, 95% confidence interval: 1.1, 1.2; narrowest vs. widest quintile, odds ratio = 1.6, 95% confidence interval: 1.2, 2.1). These findings support structural narrowing in small arteries and arterioles antecedent to clinical onset of severe hypertension.

Differences in kidney function and incident hypertension: the multi-ethnic study of atherosclerosis

BACKGROUND

Kidney disease and hypertension commonly coexist, yet the direction of their association is still debated.

OBJECTIVE

To evaluate whether early kidney dysfunction, measured by serum cystatin C levels and urinary albumin excretion, predates hypertension in adults without clinically recognized kidney or cardiovascular disease.

DESIGN

Observational cohort study using data from 2000 to 2005.

SETTING

The MESA (Multi-Ethnic Study of Atherosclerosis), a community-based study of subclinical cardiovascular disease in adults age 45 to 84 years.

PARTICIPANTS

2767 MESA participants without prevalent hypertension, cardiovascular disease, or clinically recognized kidney disease (an estimated glomerular filtration rate <60 mL/min per 1.73 m2 or microalbuminuria).

MEASUREMENTS

Cystatin C was measured by using a nephelometer, and urinary albumin and creatinine were measured from a spot morning collection. The primary outcome was incident hypertension, defined as systolic blood pressure of at least 140 mm Hg, diastolic blood pressure of at least 90 mm Hg, or use of an antihypertensive medication.

RESULTS

During a median follow-up of 3.1 years, 19.7% of the cohort (545 participants) developed hypertension. After adjustment for established hypertension risk factors, each 15-nmol/L increase in cystatin C was associated with a statistically significant 15% greater incidence of hypertension (P = 0.017). The highest sex-specific quartile of urinary albumin-creatinine ratio was associated with a statistically insignificant 16% greater incidence of hypertension (P = 0.192) compared with the lowest quartile. No statistical evidence suggested a multiplicative interaction.

LIMITATIONS

Unmeasured characteristics may have confounded observed associations of kidney markers with hypertension. Follow-up was relatively short. Hypertension that may have occurred between study visits or hypertension that was not captured by standard cuff measurements may have been missed.

CONCLUSION

Differences in kidney function, indicated by cystatin C levels, are associated with incident hypertension among individuals without clinical kidney or cardiovascular disease. These population-based findings complement experimental work implicating early kidney damage in the pathogenesis of essential hypertension.

Pathophysiology of salt-sensitive hypertension: a new scope of an old problem

It has been recognized for many years that salt intake is one of the main environmental factors responsible for the development of hypertension. More than 30 years ago, Guyton and co-workers postulated a relationship between blood pressure and natriuresis which maintains sodium balance and extracellular volume; thus an impaired ability of the kidney to excrete sodium requires an increase in blood pressure to increase natriuresis and correct the sodium balance, resulting in hypertension. Currently, the mechanisms responsible for the alterations mentioned above remain under investigation. Among them, microvascular and tubulointerstitial injury induce salt retention and development of salt-sensitive hypertension that appears to be mediated in part by lymphocytes and macrophages infiltrating the tubulointerstitium that produce angiotensin II and stimulate oxidative stress. In the post-angiotensin salt-sensitive hypertension model, angiotensin levels are elevated despite systemic angiotensin II levels being suppressed, and the local angiotensin II levels correlate with the presence of intrarenal inflammation and cortical vasoconstriction. Under these conditions, blockade of the angiotensin II AT1 receptors ameliorate cortical vasoconstriction. Thus, the renal angiotensin system in association with interstitial immune infiltrating cells may play a pivotal role in the development and maintenance of salt-sensitive hypertension.

Genetic dissection of a blood pressure quantitative trait locus on rat chromosome 1 and gene expression analysis identifies SPON1 as a novel candidate hypertension gene

A region with a major effect on blood pressure (BP) is located on rat chromosome 1. We have previously isolated this region in reciprocal congenic strains (WKY.SHR-Sa and SHR.WKY-Sa) derived from a cross of the spontaneously hypertensive rat (SHR) with the Wistar-Kyoto rat (WKY) and shown that there are 2 distinct BP quantitative trait loci, BP1 and BP2, in this region. Sisa1, a congenic substrain from the SHR.WKY-Sa animals carrying an introgressed segment of 4.3Mb, contains BP1. Here, we report further dissection of BP1 by the creation of 2 new mutually exclusive congenic substrains (Sisa1a and Sisa1b) and interrogation of candidate genes by expression profiling and targeted transcript sequencing. Only 1 of the substrains (Sisa1a) continued to demonstrate a BP difference but with a reduced introgressed segment of 3Mb. Exonic sequencing of the 20 genes located in the Sisa1a region did not identify any major differences between SHR and WKY. However, microarray expression profiling of whole kidney samples and subsequent quantitative RT-PCR identified a single gene, Spon1 that exhibited significant differential expression between the WKY and SHR genotypes at both 6 and 24 weeks of age. Western blot analysis confirmed an increased level of the Spon1 gene product in SHR kidneys. Spon1 belongs to a family of genes with antiangiogenic properties. These findings justify further investigation of this novel positional candidate gene in BP control in hypertensive rat models and humans.

Role of Extracellular Superoxide Dismutase in the Mouse Angiotensin Slow Pressor Response

Low rates of angiotensin II (Ang II) infusion raise blood pressure, renal vascular resistance (RVR), NADPH oxidase activity, and superoxide. We tested the hypothesis that these effects are ameliorated by extracellular superoxide dismutase (EC-SOD). EC-SOD knockout (-/-) and wild type (+/+) mice were equipped with blood pressure telemeters and infused subcutaneously with Ang II (400 ng/kg per minute) or vehicle for 2 weeks. During vehicle infusion, EC-SOD -/- mice had significantly (P<0.05) higher MAP (+/+: 107+/-3 mm Hg versus -/-: 114+/-2 mm Hg; n=11 to 14), RVR, lipid peroxidation, renal cortical p22(phox) expression, and NADPH oxidase activity. Ang II infusion in EC-SOD +/+ mice significantly (P<0.05) increased MAP, RVR, p22(phox), NADPH oxidase activity, and lipid peroxidation. Ang II reduced SOD activity in plasma, aorta, and kidney accompanied by reduced renal EC-SOD expression. During Ang II infusion, both groups had similar values for MAP (+/+ Ang II: 125+/-3 versus -/- Ang II: 124+/-3 mmHg; P value not significant), RVR, NADPH oxidase activity, and lipid peroxidation. SOD activity in the kidneys of Ang II-infused mice was paradoxically higher in EC-SOD -/- mice (+/+: 8.8+/-1.2 U/mg protein(-1) versus -/-: 13.7+/-1.6 U/mg protein(-1); P<0.05) accompanied by a significant upregulation of mRNA and protein for Cu/Zn-SOD. In conclusion, EC-SOD protects normal mice against oxidative stress by attenuating renal p22(phox) expression, NADPH oxidase activation, and the accompanying renal vasoconstriction and hypertension. However, during an Ang II slow pressor response, renal EC-SOD expression is reduced and, in its absence, renal Cu/Zn-SOD is upregulated and may prevent excessive Ang II-induced renal oxidative stress, renal vasoconstriction, and hypertension.

Developmental expression of ACE2 in the SHR kidney: a role in hypertension?

The abnormal development of the intrarenal renin-angiotensin system (RAS) is thought contribute to adult-onset hypertension in the spontaneously hypertensive rat (SHR). Angiotensin-converting enzyme 2 (ACE2) is a novel enzyme with complementary actions to that of ACE. Recent studies have shown that ACE2 expression is reduced in the adult SHR. However, its regulation in pre-hypertensive animals is unknown. In this study, we examine the developmental expression of ACE2 in the rodent kidney and its temporal expression, as it relates to the development of hypertension in the SHR model. Kidneys from SHR and normotensive Wistar Kyoto (WKY) rats (n=8-12/group) at birth, 6 weeks of age, and adulthood (80 days) were examined. Gene expression and activity of ACE2 were determined by real-time reverse transcription-polymerase chain reaction and quenched fluorescence assays, respectively. Renal expression was localized by in situ hybridization and immunohistochemistry. The expression and ACE2 activity are significantly increased in the SHR kidney at birth. With the onset of hypertension, the tubular expression of ACE2 falls in SHR compared to WKY and remains reduced in the adult SHR kidney. Glomerular expression is paradoxically increased in the SHR glomerulus. The overall developmental pattern of ACE2 expression in the SHR kidney is also modified, with declining expression over the course of renal development. The developmental pattern of ACE2 expression in the SHR kidney is altered before the onset of hypertension, consistent with the key role of the RAS in the pathogenesis of adult-onset hypertension. Further research is required to distinguish the contribution of these changes to the development and progression of hypertension in this model.

Alterations in structure and mechanics of resistance arteries from ouabain-induced hypertensive rats

We have previously described that chronic administration of ouabain induces hypertension and functional alterations in mesenteric resistance arteries. The aim of this study was to analyze whether ouabain treatment also alters the structural and mechanical properties of mesenteric resistance arteries. Wistar rats were treated for 5 wk with ouabain (8.0 microg/day sc). The vascular structure and mechanics of the third-order branches of the mesenteric artery were assessed with pressure myography and confocal microscopy. Total collagen content was determined by picrosirius red staining, collagen I/III was analyzed by Western blot, and elastin was studied by confocal microscopy. Vascular reactivity was analyzed by wire myography. Internal and external diameters and cross-sectional area were diminished, whereas the wall-to-lumen ratio was increased in arteries from ouabain-treated rats compared with controls. In addition, arteries from ouabain-treated rats were stiffer. Ouabain treatment decreased smooth muscle cell number and increased total and I/III collagens in the vascular wall. However, this treatment did not modify adventitia and media thickness, nuclei morphology, elastin structure, and vascular reactivity to norepinephrine and acetylcholine. The present work shows hypotrophic inward remodeling of mesenteric resistance arteries from ouabain-treated rats that seems to be the consequence of a combination of decreased cell number and impaired distension of the artery, possibly due to a higher stiffness associated with collagen deposition. The narrowing of resistance arteries could play a role in the pathogenesis of hypertension in this model.

Retinal Vessel Diameters and Risk of Hypertension

Generalized retinal arteriolar narrowing is an important sign of systemic hypertension, and a lower arteriolar:venular diameter ratio predicts the risk of hypertension. We investigated whether this association was based on arteriolar or venular diameters or both. This study was based on the prospective population-based Rotterdam Study (1990-1993) and included 1900 participants (> or =55 years of age) of whom 739 persons had normal blood pressure (systolic <120 mm Hg and diastolic <80 mm Hg) and 1161 prehypertension (systolic 120 to 139 mm Hg or diastolic 80 to 89 mm Hg). For each participant, retinal arteriolar and venular diameters were measured on digitized images of 1 eye. After a mean follow-up of 6.6 years, 808 persons developed hypertension, defined as either systolic blood pressure > or =140 mm Hg or diastolic blood pressure > or =90 mm Hg or use of antihypertensive medication. Adjusted for age, gender, follow-up time, body mass index, smoking, diabetes mellitus, total and high-density lipoprotein cholesterol, C-reactive protein, and intima-media thickness, arteriolar narrowing was associated with an increased risk of hypertension (odds ratio per SD: 1.38; 95% CI, 1.23 to 1.55); for venular narrowing this was less striking (OR: 1.17; 95% CI, 1.04 to 1.32). Each SD decrease in the arteriolar:venular diameter ratio significantly increased the risk of hypertension by 24%. To examine the effect of baseline blood pressure, we stratified persons into those with "normal blood pressure" or "prehypertension." Within these strata, arteriolar narrowing was still related to incident hypertension. These data show that both retinal arteriolar and venular narrowing may precede the development of systemic hypertension.

Racial differences in renal arteriolar structure in children with minimal change nephropathy

BACKGROUND

African Americans are at increased risk for hypertension and chronic renal disease. Some data suggest this results from renal microvascular disease. The aim of this study was to determine if renal vascular changes were more pronounced in African Americans, were independent of blood pressure, and occurred in early childhood.

METHODS

We performed morphometric analysis on small cortical arteries and arterioles from 44 renal biopsies done in African American and white children (mean age 8.4 +/- SD 5.0 years) with minimal change nephropathy. Outer and inner vessel diameters were measured and wall:lumen and wall:outer diameter ratios (WT/OD) calculated. Clinical data on blood pressure, steroid use, serum creatinine, gender, age, and proteinuria were abstracted by chart review. A z score for systolic and diastolic blood pressure was calculated. Follow-up clinical data were available for 11 children. Data were compared using analysis of covariance (ANCOVA) and t test for paired data.

RESULTS

Lumen diameters of African Americans were 3.1 microm (23%) smaller that those of white children (P = 0.024). Similarly, their WT/OD was greater than in the whites, 0.31+/-0.03 vs. 0.28 +/- 0.02 (P= 0.048). These changes were independent of age, steroid use, systolic blood pressure and diastolic blood pressure z scores. Follow-up data showed a rise in serum creatinine (>50%) in five patients, +1.42 +/- 0.79 mg/dL (P = 0.016), of whom four were African American. There was no change in blood pressure.

CONCLUSION

The renal arterioles of African American children with minimal change nephropathy exhibit significantly smaller lumens and thicker walls than white children. The changes occur very early in life and are independent of age, blood pressure, and steroid use. Such changes may contribute to the African American predisposition to chronic renal disease and hypertension.

Oxidative stress and nitric oxide deficiency in the kidney: a critical link to hypertension?

There is growing evidence that oxidative stress contributes to hypertension. Oxidative stress can precede the development of hypertension. In almost all models of hypertension, there is oxidative stress that, if corrected, lowers BP, whereas creation of oxidative stress in normal animals can cause hypertension. There is overexpression of the p22(phox) and Nox-1 components of NADPH oxidase and reduced expression of extracellular superoxide dismutase (EC-SOD) in the kidneys of ANG II-infused rodents, whereas there is overexpression of p47(phox) and gp91(phox) and reduced expression of intracellular SOD with salt loading. Several mechanisms have been identified that can make oxidative stress self-sustaining. Reactive oxygen species (ROS) can enhance afferent arteriolar tone and reactivity both indirectly via potentiation of tubuloglomerular feedback and directly by microvascular mechanisms that diminish endothelium-derived relaxation factor/nitric oxide responses, generate a cyclooxygenase-2-dependent endothelial-derived contracting factor that activates thromboxane-prostanoid receptors, and enhance vascular smooth muscle cells reactivity. ROS can diminish the efficiency with which the kidney uses O(2) for Na(+) transport and thereby diminish the P(O(2)) within the kidney cortex. This may place a break on further ROS generation yet could further enhance vasculopathy and hypertension. There is a tight relationship between oxidative stress in the kidney and the development and maintenance of hypertension.

Sympatho-renal interactions in the determination of arterial pressure: role in hypertension

Renal mechanisms and the sympathetic nervous system contribute to the development of arterial hypertension. Renal transplantation experiments in spontaneously hypertensive rats (SHRs) were performed to investigate how the sympathetic nervous system and the kidneys interact during the development and maintenance of hypertension. Our findings indicate that the rise in arterial pressure that occurs after transplantation of a kidney from a SHR into normotensive recipients is not mediated by elevations in sympathetic activity. However, chronic reductions in sympathetic tone reduce the rise in arterial pressure which can be induced by SHR renal grafts in normotensive recipients. Untreated SHRs transplanted with a kidney from sympathectomized donors have lower arterial pressure and reduced sodium sensitivity of arterial pressure compared to SHRs transplanted with a kidney from hydralazine-treated donors. It is concluded that chronic non-adapting changes in sympathetic activity modulate the degree to which renal mechanisms can cause hypertension in SHRs. Severe reduction in sympathetic tone during early ontogeny causes long-term changes in renal function that mitigate hypertension development in SHRs even when the extrarenal neuro-hormonal environment is restored.