Angiotensin II, mechanotransduction, and pulsatile arterial hemodynamics in hypertension

Peroxisome Proliferator-Activated Receptor α Attenuates Hypertensive Vascular Remodeling by Protecting Vascular Smooth Muscle Cells from Angiotensin II-Induced ROS Production

Vascular remodeling is the fundamental basis for hypertensive disease, in which vascular smooth muscle cell (VSMC) dysfunction plays an essential role. Previous studies suggest that the activation of peroxisome proliferator-activated receptor α (PPARα) by fibrate drugs has cardiovascular benefits independent of the lipid-lowering effects. However, the underlying mechanism remains incompletely understood. This study explored the role of PPARα in angiotensin II (Ang II)-induced vascular remodeling and hypertension using VSMC-specific Ppara-deficient mice. The PPARα expression was markedly downregulated in the VSMCs upon Ang II treatment. A PPARα deficiency in the VSMC significantly aggravated the Ang II-induced hypertension and vascular stiffness, with little influence on the cardiac function. The morphological analyses demonstrated that VSMC-specific Ppara-deficient mice exhibited an aggravated vascular remodeling and oxidative stress. In vitro, a PPARα deficiency dramatically increased the production of mitochondrial reactive oxidative species (ROS) in Ang II-treated primary VSMCs. Finally, the PPARα activation by Wy14643 improved the Ang II-induced ROS production and vascular remodeling in a VSMC PPARα-dependent manner. Taken together, these data suggest that PPARα plays a critical protective role in Ang II-induced hypertension via attenuating ROS production in VSMCs, thus providing a potential therapeutic target for hypertensive diseases.

Computational analysis of the role of mechanosensitive Notch signaling in arterial adaptation to hypertension

Arteries grow and remodel in response to mechanical stimuli. Hypertension, for example, results in arterial wall thickening. Cell-cell Notch signaling between vascular smooth muscle cells (VSMCs) is known to be involved in this process, but the underlying mechanisms are still unclear. Here, we investigated whether Notch mechanosensitivity to strain may regulate arterial thickening in hypertension. We developed a multiscale computational framework by coupling a finite element model of arterial mechanics, including residual stress, to an agent-based model of mechanosensitive Notch signaling, to predict VSMC phenotypes as an indicator of growth and remodeling. Our simulations revealed that the sensitivity of Notch to strain at mean blood pressure may be a key mediator of arterial thickening in hypertensive arteries. Further simulations showed that loss of residual stress can have synergistic effects with hypertension, and that changes in the expression of Notch receptors, but not Jagged ligands, may be used to control arterial growth and remodeling and to intensify or counteract hypertensive thickening. Overall, we identify Notch mechanosensitivity as a potential mediator of vascular adaptation, and we present a computational framework that can facilitate the testing of new therapeutic and regenerative strategies.

Aerobic training-mediated DNA hypermethylation of Agtr1a and Mas1 genes ameliorate mesenteric arterial function in spontaneously hypertensive rats

BACKGROUND

The imbalance of vasoconstrictor and vasodilator axes of the renin-angiotensin system (RAS) is observed in hypertension. Exercise regulates RAS level and improves vascular function. This study focused on the contribution of RAS axes in vascular function of mesenteric arteries and exercise-induced DNA methylation of the Agtr1a (AT_1aR) and Mas1 (MasR) genes in hypertension.

METHODS

Spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats were randomized into exercise or sedentary group. Levels of plasma RAS components, vascular tone, and DNA methylation markers were measured.

RESULTS

Blood pressure of SHR was markedly reduced after 12 weeks of aerobic exercise. RAS peptides in plasma were all increased with an imbalanced upregulation of Ang II and Ang-(1-7) in SHR, exercise revised the level of RAS and increased Ang-(1-7)/Ang II. The vasoconstriction response induced by Ang II was mainly via type 1 receptors (AT₁R), while this contraction was inhibited by Mas receptor (MasR). mRNA and protein of AT₁R and MasR were both upregulated in SHR, whereas exercise significantly suppressed this imbalanced increase and increased MasR/AT₁R ratio. Exercise hypermethylated Agtr1a and Mas1 genes, associating with increased DNMT1 and DNMT3b and SAM/SAH.

CONCLUSIONS

Aerobic exercise ameliorates vascular function via hypermethylation of the Agtr1a and Mas1 genes and restores the vasoconstrictor and vasodilator axes balance.

Vascular Mechanobiology: Homeostasis, Adaptation, and Disease

Cells of the vascular wall are exquisitely sensitive to changes in their mechanical environment. In healthy vessels, mechanical forces regulate signaling and gene expression to direct the remodeling needed for the vessel wall to maintain optimal function. Major diseases of arteries involve maladaptive remodeling with compromised or lost homeostatic mechanisms. Whereas homeostasis invokes negative feedback loops at multiple scales to mediate mechanobiological stability, disease progression often occurs via positive feedback that generates mechanobiological instabilities. In this review, we focus on the cell biology, wall mechanics, and regulatory pathways associated with arterial health and how changes in these processes lead to disease. We discuss how positive feedback loops arise via biomechanical and biochemical means. We conclude that inflammation plays a central role in overriding homeostatic pathways and suggest future directions for addressing therapeutic needs.

Sympathetic neural modulation of arterial stiffness in humans

Elevated large-artery stiffness is recognized as an independent predictor of cardiovascular and all-cause mortality. The mechanisms responsible for such stiffening are incompletely understood. Several recent cross-sectional and acute experimental studies have examined whether sympathetic outflow, quantified by microneurographic measures of muscle sympathetic nerve activity (MSNA), can modulate large-artery stiffness in humans. A major methodological challenge of this research has been the capacity to evaluate the independent neural contribution without influencing the dynamic blood pressure dependence of arterial stiffness. The focus of this review is to summarize the evidence examining 1) the relationship between resting MSNA and large-artery stiffness, as determined by carotid-femoral pulse wave velocity or pulse wave reflection characteristics (i.e., augmentation index) in men and women; 2) the effects of acute sympathoexcitatory or sympathoinhibitory maneuvers on carotid-femoral pulse wave velocity and augmentation index; and 3) the influence of sustained increases or decreases in sympathetic neurotransmitter release or circulating catecholamines on large-artery stiffness. The present results highlight the growing evidence that the sympathetic nervous system is capable of modulating arterial stiffness independent of prevailing hemodynamics and vasomotor tone.

Astaxanthin Attenuates Hypertensive Vascular Remodeling by Protecting Vascular Smooth Muscle Cells from Oxidative Stress-Induced Mitochondrial Dysfunction

Oxidative stress aggravates mitochondrial injuries and accelerates the proliferation of vascular smooth muscle cells (VSMCs), which are important mechanisms contributing to vascular remodeling in hypertension. We put forward the hypothesis that Astaxanthin (ATX), known to possess strong features of antioxidant, could attenuate vascular remodeling by inhibiting VSMC proliferation and improving mitochondrial function. The potential effects of ATX were tested on spontaneously hypertensive rats (SHRs) and cultured VSMCs that injured by angiotensin II (Ang II). The results showed that ATX lowered blood pressure, reduced aortic wall thickness and fibrosis, and decreased the level of reactive oxygen species (ROS) and H₂O₂ in tunica media. Moreover, ATX decreased the expression of proliferating cell nuclear antigen (PCNA) and ki67 in aortic VSMCs. In vitro, ATX mitigated VSMC proliferation and migration, decreased the level of cellular ROS, and balanced the activities of ROS-related enzymes including NADPH oxidase, xanthine oxidase, and superoxide dismutase (SOD). Besides, ATX mitigated Ca²⁺ overload, the overproduction of mitochondrial ROS (mtROS), mitochondrial dysfunction, mitochondrial fission, and Drp1 phosphorylation at Ser616. In addition, ATX enhanced mitophagy and mitochondrial biosynthesis by increasing the expression of PINK, parkin, mtDNA, mitochondrial transcription factor A (Tfam), and PGC-1α. The present study indicated that ATX could efficiently treat vascular remodeling through restraining VSMC proliferation and restoring mitochondrial function. Inhibiting mitochondrial fission by decreasing the phosphorylation of Drp1 and stimulating mitochondrial autophagy and biosynthesis via increasing the expression of PINK, parkin, Tfam, and PGC-1α may be part of its underlying mechanisms.

Computational Modeling Predicts Immuno-Mechanical Mechanisms of Maladaptive Aortic Remodeling in Hypertension

Uncontrolled hypertension is a major risk factor for myriad cardiovascular diseases. Among its many effects, hypertension increases central artery stiffness which in turn is both an initiator and indicator of disease. Despite extensive clinical, animal, and basic science studies, the biochemomechanical mechanisms by which hypertension drives aortic stiffening remain unclear. In this paper, we show that a new computational model of aortic growth and remodeling can capture differential effects of induced hypertension on the thoracic and abdominal aorta in a common mouse model of disease. Because the simulations treat the aortic wall as a constrained mixture of different constituents having different material properties and rates of turnover, one can gain increased insight into underlying constituent-level mechanisms of aortic remodeling. Model results suggest that the aorta can mechano-adapt locally to blood pressure elevation in the absence of marked inflammation, but large increases in inflammation drive a persistent maladaptive phenotype characterized primarily by adventitial fibrosis. Moreover, this fibrosis appears to occur via a marked increase in the rate of deposition of collagen having different material properties in the absence of a compensatory increase in the rate of matrix degradation. Controlling inflammation thus appears to be key to reducing fibrosis, but therapeutic strategies should not compromise the proteolytic activity of the wall that is essential to mechanical homeostasis.

Compromised mechanical homeostasis in arterial aging and associated cardiovascular consequences

Aging leads to central artery stiffening and associated hemodynamic sequelae. Because healthy arteries exhibit differential geometry, composition, and mechanical behaviors along the central vasculature, we sought to determine whether wall structure and mechanical function differ across five vascular regions-the ascending and descending thoracic aorta, suprarenal and infrarenal abdominal aorta, and common carotid artery-in 20 versus 100-week-old male wild-type mice. Notwithstanding generally consistent changes across these regions, including a marked thickening of the arterial wall, diminished in vivo axial stretch, and loss of elastic energy storage capacity, the degree of changes tended to be slightly greater in abdominal than in thoracic or carotid vessels. Likely due to the long half-life of vascular elastin, most mechanical changes in the arterial wall resulted largely from a distributed increase in collagen, including thicker fibers in the media, and localized increases in glycosaminoglycans. Changes within the central arteries associated with significant increases in central pulse pressure and adverse changes in the left ventricle, including increased cardiac mass and decreased diastolic function. Given the similar half-life of vascular elastin in mice and humans but very different life-spans, there are important differences in the aging of central vessels across these species. Nevertheless, the common finding of aberrant matrix remodeling contributing to a compromised mechanical homeostasis suggests that studies of central artery aging in the mouse can provide insight into mechanisms and treatment strategies for the many adverse effects of vascular aging in humans.

Angiotensin-(1-7) and Alamandine on Experimental Models of Hypertension and Atherosclerosis

PURPOSE OF REVIEW

The purpose of this review was to summarize the current knowledge on the role of angiotensin-(1-7) [Ang-(1-7)] and alamandine in experimental hypertension and atherosclerosis.

RECENT FINDINGS

The renin-angiotensin system (RAS) is a very complex system, composed of a cascade of enzymes, peptides, and receptors, known to be involved in the pathogenesis of hypertension and atherosclerosis. Ang-(1-7), identified and characterized in 1987, and alamandine, discovered 16 years after, are the newest two main effector molecules from the RAS, protecting the vascular system against hypertension and atherosclerosis. While the beneficial effects of Ang-(1-7) have been widely studied in several experimental models of hypertension, much less studies were performed in experimental models of atherosclerosis. Alamandine has shown similar vascular effects to Ang-(1-7), namely, endothelial-dependent vasorelaxation mediated by nitric oxide and hypotensive effects in experimental hypertension. There are few studies on the effects of alamandine on atherosclerosis.

Effects of losartan on vasomotor function and canonical transient receptor potential channels in the aortas of sinoaortic denervation rats

Increased short-term blood pressure variability (BPV) is strongly correlated with target organ damage. However, the molecular mechanisms underlying abnormal BPV-induced organ damage and effective therapeutic targets are poorly understood. The purpose of this study was to investigate the effects of losartan on vasomotor function and canonical transient receptor potential (TRPC) channels in the aortas of rats with arterial pressure lability induced by sinoaortic denervation (SAD). SAD was performed in male Sprague-Dawley rats at the age of 10 weeks. The experiment included sham-operated (Sham), SAD, and losartan-treated SAD (SAD+Los) groups. After 8 weeks of treatment, hemodynamic parameters were measured via catheterization, thoracic aortic vasomotor functions were evaluated using a physiological vascular ring tension recording system, and TRPC1 and 6 mRNA and protein expression levels in the endothelial cells (ECs) and smooth muscle cells (SMCs) of the thoracic aorta were determined via reverse transcription polymerase chain reaction (RT-PCR) and Western-blotting, respectively. Compared with Sham rats, SAD rats exhibited significantly increased BPV, enhanced norepinephrine-induced aortic contraction, and attenuated acetylcholine-induced aortic relaxation. Both the mRNA and the protein expression levels of TRPC1 and 6 were significantly downregulated in the ECs and upregulated in the SMCs of the thoracic aortas of SAD rats. Losartan treatment prevented these SAD-induced changes. In conclusion, losartan efficiently prevented vasomotor function impairment in SAD rats by reducing BPV and regulating TRPC1 and 6 expression levels.

Vascular Smooth Muscle Cells and Arterial Stiffening: Relevance in Development, Aging, and Disease

The cushioning function of large arteries encompasses distension during systole and recoil during diastole which transforms pulsatile flow into a steady flow in the microcirculation. Arterial stiffness, the inverse of distensibility, has been implicated in various etiologies of chronic common and monogenic cardiovascular diseases and is a major cause of morbidity and mortality globally. The first components that contribute to arterial stiffening are extracellular matrix (ECM) proteins that support the mechanical load, while the second important components are vascular smooth muscle cells (VSMCs), which not only regulate actomyosin interactions for contraction but mediate also mechanotransduction in cell-ECM homeostasis. Eventually, VSMC plasticity and signaling in both conductance and resistance arteries are highly relevant to the physiology of normal and early vascular aging. This review summarizes current concepts of central pressure and tensile pulsatile circumferential stress as key mechanical determinants of arterial wall remodeling, cell-ECM interactions depending mainly on the architecture of cytoskeletal proteins and focal adhesion, the large/small arteries cross-talk that gives rise to target organ damage, and inflammatory pathways leading to calcification or atherosclerosis. We further speculate on the contribution of cellular stiffness along the arterial tree to vascular wall stiffness. In addition, this review provides the latest advances in the identification of gene variants affecting arterial stiffening. Now that important hemodynamic and molecular mechanisms of arterial stiffness have been elucidated, and the complex interplay between ECM, cells, and sensors identified, further research should study their potential to halt or to reverse the development of arterial stiffness.

miR-181b regulates vascular stiffness age dependently in part by regulating TGF-β signaling

BACKGROUND

Endothelial dysfunction and arterial stiffening play major roles in cardiovascular diseases. The critical role for the miR-181 family in vascular inflammation has been documented. Here we tested whether the miR-181 family can influence the pathogenesis of hypertension and vascular stiffening.

METHODS AND RESULTS

qPCR data showed a significant decrease in miR-181b expression in the aorta of the older mice. Eight miR-181a1/b1-/- mice and wild types (C57BL6J:WT) were followed weekly for pulse wave velocity (PWV) and blood pressure measurements. After 20 weeks, the mice were tested for endothelial function and aortic modulus. There was a progressive increase in PWV and higher systolic blood pressure in miR-181a1/b1-/- mice compared with WTs. At 21 weeks, aortic modulus was significantly greater in the miR-181a1/b1-/- group, and serum TGF-β was found to be elevated at this time. A luciferase reporter assay confirmed miR-181b targets TGF-βi (TGF-β induced) in the aortic VSMCs. In contrast, wire myography revealed unaltered endothelial function along with higher nitric oxide production in the miR-181a1/b1-/- group. Cultured VECs and VSMCs from the mouse aorta showed more secreted TGF-β in VSMCs of the miR-181a1/b1-/- group; whereas, no change was observed from VECs. Circulating levels of angiotensin II were similar in both groups. Treatment with losartan (0.6 g/L) prevented the increase in PWV, blood pressure, and vascular stiffness in miR-181a1/b1-/- mice. Immunohistochemistry and western blot for p-SMAD2/3 validated the inhibitory effect of losartan on TGF-β signaling in miR-181a1/b1-/- mice.

CONCLUSIONS

Decreased miR-181b with aging plays a critical role in ECM remodeling by removing the brake on the TGF-β, pSMAD2/3 pathway.

Comparative Study of the Efficacy of Olmesartan/Amlodipine vs. Perindopril/Amlodipine in Peripheral and Central Blood Pressure Parameters After Missed Dose in Type 2 Diabetes

BACKGROUND

Central aortic blood pressure (CBP) and CBP-derived parameters are independent predictors of cardiovascular risk. Angiotensin II receptor blockers (ARBs) or angiotensin-converting enzyme inhibitors plus calcium channel blockers are the recommended first-line treatments in hypertensive diabetic patients; however, the effect in reducing CBP when a dose is skipped has not been established yet. The aim was to determine whether the fixed-dose combination of olmesartan/amlodipine (OLM/AML) provides equal efficacy and safety as the perindopril/AML (PER/AML) combination in reducing CBP, augmentation index (AIx), and pulse wave velocity (PWV) when a drug dose is missed.

METHODS

In this noninferiority, randomized, double-blind, double-dummy parallel group, controlled design trial, 88 patients received either OLM 20-40mg/AML 5-10mg (41 patients) or PER 4-8mg/AML 5-10mg (47 patients) for 24 weeks. The main endpoint was the aortic systolic BP (SBP) after 24 weeks of treatment at 48 hours from the last administration.

RESULTS

The OLM/AML combination reached the noninferiority criteria in reducing central systolic BP after 24 weeks of treatment and after the missed dose, compared to the PER/AML combination (-17 and -8mm Hg, respectively). Peripheral BP, AIx, and PWV were significantly lower in both groups after 24 weeks of treatment and 48 hours after the missed dose, observing a trend to a greater reduction in CBP-derived parameters in the OLM/AML group.

CONCLUSIONS

The OLM/AML combination is safe, well tolerated, and not inferior to the combination of PER/AML in lowering CBP and CBP-derived parameters in diabetic patients. OLM/AML provides longer-lasting efficacy in terms of CBP reduction compared to PER/AML.

Increased stiffness and cell-matrix interactions of abdominal aorta in two experimental nonhypertensive models: long-term chemically sympathectomized and sinoaortic denervated rats

RATIONALE

Sinoaortic denervated (SAD) and chemically sympathectomized (SNX) rats are characterized by a decrease in arterial distensibility without hypertension and would, thus, be relevant for analyzing arterial wall stiffening independently of blood pressure level. The fibronectin network, which plays a pivotal role in cell-matrix interactions, is a major determinant of arterial stiffness. We hypothesized that in SAD and SNX rats, arterial stiffness is increased, due to alterations of cell-matrix anchoring leading to spatial reorganization of the extracellular matrix.

METHODS

The intrinsic elastic properties of the arterial wall were evaluated in vivo by the relationship between incremental elastic modulus determined by echotracking and circumferential wall stress. The changes of cell-extracellular matrix links in the abdominal aorta were evaluated by studying fibronectin, vascular integrin receptors, and ultrastructural features of the aorta by immunochemistry.

RESULTS

In both experimental conditions, wall stiffness increased, associated with different modifications of cell-extracellular matrix adhesion. In SAD rats, increased media cross-sectional area was coupled with an increase of muscle cell attachments to its extracellular matrix via fibronectin and its α5-β1 integrin. In SNX rats, reduced media cross-sectional area was associated with upregulation of αv-β3 integrin and more extensive connections between dense bands and elastic fibers despite the disruption of the elastic lamellae.

CONCLUSION

In aorta of SNX and SAD rats, a similar arterial stiffness is associated to different structural alterations. An increase in αvβ3 or α5β1 integrins together with the already reported increase in the proportion of less distensible (collagen) to more distensible (elastin) components in both models contributes to remodeling and stiffening of the abdominal aorta.

High molecular weight components of the injected venom of fish-hunting cone snails target the vascular system

The venom of marine cone snails is a rich source of pharmacotherapeutic compounds with striking target specificity and functional diversity. Small, disulfide-rich peptide toxins are the most well characterized active compounds in cone snail venom. However, reports on the presence of larger polypeptides have recently emerged. The majority of these studies have focused on the content of the dissected venom gland rather than the injected venom itself. Recent breakthroughs in the sensitivity of protein and nucleotide sequencing techniques allow for the exploration of the proteomic diversity of injected venom. Using mass spectrometric analysis of injected venoms of the two fish-hunting cone snails Conus purpurascens and Conus ermineus, we demonstrate the presence of angiotensin-converting enzyme-1 (ACE-1) and endothelin converting enzyme-1 (ECE-1), metalloproteases that activate potent vasoconstrictive peptides. ACE activity was confirmed in the venom of C. purpurascens and was significantly reduced in venom preincubated with the ACE inhibitor captopril. Reverse-transcription PCR demonstrated that these enzymes are expressed in the venom glands of other cone snail species with different prey preferences. These findings strongly suggest that cone snails employ compounds that cause disruption of cardiovascular function as part of their complex envenomation strategy, leading to the enhancement of neurotropic peptide toxin activity.

BIOLOGICAL SIGNIFICANCE

To our knowledge, this is the first study to show the presence of ACE and ECE in the venom of cone snails. Identification of these vasoactive peptide-releasing proteases in the injected venoms of two fish-hunting cone snails highlights their role in envenomation and enhances our understanding of the complex hunting strategies utilized by these marine predators. Our findings on the expression of these enzymes in other cone snail species suggests an important biological role of ACE and ECE in these animals and points towards recruitment into venom from general physiological processes.

Heart rate reduction by ivabradine improves aortic compliance in apolipoprotein E-deficient mice

BACKGROUND

Impaired vascular compliance is associated with cardiovascular mortality. The effects of heart rate on vascular compliance are unclear. Therefore, we characterized effects of heart rate reduction (HRR) by I(f) current inhibition on aortic compliance and underlying molecular mechanisms in apolipoprotein E-deficient (ApoE(-)/(-)) mice.

METHODS

ApoE(-)/(-) mice fed a high-cholesterol diet and wild-type (WT) mice were treated with ivabradine (20 mg/kg/d) or vehicle for 6 weeks. Compliance of the ascending aorta was evaluated by MRI.

RESULTS

Ivabradine reduced heart rate by 113 ± 31 bpm (~19%) in WT mice and by 133 ± 6 bpm (~23%) in ApoE(-)/(-) mice. Compared to WT controls, ApoE(-)/(-) mice exhibited reduced distensibility and circumferential strain. HRR by ivabradine increased distensibility and circumferential strain in ApoE(-)/(-) mice but did not affect both parameters in WT mice. Ivabradine reduced aortic protein and mRNA expression of the angiotensin II type 1 (AT1) receptor and reduced rac1-GTPase activity in ApoE(-)/(-) mice. Moreover, membrane translocation of p47(phox) was inhibited. In ApoE(-)/(-) mice, HRR induced anti-inflammatory effects by reduction of aortic mRNA expression of IL-6, TNF-alpha and TGF-beta.

CONCLUSION

HRR by ivabradine improves vascular compliance in ApoE(-)/(-) mice. Contributing mechanisms include downregulation of the AT1 receptor, attenuation of oxidative stress and modulation of inflammatory cytokine expression.

The roles of integrins in mediating the effects of mechanical force and growth factors on blood vessels in hypertension

Hypertension is characterized by a sustained increase in vasoconstriction and attenuated vasodilation in the face of elevated mechanical stress in the blood vessel wall. To adapt to the increased stress, the vascular smooth muscle cell and its surrounding environment undergo structural and functional changes known as vascular remodeling. Multiple mechanisms underlie the remodeling process, including increased expression of humoral factors and their receptors as well as adhesion molecules and their receptors, all of which appear to collaborate and interact in the response to pressure elevation. In this review, we focus on the interactions between integrin signaling pathways and the activation of growth factor receptors in the response to the increased mechanical stress experienced by blood vessels in hypertension.

Effect of Tulbaghia violacea on the blood pressure and heart rate in male spontaneously hypertensive Wistar rats

ETHNOPHARMACOLOGICAL RELEVANCE

Tulbaghia violacea Harv. (Alliaceae) is a small bulbous herb which belongs to the family Alliaceae, most commonly associated with onions and garlic. In South Africa, this herb has been traditionally used in the treatment of various ailments, including fever, colds, asthma, paralysis, hypertension and stomach problems. The aim of this study was to evaluate the effect of methanol leaf extracts (MLE) of Tulbaghia violacea on the blood pressure (BP) and heart rate (HR) in anaesthetized male spontaneously hypertensive rats; and to find out the mechanism(s) by which it acts.

MATERIALS AND METHODS

The MLE of Tulbaghia violacea (5-150mg/kg), angiotensin I human acetate salt hydrate (ang I, 3.1-100μg/kg), angiotensin II human (ang II, 3.1-50μg/kg), phenylephrine hydrochloride (phenylephrine, 0.01-0.16mg/kg) and dobutamine hydrochloride (dobutamine, 0.2-10.0μg/kg) were infused intravenously, while the BP and HR were measured via a pressure transducer connecting the femoral artery and the Powerlab.

RESULTS

Tulbaghia violacea significantly (p<0.01) reduced the systolic, diastolic, and mean arterial BP; and HR dose-dependently. Ang I, ang II, phenylephrine and dobutamine all increased the BP dose-dependently. The hypertensive effect of ang I and the HR-increasing effect of dobutamine were significantly (p<0.01) decreased by their co-infusion with Tulbaghia violacea (60mg/kg). However, the co-infusion of ang II or phenylephrine with Tulbaghia violacea (60mg/kg) did not produce any significant change in BP or HR when compared to the infusion of either agent alone in the same animal.

CONCLUSIONS

Tulbaghia violacea reduced BP and HR in the SHR. The reduction in BP may be due to actions of the MLE on the ang I converting enzyme (ACE) and β(1) adrenoceptors.

Fatty acids impair endothelium-dependent vasorelaxation: a link between obesity and arterial stiffness in very old Zucker rats

To analyze age-related interactions between obesity, its associated metabolic disorders, and macrocirculation, we studied large artery stiffness and fatty acid responsiveness in lean and obese Zucker rats, aged 25 (adult) and 80 weeks (very old). Systolic arterial pressure was higher in old obese than in old lean rats (178 ± 10 vs 134 ± 8 mmHg, respectively). Carotid elastic modulus-wall stress curves showed increased age-dependent arterial stiffening, which was greater in obese animals. Old obese exhibited endothelial dysfunction with increased systemic oxidative stress. Adult obese had elevated plasma free fatty acid levels (1,866 ± 177 vs 310 ± 34 μg/μL in lean animals). In old obese, linoleate and palmitate increased contractility to phenylephrine and reduced relaxation to acetylcholine. Thus, obesity at 25 weeks appears to trigger accelerated arterial aging observed at 80 weeks. The early increase in free fatty acids may be a key effector in the severe arterial stiffness of the aged obese Zucker model.

Vascular compliance in blood pressure

PURPOSE OF REVIEW

Vascular stiffening is a hallmark of the aging process. Improvements in the methods used to measure central stiffness, particularly applanation tonometry, and their use as therapeutic targets have generated great interest.

RECENT FINDINGS

Vascular stiffness is associated with increases in pulse pressure (PP), aortic augmentation index, and pulse wave velocity (PWV). This last has emerged as the gold standard for evaluation of vascular stiffness, as it is an independent predictor of coronary heart disease, stroke, and mortality. Angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and calcium-channel blockers with or without diuretics are all commonly used to ameliorate vascular stiffness; however, selective β-1 blockers (β-blockers) may actually worsen aortic PP and aortic augmentation index.

SUMMARY

Serial measurements of vascular stiffness, including PWV, augmentation index, and PP, may be especially beneficial in older patients to supplement brachial blood pressure. At present, given the lack of universally accepted normal values for vascular stiffness as measured by applanation tonometry, serial measurements over time may be more helpful than a single isolated value. In patients with suspected vascular stiffening, therapy should include inhibition of the renin-angiotensin-aldosterone system with ACE inhibitors or ARBs, calcium-channel blockers, and diuretics as needed to normalize blood pressure. β-Blockers should be reserved for patients with a history of myocardial infarction or congestive heart disease. It remains to be established whether β-blockers with vasodilator properties could improve the assessment of vascular compliance.

Pharmacological modulation of arterial stiffness

Arterial stiffness has emerged as an important marker of cardiovascular risk in various populations and reflects the cumulative effect of cardiovascular risk factors on large arteries, which in turn is modulated by genetic background. Arterial stiffness is determined by the composition of the arterial wall and the arrangement of these components, and can be studied in humans non-invasively. Age and distending pressure are two major factors influencing large artery stiffness. Change in arterial stiffness with drugs is an important endpoint in clinical trials, although evidence for arterial stiffness as a therapeutic target still needs to be confirmed. Drugs that independently affect arterial stiffness include antihypertensive drugs, mostly blockers of the renin-angiotensin-aldosterone system, hormone replacement therapy and some antidiabetic drugs such as glitazones. While the quest continues for 'de-stiffening drugs', so far only advanced glycation endproduct cross-link breakers have shown promise.

Losartan abolishes oxidative stress induced by intermittent hypoxia in humans

The aim of this study was to assess the role of the type 1 angiotensin II (AT(1)) receptor in the increase of oxidative stress and NO metabolism during a single 6 h exposure to intermittent hypoxia (IH). Nine healthy young men were exposed, while awake, to sham IH, IH with placebo medication, and IH with the AT(1) receptor antagonist, losartan, using a double-blind, placebo-controlled, randomized, crossover study design. In addition to blood pressure, oxidative stress, peroxynitrite activity, uric acid, global antioxidant status and the end-products of NO (NOx) metabolism were measured in plasma before and after 6 h of IH. Oxidative stress and peroxynitrite activity increased and NOx decreased during IH with placebo. In contrast, neither sham IH nor IH with losartan affected these parameters. With respect to each condition, blood pressure had the same profile as oxidative stress. These results demonstrate that blockade of AT(1) receptors prevented the increase in oxidative stress and peroxynitrite activity and the decrease in NO metabolism induced by IH. Finally, this study suggests that the renin-angiotensin system may participate in the overproduction of reactive oxygen species associated with IH by upregulation of the actions of angiotensin II.

Angiotensin-converting enzyme inhibitor limits pulse-wave velocity and aortic calcification in a rat model of cystic renal disease

The effect of angiotensin-converting enzyme inhibition on function and structure of the aorta was studied in the Lewis polycystic kidney (LPK) rat model of cystic renal disease and Lewis controls. Pulse-wave velocity (PWV) was recorded under urethane anesthesia (1.3 g/kg ip) in mixed-sex animals aged 6 and 12 wk and in 12-wk-old animals treated with perindopril (3 mg·kg(-1)·day(-1) po) from age 6-12 wk. Tail-cuff systolic pressures were recorded over the treatment period. After PWV measurements, animals were euthanized and the aorta was removed for histomorphological and calcium analysis. Hypertension in LPK at 6 and 12 wk was associated with a shift of the PWV curve upward and to the right, indicating a decrease in aortic compliance, which was significantly reduced by perindopril. LPK demonstrated greater aortic calcification (6 wk: 123 ± 19 vs. 65 ± 7 and 12 wk: 406 ± 6 vs. 67 ± 6 μmol/g, P < 0.001, LPK vs. Lewis, respectively). This was reduced by treatment with perindopril (172 ± 48 μmol/g, 12 wk LPK P < 0.001). Medial cross-sectional area and elastic modulus/wall stress of the aorta were greater in LPK vs. Lewis control animals at 6 and 12 wk of age and showed an age-related increase that was prevented by treatment with perindopril (P < 0.001). Perindopril also ameliorated the degradation of elastin, increase in collagen content, and medial elastocalcinosis seen in 12-wk LPK. Overall, perindopril improved the structural and functional indices of aortic stiffness in the LPK rats, demonstrating a capacity for angiotensin-converting enzyme inhibition to limit vascular remodeling in chronic kidney disease.

Angiotensin II and the vascular phenotype in hypertension

Hypertension is associated with vascular changes characterised by remodelling, endothelial dysfunction and hyperreactivity. Cellular processes underlying these perturbations include altered vascular smooth muscle cell growth and apoptosis, fibrosis, hypercontractility and calcification. Inflammation, associated with macrophage infiltration and increased expression of redox-sensitive pro-inflammatory genes, also contributes to vascular remodelling. Many of these features occur with ageing, and the vascular phenotype in hypertension is considered a phenomenon of ‘premature vascular ageing’. Among the many factors involved in the hypertensive vascular phenotype, angiotensin II (Ang II) is especially important. Ang II, previously thought to be the sole effector of the renin–angiotensin system (RAS), is converted to smaller peptides [Ang III, Ang IV, Ang-(1-7)] that are biologically active in the vascular system. Another new component of the RAS is the (pro)renin receptor, which signals through Ang-II-independent mechanisms and might influence vascular function. Ang II mediates effects through complex signalling pathways on binding to its G-protein-coupled receptors (GPCRs) AT1R and AT2R. These receptors are regulated by the GPCR-interacting proteins ATRAP, ARAP1 and ATIP. AT1R activation induces effects through the phospholipase C pathway, mitogen-activated protein kinases, tyrosine kinases/phosphatases, RhoA/Rhokinase and NAD(P)H-oxidase-derived reactive oxygen species. Here we focus on recent developments and new research trends related to Ang II and the RAS and involvement in the hypertensive vascular phenotype.

Arterial aging--hemodynamic changes and therapeutic options

Arterial aging can be attributed to two different pathophysiological changes--increase in arterial stiffness and disturbed wave reflections. The capacity of the aorta to absorb the force exerted by the left ventricular ejection and dampen pulsatile flow becomes diminished with advancing age, owing to the progressive hardening of the arterial wall. These changes contribute to increase blood pressure, mainly systolic blood pressure and pulse pressure, which can trigger cardiovascular events. Understanding the pulsatile arterial hemodynamics that elevate cardiovascular risk has led to the use of pharmacological therapies, which prevent arterial stiffness and reduce wave reflections, and improve cardiovascular morbidity and mortality. Antifibrotic agents, such as those that block the renin-angiotensin-aldosterone pathway, are often given in association with diuretics, calcium-channel blockers, or both, but not with standard beta-blockers. Consistent reductions in cardiovascular outcomes obtained using these agents can be predicted through noninvasive measurements of central systolic blood pressure and pulse pressure.