In spontaneously hypertensive rats alterations in aortic wall properties precede development of hypertension

Dissociation of pulse wave velocity and aortic wall stiffness in diabetic db/db mice: The influence of blood pressure

Introduction: Vascular stiffness is a predictor of cardiovascular disease and pulse wave velocity (PWV) is the current standard for measuring in vivo vascular stiffness. Mean arterial pressure is the largest confounding variable to PWV; therefore, in this study we aimed to test the hypothesis that increased aortic PWV in type 2 diabetic mice is driven by increased blood pressure rather than vascular biomechanics. Methods and Results: Using a combination of in vivo PWV and ex vivo pressure myography, our data demonstrate no difference in ex vivo passive mechanics, including outer diameter, inner diameter, compliance (Db/db: 0.0094 ± 0.0018 mm²/mmHg vs. db/db: 0.0080 ± 0.0008 mm²/mmHg, p > 0.05 at 100 mmHg), and incremental modulus (Db/db: 801.52 ± 135.87 kPa vs. db/db: 838.12 ± 44.90 kPa, p > 0.05 at 100 mmHg), in normal versus diabetic 16 week old mice. We further report no difference in basal or active aorta biomechanics in normal versus diabetic 16 week old mice. Finally, we show here that the increase in diabetic in vivo aortic pulse wave velocity at baseline was completely abolished when measured at equivalent pharmacologically-modulated blood pressures, indicating that the elevated PWV was attributed to the concomitant increase in blood pressure at baseline, and therefore "stiffness." Conclusions: Together, these animal model data suggest an intimate regulation of blood pressure during collection of pulse wave velocity when determining in vivo vascular stiffness. These data further indicate caution should be exerted when interpreting elevated PWV as the pure marker of vascular stiffness.

Role of Vascular Receptors in the Development of Hypertension in the Elderly Population

Hypertension is a disease common in adults, with many risk factors and potentially life-threatening outcomes. Blood pressure is controlled by receptors that inform the brain about the amount of pressure inside the arteries, and the amount of oxygen and carbon dioxide in the blood, respectively. Research has revealed that baroreflex sensitivity (BRS) decreases with increasing age and that there is a high correlation between hypertension and low BRS. However, various studies with differing results have indicated that high blood pressure is what causes BRS to decline, and vice versa. Several studies have shown very conflicting results on the correlation between chemoreflex and age; there have been indications of chemoreflex having a positive, negative, and zero correlation with age. In several experiments, the surgical removal of the chemoreceptors of hypertensive rats was followed by a decrease in blood pressure. These animal experiments, and an additional noninvasive human experiment in which the chemoreceptors were temporarily "shut off," are reasons why more attention should be given to chemoreceptors as a route of alleviating hypertension.

Pathophysiology of Hypertension: The Mosaic Theory and Beyond

Dr Irvine Page proposed the Mosaic Theory of Hypertension in the 1940s advocating that hypertension is the result of many factors that interact to raise blood pressure and cause end-organ damage. Over the years, Dr Page modified his paradigm, and new concepts regarding oxidative stress, inflammation, genetics, sodium homeostasis, and the microbiome have arisen that allow further refinements of the Mosaic Theory. A constant feature of this approach to understanding hypertension is that the various nodes are interdependent and that these almost certainly vary between experimental models and between individuals with hypertension. This review discusses these new concepts and provides an introduction to other reviews in this compendium of Circulation Research.

Potential role of intermittent functioning of baroreflexes in the etiology of hypertension in spontaneously hypertensive rats

The spontaneously hypertensive rat (SHR) is a genetic model of primary hypertension with an etiology that includes sympathetic overdrive. To elucidate the neurogenic mechanisms underlying the pathophysiology of this model, we analyzed the dynamic baroreflex response to spontaneous fluctuations in arterial pressure in conscious SHRs, as well as in the Wistar-Kyoto (WKY), the Dahl salt-sensitive, the Dahl salt-resistant, and the Sprague-Dawley rat. Observations revealed the existence of long intermittent periods (lasting up to several minutes) of engagement and disengagement of baroreflex control of heart rate. Analysis of these intermittent periods revealed a predictive relationship between increased mean arterial pressure and progressive baroreflex disengagement that was present in the SHR and WKY strains but absent in others. This relationship yielded the hypothesis that a lower proportion of engagement versus disengagement of the baroreflex in SHR compared with WKY contributes to the hypertension (or increased blood pressure) in SHR compared with WKY. Results of experiments using sinoaortic baroreceptor denervation were consistent with the hypothesis that dysfunction of the baroreflex contributes to the etiology of hypertension in the SHR. Thus, this study provides experimental evidence for the roles of the baroreflex in long-term arterial pressure regulation and in the etiology of primary hypertension in this animal model.

Baroreflex dysfunction contributes to the etiology of hypertension in a genetic model of primary hypertension.

Mechanisms underlying Eugenia mattosii D. Legrand leaves extract, fractions and compounds induce relaxation of the aorta from normotensive and hypertensive rats

The present study aimed to verify the effect of methanolic extract, fractions, and phenolic compounds of Eugenia mattosii D. Legrand leaves on the aorta relaxation. Isometric tensions were measured on the aorta of normotensive (NTR) and spontaneously hypertensive rats (SHR). The results showed that both methanolic extracts of leaves and stems, as well as, fractions obtained from leaves were able to induce a concentration-dependent relaxation in both endothelium-intact and -denuded aortas. The methanolic extract of leaves (ME-leaves) was the most effective since the maximal relaxation (≈ 83%) obtained was at the concentration of 300 μg/mL. As the endothelium-dependent relaxation was more significant, we investigated the mechanisms by which ME-leaves induced this effect. After the pretreatment with LNAME, ME-leaves-induced relaxation was decreased in the aorta of NTR and SHR. However, the pretreatment with methylene blue only reduced the relaxation in the aorta of NTR. Furthermore, pretreatment with ME-leaves decreased phenylephrine-induced contraction in preparation Ca²⁺-free only in aortic rings from NTR. This study also reveals that both compounds, cryptostrobin isolated from chloroform fraction and catechin from the ethyl acetate fraction induced a marked relaxation in endotheliumintact aortic rings of NTR. In conclusion, ME-leaves induces relaxation in the rat aorta involves the modulation of NO/cGMP dependent signaling pathway, this mechanism may at least, in part, explain the endothelium-dependent relaxation. Furthermore, cryptostrobin and catechin also induced relaxation, which may contribute synergistically to the vasorelaxation effect of the ME-leaves.

Dietary Supplementation with Silicon-Enriched Spirulina Improves Arterial Remodeling and Function in Hypertensive Rats

Vascular aging is characterized by increase in arterial stiffness and remodeling of the arterial wall with a loss of elastic properties. Silicon is an essential trace element highly present in arteries. It is involved in the constitution and stabilization of elastin fibers. The nutritional supply and bioavailability of silicon are often inadequate. Spirulina (Sp), micro algae have recognized nutritional properties and are able to incorporate minerals in a bioavailable form. We evaluated the effects of nutritional supplementation with silicon-enriched spirulina (SpSi) on arterial system structure and function in hypertension. Experiments were performed on hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats supplemented with SpSi or Sp over a period of three months. Arterial pressure, vascular function and morphometric parameters of thoracic aorta were analyzed. SpSi supplementation lowered arterial pressure in SHR and minimized morphometric alterations induced by hypertension. Aortic wall thickness and elastic fibers fragmentation were partially reversed. Collagen and elastin levels were increased in association with extracellular matrix degradation decrease. Vascular reactivity was improved with better contractile and vasorelaxant responses to various agonists. No changes were observed in SHR supplemented with Sp. The beneficial effects of SpSi supplementation evidenced here, may be attributable to Si enrichment and offer interesting opportunities to prevent cardiovascular risks.

Conditional deletion of smooth muscle Cullin-3 causes severe progressive hypertension

Patients with mutations in Cullin-3 (CUL3) exhibit severe early onset hypertension but the contribution of the smooth muscle remains unclear. Conditional genetic ablation of CUL3 in vascular smooth muscle (S-CUL3KO) causes progressive impairment in responsiveness to nitric oxide (NO), rapid development of severe hypertension, and increased arterial stiffness. Loss of CUL3 in primary aortic smooth muscle cells or aorta resulted in decreased expression of the NO receptor, soluble guanylate cyclase (sGC), causing a marked reduction in cGMP production and impaired vasodilation to cGMP analogues. Vasodilation responses to a selective large conductance Ca2+-activated K+-channel activator were normal suggesting that downstream signals which promote smooth muscle-dependent relaxation remained intact. We conclude that smooth muscle specific CUL3 ablation impairs both cGMP production and cGMP responses and that loss of CUL3 function selectively in smooth muscle is sufficient to cause severe hypertension by interfering with the NO-sGC-cGMP pathway. Our study provides compelling evidence for the sufficiency of vascular smooth muscle CUL3 as a major regulator of BP. CUL3 mutations cause severe vascular dysfunction, arterial stiffness and hypertension due to defects in vascular smooth muscle.

Sex differences in mechanisms of arterial stiffness

Arterial stiffness progressively increases with aging and is an independent predictor of cardiovascular disease (CVD) risk. Evidence supports that there are sex differences in the time course of aging-related arterial stiffness and the associated CVD risk, which increases disproportionately in postmenopausal women. The association between arterial stiffness and mortality is almost twofold higher in women versus men. The differential clinical characteristics of the development of arterial stiffness between men and women indicate the involvement of sex-specific mechanisms. This review summarizes the current literature on sex differences in vascular stiffness induced by aging, obesity, hypertension, and sex-specific risk factors as well as the impact of hormonal status, diet, and exercise on vascular stiffness in males and females. An understanding of the mechanisms driving sex differences in vascular stiffness has the potential to identify novel sex-specific therapies to lessen CVD risk, the leading cause of death in males and females. LINKED ARTICLES: This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

Different Structural Alterations in Individual Conduit Arteries of SHRs Compared to Wistar Rats From the Prehypertensive Period to Late Adulthood

Structural changes of thoracic aorta (TA), carotid (CA) and iliac artery (IA) were assessed in Wistar and spontaneously hypertensive rats (SHR) aged 3, 17, and 52 weeks. Systolic blood pressure (sBP) was measured by plethysmography weekly. After perfusion fixation the arteries were processed for electron microscopy. The wall thickness (WT), cross-sectional area (CSA), inner diameter (ID), and WT/ID in all arteries and volume densities of endothelial cells (ECs), muscle cells (SMCs), and extracellular matrix (ECM) in TA were measured and their CSAs were calculated. In 3-week-old SHR compared to Wistar rats, sBP did not differ; in the TA, all parameters (WT, CSA, ID, WT/ID, CSA of SMCs, CSA of ECs, and CSA of ECM) were decreased; in CA, WT and CSA did not differ, ID was decreased, and WT/ID was increased; in IA, WT, CSA, and ID were increased. In 17- and 52-week-old SHRs, sBP and all parameters in all arteries were increased, only ID in IE in 52-week-old SHRs and CSA of ECs in the TA in 17-week-old SHRs did not change. Disproportionality between BP increase and structural alterations during ontogeny in SHR could reflect the flexibility of the arterial tree to the different needs of supplied areas.

Arterial stiffness and stroke: de-stiffening strategy, a therapeutic target for stroke

Stroke is the second leading cause of mortality and morbidity worldwide. Early intervention is of great importance in reducing disease burden. Since the conventional risk factors cannot fully account for the pathogenesis of stroke, it is extremely important to detect useful biomarkers of the vascular disorder for appropriate intervention. Arterial stiffness, a newly recognised reliable feature of arterial structure and function, is demonstrated to be associated with stroke onset and serve as an independent predictor of stroke incidence and poststroke functional outcomes. In this review article, different measurements of arterial stiffness, especially pressure wave velocity, were discussed. We explained the association between arterial stiffness and stroke occurrence by discussing the secondary haemodynamic changes. We reviewed clinical data that support the prediction role of arterial stiffness on stroke. Despite the lack of long-term randomised double-blind controlled therapeutic trials, it is high potential to reduce stroke prevalence through a significant reduction of arterial stiffness (which is called de-stiffening therapy). Pharmacological interventions or lifestyle modification that can influence blood pressure, arterial function or structure in either the short or long term are promising de-stiffening therapies. Here, we summarised different de-stiffening strategies including antihypertension drugs, antihyperlipidaemic agents, chemicals that target arterial remodelling and exercise training. Large and well-designed clinical trials on de-stiffening strategy are needed to testify the prevention effect for stroke. Novel techniques such as modern microscopic imaging and reliable animal models would facilitate the mechanistic analyses in pathophysiology, pharmacology and therapeutics.

Age and hypertension strongly induce aortic stiffening in rats at basal and matched blood pressure levels

Age and hypertension are major causes of large artery remodeling and stiffening, a cardiovascular risk factor for heart and kidney damage. The aged spontaneously hypertensive rat (SHR) model is recognized for human cardiovascular pathology, but discrepancies appeared in studies of arterial stiffness. We performed experiments using a robust analysis via echo tracking in 20-week adult (n = 8) and 80-week-old SHR (n = 7), with age-matched normotensive Wistar Kyoto rats (WKY, n = 6;6) at basal and matched levels of blood pressure (BP). After anesthesia with pentobarbital, abdominal aortic diameter and pressure were recorded and BP was decreased by clonidine i.v. At basal BP, aortic pulse distension, compliance, and distensibility (AD) were reduced and stiffness index increased with age and hypertension and further altered with age + hypertension. When BP was adjusted in SHR to that of normotensive rats (130 mmHg), there was no difference between 20-week-old SHR and WKY Importantly, the age effect was maintained in both WKY and SHR and accentuated by hypertension in old rats. At 130 mmHg, with similar pulse pressure in the four groups, AD (kPa(-3)) = 24.2 ± 1 in 20 weeks WKY, 19.7 ± 1.4 in 20 weeks SHR, 12.4 ± 1.3 in 80 weeks WKY and 6.6 ± 0.6 in 80 weeks SHR; distension = 7.6 ± 0.4%, 6.7 ± 0.6%, 3.7 ± 0.3%, and 1.8 ± 0.2% in the same groups. In conclusion, reduced distensibility, that is, stiffening due to age is clearly shown here in both WKY and SHR as well as a synergistic effect of age and hypertension. This technique will allow new studies on the mechanisms responsible and drug intervention.

"Smooth Muscle Cell Stiffness Syndrome"-Revisiting the Structural Basis of Arterial Stiffness

In recent decades, the pervasiveness of increased arterial stiffness in patients with cardiovascular disease has become increasingly apparent. Though, this phenomenon has been well documented in humans and animal models of disease for well over a century, there has been surprisingly limited development in a deeper mechanistic understanding of arterial stiffness. Much of the historical literature has focused on changes in extracellular matrix proteins—collagen and elastin. However, extracellular matrix changes alone appear insufficient to consistently account for observed changes in vascular stiffness, which we observed in our studies of aortic stiffness in aging monkeys. This led us to examine novel mechanisms operating at the level of the vascular smooth muscle cell (VSMC)—that include increased cell stiffness and adhesion to extracellular matrix—which that may be interrelated with other mechanisms contributing to arterial stiffness. We introduce these observations as a new concept—the Smooth Muscle Cell Stiffness Syndrome (SMCSS)—within the field of arterial stiffness and posit that stiffening of vascular cells impairs vascular function and may contribute stiffening to the vasculature with aging and cardiovascular disease. Importantly, this review article revisits the structural basis of arterial stiffness in light of these novel findings. Such classification of SMCSS and its contextualization into our current understanding of vascular mechanics may be useful in the development of strategic therapeutics to directly target arterial stiffness.

Cerebral angiography, blood flow and vascular reactivity in progressive hypertension

Chronic hypertension alters cerebral vascular morphology, cerebral blood flow (CBF), cerebrovascular reactivity, and increses susceptibility to neurological disorders. This study evaluated: i) the lumen diameters of major cerebral and downstream arteries using magnetic resonance angiography, ii) basal CBF, and iii) cerebrovascular reactivity to hypercapnia of multiple brain regions using arterial-spin-labeling technique in spontaneously hypertensive rats (SHR) at different stages. Comparisons were made with age-matched normotensive Wistar Kyoto (WKY) rats. In 10-week SHR, lumen diameter started to reduce, basal CBF, and hypercapnic CBF response were higher from elevated arterial blood pressure, but there was no evidence of stenosis, compared to age-matched WKY. In 20-week SHR, lumen diameter remained reduced, CBF returned toward normal from vasoconstriction, hypercapnic CBF response reversed and became smaller, but without apparent stenosis. In 40-week SHR, lumen diameter remained reduced and basal CBF further decreased, resulting in larger differences compared to WKY. There was significant stenosis in main supplying cerebral vessels. Hypercapnic CBF response further decreased, with some animals showing negative hypercapnic CBF responses in some brain regions, indicative of compromised cerebrovascular reserve. The territory with negative hypercapnia CBF responses corresponded with the severity of stenosis in arteries that supplied those territories. We also found enlargement of downstream vessels and formation of collateral vessels as compensatory responses to stenosis of upstream vessels. The middle cerebral and azygos arteries were amongst the most susceptible to hypertension-induced changes. Multimodal MRI provides clinically relevant data that might be useful to characterize disease pathogenesis, stage disease progression, and monitor treatment effects in hypertension.

Augmented vascular smooth muscle cell stiffness and adhesion when hypertension is superimposed on aging

Hypertension and aging are both recognized to increase aortic stiffness, but their interactions are not completely understood. Most previous studies have attributed increased aortic stiffness to changes in extracellular matrix proteins that alter the mechanical properties of the vascular wall. Alternatively, we hypothesized that a significant component of increased vascular stiffness in hypertension is due to changes in the mechanical and adhesive properties of vascular smooth muscle cells, and that aging would augment the contribution from vascular smooth muscle cells when compared with the extracellular matrix. Accordingly, we studied aortic stiffness in young (16-week-old) and old (64-week-old) spontaneously hypertensive rats and Wistar-Kyoto wild-type controls. Systolic and pulse pressures were significantly increased in young spontaneously hypertensive rats when compared with young Wistar-Kyoto rats, and these continued to rise in old spontaneously hypertensive rats when compared with age-matched controls. Excised aortic ring segments exhibited significantly greater elastic moduli in both young and old spontaneously hypertensive rats versus Wistar-Kyoto rats. were isolated from the thoracic aorta, and stiffness and adhesion to fibronectin were measured by atomic force microscopy. Hypertension increased both vascular smooth muscle cell stiffness and vascular smooth muscle cell adhesion, and these increases were both augmented with aging. By contrast, hypertension did not affect histological measures of aortic collagen and elastin, which were predominantly changed by aging. These findings support the concept that stiffness and adhesive properties of vascular smooth muscle cells are novel mechanisms contributing to the increased aortic stiffness occurring with hypertension superimposed on aging.

Heterogeneity in arterial remodeling among sublines of spontaneously hypertensive rats

OBJECTIVES

Spontaneously hypertensive rats (SHR) have been used frequently as a model for human essential hypertension. However, both the SHR and its normotensive control, the Wistar Kyoto rat (WKY), consist of genetically different sublines. We tested the hypothesis that the pathophysiology of vascular remodeling in hypertension differs among rat sublines.

METHODS AND RESULTS

We studied mesenteric resistance arteries of WKY and SHR from three different sources, at 6 weeks and 5 months of age. Sublines of WKY and SHR showed differences in blood pressure, body weight, vascular remodeling, endothelial function, and vessel ultrastructure. Common features in small mesenteric arteries from SHR were an increase in wall thickness, wall-to-lumen ratio, and internal elastic lamina thickness.

CONCLUSIONS

Endothelial dysfunction, vascular stiffening, and inward remodeling of small mesenteric arteries are not common features of hypertension, but are subline-dependent. Differences in genetic background associate with different types of vascular remodeling in hypertensive rats.

Remodeling of aorta extracellular matrix as a result of transient high oxygen exposure in newborn rats: implication for arterial rigidity and hypertension risk

Neonatal high-oxygen exposure leads to elevated blood pressure, microvascular rarefaction, vascular dysfunction and arterial (aorta) rigidity in adult rats. Whether structural changes are present in the matrix of aorta wall is unknown. Considering that elastin synthesis peaks in late fetal life in humans, and early postnatal life in rodents, we postulated that transient neonatal high-oxygen exposure can trigger premature vascular remodelling. Sprague Dawley rat pups were exposed from days 3 to 10 after birth to 80% oxygen (vs. room air control) and were studied at 4 weeks. Blood pressure and vasomotor response of the aorta to angiotensin II and to the acetylcholine analogue carbachol were not different between groups. Vascular superoxide anion production was similar between groups. There was no difference between groups in aortic cross sectional area, smooth muscle cell number or media/lumen ratio. In oxygen-exposed rats, aorta elastin/collagen content ratio was significantly decreased, the expression of elastinolytic cathepsin S was increased whereas collagenolytic cathepsin K was decreased. By immunofluorescence we observed an increase in MMP-2 and TIMP-1 staining in aortas of oxygen-exposed rats whereas TIMP-2 staining was reduced, indicating a shift in the balance towards degradation of the extra-cellular matrix and increased deposition of collagen. There was no significant difference in MMP-2 activity between groups as determined by gelatin zymography. Overall, these findings indicate that transient neonatal high oxygen exposure leads to vascular wall alterations (decreased elastin/collagen ratio and a shift in the balance towards increased deposition of collagen) which are associated with increased rigidity. Importantly, these changes are present prior to the elevation of blood pressure and vascular dysfunction in this model, and may therefore be contributory.

Increased vascular smooth muscle cell stiffness: a novel mechanism for aortic stiffness in hypertension

Increased vascular stiffness is fundamental to hypertension, and its complications, including atherosclerosis, suggest that therapy should also be directed at vascular stiffness, rather than just the regulation of peripheral vascular resistance. It is currently held that the underlying mechanisms of vascular stiffness in hypertension only involve the extracellular matrix and endothelium. We hypothesized that increased large-artery stiffness in hypertension is partly due to intrinsic mechanical properties of vascular smooth muscle cells. After confirming increased arterial pressure and aortic stiffness in spontaneously hypertensive rats, we found increased elastic stiffness of aortic smooth muscle cells of spontaneously hypertensive rats compared with Wistar-Kyoto normotensive controls using both an engineered aortic tissue model and atomic force microscopy nanoindentation. Additionally, we observed different temporal oscillations in the stiffness of vascular smooth muscle cells derived from hypertensive and control rats, suggesting that a dynamic component to cellular elastic stiffness is altered in hypertension. Treatment with inhibitors of vascular smooth muscle cell cytoskeletal proteins reduced vascular smooth muscle cell stiffness from hypertensive and control rats, suggesting their participation in the mechanism. This is the first study demonstrating that stiffness of individual vascular smooth muscle cells mediates vascular stiffness in hypertension, a novel concept, which may elucidate new therapies for hypertension and for vascular stiffness.

Beneficial effects of nebivolol and hydrochlorothiazide combination in spontaneously hypertensive rats

Objective

This study examined the combined effect of nebivolol (NEB) and hydrochlorothiazide (HCTZ) on cardiovascular function in spontaneously hypertensive rats (SHR).

Methods

SHR normotensive male rats were randomly assigned to five groups ( n = 8 per group): (i) SHR control group; (ii) NEB 2 mg/kg per day group; (iii) HCTZ 10 mg/kg per day group; (iv) NEB 2 mg/kg per day + HCTZ 10 mg/kg per day group; (v) Eight age-matched Wistar-Kyoto normotensive male rats served as the control group. All groups were treated orally for 8 weeks.

Results

The combination of NEB + HCTZ synergistically reduced systolic blood pressure and heart rate compared with either monotherapy. HCTZ increased water intake, which is a sign of diuresis. NEB reduced plasma angiotensin II concentration, which was increased in SHR and after HCTZ treatment. NEB + HCTZ increased plasma nitric oxide (NO) concentration and NO synthase activity, which were both reduced in SHR. NEB + HCTZ normalized femoral arterial vasorelaxation induced by acetylcholine, which was impaired in SHR.

Conclusions

The combination of NEB + HCTZ provided a number of beneficial and additive effects due to the synergistic characteristics of both drugs, in an experimental rat model of hypertension.

The onset of left ventricular diastolic dysfunction in SHR rats is not related to hypertrophy or hypertension

Left ventricular (LV) diastolic dysfunction, particularly relaxation abnormalities, are known to be associated with the development of LV hypertrophy (LVH). Preliminary human and animal studies suggested that early LV diastolic dysfunction may be revealed independently of LVH. However, whether LV diastolic dysfunction is compromised before the onset of hypertension and LVH remains unknown. We therefore evaluated LV diastolic function in spontaneously hypertensive rats (SHR) at different ages and tested whether LV diastolic dysfunction is associated with abnormal intracellular calcium homeostasis. LV systolic and diastolic functions were evaluated by invasive and echocardiographic methods in 3-week-old (without hypertension) and 5-week-old (with hypertension) SHR and Wistar-Kyoto control rats. Basal intracytoplasmic calcium and sarcoplasmic reticulum (SR) Ca2+ contents were measured in cardiomyocytes using fura-2 AM. Sarco(endo)plasmic Ca2+-ATPase isoform 2a (SERCA 2a) and phospholamban (PLB) expressions were quantified by Western blot and quantitative RT-PCR techniques. LV relaxation dysfunction was observed in 3-week-old SHR rats before onset of hypertension and LVH. An increase in basal intracytoplasmic Ca2+ and a decrease in SR Ca2+ release were demonstrated in SHR. Decreased expression of SERCA 2a and Ser16 PLB (p16-PLB) protein levels was also observed in SHR rats, whereas mRNA expression was not decreased. For the first time, we have shown that LV myocardial dysfunction precedes hypertension in 3-week-old SHR rats. This LV myocardial dysfunction was associated with high diastolic [Ca2+]i possibly due to decreased SERCA 2a and p16-PLB protein levels. Diastolic dysfunction may be a potential predictive marker of arterial hypertension in genetic hypertension syndromes.

Effect of tamoxifen on the coronary vascular reactivity of spontaneously hypertensive female rats

Tamoxifen has been associated with a reduction in the incidence of myocardial infarction. However, the effects of tamoxifen on coronary reactivity have not been fully elucidated. The objective of this study was to determine the effects of chronic treatment with tamoxifen on coronary vascular reactivity in spontaneously hypertensive rats (SHR). Female SHR were divided into four groups (N = 7 each): sham-operated (SHAM), sham-operated and treated with tamoxifen (10 mg/kg) by gavage for 90 days (TAMOX), ovariectomized (OVX), and ovariectomized and treated with tamoxifen (OVX+TAMOX). Mean arterial pressure (MAP), heart rate (HR), coronary perfusion pressure (CPP), and coronary vascular reactivity were measured. MAP and HR were reduced (9.42 and 11.67%, respectively) in the OVX+TAMOX group compared to the OVX group (P < 0.01). The coronary vascular reactivity of the OVX+TAMOX group presented smaller vasoconstrictor responses to acetylcholine (2-64 µg) when compared to the OVX group (P < 0.01) and this response was similar to that of the SHAM group. The adenosine-induced vasodilator response was greater in the TAMOX group compared to the SHAM and OVX groups (P < 0.05). Baseline CPP was higher in OVX+TAMOX and TAMOX groups (136 ± 3.6 and 130 ± 1.5 mmHg) than in OVX and SHAM groups (96 ± 2 and 119 ± 2.3 mmHg; P < 0.01). Tamoxifen, when combined with OVX, attenuated the vasoconstriction induced by acetylcholine and increased the adenosine-induced vasodilatory response, as well as reducing the MAP, suggesting beneficial effects of tamoxifen therapy on coronary vascular reactivity after menopause.

Aortic stiffness in vivo in hypertensive rat via echo-tracking: analysis of the pulsatile distension waveform

Large-artery stiffening is a major risk factor in aging and hypertension. Elevated blood pressure (BP) and vascular wall properties participate in arterial stiffening; we aimed to evaluate their respective role by combining echo-tracking and the spontaneously hypertensive rats (SHR) treated with low doses of a nitric oxide synthase inhibitor, shown to have arterial stiffening. Normotensive [Wistar-Kyoto (WKY)], SHR, and SHR treated for 2 wk with NG-nitro-l-arginine methyl ester (SHRLN) were anesthetized; BP and distension (pulsatile displacement) of the aortic walls with the ArtLab echo-tracking device were measured. Stiffness index increased in SHRLN vs. SHR; compliance, distensibility, and the slopes and area of the distension-pressure loop curve decreased. The pulsatile distension and pressure waveforms were strongly altered in SHRLN. Maximal values were decreased and increased, respectively, and the waveform kinetics also differed. Thus the area under the curve adjusted to heart rate (AUC/ms) was calculated. Acute BP reductions were induced by diltiazem in SHR and SHRLN, to levels similar to those of WKY. In SHR, compliance, distensibility, stiffness index, and the ascending slope of the distension-pressure loop reached the values of WKY, whereas they were only partially improved in SHRLN. Aortic distension (maximal value and AUC/ms) and the area of the distension-pressure loop were improved in SHR, but not in SHRLN. These data confirm the aortic stiffening induced by nitric oxide reduction in SHR. They show that the ArtLab system analyzes aortic stiffness in rats, and that the aortic pulsatile distension waveform is a parameter strongly dependent on the vascular wall properties.

Alteration of enzyme expressions in mevalonate pathway: possible role for cardiovascular remodeling in spontaneously hypertensive rats

BACKGROUND

The mevalonate pathway is an important metabolic pathway that plays a key role in multiple cellular processes. The aim of this study was to define whether the enzyme expression in mevalonate pathway changes during cardiovascular remodelling in spontaneously hypertensive rats (SHR).

METHODS AND RESULTS

Hearts and thoracic aortas were removed for the study of cardiovascular remodeling in SHR and Wistar-Kyoto rats (WKY). The protein expression of the enzymes in hearts, aortas and livers was analyzed by western blot. The histological measurements showed that the mass and the size of cardiomyocytes, the media thickness and the media cross-sectional area (MCSA) of the thoracic aorta were all increased in SHR since 3 weeks of age. In the heart, there was overexpression of some enzymes, including 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), farnesyl diphosphate synthase (FDPS), and geranylgeranyltransferase type I (GGTase-I), and downregulation of squalene synthetase (SQS) in SHR since 3 weeks of age. In the aorta, besides similar expressions of HMGR, SQS, FDPS and GGTase-I as in the heart, there was upregulation of farnesyltransferase α at 16 and 25 weeks of age and of farnesyltransferase β in 25-weeks-old SHR. Western blot demonstrated overexpression of HMGR and downregulation of SQS in SHR livers at all ages tested.

CONCLUSIONS

The cardiovascular remodeling of SHR preceded the development of hypertension, and altered expression of several key enzymes in the mevalonate pathway may play a potential pathophysiological role in cardiovascular remodeling.

IL-18 overexpression promotes vascular inflammation and remodeling in a rat model of metabolic syndrome

Although considerable evidence implicates the cytokine interlukin-18 (IL-18) in metabolic syndrome (MetS), the direct effect of IL-18 on vascular changes of MetS remains unknown. We investigated the chronic in vivo effect of IL-18 on development of MetS and vascular inflammation and remodeling by overexpressing IL-18 protein in fructose-fed rats (FFR), a model of MetS using intravenous administration of an adenovirus encoding rat IL-18. Increased serum IL-18 and vascular inflammatory response were found in FFR. Overexpression of IL-18 aggravated insulin resistance and enhance vascular inflammation and remodeling, which can be reflected by increased aortic expressions of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) and enhanced infiltration of macrophages and increased aortic wall thickness and wall-to-lumen ratio. Interestingly, the levels of interleukin-1 receptor-associated kinase 1 (IRAK1) and the activity of nucleus factor-kappaB (NF-kappaB) were also significantly increased. Together, these results indicated that chronic elevated IL-18 levels at a supraphsiological concentration aggravated insulin resistance, enhanced vascular inflammation and remodeling, probably by increasing the level of IRAK1 and the activity of NF-kappaB. Targeting expression of IL-18 or its specific downstream mediators may retard the progression of MetS and its complications.

Docosahexaenoic acid, but not eicosapentaenoic acid, lowers ambulatory blood pressure and shortens interval QT in spontaneously hypertensive rats in vivo

This study was designed to evaluate the effects of individual dietary long-chain n-3 polyunsaturated fatty acids (LCPUFA) on hypertension and cardiac consecutive disorders in spontaneously hypertensive rats (SHR) as compared to Wistar-Kyoto rats (WKY). Rats were fed for 2 months an eicosapentaenoic (EPA)- or docosahexaenoic acid (DHA)-rich diet (240 mg/day) or an n-3 PUFA-free diet. Male SHR (n=6), implanted with cardiovascular telemetry devices, were housed in individual cages for continuous measurements of cardiovascular parameters (blood pressure (BP) and heart rate (HR)) during either activity or rest periods, ECG were recorded during the quiet period. The n-6 PUFA upstream of arachidonic acid was affected in SHR tissues. The cardiac phospholipid fatty acid profile was significantly affected by dietary DHA supply, and EPA in a very lower extent, since DHA only was incorporated in the membranes instead of n-6 PUFAs. Endothelium n-6 PUFA content increased in all SHR groups. Compared to WKY, linoleic acid content decreased in both studied tissues. Cardiac noradrenalin decreased while the adrenal catecholamine stores decreased in SHR as compared to WKY. Both n-3 PUFA supply induced a decrease of adrenal catecholamine stores. Nevertheless after 6 weeks, DHA but not EPA induced a lowering-blood pressure effect and shortened the QT interval in SHR, most probably through its tissue enrichment and a specific effect on adrenergic function. Dietary DHA supply retards blood pressure development and has cardioprotective effect. These findings, showing the cardioprotective effects of DHA in living animals, were obtained in SHR, but may relate to essential hypertension in humans.

Heightened aberrant deposition of hard-wearing elastin in conduit arteries of prehypertensive SHR is associated with increased stiffness and inward remodeling

Elastin is a major component of conduit arteries and a key determinant of vascular viscoelastic properties. Aberrant organization of elastic lamellae has been reported in resistance vessels from spontaneously hypertensive rats (SHR) before the development of hypertension. Hence, we have characterized the content and organization of elastic lamellae in conduit vessels of neonatal SHR in detail, comparing the carotid arteries from 1-wk-old SHR with those from Wistar-Kyoto (WKY) and Sprague Dawley (SD) rats. The general structure and mechanics were studied by pressure myography, and the internal elastic lamina organization was determined by confocal microscopy. Cyanide bromide-insoluble elastin scaffolds were also prepared from 1-mo-old SHR and WKY aortas to assess their weight, amino acid composition, three-dimensional lamellar organization, and mechanical characteristics. Carotid arteries from 1-wk-old SHR exhibited narrower lumen and greater intrinsic stiffness than those from their WKY and SD counterparts. These aberrations were associated with heightened elastin content and with a striking reduction in the size of the fenestrae present in the elastic lamellae. The elastin scaffolds isolated from SHR aortas also exhibited increased relative weight and stiffness, as well as the presence of peculiar trabeculae inside the fenestra that reduced their size. We suggest that the excessive and aberrant elastin deposited in SHR vessels during perinatal development alters their mechanical properties. Such abnormalities are likely to compromise vessel expansion during a critical period of growth and, at later stages, they could compromise hemodynamic function and participate in the development of systemic hypertension.

Changes in the structure-function relationship of elastin and its impact on the proximal pulmonary arterial mechanics of hypertensive calves

Extracellular matrix remodeling has been proposed as one mechanism by which proximal pulmonary arteries stiffen during pulmonary arterial hypertension (PAH). Although some attention has been paid to the role of collagen and metallomatrix proteins in affecting vascular stiffness, much less work has been performed on changes in elastin structure-function relationships in PAH. Such work is warranted, given the importance of elastin as the structural protein primarily responsible for the passive elastic behavior of these conduit arteries. Here, we study structure-function relationships of fresh arterial tissue and purified arterial elastin from the main, left, and right pulmonary artery branches of normotensive and hypoxia-induced pulmonary hypertensive neonatal calves. PAH resulted in an average 81 and 72% increase in stiffness of fresh and digested tissue, respectively. Increase in stiffness appears most attributable to elevated elastic modulus, which increased 46 and 65%, respectively, for fresh and digested tissue. Comparison between fresh and digested tissues shows that, at 35% strain, a minimum of 48% of the arterial load is carried by elastin, and a minimum of 43% of the change in stiffness of arterial tissue is due to the change in elastin stiffness. Analysis of the stress-strain behavior revealed that PAH causes an increase in the strains associated with the physiological pressure range but had no effect on the strain of transition from elastin-dominant to collagen-dominant behavior. These results indicate that mechanobiological adaptations of the continuum and geometric properties of elastin, in response to PAH, significantly elevate the circumferential stiffness of proximal pulmonary arterial tissue.

Mechanisms of augmented vasoconstriction induced by 5-hydroxytryptamine in aortic rings from spontaneously hypertensive rats

BACKGROUND AND PURPOSE

To test whether development of enhanced vasoconstriction to 5-hydroxytryptamine (5-HT; serotonin) in SHR was temporally related to hypertension, elevated vascular superoxide (O(2)(-)) levels, decreased NO bioavailability, or increased contractile effects of cyclooxygenase or rho-kinase and/or PKC.

EXPERIMENTAL APPROACH

We examined systolic blood pressure (SBP), vascular O(2)(-), and 5-HT-induced contractile responses of aortic segments from 4- and 8-week-old WKY and SHR.

KEY RESULTS

SBP was 35% higher in SHR than WKY at 4 weeks and 60% higher at 8 weeks. Contractile responses to 5-HT were similar in WKY and SHR at 4 weeks, but were markedly augmented in SHR at 8 weeks. The NO synthase inhibitor, L-NAME, enhanced contractile responses to 5-HT markedly in both strains at 4 weeks and in WKY at 8 weeks, but only very modestly in SHR at 8 weeks. These functional differences were associated with higher O(2)(-) levels in SHR versus WKY at 8 weeks, but not at 4 weeks. The rho-kinase inhibitor, Y-27632, and the PKC inhibitor, Ro 31-8220, each only modestly attenuated contractions in WKY and SHR in each age group, and their effects in each strain were more pronounced at 8 weeks. The cyclooxygenase inhibitor, indomethacin, had no effect on contractile responses.

CONCLUSIONS AND IMPLICATIONS

Development of augmented vascular contractile responses to 5-HT in SHR is preceded by hypertension. It is associated with increased vascular O(2)(-) levels and reduced modulatory effects of NO, and is unlikely to be due to enhanced activity of rho-kinase, PKC or cyclooxygenase.

Hypertension increases middle cerebral artery resting tone in spontaneously hypertensive rats: role of tonic vasoactive factor availability

The present study explores the contribution of alterations in resting tone to cerebral artery narrowing in SHRs (spontaneously hypertensive rats) and the role of hypertension development. Young pre-hypertensive and adult fully hypertensive SHRs and age-matched Wistar–Kyoto rat controls were used. The contribution of basal vasoactive factors to resting tone was studied in middle cerebral arteries with pressure myography. Basal NO and O2− (superoxide anion) availability were determined with fluorescent indicators using confocal microscopy and lucigenin-enhanced chemiluminescence. Basal O2− was also assessed in mesenteric resistance arteries. Middle cerebral arteries from adult rats, but not young pre-hypertensive rats, had augmented myogenic responses and resting tone and decreased relaxation to sodium nitroprusside compared with their normotensive counterparts. Cerebral arteries from adult SHRs also had an increase in tonic NO associated with a decrease in basal O2− availability. Basal O2− was instead increased in mesenteric arteries from SHRs. The present results indicate that large cerebral arteries from SHRs have an increase in their resting tone as a consequence of sustained hypertension and that this is related to a decrease in NO responsiveness. We suggest that this increase in resting tone and myogenic responses could act as a protective mechanism against the development of stroke in SHRs. The present study also demonstrates some unusual findings regarding the current understanding of the NO/O2− balance in hypertension with important differences between vascular beds and draws attention to the complexity of this balance in cardiovascular health and disease.

Role of Matrix Metalloproteinases in Early Hypertensive Vascular Remodeling

Hypertension is associated with vascular remodeling characterized by rearrangement of extracellular matrix proteins. To evaluate how matrix metalloproteinase (MMP)-9 contributes to the progression of hypertensive vascular disease in vivo, wild-type (wt) or MMP-9(-/-) mice were treated with angiotensin II (Ang II; 1 microg/kg per minute, by minipump) plus a 5% NaCl diet during 10 days. Baseline blood pressure was equivalent in wt and knockout mice, but Ang II treatment increased systolic blood pressure to a greater extent (P<0.05) in MMP-9(-/-) mice (94+/-6 to 134+/-6 mm Hg; P<0.001) than in wt animals (93+/-4 to 114+/-6 mm Hg; P<0.01). In wt mice, Ang II treatment increased the carotid artery pressure-diameter relationship significantly, and maximal diameter reached 981+/-19 microm (P<0.01 versus sham; 891+/-10 microm). In contrast, in MMP-9(-/-) mice, carotid artery compliance was actually reduced after Ang II (P<0.05), and maximal diameter only reached 878+/-13 microm. Ang II treatment induced MMP-2 and increased carotid media thickness equally in both phenotypes. However, MMP-9 induction and in situ gelatinase activity were only enhanced in Ang II-treated wt mice, and vessels from these mice also produced more collagen I breakdown products than their MMP-9(-/-) counterparts (P<0.05). Inversely, staining for collagen IV was particularly enhanced in vessels from MMP-9(-/-) mice treated with Ang II. These results demonstrate the following: (1) the onset of Ang II-induced hypertension is accompanied by increased MMP-9 activity in conductance vessels; (2) absence of MMP-9 activity results in vessel stiffness and increased pulse pressure; and (3) MMP-9 activation is associated with a beneficial role early on in hypertension by preserving vessel compliance and alleviating blood pressure increase.

Etiologic factors associated with symptomatic achilles tendinopathy

BACKGROUND

The purpose of this study was to determine if a statistical association exists between Achilles tendinopathy (also referred to as tendinosis) and obesity, diabetes mellitus, hypertension, the supplemental use of estrogen, and exposure to local or systemic steroids.

METHODS

From July, 1997, to February, 2003, 82 patients with a diagnosis of Achilles tendinopathy were identified. The diagnosis of Achilles tendinopathy was confirmed by a review of medical records, radiographs, and MRI. There were 44 women and 38 men with an average age of 50 (range 27 to 77) years. For the parameters of obesity, hypertension, diabetes, steroid exposure, and the use of estrogen compounds, all patients were analyzed both cumulatively and stratified into subgroups by gender and age. Chi-square 2 x 2 tables were used to compare the observed prevalence of the parameters in patients with Achilles tendinopathy to the expected prevalence of these disorders and exposures in the population at large.

RESULTS

Cumulatively, 98% percent (43 of 44 women; 29 of 38 men) had hypertension, diabetes, obesity, and steroid or estrogen exposure. Seventy-six percent of men (29) had hypertension, diabetes, and obesity, or steroid exposure. Sixty-eight percent of women (15 of 22) had a history of hormone replacement therapy and 44% (8 of 15) had a positive history for use of oral contraceptives. When compared with published national data using Chi-square analysis, the association between tendinopathy and hormone replacement therapy and oral contraceptives was found to be statistically significant with p-values of 0.01 and 0.001, respectively. For both women and men, obesity was statistically associated with Achilles tendinopathy with p-values of 0.025 and. 001, respectively. Hypertension was statistically associated with Achilles tendinopathy only for women. Diabetes mellitus and Achilles tendinopathy were found to have a statistical association only for men younger than 44 years old

CONCLUSIONS

Obesity, hypertension, and steroids have as their end-organ effect a diminution of local microvascularity. The significant correlation of these factors with Achilles tendinopathy suggests the importance of their effect on microvascularity in the development of Achilles tendinopathy.

Dissociation between vascular oxidative stress and cardiovascular function in Wistar Kyoto and spontaneously hypertensive rats

It has not been completely demonstrated if hypertension may, in part, develop as a result of increased oxidative stress (OS), inflammation and little is known about the short-term effects of antioxidant therapy. This study was designed to appreciate the effect of 7 days vitamin C-enriched diet (5 g/kg/day) on hemodynamic function and vascular OS in normotensive Wistar Kyoto rats and hypertensive rats (SHR). Aorta NAD(P)H oxidase activity was determinate and free radicals evaluated by electron spin resonance with a spin probe CP-H. Matrix metalloproteinase-1 (MMP-1) and monocyte chemoattractant protein-1 (MCP-1) expression were measured. The treatment with vitamin C did not change arterial pressure in SHR but prevented the increase in OS levels in SHR aortas. MMP-1 and MCP-1 expressions were more intense in the media of SHR aortas than in those of WKY rats but these expressions were not modified by vitamin C-pretreatment. Vitamin C-pretreatment was not able to protect heart against in vitro ischemia-reperfusion dysfunctions. These data may suggest that treatment with high doses of vitamin C in SHR can limit over-production of reactive oxygen species; however this effect was not accompanied with changes in arterial pressure and protection against I-R dysfunctions. Dissociation between vascular oxidative stress and cardiovascular function may be evoked.

Differential renal gene expression in prehypertensive and hypertensive spontaneously hypertensive rats

Development of hypertension stems from both environmental and genetic factors wherein the kidney plays a central role. Spontaneously hypertensive rats (SHR) and the nonhypertensive Wistar-Kyoto (WKY) controls are widely used as a model for studying hypertension. The present study examined the renal gene expression profiles between SHR and WKY at a prehypertensive stage (3 wk of age) and hypertensive stage (9 wk of age). Additionally, age-related changes in gene expression patterns were examined from 3 to 9 wk in both WKY and SHR. Five to six individual kidney samples of the same experimental group were pooled together, and quadruplicate hybridizations were performed using the National Institute of Environmental Health Sciences Rat version 2.0 Chip, which contains ∼6,700 genes. Twenty two genes were found to be differentially expressed between SHR and WKY at 3 wk of age, and 104 genes were differentially expressed at 9 wk of age. Soluble epoxide hydrolase ( Ephx2) was found to be significantly upregulated in SHR at both time points and was the predominant outlier. Conversely, elastase 1 ( Ela1) was found to be the predominant gene downregulated in SHR at both time points. Analysis of profiles at 3 vs. 9 wk of age identified 508 differentially expressed genes in WKY rats. In contrast, only 211 genes were found to be differentially expressed during this time period in SHR. The altered gene expression patterns observed in the age-related analysis suggested significant differences in the vascular extracellular matrix system between SHR and WKY kidney. Together, our data highlight the complexity of hypertension and the numerous genes involved in and affected by this condition.

Urotensin II-induced hypotensive responses in Wistar-Kyoto (Wky) and spontaneously hypertensive (Shr) rats

Human urotensin II (hU-II) is a potent vasoactive peptide which modulates some of the functions of the cardiovascular and other systems. The in vivo mechanism of action by which hU-II may influence blood pressure in developmental and pathological conditions, is poorly understood. Herein, the blood pressure effects of hU-II (0.1-10 nmol/kg) injected intravenously (i.v.) were studied on ketamine/xylazine anesthetized male WKY and SHR rats aged 4 and 8 weeks. hU-II elicited dose-dependent decreases in mean arterial pressure in both strains of animals. The hypotensive responses to hU-II were, however, significantly higher in SHR rats, independently of age. Four-week-old SHR rats (which are normotensive) were, however, less responsive than their hypertensive 8-week-old counterparts. A series of pharmacological inhibitors were used to identify putative endogenous (endothelial) factors that might account for the hU-II-mediated hypotension in 8-week-old SHR. These include the non-selective nitric oxide synthase inhibitor L-NAME (5 micromol/kg), the non-selective cyclooxygenase inhibitor meclofenamate (16 micromol/kg), the voltage-sensitive and ATP-sensitive K+-channel inhibitors, 4-aminopyridine (5 micromol/kg) and glybenclamide (10 micromol/kg), the cytochrome P450 CYP2C9 inhibitor sulfaphenazole (15 micromol/kg), the cytoskeletal fixation agent phalloidin (15 micromol/kg), the endothelin ETB receptor antagonist BQ-788(35 micromol/kg), the bradykinin B2 receptor antagonist HOE 140 (0.5 micromol/kg), the angiotensin AT2 antagonist PD 123319(10 micromol/kg) and the UT receptor antagonist urantide (10 micromol/kg). These agents were administered i.v. either at 2.5, 10 or 40 min prior hU-II injection (10 nmol/kg). Among these inhibitors, sulfaphenazole and phalloidin were able to reduce hU-II-induced hypotension. This suggests that the vasodepressor effect of hU-II is mediated by UT receptors and relies in part on the release of epoxide related products; increased microvascular permeability may also contribute to the blood pressure lowering effect of hU-II. Since urantide blocks the constrictor effects of hU-II on isolated aorta, but is inactive against the hypotensive action of hU-II in vivo, the results presented in this paper provide, for the first time, evidence for the existence of two different functional sites for hU-II.

Developmental programming of aortic and renal structure in offspring of rats fed fat-rich diets in pregnancy

Evidence from human and animal studies suggests that maternal nutrition can induce developmental programming of adult hypertension in offspring. We have previously described a model of maternal dietary imbalance in Sprague-Dawley rats whereby administration of a maternal diet rich in animal lard programmes the development of increased blood pressure, insulin resistance, dyslipidaemia, obesity and mesenteric artery endothelial dysfunction in adult offspring. To further characterize the mechanism of hypertension in this model we have examined vascular and renal structure in adult offspring of Sprague-Dawley rats fed a control diet (OC) or lard-rich diet (OHF) during pregnancy and suckling followed by a control diet post-weaning. To gain further insight, we assessed aortic reactivity and elasticity in an organ bath preparation and renal renin and Na+,K+-ATPase activity. Plasma aldosterone concentration was also measured. Stereological examination of the aorta in OHF demonstrated reduced endothelial cell volume and smooth muscle cell number compared with OC. Adult OHF animals showed increased aortic stiffness and reduced endothelium-dependent relaxation. Renal stereology showed no differences in kidney weight, glomerular number or volume in OHF compared with OC, but renin and Na+,K+-ATPase activity were significantly reduced in OHF compared with controls. Programmed alterations to aortic structure and function are consistent with previous observations that exposure to maternal high fat diets produces systemic vascular changes in the offspring. Despite normal renal stereology, altered renal Na+,K+-ATPase and renin activity offers further insight into the mechanism underlying the increased blood pressure characteristic of this model.

Non-invasive ultrasound in arterial wall dynamics in humans: what have we learned and what remains to be solved

In the past decades, non-invasive vascular ultrasound has substantially improved our insights into artery wall dynamics under normal circumstances and in disease. Although we have learned a lot, the methods in use are subject to improvement. In this review, we discuss the most important achievements in non-invasive assessment of dynamic artery wall properties in humans with emphasis on the clinical relevance of the observations. Special attention will be paid to the changes observed in aging, and in essential and borderline hypertension, because the loss of compliance (i.e. the ability to store volume thereby reducing pressure increases during ejection) of the elastic arteries in the elderly and in these patients possibly has consequences on their management. The changes in dynamic artery wall properties in diabetes and atherosclerosis are briefly discussed as well. A new approach to the determination of baroreceptor sensitivity, using artery stretch as input, is presented. The review starts with a description of the parameters most commonly used to describe dynamic artery wall properties and of the techniques employed to assess these parameters. The problems encountered in these assessments and the possible solutions to these problems are addressed as well.

Contractile Responses of Aortae from WKY and SHR to Vasoconstrictors

Aortae taken from spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats aged 4, 8 and 16 weeks were prepared as rings and used to measure the effects of five vasoconstrictors. The endothelium was removed in order to measure selectively the contractile responses induced by potassium chloride (KCl), phenylephrine (PHE), angiotensin-II (Ang II), endothelin-1 (ET-1) and human urotensin-II (U-II). These responses were assumed to derive from the activation of specific receptors (namely alpha1, AT1, ETA and UT-II) or from depolarization of the smooth muscle fibers by KCl. Specific antagonists prazosin, losartan, BQ-123 and [Orn8]-UII were used at various concentrations for a pharmacological characterization of these latter receptor systems. The primary purpose of the study was to explore mechanisms or factors that may intervene in the development and maintenance of high blood pressure in SHR. Results indicate that isolated aortae of SHR and WKY contain contractile sites (receptors) whose pharmacological profiles (pEC50 for agonists, pA2 for antagonists) are very similar to those of other biological systems and should be considered as typical for the alpha1, AT1, ETA and UT-II receptor types. Aortae taken from SHR 4 (non hypertensive), 8 and 16 weeks old (hypertensive) responded to the vasoconstrictors with reduced maximal contractions compared to those of age-matched WKY. These unexpected reduced responses of aortae, observed with the five vasoconstrictors, may be attributed to a non specific lesions. Maximal contraction of aortae from SHR increased from 4 to 16 weeks for KCI, PHE and U-II, decreased for Ang II, and remained stable for ET-1. There was also an age-dependent increase of maximal contraction induced by U-II in WKY. It is suggested that aortae from SHR undergo early remodelling that leads to reduced contractility in vitro and possibly to vessel rigidity in vivo. The factors involved in this process appear to be of genetic origin since they are present before hypertension: they may contribute to modify aortic compliance and perhaps vascular resistance in hypertensive animals and thus being the cause and not the consequence of high blood pressure.

Erectile dysfunction: an early marker for hypertension? A longitudinal study in spontaneously hypertensive rats

Erectile dysfunction (ED) is another manifestation of vascular disease. We evaluated the natural history of ED in the spontaneously hypertensive rat (SHR) and the respective participation of associated pathophysiological modifications, i.e., endothelial dysfunction and tissue remodeling. SHR and their normotensive counterparts [Wistar-Kyoto rats (WKY)] of 6, 12, and 24 wk of age (n = 12) were used to evaluate erectile function, erectile and aortic tissue reactivity, and remodeling. Erectile responses in SHR are reduced at all ages (P < 0.001). In both aortic and erectile tissues of SHR and WKY, relaxations to ACh are altered progressively with age, although more markedly in SHR. They are decreased at 12 wk of age in erectile tissue of SHR compared with WKY (maximal relaxation: -19.2 +/- 2.8% vs. -28.3 +/- 3.9%, P < 0.001) but only at 24 wk of age in aortas (-47.9 +/- 6.4% vs. -90.5 +/- 2.9%, P < 0.001). Relaxations to sodium nitroprusside are unaltered in aortic rings of both strains but enhanced in erectile tissue of SHR at 12 wk of age. Major modifications in the distribution of collagen I, III, and V in SHR occur in both types of tissue and are detectable sooner in erectile tissue compared with aortic tissue. The onset of ED is detectable before the onset of hypertension in the SHR. Structural and functional alterations, while similar, occur earlier in erectile compared with vascular tissue. If confirmed in humans, ED could be an early warning sign for hypertension, and common therapeutic strategies targeting both ED and hypertension could be investigated.

Hypoxia induces aortic hypertrophic growth, left ventricular dysfunction, and sympathetic hyperinnervation of peripheral arteries in the chick embryo

BACKGROUND

Low birth weight is associated with an increased incidence of cardiovascular diseases, including hypertension, later in life. This suggests that antenatal insults program for fetal adaptations of the circulatory system. In the present study, we evaluated the effects of mild hypoxia on cardiac function, blood pressure control, and arterial structure and function in near-term chick embryos.

METHODS AND RESULTS

Chick embryos were incubated under normoxic (21% O2) or hypoxic (15% O2) conditions and evaluated at incubation day 19 by use of histological techniques, isolated heart preparations, and in vivo measurements of sympathetic arterial tone and systemic hemodynamics. Chronic hypoxia caused a 33% increase in mortality and an 11% reduction in body weight in surviving embryos. The lumen of the ascending aorta in hypoxic embryos was 23% smaller. Left ventricular systolic pressure was 22% lower, and heart weight/body weight ratio was 14% higher. In resistance arteries of hypoxic embryos, in vivo baseline tone was 23% higher, norepinephrine sensitivity was similar, and norepinephrine release from sympathetic nerves increased 2-fold, indicating sympathetic hyperinnervation. Mean arterial pressure and heart rate were similar under resting conditions, but chronically hypoxic embryos failed to maintain blood pressure during acute stress.

CONCLUSIONS

This study indicates that mild hypoxia during embryonic development induces alterations in cardiac and vascular function and structure and affects hemodynamic regulation. These findings reveal that antenatal insults have profound effects on the control and design of the circulatory system that are already established at birth and may program for hypertension and heart failure at a later age.

Early changes in proteoglycans production by resistance arteries smooth muscle cells of hypertensive rats

Several functional and structural modifications at the vascular level have been described in spontaneously hypertensive rats (SHR) during the early development of hypertension. In this study, we hypothesize that changes in the extracellular matrix (ECM) could precede the development of hypertension. Synthesis of secreted and membrane-bound sulfated proteoglycans (S-PG) by cultured vascular smooth muscle cells (VSMC) obtained from young spontaneously hypertensive rats (pSHR) mesenteric resistance arteries, during the period preceding the elevation of blood pressure (BP) was tested. After 24 h of stimulation with angiotensin II (Ang II), 10% fetal calf serum (FCS), or 0.1% FCS as control, medium and cell layer S-PG synthesis was evaluated by labeling sulfated disaccharides with [35S] sodium sulfate. To relate this variable with cell proliferation, DNA synthesis was measured by incorporation of [3H]thymidine in the cell lysate. The VSMC from pSHR synthesized more secreted and membrane-bound S-PG than age-matched Wistar rat (pW) cells in the nonstimulated (0.1% FCS) and stimulated (Ang II or 10% FCS) experimental groups. When data were expressed as percent of their own control value, both Ang II and 10% FCS lowered basal secreted and cell-associated S-PG content in VSMC from pSHR, whereas in pW rat cells, these agents produced a small increase or no change. An inverse relationship between proliferation and total S-PG production (secreted plus membrane-bound) was found in pSHR cells, but not in pW cells. In conclusion, the present study demonstrates that changes in S-PG synthesis by VSMC of resistance arteries precede the vascular dysfunction associated with the development of hypertension in SHR.

Effect of a COL1A1 Sp1 binding site polymorphism on arterial pulse wave velocity: an index of compliance

-Reduced arterial compliance precedes changes in blood pressure, which may be mediated through alterations in vessel wall matrix composition. We investigated the effect of the collagen type I-alpha1 gene (COL1A1) +2046G>T polymorphism on arterial compliance in healthy individuals. We recruited 489 subjects (251 men and 238 women; mean age, 22.6+/-1.6 years). COL1A1 genotypes were determined using polymerase chain reaction and digestion by restriction enzyme Bal1. Arterial pulse wave velocities were measured in 3 segments, aortoiliac (PWVA), aortoradial (PWVB), and aorto-dorsalis-pedis (PWVF), as an index of compliance using a noninvasive optical method. Data were available for 455 subjects. The sample was in Hardy-Weinberg equilibrium with genotype distributions and allele frequencies that were not significantly different from those reported previously. The T allele frequency was 0.22 (95% confidence interval, 0.19 to 0.24). Two hundred eighty-three (62.2%) subjects were genotype GG, 148 (35.5%) subjects were genotype GT, and 24 (5.3%) subjects were genotype TT. A comparison of GG homozygotes with GT and TT individuals demonstrated a statistically significant association with arterial compliance: PWVF 4.92+/-0.03 versus 5.06+/-0.05 m/s (ANOVA, P=0.009), PWVB 4.20+/-0.03 versus 4.32+/-0.04 m/s (ANOVA, P=0.036), and PWVA 3.07+/-0.03 versus 3.15+/-0.03 m/s (ANOVA, P=0.045). The effects of genotype were independent of age, gender, smoking, mean arterial pressure, body mass index, family history of hypertension, and activity scores. We report an association between the COL1A1 gene polymorphism and arterial compliance. Alterations in arterial collagen type 1A deposition may play a role in the regulation of arterial compliance.