??-Adrenoceptor-mediated, nitric-oxide-dependent vasodilatation is abnormal in early hypertension

Sinapine Thiocyanate Ameliorates Vascular Endothelial Dysfunction in Hypertension by Inhibiting Activation of the NLRP3 Inflammasome

The increase of blood pressure is accompanied by the changes in the morphology and function of vascular endothelial cells. Vascular endothelial injury and hypertension actually interact as both cause and effect. A large number of studies have proved that inflammation plays a significant role in the occurrence and development of hypertension, but the potential mechanism between inflammation and hypertensive endothelial injury is still ambiguous. The purpose of this study was to explore the association between the activation of NLRP3 inflammasome and hypertensive endothelial damage, and to demonstrate the protective effect of sinapine thiocyanate (ST) on endothelia in hypertension. The expression of NLRP3 gene was silenced by tail vein injection of adeno-associated virus (AAVs) in spontaneously hypertensive rats (SHRs), indicating that activation of NLRP3 inflammasome accelerated hypertensive endothelial injury. ST not only protected vascular endothelial function in SHRs by inhibiting the activation of NLRP3 inflammasome and the expression of related inflammatory mediators, but also improved AngII-induced huvec injury. In summary, our results show that alleviative NLRP3 inflammasome activation attenuates hypertensive endothelial damage and ST ameliorates vascular endothelial dysfunction in hypertension via inhibiting activation of the NLRP3 inflammasome.

Forearm vasodilatation to a β2 -adrenergic receptor agonist in premenopausal and postmenopausal women

NEW FINDINGS

What is the central question of this study? What is the role of β₂ -adrenergic receptor (β₂ AR) vasodilatation in older postmenopausal women as compared to premenopausal women and the role of nitric oxide (NO) in β₂ AR-mediated vasodilatation in both groups of women? What is the main finding and its importance? β₂ AR responsiveness is blunted in postmenopausal women compared to young premenopausal women. Additionally, NO may contribute to β₂ AR-mediated vasodilatation in young premenopausal women.

ABSTRACT

β₂ -Adrenergic receptor (β₂ AR)-mediated vasodilatation, which is partially dependent on nitric oxide (NO) formation, is blunted in men at risk for developing hypertension. However, the role of β₂ AR vasodilatation in hypertension pathophysiology in ageing postmenopausal women is unclear. Therefore, the goals of this study were to determine if forearm vasodilatation to the selective β₂ AR agonist terbutaline is blunted in older postmenopausal women (59 ± 4 years) compared to young premenopausal women (27 ± 3 years) and to assess NO contribution to β₂ AR-mediated vasodilatation in both groups of women. Forearm blood flow (FBF) and forearm vascular conductance (FVC) were measured using venous occlusion plethysmography at baseline and during intra-arterial infusions of terbutaline at 0.1-2.0 µg (100 ml tissue)^-1  min^-1 with and without the NO synthase inhibitor l-N^G -monomethylarginine (l-NMMA). Mean arterial pressure was significantly greater in postmenopausal women than in young women at baseline (P = 0.01). Baseline FBF and FVC did not differ between young and postmenopausal women (P > 0.05) and rose significantly within each group during terbutaline infusion (P < 0.05). There were significant group × dose interactions for FBF (P = 0.01) and FVC (P = 0.001), indicating vasodilator responses were lower in postmenopausal women. In young women, FVC response to the highest dose of terbutaline tended to be lower with l-NMMA co-infusion vs. without l-NMMA (P = 0.05). There were no significant decreases in FBF or FVC responses to terbutaline in postmenopausal women with l-NMMA co-infusion (P > 0.05 for all). These data suggest that β₂ AR responsiveness is blunted in postmenopausal women compared to young premenopausal women, and that NO may contribute to β₂ AR-mediated vasodilatation in young premenopausal women.

Forearm vasodilator responses to environmental stress and reactive hyperaemia are impaired in young South Asian men

Purpose

Prevalence of cardiovascular disease (CVD) is greater in South Asians (SAs) than White Europeans (WEs). Endothelial dysfunction and blunted forearm vasodilatation to environmental stressors have been implicated in CVD. We investigated whether these features are present in young SA men.

Methods

In 15 SA and 16 WE men (19–23 years), we compared changes in forearm blood flow, arterial blood pressure (ABP), forearm vascular conductance (FVC), heart rate, and electrodermal resistance (EDR; sweating) following release of arterial occlusion (reactive hyperaemia endothelium-dependent) and 5 single sounds at 5–10 min intervals (stressors).

Results

All were normotensive. Peak reactive hyperaemia was smaller in SAs than WEs (FVC increase: 0.36 ± 0.038 vs 0.44 ± 0.038 units; P < 0.05). Furthermore, in WEs, mean FVC increased at 5, 15, and 20 s of each sound (vasodilatation), but increased at 5 s only in SAs, decreasing by 20 s (vasoconstriction). This reflected a smaller proportion of SAs showing forearm vasodilatation at 15 s (5/15 SAs vs 11/16 WEs: P < 0.01), the remainder showing vasoconstriction. Concomitantly, WEs showed greater bradycardia and EDR changes. Intra-class correlation analyses showed that all responses were highly reproducible over five sounds in both WEs and SAs. Moreover, sound-evoked changes in ABP and FVC were negatively correlated in each ethnicity (P < 0.01). However, WEs showed preponderance of forearm vasodilatation and depressor responses; SAs showed preponderance of vasoconstriction and pressor responses.

Conclusions

Endothelium-dependent vasodilatation is blunted in young SA men. This could explain their impaired forearm vasodilatation and greater pressor responses to repeated environmental stressors, so predisposing SAs to hypertension and CVD.

Pressor recovery after acute stress is impaired in high fructose-fed Lean Zucker rats

Insulin resistance is a powerful predictor of cardiovascular disease; however, the mechanistic link remains unclear. This study aims to determine if early cardiovascular changes associated with short‐term fructose feeding in the absence of obesity manifest as abnormal blood pressure control. Metabolic dysfunction was induced in Lean Zucker rats by short‐term high‐fructose feeding. Rats were implanted with telemetry devices for the measurement of mean arterial blood pressure (MAP) and subjected to air jet stress at 5 and 8 weeks after feeding. Additional animals were catheterized under anesthesia for the determination of MAP and blood flow responses in the hind limb and mesenteric vascular beds to intravenous injection of isoproterenol (0.001–0.5 μm), a β‐adrenergic agonist. Metabolic dysfunction in high‐fructose rats was not accompanied by changes in 24‐h MAP. Yet, animals fed a high‐fructose diet for 8 weeks exhibited a marked impairment in blood pressure recovery after air‐jet stress. Dose‐dependent decreases in MAP and peripheral blood flow in response to isoproterenol treatment were significantly attenuated in high‐fructose rats. These data suggest that impaired blood pressure recovery to acute mental stress precedes the onset of hypertension in the early stages of insulin resistance. Further, blunted responses to isoproterenol implicate β₂‐adrenergic sensitivity as a possible mechanism responsible for altered blood pressure control after short‐term high‐fructose feeding.

Abnormal mitochondrial L-arginine transport contributes to the pathogenesis of heart failure and rexoygenation injury

Background

Impaired mitochondrial function is fundamental feature of heart failure (HF) and myocardial ischemia. In addition to the effects of heightened oxidative stress, altered nitric oxide (NO) metabolism, generated by a mitochondrial NO synthase, has also been proposed to impact upon mitochondrial function. However, the mechanism responsible for arginine transport into mitochondria and the effect of HF on such a process is unknown. We therefore aimed to characterize mitochondrial L-arginine transport and to investigate the hypothesis that impaired mitochondrial L-arginine transport plays a key role in the pathogenesis of heart failure and myocardial injury.

Methods and Results

In mitochondria isolated from failing hearts (sheep rapid pacing model and mouse Mst1 transgenic model) we demonstrated a marked reduction in L-arginine uptake (p<0.05 and p<0.01 respectively) and expression of the principal L-arginine transporter, CAT-1 (p<0.001, p<0.01) compared to controls. This was accompanied by significantly lower NO production and higher 3-nitrotyrosine levels (both p<0.05). The role of mitochondrial L-arginine transport in modulating cardiac stress responses was examined in cardiomyocytes with mitochondrial specific overexpression of CAT-1 (mtCAT1) exposed to hypoxia-reoxygenation stress. mtCAT1 cardiomyocytes had significantly improved mitochondrial membrane potential, respiration and ATP turnover together with significantly decreased reactive oxygen species production and cell death following mitochondrial stress.

Conclusion

These data provide new insights into the role of L-arginine transport in mitochondrial biology and cardiovascular disease. Augmentation of mitochondrial L-arginine availability may be a novel therapeutic strategy for myocardial disorders involving mitochondrial stress such as heart failure and reperfusion injury.

Suplementação proteica não aumenta a concentração plasmática de óxido nítrico em homens saudáveis

Suplementos nutricionais, supostamente, capazes de potencializar a produção endógena de óxido nítrico (NO) têm experimentado crescente popularidade entre os indivíduos fisicamente ativos. Diante da carência de informações sobre o assunto, o objetivo do presente estudo foi avaliar o efeito de um suplemento comercial à base de proteínas e aminoácidos sobre a produção endógena de NO. MÉTODOS: A amostra foi constituída de 12 homens sedentários, mas sem fatores de risco para doenças cardiovasculares. O protocolo de suplementação foi conduzido conforme o arranjo experimental duplo-cego cruzado. Os participantes receberam, aleatoriamente, placebo (PLA) ou suplemento proteico (SP), em dois momentos diferentes, separados por uma semana. Com o intuito de determinar a concentração plasmática de NO, amostras de sangue foram coletadas antes (24h e imediatamente antes) e depois (30 e 60 minutos) do consumo da substância PLA ou do SP. RESULTADOS: Não foi observada alteração na concentração plasmática de NO após a ingestão do SP em comparação com o PLA (pós-suplementação 30min - PLA: 19,3 ± 4,7µmol.L- 1 vs. SP: 18,9 ± 4,4µmol.L-1 e pós-suplementação 60min - PLA: 21,3 ± 6,5µmol.L-1 vs. SP: 20,3 ± 4,9µmol.L-1). Também não foi verificada alteração da pressão arterial. CONCLUSÃO: O suplemento nutricional à base de proteínas e aminoácidos, testado no presente estudo, não potencializou a produção endógena de NO.

Targeting reactive oxygen species in hypertension

Oxidative stress plays an important role in the pathogenesis of hypertension. A number of sources of reactive oxygen species have been identified including NADPH oxidase, endothelial NO synthase, and xanthine oxidase. Inhibitors of these systems reduce blood pressure in experimental models. Targeted overexpression of antioxidant systems and interference with expression of oxidant systems has also been successfully used in animal models of hypertension. It is expected that these strategies will eventually be translated to human disease, but currently, the specificity and toxicity of such measures are not yet fulfilling quality criteria for treatment of humans. In the meantime, presumably nontoxic measures, such as administration of antioxidant vitamins, are the only available treatments for oxidative stress in humans. In this review, we discuss strategies to target oxidative stress both in experimental models and in humans. We also discuss how patients could be selected who particularly benefit from antioxidant treatment. In clinical practice, diagnostic procedures beyond measurement of blood pressure will be necessary to predict the response to antioxidants; these procedures will include measurement of antioxidant status and detailed assessment of vascular structure and function.

Decreased NO signaling leads to enhanced vasoconstrictor responsiveness in skeletal muscle arterioles of the ZDF rat prior to overt diabetes and hypertension

Approximately 40% of patients with type 2 diabetes present with concurrent hypertension at the time of diabetes diagnosis. Increases in peripheral vascular resistance and correspondingly enhanced vasoconstrictor capacity could have profound implications for the development of hypertension and the progression of insulin resistance to overt diabetes. The purpose of this study was to determine whether skeletal muscle arteriolar vasoconstrictor dysfunction precedes or occurs concurrently with the onset of diabetes and hypertension. Male Zucker diabetic fatty (ZDF) rats were studied at 7, 13, and 20 wk of age to represent prediabetic and short-term and long-term diabetic states, respectively. Conscious mean arterial pressure (MAP), fasted plasma insulin and glucose, vasoconstrictor responses, and passive mechanical properties of isolated skeletal muscle arterioles were measured in prediabetic, diabetic, and age-matched control rats. Elevated MAP was manifest in short-term diabetes (control 117 +/- 1, diabetic 135 +/- 3 mmHg) and persisted with long-term diabetes (control 113 +/- 2, diabetic 135 +/- 3 mmHg). This higher MAP was preceded by augmented arteriolar vasoconstrictor responses to norepinephrine and endothelin-1 and followed by diminished beta-adrenergic vasodilation and enhanced myogenic constriction in long-term diabetes. Furthermore, we demonstrate that diminished nitric oxide (NO) signaling underlies the increases in vasoconstrictor responsiveness in arterioles from prediabetic and diabetic rats. Arteriolar stiffness was not different between control and prediabetic or diabetic rats at any time point studied. Collectively, these results indicate that increases in vasoconstrictor responsiveness resulting from diminished NO signaling in skeletal muscle arterioles precede the development of diabetes and hypertension in ZDF rats.

l-Arginine transporters in cardiovascular disease: A novel therapeutic target

The amino acid l-arginine participates in a variety of key biochemical and physiological activities, including its well-recognized role as the key substrate for nitric oxide (NO) biosynthesis. The current review describes the cellular influences on arginine metabolism with particular focus on the transport of l-arginine in the endothelium. It details the processes by which intracellular and extracellular levels of l-arginine may influence nitric oxide production and further documents the imbalance that is evident in various cardiovascular disease states. In man, impairment of l-arginine transport has been observed in hypertension, heart failure, and renal disease, and it may thus be a relevant therapeutic target for rectification of nitric oxide pathogenesis in these conditions.

Defective vasodilatory mechanisms in hypertension: a G-protein-coupled receptor perspective

PURPOSE OF REVIEW

The purpose of this article is to review recent evidence relating to the regulation of vasodilatation and alterations in these mechanisms in the hypertensive state. In particular, we will focus on signaling systems regulating nitric oxide synthase and intracellular cyclic AMP - the two principal mechanisms mediating vasodilatation.

RECENT FINDINGS

G-protein-coupled-receptor-mediated, endothelial-dependent processes are increasingly being seen as critical vasodilatory mechanisms. Impairment of endothelial responses to G-protein-coupled receptor activation is a key component of the decrease in G-protein-coupled-receptor-mediated vasodilatation in hypertension. In addition, an 'uncoupling' of the G-protein-coupled receptor/G-protein complex is the principal mechanism underlying impaired G-protein-coupled-receptor-mediated vasodilatation in hypertension. Alterations in G-protein-coupled receptor kinase function have a central role underlying this defect. Finally, the importance of the expression of genetic variants of G-protein-coupled receptors and G-proteins underlying the defect in vasodilatation in hypertension remains contentious.

SUMMARY

G-protein signaling pathways in the vasculature play an important role in both the development and the maintenance of the hypertensive state. It is unlikely, however, that any single defect in the G-protein-linked vasodilatory pathway will ever be shown to be the sole cause of hypertension.

Does estrogen affect the development of abnormal vascular function in offspring of rats fed a low-protein diet in pregnancy?

It is established that there are gender-related differences in the effects on offspring blood pressure induced by maternal protein restriction in animal studies. Since such effects may depend on estrogen levels, we hypothesized that lower estrogen would induce an earlier onset of hypertension caused by maternal under-nutrition. Wistar rats were fed a diet containing either 18% (C) or 9% (R) casein throughout pregnancy. Half of the offspring in both C and R groups were ovariectomized on day 50 (CX, RX), and the other half underwent a sham operation (CO, RO). On d 175, offspring were killed for small artery reactivity and histologic investigation. Birth weight and later growth were not significantly different between C and R. RX had higher systolic blood pressure than CX on d125, but no difference was seen between RO and CO. On d 175, systolic blood pressure was higher in R than in C, whether or not ovariectomized. Dilator responses to acetylcholine and bradykinin in small mesenteric arteries were significantly attenuated in RX, although responses to SNP and isoprenaline showed no attenuation in R. The ratio of coronary peri-vascular fibrosis to total vascular area was higher in R, and the fibrosis became prominent in ovariectomized rats. These findings suggest that estrogen plays an important role in limiting the elevation of offspring blood pressure induced by maternal under-nutrition, possibly via BK-mediated mechanisms. The processes may underlie gender and life course patterns of hypertension and also the developmental origins of this disease.

Amino acids, arginase and nitric oxide in vascular health

1. Nitric oxide (NO) plays a fundamental role in the vasculature because of its diverse influence in vascular protection, including its well-reported antiproliferative, anti-inflammatory, antithrombotic and vasodilator effects. In many vascular disease states, NO production is reduced as a result of endothelial dysfunction, in part caused by a decrease in substrate (L-arginine) availability. 2. The role of L-arginine and other amino acids important in nitrogen balance has been re-examined in the context of their effects on vascular health. The metabolism of L-arginine is complex because it is involved in a plethora of other pathways, such as urea, creatine and agmatine production. L-Arginine supplementation in patients with vascular disease is well reported to benefit patients therapeutically because of its effect on both NO-dependent and -independent mechanisms. 3. L-Arginine availability depends on the flux of other amino acids in the body, including L-glutamine, L-glutamate, L-ornithine, L-citrulline and L-lysine. The role of L-methionine and homocystine and their effect on NO also play an influential role in the body. 4. Recent data suggest that the key enzyme involved in the L-arginine-urea cycle, arginase, is coexpressed in NO-producing cells in the vasculature. In the present review, we examine the potential role of arginase as a therapeutic target for vascular health.

L-arginine fails to protect against myocardial remodelling in L-NAME-induced hypertension

BACKGROUND

We investigated whether the substrate for nitric oxide synthesis L-arginine is able to modify hypertension and left ventricular hypertrophy development induced by chronic blockade of nitric oxide synthase activity by NG-nitro-L-arginine-methyl ester (L-NAME).

MATERIAL AND METHODS

Four groups of rats were investigated: control, L-arginine 1.5 g kg-1, L-NAME 40 mg kg-1, and L-NAME +L-arginine in corresponding doses. Systolic blood pressure was measured by non-invasive tail-cuff plethysmography each week. After 4 weeks, the animals were sacrificed and hydroxyproline and coenzyme Q9 and Q10 concentrations in the left ventricle, and nitric oxide synthase activity in the left ventricle, kidney and brain were investigated.

RESULTS

In the L-NAME group, nitric oxide synthase activity was decreased in the left ventricle, kidney and brain, and hypertension, left ventricular hypertrophy and fibrosis developed. Heart remodelling was associated with the decrease of coenzyme Q9 and Q10 concentrations in the left ventricle. Simultaneous treatment with L-NAME and L-arginine prevented nitric oxide synthase activity diminution in the left ventricle but not in the kidney and brain, and completely failed to prevent hypertension, left ventricular hypertrophy and fibrosis. Nevertheless, l-arginine prevented the diminution of coenzyme Q9 and Q10 concentrations in the left ventricle.

CONCLUSIONS

We conclude that L-arginine failed to prevent hypertension, left ventricular hypertrophy and fibrosis development despite restoration of nitric oxide synthase activity in the left ventricle. However, L-arginine prevented the diminution of coenzyme Q levels in the left ventricle.