Clare Austin

αV Integrins Are Necessary for Eutrophic Inward Remodeling of Small Arteries in Hypertension

Human essential hypertension is characterized by eutrophic remodeling of small arteries, with little evidence of hypertrophy. Likewise, vessels of young hypertensive TGR(mRen2)27 animals have undergone similar structural alterations. The role of integrins in resistance arteries of TGR(mRen2)27 during the eutrophic-remodeling process was examined as blood pressure rose. Initially, 8 &agr; and 3 &bgr; integrins were identified and levels of expression investigated using RT-PCR. As pressure increased and remodeling advanced, integrin expression profiles revealed that only &agr;V was significantly raised. In conjunction, we confirmed elevated integrin &agr;V protein levels in TGR(mRen2)27 rat arteries and localization to the media using immunofluorescence. &bgr;1 and &bgr;3, but not &bgr;5 integrin subunits were coprecipitated with integrin &agr;V and are implicated in the eutrophic remodeling process. Administration of a peptide antagonist of &agr;V&bgr;3 abolished remodeling but enhanced growth, indicating that hypertrophy supervened as a response to hypertension-induced increases in wall stress. We have established that the only upregulated integrin, the &agr;V subunit of integrin &agr;V&bgr;3, has a crucial role in the hypertensive remodeling process of TGR(mRen2)27 rat resistance arteries. During hypertensive remodeling, functions of specific &agr;V&bgr;3-extracellular matrix interactions are likely to allow vascular smooth muscle cell–length autoregulation, which includes a migratory process, to maintain a narrowed lumen after a prolonged constricted state.

Effects of Angiotensin Type-1 Receptor Antagonism on Small Artery Function in Patients With Type 2 Diabetes Mellitus

Endothelial dysfunction has been demonstrated to occur in small arteries from patients with type 2 diabetes and hypertension. The effects of angiotensin II receptor blockade on vessel function were examined using pressure myography in a randomized 12-week double-blind placebo-controlled parallel group study using candesartan cilexitil. The maximal vascular response to acetylcholine (Ach) was impaired at baseline and improved with candesartan. This improvement was primarily caused by an effect in the nitric oxide component of Ach-mediated dilatation. The degree of endothelial dysfunction directly correlated with serum low-density lipoprotein cholesterol levels. Sodium nitroprusside-induced endothelium-independent dilatation was reduced in diabetic patients and intervention with candesartan lead to an improvement in EC50 with no change in maximal response. Vasoconstriction to norepinephrine was normal and did not change with intervention, but responses to angiotensin II were reduced after candesartan in diabetic patients. These results demonstrate that even brief treatment with angiotensin II receptor blockade is associated with a significant improvement in resistance vessel endothelial function.

Chronic and acute effects of oestrogens on vascular contractility.

In addition to their role as sex hormones, it has been known for many years that oestrogens have protective effects on the vasculature. These have been implicated in the reduced incidence of cardiovascular disorders in premenopausal women and in post-menopausal women receiving oestrogen replacement therapy. This protection has been found to be due, in part at least, to direct effects of oestrogens on blood vessels. This review will summarize the available literature regarding oestrogenic effects on vascular contractility. Two major influences of oestrogens will be discussed; first the genomic effects induced by chronic administration of steroid hormones, and second, the rapid effects on vascular smooth muscle by non-genomic, and as yet not fully identified, mechanisms. In so doing, the diversity of oestrogenic actions on vascular contractility will be highlighted and the protective role of these agents against adverse cardiovascular events discussed.

Loss of anti-contractile effect of perivascular adipose tissue in offspring of obese rats.

Rationale:Maternal obesity pre-programmes offspring to develop obesity and associated cardiovascular disease. Perivascular adipose tissue (PVAT) exerts an anti-contractile effect on the vasculature, which is reduced in hypertension and obesity.Objective:The objective of this study was to determine whether maternal obesity pre-programmes offspring to develop PVAT dysfunction in later life.Methods:Female Sprague–Dawley rats were fed a diet containing 10% (control) or 45% fat (high fat diet, HFD) for 12 weeks prior to mating and during pregnancy and lactation. Male offspring were killed at 12 or 24 weeks of age and tension in PVAT-intact or -denuded mesenteric artery segments was measured isometrically. Concentration–response curves were constructed to U46619 and norepinephrine.Results:Only 24-week-old HFD offspring were hypertensive (P<0.0001), although the anti-contractile effect of PVAT was lost in vessels from HFD offspring of each age. Inhibition of nitric oxide (NO) synthase with 100u2009μM l-NMMA attenuated the anti-contractile effect of PVAT and increased contractility of PVAT-denuded arteries (P<0.05, P<0.0001). The increase in contraction was smaller in PVAT-intact than PVAT-denuded vessels from 12-week-old HFD offspring, suggesting decreased PVAT-derived NO and release of a contractile factor (P<0.07). An additional, NO-independent effect of PVAT was evident only in norepinephrine-contracted vessels. Activation of AMP-activated kinase (with 10u2009μM A769662) was anti-contractile in PVAT-denuded (P<0.0001) and -intact (P<0.01) vessels and was due solely to NO in controls; the AMPK effect was similar in HFD offspring vessels (P<0.001 and P<0.01, respectively) but was partially NO-independent.Conclusions:The diminished anti-contractile effects of PVAT in offspring of HFD dams are primarily due to release of a PVAT-derived contractile factor and reduced NO bioavailability.

The effects of resveratrol on aging vessels

Aging is a major risk factor for the development of cardiovascular disease. Despite a significant reduction in the mortality and morbidity rates over the last decade, the socio-economic burden of cardiovascular disease is still substantial. Consequently, there is a considerable need for alternative strategies, such as nutraceutical supplementation, that delay the functional vascular decline present in the elderly. Compromised autophagy and oxidative stress (OS) are considered major causes of the age-related endothelial dysfunction. OS reduces the bioavailability of nitric oxide (NO), which has been associated with hypertension, arteriosclerosis, and a reduced vasodilatory response. High levels of free radicals and the low bioavailability of NO lead to a positive feedback loop of further OS, organelle damage, poor repair, and endothelial dysfunction. Here we draw attention to the relationship between OS and autophagy in the aged vasculature. We have reviewed the published literature and provided arguments that support that treatment with resveratrol stimulates autophagy and thereby has the potential to restore oxidative balance in the endothelium, which indicates that treatment with resveratrol might have therapeutic potential to restore endothelial function in the elderly.

Effects of diabetes and hypertension on structure and distensibilty of human small coronary arteries.

Objectives: Previous studies have demonstrated that hypertension and diabetes induce significant structural remodelling of resistance arteries from various vascular beds. The hypothesis of this study is that structural alterations of small coronary arteries may occur during hypertension and diabetes. This study is the first to compare human coronary small resistance artery structure from normotensive and hypertensive patients, with and without diabetes undergoing coronary arterial bypass graft surgery. Methods: Small arteries were dissected from the atrial appendage removed from nondiabetic normotensive patients, nondiabetic hypertension and diabetic normotensive patients and hypertensive diabetic patients. Arteries were mounted in a pressure myograph and lumen diameter and wall thickness were measured across the pressure range of 3–100 mmHg to assess vessel structure and distensibility. Results: There were no significant differences in the lumen diameter, wall thickness, wall-to-lumen ratio and cross-sectional area of arteries in all groups. Arteries from nondiabetic patients with hypertension demonstrated decreased distensibility compared with nondiabetic normotensive patients. There is no difference in distensibility between vessels from diabetic hypertensive patients and either diabetic or nondiabetic normotensive patients. Conclusion: Neither diabetes nor hypertension appears to have influenced arterial structure which may indicate that successful treatment of hypertension is associated with normal vascular structure in coronary small arteries.

Plasma membrane calcium ATPases (PMCAs) as potential targets for the treatment of essential hypertension

The incidence of hypertension, the major modifiable risk factor for cardiovascular disease, is increasing. Thus, there is a pressing need for the development of new and more effective strategies to prevent and treat hypertension. Development of these relies on a continued evolution of our understanding of the mechanisms which control blood pressure (BP). Resistance arteries are important in the regulation of total peripheral resistance and BP; changes in their structure and function are strongly associated with hypertension. Anti-hypertensives which both reduce BP and reverse changes in resistance arterial structure reduce cardiovascular risk more than therapies which reduce BP alone. Hence, identification of novel potential vascular targets which modify BP is important. Hypertension is a multifactorial disorder which may include a genetic component. Genome wide association studies have identified ATP2B1, encoding the calcium pump plasma membrane calcium ATPase 1 (PMCA1), as having a strong association with BP and hypertension. Knockdown or reduced PMCA1 expression in mice has confirmed a physiological role for PMCA1 in BP and resistance arterial regulation. Altered expression or inhibition of PMCA4 has also been shown to modulate these parameters. The mechanisms whereby PMCA1 and 4 can modulate vascular function remain to be fully elucidated but may involve regulation of intracellular calcium homeostasis and/or comprise a structural role. However, clear physiological links between PMCA and BP, coupled with experimental studies directly linking PMCA1 and 4 to changes in BP and arterial function, suggest that they may be important targets for the development of new pharmacological modulators of BP.

The Role of O-Glcnacylation in Perivascular Adipose Tissue Dysfunction of Offspring of High Fat Diet-Fed Rats.

Perivascular adipose tissue (PVAT), which reduces vascular contractility, is dysfunctional in the male offspring of rats fed a high-fat diet (HFD), partially due to a reduced NO bioavailability. O-GlcNAcylation of eNOS decreases its activity, thus we investigated the role of O-GlcNAcylation in the prenatal programming of PVAT dysfunction. Female Sprague-Dawley rats were fed either a control (10% fat) or an obesogenic HFD (45% fat) diet for 12 weeks prior to mating, and throughout pregnancy and lactation. Offspring were weaned onto the control diet and were killed at 12 and 24 weeks of age. Mesenteric arteries from the 12-week-old offspring of HFD dams (HFDO) contracted less to U46619; these effects were mimicked by glucosamine in control arteries. PVAT from 12- and 24-week-old controls, but not from HFDO, exerted an anticontractile effect. Glucosamine attenuated the anticontractile effect of PVAT in the vessels from controls but not from HFDO. AMP-activated protein kinase (AMPK) activation (with A769662) partially restored an anticontractile effect in glucosamine-treated controls and HFDO PVAT. Glucosamine decreased AMPK activity and expression in HFDO PVAT, although phosphorylated eNOS expression was only reduced in that from males. The loss of anticontractile effect of HFDO PVAT is likely to result from increased O-GlcNAcylation, which decreased AMPK activity and, in males, decreased NO bioavailability.

Comparisons between perivascular adipose tissue and the endothelium in their modulation of vascular tone

The endothelium is an established modulator of vascular tone; however, the recent discovery of the anti‐contractile nature of perivascular adipose tissue (PVAT) suggests that the fat, which surrounds many blood vessels, can also modulate vascular tone. Both the endothelium and PVAT secrete vasoactive substances, which regulate vascular function. Many of these factors are common to both the endothelium and PVAT; therefore, this review will highlight the potential shared mechanisms in the modulation of vascular tone. Endothelial dysfunction is a hallmark of many vascular diseases, including hypertension and obesity. Moreover, PVAT dysfunction is now being reported in several cardio‐metabolic disorders. Thus, this review will also discuss the mechanistic insights into endothelial and PVAT dysfunction in order to evaluate whether PVAT modulation of vascular contractility is similar to that of the endothelium in health and disease.

LB03.05: THE ANTI-CONTRACTILE EFFECTS OF PVAT ARE MODULATED BY AGE. THE ROLE OF NITRIC OXIDE.

Objective: Ageing is the biggest independent risk factor for cardiovascular disease; the leading cause of death worldwide. Recent studies demonstrate that age-related endothelial dysfunction, a major risk factor for cardiovascular disease, may be due to decreased bioavailability of the endogenous vasodilator nitric oxide (NO), synthesised in the vascular endothelium by endothelial nitric oxide synthase (eNOS); which is phosphorylated and thus activated by AMP-activated protein kinase (AMPK). Vascular reactivity is further regulated via the perivascular adipose tissue (PVAT), which has a net anti-contractile effect. PVAT is known to be a source of additional NO, as well as secreting factors that augment local endothelial NO production, potentially through AMPK activation. Whilst this anti-contractile effect of PVAT is well characterised in young animals, it is unknown what effects ageing has on this relationship. Our hypothesis is that PVAT dysfunction may occur with ageing. Design and method: Small diameter mesenteric arteries were taken from male Wistar rats aged 3 months old (m.o.), 12m.o., 18m.o. and 24m.o. and contractility to U46619 (10nM-3u200a&mgr;M) and phenylephrine (1nM-30u200a&mgr;M) assessed via wire-myography in the presence and absence of PVAT and the NO-synthesis inhibitor L-NNA (50u200a&mgr;M). Western blotting for AMPK, p-AMPK, eNOS and p-eNOS was performed on mesenteric artery samples from rats aged 3m.o. and 24m.o. Results: Results showed that PVAT was anti-contractile in 3m.o. and 12m.o. old rats but that this effect was lost by 18m.o., remaining absent at 24m.o.. Incubation with L-NNA reversed the anti-contractile effect of PVAT at 3m.o., but not 24m.o. Expression of total AMPK was reduced in arteries from 24m.o. compared to 3m.o. whereas the ratio of p-AMPK/total AMPK remained unchanged. Expression of eNOS remained unchanged at 24m.o., whereas p-eNOS/total eNOS ratio was significantly decreased. Conclusions: The anti-contractile effect of PVAT is lost with age in rats, due at least in part to reduced NO bioavailability. This reduced bioavailability may be the result of reduced eNOS phosphorylation downstream of reduced AMPK expression.