Deficiency of receptor-associated protein attenuates angiotensin II-induced atherosclerosis in hypercholesterolemic mice without influencing abdominal aortic aneurysms

ObjectiveReceptor-associated protein (RAP) was initially described as a regulator of low density lipoprotein receptor-related protein 1 (LRP1), but is now known to regulate many proteins. Since the direct effects of RAP on vascular pathologies have not been studied, this study determined whether RAP deficiency influenced angiotensin II (AngII)-induced atherosclerosis and abdominal aortic aneurysms (AAAs) in hypercholesterolemic mice.Methods and resultsMale LDL receptor ?/? mice that were either RAP +/+ or ?/? were infused with AngII (500 ng/kg/min) for 4 weeks while consuming a saturated fat-enriched diet. RAP deficiency had no effects on body weight or AngII-induced increases of systolic blood pressure. Despite increased plasma cholesterol concentrations, RAP deficiency reduced atherosclerotic lesion size in aortic arches, while having no effect on AngII-induced AAAs. RAP deficiency profoundly reduced LRP1 protein abundance in macrophages, but did not change its abundance in aortic smooth muscle cells. Also, RAP deficiency had no effects on mRNA abundance of LRP1 or lipoprotein lipase in macrophages. To determine whether RAP deficiency in leukocytes influenced AngII-induced atherosclerosis, irradiated male LDL receptor ?/? mice were repopulated with bone marrow-derived cells from either RAP +/+ or ?/? male mice. The chimeric mice were infused with AngII (500 ng/kg/min) for 4 weeks while fed the saturated fat-enriched diet. RAP deficiency in bone marrow-derived cells did not influence either plasma cholesterol concentrations or atherosclerotic lesion size.ConclusionsWhole body RAP deficiency attenuated atherosclerosis without influencing AAAs in hypercholesterolemic mice infused with AngII. The anti-atherogenic effect was not attributable to RAP deficiency in bone marrow-derived cells.     

Angiotensin type 2 receptor-mediated phosphorylation of eNOS in the aortas of mice with 2-kidney, 1-clip hypertension

To evaluate the role of vascular angiotensin II (Ang II) type 2 (AT2) receptor in renovascular hypertension, we investigated expressions of AT2 receptor and endothelial nitric oxide synthase (eNOS) in thoracic aortas of mice with 2-kidney, 1-clip (2K1C) hypertension. The mRNA levels of AT2 receptor in aortas, but not those of AT1 and bradykinin B2 receptors, increased 14 days but not 42 days after clipping. The contractile response to Ang II (>0.1 micromol/L) was attenuated in aortic rings excised 14 days after clipping and was restored to that of rings from sham mice by antagonists of AT2 receptor (PD123319) and B2 receptor (icatibant). The aortic levels of total eNOS, phosphorylated eNOS at Ser1177 (p-eNOS), total Akt, and phosphorylated Akt at Ser473 (p-Akt) were increased in 2K1C mice on day 14, whereas only eNOS levels were increased on day 42. The aortic cGMP levels were 20-fold greater in 2K1C mice on day 14 compared with sham mice. Administration of nicardipine for 4 days before the excision of aortas 14 days after clipping not only reduced blood pressure but also decreased the aortic levels of eNOS, p-eNOS, Akt, p-Akt, and cGMP to sham levels, whereas the administration of PD123319 or icatibant to 2K1C mice decreased p-eNOS and cGMP to sham levels without affecting blood pressure and the levels of eNOS, Akt and p-Akt. These results suggest that vascular NO production is enhanced by increased eNOS phosphorylation via the activation of AT2 receptors in the course of 2K1C hypertension.     

Increased magnitude of relaxation to oestrogen in aorta from oestrogen receptor beta knock-out mice

Micromolar concentrations of the biologically active oestrogen 17beta-oestradiol reduce agonist-induced force in vascular preparations through an unidentified mechanism. The aim of the present study was to investigate the importance of oestrogen receptor beta (ERbeta) for oestrogen-induced vascular relaxation. 17beta-oestradiol was added to aortic rings from ERbeta knock-out (-/-) and wild-type (+/+) mice precontracted with noradrenaline. 17beta-oestradiol caused a concentration-dependent (1-100 microM) relaxation of aortic rings from both -/- and +/+ animals of both sexes. Rings from male and female -/- mice were more sensitive to 17beta-oestradiol than those from +/+ mice. Medial thickness, determined by computerized image analysis, was similar in rings from -/- and +/+ animals. Endothelium, as determined by immuno-cytochemistry, was present in -/- and +/+ aorta. Maximal noradrenaline evoked force and sensitivity to noradrenaline were similar in both groups. In summary ERbeta modulates vascular relaxation to microM concentrations of oestrogen; lack of ERbeta renders the vascular wall supersensitive to 17beta-oestradiol. Lack of ERbeta caused no change in vascular wall morphology suggesting that this ER subtype is not involved in vascular structure development.     

Angiotensin II stimulates endothelial NO synthase phosphorylation in thoracic aorta of mice with abdominal aortic banding via type 2 receptor

Abdominal aortic banding in mice induces upregulation of angiotensin II (Ang II) type 2 (AT2) receptors in the pressure-overloaded thoracic aorta. To clarify mechanisms underlying the vascular AT2 receptor-dependent NO production, we measured aortic levels of endothelial NO synthase (eNOS), eNOS phosphorylated at Ser633 and Ser1177, protein kinase B (Akt), and Akt phosphorylated at Ser473 in thoracic aortas of mice after banding. Total eNOS, both forms of phosphorylated eNOS, Akt, and phosphorylated Akt levels, as well as cGMP contents, were significantly increased 4 days after banding. The administration of PD123319 (an AT2 receptor antagonist) or icatibant (a bradykinin B2 receptor antagonist) abolished the banding-induced upregulation of both forms of phosphorylated eNOS, as well as elevation of cGMP, but did not affect the upregulation of eNOS, Akt, and phosphorylated Akt. In the in vitro experiments using aortic rings prepared from banded mice, Ang II produced significant increases in both forms of phosphorylated eNOS, as well as cGMP, and these effects were blocked by PD123319 and icatibant. Ang II-induced eNOS phosphorylation and cGMP elevation in aortic rings were inhibited by protein kinase A (PKA) inhibitors H89 and KT5720 but not by phosphatidylinositol 3-kinase inhibitors wortmannin and LY24002. The contractile response to Ang II was attenuated in aortic rings from banded mice via AT2 receptor, and this attenuation was blocked by PKA inhibitors. These results suggest that the activation of AT2 receptor by Ang II induces phosphorylation of eNOS at Ser633 and Ser1177 via a PKA-mediated signaling pathway, resulting in sustained activation of eNOS.     

Abdominal aortic aneurysms: fresh insights from a novel animal model of the disease

Abdominal aortic aneurysms (AAA) have a high prevalence in aged populations and are responsible for a large number of deaths. Despite the widespread nature of the disease, relatively little is known regarding mechanisms for formation and progression of aortic aneurysms. In part, this lack of knowledge is attributable to a paucity of animal models for this disease. This review summarizes the available animal models of AAA and focuses on a novel model of reproducible AAA generated by infusion of angiotensin II (AngII) into mice rendered hyperlipidemic by the absence of either apolipoprotein E or low-density lipoprotein receptors. AAA generated by AngII infusion have many characteristics of the human disease including marked luminal expansions, perimedial remodeling, inflammation, thrombosis and a link to hyperlipidemia. As in the human disease, male mice are more susceptible to the development of AAA than females. The vascular pathology occurs from the effects of AngII at AT1 receptors present on bone marrow-derived cells. Studies are ongoing to define the mediators responsible for AngII-induced inflammation and degradation of the medial layer of the vascular wall. The AngII-induced model of AAA has the potential to provide novel insights into the underlying mechanisms of this disease and assist with the development of pharmacological therapies.     

Beta-migrating very low density lipoprotein attenuates endothelium-dependent relaxation in rabbit atherosclerotic aortas

We studied the effects of beta-migrating very low density lipoprotein (beta-VLDL) on the vascular responses of isolated thoracic aortic preparations taken from normal and hypercholesterolemic rabbits. The endothelium-dependent relaxation induced by acetylcholine or adenosine triphosphate (ATP) was attenuated in the arteries from hypercholesterolemic rabbits that were fed a cholesterol-rich diet for 12 weeks. In these aortas, the lesional circumference of the atherosclerotic plaques (fatty streaks) was only 12.18 +/- 1.98%. The relaxation induced by the Ca2+ ionophore A23187 or nitroglycerin was not altered. Preincubation with beta-VLDL significantly inhibited the relaxation due to acetylcholine, ATP, or A23187, especially in the aortas of hypercholesterolemic rabbits. However, beta-VLDL did not alter the response to nitroglycerin. Preincubation with high density lipoprotein had no significant effect on vessel relaxation. These results indicated that endothelium-dependent relaxation was already inhibited in the early stages of atherosclerosis, and that the atherogenic lipoprotein, beta-VLDL, further inhibited endothelium-dependent relaxation in atherosclerotic aortas. It may be that beta-VLDL also plays a role in determining the level of vascular tonus in atherosclerosis.     

Wall properties of the apolipoprotein E-deficient mouse aorta

ObjectivesWe quantified the dysfunction of the aortic wall, determined structural and elastic properties, and provided histological data of the thoracic aortas of apolipoprotein E (apoE)-deficient mice which are used as model of atherosclerosis.MethodsSix young 10–12 week-old (apoE)-deficient mice of both sexes were studied and six age-matched C57BL/6J wild-type mice were used as control group. We performed extension-inflation mechanical tests at three different axial stretches (λ_z = 1.6, 1.8, and 2.0), under maximally contracted or totally relaxed state of the vascular smooth muscle cells. Classical histology was performed to the arterial segments.ResultsControl aortas were generally more distensible than the (apoE)-deficient mouse aortas under both relaxed and contracted smooth muscle. Also, aortas from (apoE)-deficient mice were stiffer (higher incremental elastic modulus) than control aortas. Control aortas exhibited a higher active diameter response compared to (apoE)-deficient mouse aortas, despite the fact that vascular smooth muscle cell density was increased by approximately 15% in the (apoE)-deficient mouse aortas.ConclusionWe found substantial changes in the structural and elastic properties of the wall, in the active diameter response and in the histology of (apoE)-deficient mouse aortas compared to the control group. Our data can be used in the development of constituent-based models of the arterial wall and in studying the changes in arterial wall properties in presence of disease, such as atherosclerosis.     

Biglycan deficiency: Increased aortic aneurysm formation and lack of atheroprotection

Proteoglycans of the arterial wall play a critical role in vascular integrity and the development of atherosclerosis owing to their ability to organize extracellular matrix molecules and to bind and retain atherogenic apolipoprotein (apo)-B containing lipoproteins. Prior studies have suggested a role for biglycan in aneurysms and in atherosclerosis. Angiotensin II (angII) infusions into mice have been shown to induce abdominal aortic aneurysm development, increase vascular biglycan content, increase arterial retention of lipoproteins, and accelerate atherosclerosis. The goal of this study was to determine the role of biglycan in angII-induced vascular diseases. Biglycan-deficient or biglycan wildtype mice crossed to LDL receptor deficient (Ldlr-/-) mice (C57BL/6 background) were infused with angII (500 or 1000 ng/kg/min) or saline for 28 days while fed on normal chow, then pumps were removed, and mice were switched to an atherogenic Western diet for 6 weeks. During angII infusions, biglycan-deficient mice developed abdominal aortic aneurysms, unusual descending thoracic aneurysms, and a striking mortality caused by aortic rupture (76% for males and 48% for females at angII 1000 ng/kg/min). Histological analyses of non-aneurysmal aortic segments from biglycan-deficient mice revealed a deficiency of dense collagen fibers and the aneurysms demonstrated conspicuous elastin breaks. AngII infusion increased subsequent atherosclerotic lesion development in both biglycan-deficient and biglycan wildtype mice. However, the biglycan genotype did not affect the atherosclerotic lesion area induced by the Western diet after treatment with angII. Biglycan-deficient mice exhibited significantly increased vascular perlecan content compared to biglycan wildtype mice. Analyses of the atherosclerotic lesions demonstrated that vascular perlecan co-localized with apoB, suggesting that increased perlecan compensated for biglycan deficiency in terms of lipoprotein retention. Biglycan deficiency increases aortic aneurysm development and is not protective against the development of atherosclerosis. Biglycan deficiency leads to loosely packed aortic collagen fibers, increased susceptibility of aortic elastin fibers to angII-induced stress, and up-regulation of vascular perlecan content.     

Angiotensin II-mediated development of vascular diseases

Angiotensin II (AngII) has well-characterized effects on blood pressure and fluid balance that adversely affect atherosclerotic cardiovascular disease. More recently, there is a realization that AngII exerts direct effects on arterial wall cells to influence atherosclerotic lesion formation. Several groups have shown that infusion of AngII into hyperlipidemic mice rapidly and profoundly augments lesion formation. The increase in lesions from AngII was not attributable to elevated blood pressure. The lesions formed from AngII infusion are overtly similar to those formed during hypercholesterolemia, with infiltration of macrophages and T lymphocytes. Unexpectedly, AngII infusion into these mice also led to the development of abdominal aortic aneurysms. These aneurysms exhibit many aspects of the human disease including medial degeneration, inflammation, thrombus, and rupture. The definition of the cellular mechanisms by which Ang II promotes these vascular pathologies may provide new therapeutic strategies.     

Ferulic acid restores endothelium-dependent vasodilation in aortas of spontaneously hypertensive rats

BACKGROUND: Ferulic acid (FA), a phytochemical constituent, has antihypertensive effects, but a detailed understanding of its effects on vascular function remains unclear. The vasoreactivity of FA was assessed using aortic rings isolated from normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). METHODS: The effects of FA (10(-5) to 10(-3) mol/L) on vasodilatory responses were evaluated based on contractile responses induced by phenylephrine (10(-6) mol/L) in thoracic aortic rings from male WKY rats and SHR. Basal nitric oxide (NO) bioavailability in the aorta was determined from the contractile response induced by the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 10(-4) mol/L). The effects of FA on the production of NADPH-dependent superoxide anion were examined in SHR aortas. The impact of hydroxyhydroquinone, a generator of superoxide anions, on the FA-induced enhancement in acetylcholine-stimulated vasodilation was also investigated. RESULTS: The FA (10(-3) mol/L)-induced relaxation was partially blocked by removal of the endothelium or by pretreating SHR aortas with L-NAME. FA increased NO bioavailability, and decreased NADPH-dependent superoxide anion levels in SHR aortas. Ferulic acid improved acetylcholine-induced endothelium-dependent vasodilation in SHR, but not in WKY. Furthermore, the simultaneous addition of hydroxyhydroquinone significantly inhibited the increase in acetylcholine-induced vasodilation by FA. CONCLUSIONS: Ferulic acid restores endothelial function through enhancing the bioavailability of basal and stimulated NO in SHR aortas. The results explain, in part, the mechanisms underlying the effects of FA on blood pressure (BP) in SHR.     

Dietary ellagic acid improves oxidant-induced endothelial dysfunction and atherosclerosis: Role of Nrf2 activation

Background

Oxidative stress-induced vascular endothelial cell injury is a major factor in the pathogenesis of atherosclerosis. Several evidences indicate that ellagic acid (EA), a phenolic compound, contributes to cardiovascular health. This study was to investigate the effects of EA on endothelial dysfunction and atherosclerosis via antioxidant-related mechanisms.

Methods

In animal studies, wild-type (WT) C57BL/6 mice and apolipoprotein E-deficient mice (ApoE^−/−) mice were fed: a high-fat (21%) diet (HFD) or a HFD plus with EA (HFD + EA), for 14 weeks. Vascular reactivity was studied in mice aortas. The effect of EA in human umbilical vein endothelial cells (HAECs) exposed to hypochlorous acid (HOCl) was also investigated.

Results

Compared with animals on HFD alone, EA attenuated atherosclerosis in WT mice. In aortic rings from two mice models, EA significantly improved endothelium-dependent relaxation and attenuated HOCl-induced endothelial dysfunction. Besides, EA significantly improved nitric oxide synthase activity, antioxidant capacity and markers of endothelial dysfunction in plasma. Western blot analysis showed that EA increased NF-E2-related factor 2 (Nrf2) and heme oxygenase-1(HO-1) expression in the aortas (P < 0.05). In a separate experiment, EA did not protect against HOCl-induced endothelial dysfunction in arteries obtained from Nrf2 gene knockout mice compared with WT mice. In HAECs, EA prevented HOCl-induced cellular damage and induced HO-1 protein expression, and these effects markedly abolished by the siRNA of Nrf2.

Conclusions

Our results provide further support for the protective effects of dietary EA particularly oxidant-induced endothelial dysfunction and atherosclerosis partly via Nrf2 activation.     

Enhanced expression of vascular cell adhesion molecule-1 by corticotrophin-releasing hormone contributes to progression of atherosclerosis in LDL receptor-deficient mice

Peripherally produced corticotrophin-releasing hormone (CRH) is a strong proinflammatory factor involved in many inflammatory diseases. However, to date, there is no evidence about the action of CRH on atherosclerosis, a chronic disease characterized by inflammatory reactions. In this study we observed the effect of CRH on atherosclerosis in low-density lipoprotein receptor-deficient (LDLr-/-) mice. Twelve-week-old, male LDLr-/- mice were subcutaneously injected with CRH (10microg/kg) or vehicle once a day for 8 weeks. The results indicated aortic atherosclerotic lesions were larger (P<0.01) in CRH-treated mice than those in untreated mice. CRH significantly up-regulated the expression of both protein and mRNA for vascular cell adhesion molecule-1 (VCAM-1), together with a markedly increased activation of nuclear factor kappa B (NF-kappaB) in aortas. In addition, the blood lipid levels were not influenced by CRH subcutaneous injection. The significant proatherogenic effect of CRH in LDLr-/- mice was largely attenuated by selective CRH receptor 1 (CRHR1) antagonist NBI27914 but not by specific CRH receptor 2 (CRHR2) antagonist antisauvagine-30 (anti-Svg-30). Meanwhile, both the enhanced expression of VCAM-1 and increased activation of NF-kappaB induced by CRH in aortas of LDLr-/- mice were also largely suppressed by NBI27914, whereas these inhibitory effects were not observed in anti-Svg-30 group. Taken together, these findings indicated that CRH may accelerate atherosclerosis progression in LDLr-/- mice via CRHR1. The enhanced VCAM-1 expression which probably resulted from increased activation of NF-kappaB induced by CRH, may be one of the important molecular mechanisms by which CRH accelerates atherosclerosis. This study provides a new insight into the effect of CRH on atherosclerosis and suggests a potential target for the prevention and treatment of atherosclerosis.     

Orchidectomy, but not ovariectomy, regulates angiotensin II-induced vascular diseases in apolipoprotein E-deficient mice

In humans, the incidence and severity of abdominal aortic aneurysms (AAA) are greater in males than in females. Chronic infusion of angiotensin II (AngII) into apolipoprotein E-deficient (apoE(-/-)) mice promotes atherosclerosis and causes the formation of AAAs. Just as human males are more susceptible to developing AAAs, male mice are more susceptible to AngII-induced AAAs. We hypothesized that sex steroid hormones mediate gender differences in AngII-induced AAA through regulation of the renin-angiotensin system. To define the role of ovarian hormones, female apoE(-/-) mice were subjected to ovariectomy or sham operation and infused with AngII (1000 ng/kg x min) for 28 d. Ovariectomy had no effect on AngII-induced atherosclerosis, nor did it influence the incidence or severity of AAA. To define the role of testicular hormones, male apoE(-/-) mice were subjected to orchidectomy (orx) or sham operation and infused with AngII (1000 ng/kg x min) for 28 d. Orx resulted in a profound reduction in AAA incidence (85% vs. 18%, sham vs. orx; P = 0.003) to the level observed in females (25%). However, orx had no effect on AngII-induced reductions in plasma renin concentration or spleen AngII receptor density. In contrast, orx resulted in an increase in atherosclerosis (0.46 +/- 0.07 vs. 1.20 +/- 0.21 mm(2), sham vs. orx; P = 0.002). These results suggest that estrogen does not mediate gender differences in AngII-induced AAA. In contrast, androgens mediate a higher incidence of AngII- induced AAA, through mechanisms that do not appear to involve circulating renin or angiotensin receptor density.     

金雀异黄素对大鼠胸主动脉舒张功能的影响及其机制

目的观察植物雌激素金雀异黄素(genistein,GST)的快速舒张血管效应,并探讨其作用机制。方法选择雌性SD大鼠30只,取胸主动脉后,每条制成4个血管环(共120个血管环),采用血管张力仪进行体外血管灌注实验,测量不同浓度GST和17β-雌二醇(E2)大鼠体外胸主动脉环等长张力;另将血管按不同实验分为4组:对照组、左旋硝精氨酸甲酯(L-NAME)组、他莫昔芬(TAM)组和过氧化物酶体增殖物激活受体γ(PPARγ)组,并测量各组血管环张力。结果不同浓度GST(10-9~10-6mol/L)对苯肾上腺素(10-6mol/L)预收缩的血管环能产生浓度依赖性快速舒张血管效应,其作用与E2相似。与对照组比较,L-NAME组、TAM组、PPARγ组均能抑制GST的舒张血管效应。结论GST的快速舒张血管效应主要与内皮释放的NO有关,部分与PPARγ的调节作用有关,并通过雌激素受体发挥作用。     

Interleukin-1 plays a major role in vascular inflammation and atherosclerosis in male apolipoprotein E-knockout mice

OBJECTIVE: To examine the role of the balance between interleukin (IL)-1 and IL-1 receptor antagonist (IL-1Ra) in atherosclerosis and vascular inflammation. METHODS: Transgenic (Tg) mice overexpressing either secreted IL-1Ra or intracellular IL-1Ra1 as well as IL-1Ra-deficient mice (IL-1Ra -/-) were crossed with apolipoprotein E-deficient mice (ApoE -/-). RESULTS: In males fed a cholesterol-rich diet for 10 weeks, average atherosclerotic lesion area within aortic roots was significantly decreased in ApoE -/- secreted IL-1Ra Tg (-47%) and ApoE -/- intracellular IL-1Ra1 Tg (-40%) mice as compared to ApoE -/- non-Tg controls. The extent of sudanophilic lesions was reduced within the thoraco-abdominal aorta in ApoE -/- secreted IL-1Ra (-53%) and ApoE -/- intracellular IL-1Ra1 (-67%) Tg mice. In parallel experiments, we observed early mortality and illness among double deficient mice, whereas ApoE -/- IL-1Ra +/+ and ApoE +/+ IL-1Ra -/- mice were apparently healthy. After 7 weeks of diet, ApoE -/- IL-1Ra -/- mice exhibited massive aortic inflammation with destruction of the vascular architecture, but no signs of atherosclerosis. ApoE -/- IL-1Ra +/+ had atherosclerosis and a moderate inflammatory reaction, whereas ApoE +/+ IL-1Ra -/- mice were free of vascular lesions. Macrophages were present in large amounts within inflammatory lesions in the adventitia of ApoE -/- IL-1Ra -/- mice. CONCLUSION: Our results demonstrate that the IL-1/IL-1Ra ratio plays a critical role in the pathogenic mechanisms leading to vascular inflammation and atherosclerosis in ApoE -/- mice.     

Localized reduction of atherosclerosis in von Willebrand factor-deficient mice

To examine the role of the platelet adhesion molecule von Willebrand factor (vWf) in atherogenesis, vWf-deficient mice (vWf-/-) were bred with mice lacking the low-density lipoprotein receptor (LDLR-/-) on a C57BL/6J background. LDLR-/-vWf+/+ and LDLR-/-vWf-/- mice were placed on a diet rich in saturated fat and cholesterol for different lengths of time. The atherogenic diet stimulated leukocyte rolling in the mesenteric venules in both genotypes, indicating an increase in P-selectin-mediated adhesion to the endothelium. After 8 weeks on the atherogenic diet, the fatty streaks formed in the aortic sinus of LDLR-/-vWf-/- mice of either sex were 40% smaller and contained fewer monocytes than those in LDLR-/-vWf+/+ mice. After 22 weeks on the atherogenic diet (early fibrous plaque stage), the difference in lesion size in the aortic sinus persisted. Interestingly, the lesion distribution in the aortas of LDLR-/-vWf-/- animals was different from that of LDLR-/- vWf+/+ animals. In vWf-positive mice, half of all lesions were located at the branch points of the renal and mesenteric arteries, whereas lesions in this area were not as prominent in the vWf-negative mice. These results indicate that the absence of vWf primarily affects the regions of the aorta with disturbed flow that are prone to atherosclerosis. Thus, vWf may recruit platelets/leukocytes to the lesion in a flow-dependent manner or may be part of the mechano-transduction pathway regulating endothelial response to shear stress.     

Strain-dependent variation in vascular responses to nitric oxide in the isolated murine heart

Numerous studies in the literature have employed gene-modified mice to investigate vascular function. However, only very limited information exists on baseline murine vascular physiology or on potential variations between different strains. We therefore compared coronary and aortic vascular responses to endothelium-derived vasodilators and exogenous nitric oxide (NO) in three commonly used mouse strains and correlated these data with expression of eNOS, NADPH oxidase subunits, gp91(phox) and p67(phox), and superoxide production. Isolated perfused hearts from MF1, 129sv and C57BL/6J mice were subjected to: (a) increasing doses of bradykinin, acetylcholine and sodium nitroprusside, and (b) bolus doses of adenosine and the NO synthase inhibitor, N(G)-monomethyl- L -arginine. Vascular responses of thoracic aortic rings were assessed for comparison. Expression of eNOS and NADPH oxidase subunits was assessed by immunoblotting, and superoxide production by lucigenin-enhanced chemiluminescence. Coronary vasodilator responses to bradykinin, acetylcholine and sodium nitroprusside were significantly attenuated in MF1 compared with C57BL/6J and 129sv hearts. Similarly, aortic relaxation to acetylcholine was significantly impaired in MF1 aortic rings compared with in C57BL/6J aortae; these differences were reversed by Tiron. N(G)-monomethyl- L -arginine induced significantly less vasoconstriction in MF1 and 129sv hearts compared with C57BL/6J. No differences in aortic relaxation to A23187 or sodium nitroprusside were observed. Cardiac and aortic superoxide production and cardiac expression of p67(phox) and gp91(phox) were significantly greater in MF1 mice compared with the other strains. There is significant strain-dependent variation in coronary and aortic vascular responsiveness in mice, which may reflect differences in the balance between NO and superoxide generation.     

The anatomical distribution of ADPase activity in the rabbit aorta

The anatomical distribution of ADPase activity in the rabbit aorta was investigated. The aortic arch and upper thoracic regions of the rabbit aorta were found to have a reduced capacity to break down ADP and also unable to further metabolise the AMP thus formed. ADPase activity progressively increased down the aorta to the abdominal regions where it was highest. The abdominal regions of the aorta together with the lower thoracic region were able to produce adenosine from ADP. These results suggest a connection between ADPase activity and the incidence of atherosclerosis in rabbits. Thus in the aortic arch and upper thoracic regions of the aorta where the incidence of the disease is higher, the ability of the vascular tissue to break down ADP is low; therefore platelet aggregation is more likely to occur in response to minimal wear and tear. Conversely, in the abdominal regions where ADPase activity is highest and the incidence of the disease is lower ADPase may play a protective role in limiting ADP-induced thrombotic response to vascular trauma.