Structure and reactivity of small arteries in aging

Objective: Increased pulse pressure has been observed in aging subjects, but the impact on the structure and reactivity of small arteries has been scarcely evaluated. Methods: This study presents the modifications of vascular structure and function observed in female rats of 5, 18 and 32 months of age, and their relation to the prevailing hemodynamic status. Geometry and reactivity of perfused and pressurized basilar and mesenteric small arteries were analyzed in vitro using a video dimension analyzer. Results: Mean arterial pressure was similar in the three age groups, and only pulse pressure was increased in the oldest group. Media thickness and cross sectional area increased in basilar and mesenteric arteries of the oldest rats and these structural abnormalities were positively related to pulse pressure but not to mean, systolic or diastolic arterial pressure. Only minor changes of vascular reactivity were noted with age: there was a decreased contraction to angiotensin II in mesenteric arteries and an enhanced contraction to endothelin-1 in the basilar arteries. Conclusion: In conclusion, aging is associated with increased pulse pressure and hypertrophy of basilar and mesenteric resistance arteries, suggesting that this hemodynamic variable may influence cerebral and peripheral vascular structure in agin

Ultra high level liquid argon purification using electron emission from a tip array

Abstract An array of 148 sharp tips was used to inject large quantities of free electrons in liquid argon and to purify it at a level · 0.09 ppb in few hours. We also evaluated the gettering capability of the stainless steel surface and measured the I–V characteristic of the array

Chronic ETA receptor blockade prevents endothelial dysfunction of small arteries in apolipoprotein E-deficient mice

Objective: This study investigated whether endothelial dysfunction occurs in mesenteric arteries of apoE-deficient mice and determined the role of endothelin (ET)-1, which is increased in human atherosclerosis, using an orally active endothelin ETA receptor antagonist. Methods: ApoE-deficient and C57BL/6J control mice were fed for 30 weeks with normal chow or high-fat Western-type diet alone or in combination with darusentan (LU135252; 50 mg/kg/day). Vasomotor reactivity of isolated small mesenteric arteries (I.D. 200-250 μm) was studied in vitro under perfused and pressurized conditions. Results: In both mouse strains, about one fourth of the endothelium-dependent relaxant response to acetylcholine was insensitive to inhibition by l-NAME and indomethacin. In mesenteric arteries of apoE-deficient mice on Western-type diet, increased intima-media thickness and levels of endothelin-1 protein were observed. In addition, NO-mediated endothelium-dependent relaxation to acetylcholine was reduced without affecting l-NAME/indomethacin insensitive relaxation and contractions to endothelin-1 and serotonin were enhanced. Treatment with darusentan normalized vascular structure, NO-mediated relaxation to acetylcholine and contractions to endothelin-1 and serotonin without affecting blood pressure or plasma cholesterol levels. Conclusions: Severe hypercholesterolemia in apoE-deficient mice is associated with attenuation of NO-mediated relaxation to acetylcholine and increased vascular endothelin-1 content. Chronic ETA receptor blockade may provide a new therapeutic approach to improve NO-mediated endothelium-dependent vasomotion in small arterie

P-590: Obesity regulates renal endothelin and endothelin ETA receptor expression in vivo. Differential effects of chronic ETA receptor blockade

ETA receptors have been implicated in obesity-associated hypertension (Hypertension 1999; 33: 1169). We characterized the renal endothelin system in diet-induced obesity and determined the effects of chronic treatment with the ETA antagonist darusentan. C57BL/6J mice were fed a standard diet (control) or a high-fat diet (Harlan TD88137) with or without darusentan (50 mg/kg/d, 30 wk). Total RNA was extracted from whole kidneys and mRNA expression of preproendothelin-1 (ppET-1), ETA receptors, and β-actin were determined by RT-PCR using mouse-specific primers. PCR-products were normalized vs. β-actin or 18S rRNA. Renal ET-1 protein was measured by RIA/HPLC. High fat diet increased body weight by 257% compared to 54% (control diet). Darusentan had no effect on body weight in obese mice (263%) and treatments had no effect on systolic blood pressure. Obesity was associated with upregulation of renal ETA receptors (144±5% vs 100±7%, p<0.05 vs. control) and to a lesser extent, preproendothelin-1 (113±5% vs.100±2%, p<0.05 vs. control). In obese mice chronic darusentan treatment in part prevented the ETA receptor upregulation (126% vs. 144±5%, p<0.05) but had no significant effect on ppET-1 mRNA expression (101±9 vs. 100±2%, n.s.). Renal ET-1 protein increased in obese animals (from 190±18 to 267±19 pg/g tissue, p<0.05 vs. control). This increase was not affected by concomitant darusentan treatment (n.s.). These data for the first time demonstrate that obesity in normotensive rats is associated with upregulation of renal ETA receptor expression suggesting that body weight per se affects ET receptor expression in the kidney. Our data further indicate that in this model ETA receptors control expression of the ETA receptor but not the ppET-1 gene, suggesting autocrine regulation in vivo. These mechanisms might contribute to the pathogenesis of obesity-associated diseases affecting the kidney and/or blood pressur

Nitric oxide and hypoxia stimulate erythropoietin receptor via MAPK kinase in endothelial cells

Erythropoietin receptor (EPOR) expression level determines the extent of erythropoietin (EPO) response. Previously we showed that EPOR expression in endothelial cells is increased at low oxygen tension and that EPO stimulation of endothelial cells during hypoxia can increase endothelial nitric oxide (NO) synthase (eNOS) expression and activation as well as NO production. We now observe that while EPO can stimulate NO production, NO in turn can regulate EPOR expression. Human umbilical vein endothelial cells (HUVEC) treated with 10-50 pM of NO donor diethylenetriamine NONOate (DETANO) for 24 h showed significant induction of EPOR gene expression at 5% and 2% of oxygen. Also human bone marrow microvascular endothelial cell line (TrHBMEC) cultured at 21 and 2% oxygen with 50 uM DETANO demonstrated a time and oxygen dependent induction of EPOR mRNA expression after 24 and 48 h, particularly at low oxygen tension. EPOR protein was also induced by DETANO at 2% oxygen in TrHBMEC and HUVEC. The activation of signaling pathways by NO donor stimulation appeared to be distinct from EPO stimulation. In reporter gene assays, DETANO treatment of HeLa cells at 2% oxygen increased EPOR promoter activity indicated by a 48% increase in luciferase activity with a 2 kb EPOR promoter fragment and a 71% increase in activity with a minimal EPOR promoter fragment containing 0.2 kb 5'. We found that DETANO activated MAPK kinase in TrHBMEC both in normoxia and hypoxia, while MAPK kinase inhibition showed significant reduction of EPOR mRNA gene expression at low oxygen tension, suggesting MAPK involvement in NO mediated induction of EPOR Furthermore, DETANO stimulated Ala anti-apoptotic activity after 30 min in normoxia, whereas it inhibited Akt phosphorylation in hypoxia. In contrast, EPO did not significantly increase MAPK activity while EPO stimulated Akt phosphorylation in TrHBMEC in normoxia and hypoxia. These observations provide a new effect of NO on EPOR expression to enhance EPO response in endothelial cells, particularly at low oxygen tensions

Reduction of blood pressure, plasma cholesterol, and atherosclerosis by elevated endothelial nitric oxide.

In the vascular system, nitric oxide is generated by endothelial NO synthase (eNOS). NO has pleiotropic effects, most of which are believed to be atheroprotective. Therefore, it has been argued that patients suffering from cardiovascular disease could benefit from an increase in eNOS activity. However, increased NO production can cause oxidative damage, cell toxicity, and apoptosis and hence could be atherogenic rather than beneficial. To study the in vivo effects of increased eNOS activity, we created transgenic mice overexpressing human eNOS. Aortic blood pressure was approximately 20 mm Hg lower in the transgenic mice compared with control mice because of lower systemic vascular resistance. The effects of eNOS overexpression on diet-induced atherosclerosis were studied in apolipoprotein E-deficient mice. Elevation of eNOS activity decreased blood pressure ( approximately 20 mm Hg) and plasma levels of cholesterol (approximately 17%), resulting in a reduction in atherosclerotic lesions by 40%. We conclude that an increase in eNOS activity is beneficial and provides protection against atherosclerosis

Gender-Specific Modulation of the Response to Arterial Injury by Soluble Guanylate Cyclase α1

Objective: Soluble guanylate cyclase (sGC), a heterodimer composed of α and β subunits, synthesizes cGMP in response to nitric oxide (NO). NO modulates vascular tone and structure but the relative contributions of cGMP-dependent versus cGMP-independent mechanisms remain uncertain. We studied the response to vascular injury in male (M) and female (F) mice with targeted deletion of exon 6 of the sGCα1 subunit (sGCα1-/-), resulting in a non-functional heterodimer. Methods: We measured aortic cGMP levels and mRNA transcripts encoding sGC α1, α2, and β1 subunits in wild type (WT) and sGCa1-/- mice. To study the response to vascular injury, BrdU-incorporation and neointima formation (maximum intima to media (I/M) ratio) were determined 5 and 28 days after carotid artery ligation, respectively. Results: Aortic cGMP levels were 4-fold higher in F than in M mice in both genotypes, and, within each gender, 4-fold higher in WT than in sGCa1-/-. In contrast, sGCα1, sGCα2, and sGCβ1 mRNA expression did not differ between groups. 3H-thymidine incorporation in cultured sGCa1-/- smooth muscle cells (SMC) was 27%±12% lower than in WT SMC and BrdU-incorporation in carotid arteries 5 days after ligation was significantly less in sGCa1-/- M than in WT M. Neointima area and I/M 28 days after ligation were 65% and 62% lower in sGCa1-/- M than in WT M mice (p<0,05 for both) but were not different in F mice. Conclusion: Functional deletion of sGCa1 resulted in reduced cGMP levels in male sGCa1-/- mice and a gender-specific effect on the adaptive response to vascular injury