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

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

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 aging

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 arteries

Effects of obesity on endothelium-dependent reactivity during acute nitric oxide synthase inhibition: modulatory role of endothelin.

This study investigated vascular reactivity in response to acetylcholine, in the presence of acute inhibition of nitric oxide synthase, in the carotid artery and aorta of obese C57Bl6/J mice fed on a high-fat diet for 30 weeks, and of control mice. A subgroup of obese animals was also treated with the ET(A) receptor antagonist darusentan (50 mg x kg(-1) x day(-1)). In vascular rings from control animals, acetylcholine caused endothelium-dependent contractions in the carotid artery, but not in the aorta. In vascular rings from obese mice, contractility to acetylcholine was also evident in the aorta, and that in the carotid artery was increased compared with control mice. ET(A) receptor blockade by darusentan treatment of the obese mice prevented enhanced vasoconstriction to acetylcholine, resulting in mild vasodilatation. Thus obesity increases endothelium-dependent vasoconstriction in the absence of endothelial nitric oxide. This effect can be completely prevented by chronic ET(A) receptor blockade, suggesting that endothelin modulates increased endothelium-dependent vasoconstriction in obesity

Endothelium-independent relaxation and hyperpolarization to C-type natriuretic peptide in porcine coronary arteries

Endothelial cells produce C-type natriuretic peptide (CNP), which has been proposed as an endothelium-derived hyperpolarizing factor. In porcine coronary arteries, we investigated the vasodilatory effects of CNP and compared them with endothelium-dependent relaxations and hyperpolarizations to bradykinin. Isolated epicardial porcine coronary arteries were studied in organ chambers, and concentration-response curves to CNP and bradykinin were obtained. Membrane potential was measured in endothelial cells and smooth muscle of intact procine coronary arteries during stimulation with CNP or bradykinin. In precontracted porcine coronary arteries with CNP or bradykinin. In precontracted porcine coronay arteries with or without endothelium, CNP (10-10-10-6M) evoked relaxations (maximum 42 ± 4%) smaller than those evoked by bradykinin (100 ± 1%), blunted in preparations contracted by KCl instead of U46619 (9,11-dideoxy-11 a,9a-epoxymethano-prostaglandin F2α; p &lt; 0.05) and unaffected by inhibition of NO synthase (NS). CNP evoked hyperpolarization of vascular smooth muscle of similar magnitude in endothelium-intact (-4.4 ± 1 mV) and endothelium-denuded (-4.6 ± 1 mV) porcine coronary arteries. Bradykinin (10-10- 10-6 M) evoked concentration-dependent relaxations in preparations with endothelium only. Although atrial natriuretic peptide-receptor antagonist HS-142-1 (25 μM) slightly reduced the sensitivity to bradykinin (log shift at IC50, twofold; p &lt;0.05), it had no effect on the maximal response to bradykinin. Inhibition of NO synthase partially attenuated, whereas high potassium chloride (30 mM) markedly inhibited relaxations to bradykinin (p &lt; 0.05). Hyperpolarization to bradykinin was much more pronounced than that to CNP (-17 ± 3 mV; p &lt; 0.05 vs. CNP) and was observed in endothelium-intact preparations only and unaffected by HS-142-1. In conclusion, in contrast to bradykinin, CNP induces endothelium-independent and weaker relaxation and hyperpolarization of coronary artery vascular smooth muscle, suggesting that CNP is an unlikely mediator of endothelium-dependent hyperpolarization of porcine coronary arteries