Arteriosclerosis, characterized by remodeling and stiffening of large elastic arteries is the most significant manifestation of vascular aging. The increased stiffening is believed to originate from a gradual mechanical senescence of the elastic network, alterations in cross-linking of extracellular matrix components, fibrosis and calcification of elastic fibers (medial elastocalcinosis). The stiffening of large arteries reduces their capacitance and accelerates pulse wave velocity, thus contributing to a widening of pulse pressure and to the increased prevalence of isolated systolic hypertension with age. Current antihypertensive drugs were mainly designed to reduce peripheral resistance and are not adequate to alter the pathological process of vascular stiffening or even to selectively reduce systolic blood pressure in isolated systolic hypertension. This review puts forward the concept that elastocalcinosis is a valuable therapeutic target and presents evidence that this process can be prevented and reversed pharmacologically.

Aging is an important determinant of vascular disease. Endothelium-derived nitric oxide (NO) is protective as a vasodilator and inhibitor of platelet function. This study was designed to directly measure effects of prolonged aging on endotheliai NO release in isolated blood vessels and to delineate differences between the systemic and pulmonary circulation. Aortas and pulmonary arteries from 5-6-mo-old (young), 18-19-mo-old (middle-aged), and 32-33-mo-old (old) normotensive female rats were used. Blood pressure and plasma estradiol-17beta (E2) remained unchanged. In isolated blood vessels, NO release was induced by the receptor-independent agonist calcium ionophore A23187 (10 micromol/liter) and measured in situ on the endothelial surface of vessels using a porphyrinic microsensor. In vessels suspended in organ chambers isometric tension was recorded. In the aorta, the initial rate of NO release and peak NO concentration were reduced in middle-aged and old rats (P < 0.0006 vs. young rats, n = 6). Furthermore, endothelium-dependent relaxations to calcium ionophore and acetylcholine (both 10(-10) - 10(-5) mol/liter) were also reduced in aortas from old as compared with young rats (n = 6, P < 0.05). The initial rate of NO release and peak NO concentration significantly correlated with maximal relaxation to calcium ionophore A23187 (correlation coefficients r - 0.916, P < 0.0018 and r = 0.961, P < 0.0001, respectively, n = 7). In pulmonary arteries, however, the initial rate of NO release as well as peak NO concentration did not decrease with age (n = 6 for each age group, NS). In both blood vessels, the NO release was unaffected by superoxide dismutase in all age groups (n = 6, NS). Thus, aging specifically reduces initial rate and peak concentrations of endothelial NO release from aorta but not pulmonary artery indicating reduced NO production. As arterial pressure did not change with aging, the chronic exposure of the aorta to higher pressure and/or pulsatility than in the pulmonary artery may be the cause. This appears important as NO plays a protective role by preventing vasoconstriction, thrombosis and atherosclerosis.

Background In vitro studies on vascular smooth muscle cells suggest that endothelin has a stimulating effect on cellular proliferation. This study was designed to determine the endogenous effect of endothelin on angiotensin II–induced hypertrophy of small arteries in vivo. Methods and Results Two weeks of angiotensin II administration (200 ng·kg ⁻¹ ·min ⁻¹ ) increased media thickness, media/lumen ratio, and cross-sectional area of basilar and small mesenteric arteries, confirming the proliferative properties of angiotensin II. The tissue levels of endothelin-1 were elevated in mesenteric arteries after angiotensin II administration. The administration of the selective and specific ET _A -receptor antagonist LU135252 (50 mg·kg ⁻¹ ·d ⁻¹ ) in combination with angiotensin II prevented the changes of vascular geometry and partially reduced the increase in blood pressure induced by angiotensin II. Indeed, part of the effect on the vascular structure of the endothelin-receptor antagonist seemed pressure-independent. Conclusions Our results therefore demonstrate that angiotensin II increases the production of endothelin in the blood vessel wall that, via ET _A receptors, mediates changes in vascular structure of the cerebral and mesenteric circulation. Endothelin antagonists may therefore be of value to reduce blood pressure and to prevent vascular structural changes in conditions of increased activity of the renin-angiotensin system.

We investigated the effects of aging, a cardiovascular risk factor, on vascular function with regard to endothelial nitric oxide synthase (eNOS), superoxide dismutase (SOD), and endothelin (ET-1) in aorta and femoral artery of the rat. Concentration-response curves to acetylcholine, calcium ionophore A23187, norepinephrine, ET-1, big endothelin, sodium nitroprusside, and exogenous SOD were obtained. Expression of eNOS mRNA was analyzed by reverse-transcription polymerase chain reaction, SOD activity was assessed using a chemiluminescence-based cytochromecassay, and ET-1 plasma concentrations were measured by radioimmunoassay. In aorta of old rats, relaxations to acetylcholine and calcium-ionophore A23187, basal NO release, and expression of eNOS mRNA in aortic endothelial cells were reduced (P<.05). In femoral arteries, relaxations to acetylcholine were preserved, whereas basal release of NO was attenuated (P<.05). Aging selectively increased contractions to norepinephrine and functional endothelin converting enzyme activity and attenuated contractions to ET-1 in aortas but not femoral arteries. Vascular SOD activity was higher in the femoral artery (P<.05) and unaffected by aging. Plasma ET-1 levels increased and plasma SOD activity decreased with age (P<.05). Aging was associated with an anatomic heterogeneity of endothelial dysfunction, functional endothelin converting enzyme activity, and vascular SOD activity. Vascular function was impaired in the aorta but not the femoral artery, which may be related to lower eNOS mRNA expression and SOD activity. These data suggest differential regulation of the vascular aging process that may contribute to the anatomic heterogeneity of atherosclerosis.

Sodium plays an important role in the pathogenesis and therapy of hypertension, a major risk factor for cardiovascular disease. This study investigated the involvement of endothelin in vascular alterations in salt-induced Dahl hypertension. Salt-sensitive (DS) and salt-resistant (DR) Dahl rats were treated with a high-sodium diet (NaCl 4%) with or without ET _A receptor antagonist LU135252 for two months, and effects of treatments on systolic blood pressure, vascular endothelin-1 (ET-1) protein content, aortic hypertrophy, and vascular reactivity of isolated aortic rings were studied. In DS rats, a high-sodium diet increased systolic pressure (190±4 versus 152±2 mm Hg, P <.05) and aortic ET-1 protein content (4.2-fold, P <.0001) and induced aortic hypertrophy as assessed by tissue weight ( P <.0001). Sodium diet markedly reduced NO-mediated endothelium-dependent relaxations to acetylcholine (49±4% versus 81±4%, P <.0001) and contractions to ET-1 (92±7 versus 136±8% of KCl, P =.0011). ET-1 tissue levels were highly and inversely correlated with endothelium-dependent relaxations ( r =0.931, P <.0001) and contractions to ET ( r =0.77, P =.0007). LU135252 treatment reduced systolic blood pressure only in part (168±3 versus 190±4 mm Hg. P <.05) but normalized sodium-induced changes of vascular reactivity, tissue ET-1 protein content, and vascular structure ( P <.001 versus sodium). None of these effects were observed in DR rats. These results suggest that ET-1 acts as a local mediator of vascular dysfunction and aortic hypertrophy in Dahl salt-induced hypertension. ET _A receptor antagonism may have therapeutic potential for lowering vascular ET-1 content, improving endothelial function, and preventing structural changes in salt-sensitive hypertension.