Endothelium-Dependent Inhibition of the Contractile Response Is Decreased in Aorta from Aged and Spontaneously Hypertensive Rats

Avocado Oil Prevents Kidney Injury and Normalizes Renal Vasodilation after Adrenergic Stimulation in Hypertensive Rats: Probable Role of Improvement in Mitochondrial Dysfunction and Oxidative Stress

Hypertension impairs the function of the kidney and its vasculature. Adrenergic activation is involved in these processes by promoting oxidative stress and mitochondrial dysfunction. Thus, the targeting of mitochondrial function and mitochondrial oxidative stress may be an approach to alleviate hypertensive kidney damage. Avocado oil, a source of oleic acid and antioxidants, improves mitochondrial dysfunction, decreases mitochondrial oxidative stress, and enhances vascular function in hypertensive rats. However, whether avocado oil improves the function of renal vasculature during the adrenergic stimulation, and if this is related to improvement in renal damage and enhancement of mitochondrial activity is unknown. Thus, the effects of avocado oil on renal vascular responses to adrenergic stimulation, mitochondrial dysfunction, oxidative stress, and renal damage were compared with prazosin, an antagonist of α₁-adrenoceptors, in hypertensive rats induced by L-NAME. Avocado oil or prazosin decreased blood pressure, improved endothelium-dependent renal vasodilation, prevented mitochondrial dysfunction and kidney damage in hypertensive rats. However, avocado oil, but not prazosin, decreased mitochondrial ROS generation and improved the redox state of mitochondrial glutathione. These results suggest that avocado oil and prazosin prevented hypertensive renal damage due to the improvement in mitochondrial function.

Chronic Mercury Exposure in Prehypertensive SHRs Accelerates Hypertension Development and Activates Vasoprotective Mechanisms by Increasing NO and H2O2 Production

Mercury is a heavy metal associated with cardiovascular diseases. Studies have reported increased vascular reactivity without changes in systolic blood pressure (SBP) after chronic mercury chloride (HgCl₂) exposure, an inorganic form of the metal, in normotensive rats. However, we do not know whether individuals in the prehypertensive phase, such as young spontaneously hypertensive rats (SHRs), are susceptible to increased arterial blood pressure. We investigated whether chronic HgCl₂ exposure in young SHRs accelerates hypertension development by studying the vascular function of mesenteric resistance arteries (MRAs) and SBP in young SHRs during the prehypertensive phase. Four-week-old male SHRs were divided into two groups: the SHR control group (vehicle) and the SHR HgCl₂ group (4 weeks of exposure). The results showed that HgCl₂ treatment accelerated the development of hypertension; reduced vascular reactivity to phenylephrine in MRAs; increased nitric oxide (NO) generation; promoted vascular dysfunction by increasing the production of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂); increased Gp91Phox protein levels and in situ levels of superoxide anion (O₂^·-); and reduced vasoconstrictor prostanoid production compared to vehicle treatment. Although HgCl₂ accelerated the development of hypertension, the HgCl₂-exposed animals also exhibited a vasoprotective mechanism to counterbalance the rapid increase in SBP by decreasing vascular reactivity through H₂O₂ and NO overproduction. Our results suggest that HgCl₂ exposure potentiates this vasoprotective mechanism against the early establishment of hypertension. Therefore, we are concluding that chronic exposure to HgCl₂ in prehypertensive animals could enhance the risk for cardiovascular diseases.

Long-term Mercury Exposure Accelerates the Development of Hypertension in Prehypertensive Spontaneously Hypertensive Rats Inducing Endothelial Dysfunction: the Role of Oxidative Stress and Cyclooxygenase-2

Mercury is a metal widely dispersed in nature that when in contact with human organism, it damages the cardiovascular system. Long-term mercury exposure for 30 days induces endothelial dysfunction without blood pressure changes in normotensive adult rats. However, it is not known whether exposure to mercury can exacerbate endothelial dysfunction and hypertension development in predisposed animals. Thus, we aimed to investigate the effects of long-term mercury exposure on the blood pressure (BP) and in the isolated aortas of young normotensive and prehypertensive spontaneously hypertensive rats (SHRs). Four-week-old male Wistar rats and SHRs were treated daily with mercury chloride (HgCl₂) (1st dose, 4.6 μg/kg; subsequent dose, 0.07 μg/kg/day, im, 30 days) or vehicle. BP was assessed weekly and the vascular reactivity to phenylephrine was evaluated in isolated aorta from rats exposed or not to mercury. Mercury exposure did not affect BP in young Wistar rats but accelerated the development of hypertension in young SHRs. Vascular reactivity to phenylephrine increased only in the aorta from mercury-exposed SHRs. While HgCl₂ exposure in SHRs did not alter nitric oxide production, we observed increased superoxide anion production and decreased superoxide dismutase-1 protein expression, and enhanced cyclooxygenase-2 (COX-2) participation with increased prostaglandin (PGE₂) production and decreased prostacyclin. In the Wistar group, mercury exposure did not alter superoxide anion production or the COX-2 pathway. Mercury exposure accelerated the natural course of hypertension in young SHRs and increased oxidative stress associated with reduced participation of antioxidant enzymes, an activated COX-2 pathway, thereby producing endothelial dysfunction, which is a risk factor in prehypertensive individuals.

Cardiovascular Responses to 5-hydroxytryptamine in Methimazole-induced Hypothyroid Pithed Rats

BACKGROUND

Patients suffering from hypothyroidism tend to develop diastolic hypertension. 5-Hydroxytryptamine (5-HT) is an amine that contributes to the maintenance of the blood pressure through central and peripheral 5-HT receptors. Curiously, the hypothyroidism alters the density of the 5-HT receptors in rodent brains.

AIM OF THE STUDY

Analyze the effect of the methimazole-induced hypothyroidism on the peripheral cardiovascular responses elicited by 5-HT.

METHODS

The vasopressor and tachycardic responses to 5-HT (3-300 μg/kg), and the vasodepressor responses to 5-HT, 5-carboxamidotryptamine (5-CT, 0.001-0.1 μg/kg), isoprenaline (0.03-1 μg/kg) and acetylcholine (ACh, 0.03-3 μg/kg), during an infusion of methoxamine, were determined in pithed hypothyroid rats.

RESULTS

The tachycardic and vasopressor responses to 5-HT and the vasodepressor responses to 5-CT and ACh remained unaffected, the vasodepressor response to 5-HT reduced, and the vasodepressor response to isoprenaline enhanced and reduced at the lowest and highest dose, respectively.

CONCLUSION

These results suggest that hypothyroidism impairs the vasodepressor response to 5-HT, which could contribute to hypothyroidism-induced hypertension.

Increased Vascular Contractility in Hypertension Results From Impaired Endothelial Calcium Signaling

Supplemental Digital Content is available in the text.

Endothelial cells line all blood vessels and are critical regulators of vascular tone. In hypertension, disruption of endothelial function alters the release of endothelial-derived vasoactive factors and results in increased vascular tone. Although the release of endothelial-derived vasodilators occurs in a Ca²⁺-dependent manner, little is known on how Ca²⁺ signaling is altered in hypertension. A key element to endothelial control of vascular tone is Ca²⁺ signals at specialized regions (myoendothelial projections) that connect endothelial cells and smooth muscle cells. This work describes disruption in the operation of this key Ca²⁺ signaling pathway in hypertension. We show that vascular reactivity to phenylephrine is increased in hypertensive (spontaneously hypertensive rat) when compared with normotensive (Wistar Kyoto) rats. Basal endothelial Ca²⁺ activity limits vascular contraction, but that Ca²⁺-dependent control is impaired in hypertension. When changes in endothelial Ca²⁺ levels are buffered, vascular contraction to phenylephrine increased, resulting in similar responses in normotension and hypertension. Local endothelial IP₃(inositol trisphosphate)-mediated Ca²⁺ signals are smaller in amplitude, shorter in duration, occur less frequently, and arise from fewer sites in hypertension. Spatial control of endothelial Ca²⁺ signaling is also disrupted in hypertension: local Ca²⁺ signals occur further from myoendothelial projections in hypertension. The results demonstrate that the organization of local Ca²⁺ signaling circuits occurring at myoendothelial projections is disrupted in hypertension, giving rise to increased contractile responses.

The enhancement of serotonin-induced contraction of rat femoral artery is mediated by angiotensin II release from intact endothelium

We have performed an in vitro study on isolated intact or denuded femoral artery (FA) of healthy, diabetic, and/or rats submitted to the FA occlusion. The aim was to determine the contribution of endothelium and endothelial dysfunction (ED) on serotonin-induced action in FA. Further, the contribution of angiotensin II and cyclooxygenase products of arachidonic acid was investigated. A marker of ED, vWF was measured in animal serum. Serotonin induced contraction-dependent contraction of isolated FA, which was increased in preparations with endothelium. Pathological conditions such as endothelial denudation, nicotine-induced ED, diabetes or occlusion of FA reduced serotonin-induced contraction. Comparable reduction of serotonin-induced contraction was achieved after inhibition of AT1 receptors with losartan in isolated FA with intact endothelium. Our results demonstrate that angiotensin II contributes to the enhancement of serotonin-induced contraction of femoral arteries with intact endothelium. This increase is attenuated by endothelium removal, nicotine treatment, vascular occlusion, and/or hyperglycemia.

Clarification of serotonin-induced effects in peripheral artery disease observed through the femoral artery response in models of diabetes and vascular occlusion: The role of calcium ions

Recent findings have demonstrated that serotonin is an important participant in the development and progression of peripheral artery diseases. Taking this into consideration, the goals of this study were to investigate the effects of serotonin on isolated Wistar rat femoral arteries in both healthy and diabetic animals, with and without artery occlusion, with a particular focus on determining the role of calcium in this process. Contraction experiments with serotonin on intact and denuded femoral artery rings, in the presence or absence of nifedipine and ouabain (both separately, or in combination), as well as Ca²⁺ -free Krebs-Ringer bicarbonate solution were performed. The serotonin-induced results were concentration dependent, but only in healthy animals. The endothelium-dependent contraction of the femoral artery was assessed. In healthy animals, the endothelium-reliant part of contraction was dependent on the extracellular calcium, while the smooth muscle-related part was instead dependent on the intracellular calcium. In diabetic animals, both nifedipine and ouabain influenced serotonin-induced vascular effects by blocking intracellular calcium pathways. However, this was diminished after the simultaneous administration of both blockers.

Advancing Age Decreases Pressure-Sensitive Modulation of Calcium Signaling in the Endothelium of Intact and Pressurized Arteries

Aging is the summation of many subtle changes which result in altered cardiovascular function. Impaired endothelial function underlies several of these changes and precipitates plaque development in larger arteries. The endothelium transduces chemical and mechanical signals into changes in the cytoplasmic calcium concentration to control vascular function. However, studying endothelial calcium signaling in larger arteries in a physiological configuration is challenging because of the requirement to focus through the artery wall. Here, pressure- and agonist-sensitive endothelial calcium signaling was studied in pressurized carotid arteries from young (3-month-old) and aged (18-month-old) rats by imaging from within the artery using gradient index fluorescence microendoscopy. Endothelial sensitivity to acetylcholine increased with age. The number of cells exhibiting oscillatory calcium signals and the frequency of oscillations were unchanged with age. However, the latency of calcium responses was significantly increased with age. Acetylcholine-evoked endothelial calcium signals were suppressed by increased intraluminal pressure. However, pressure-dependent inhibition of calcium signaling was substantially reduced with age. While each of these changes will increase endothelial calcium signaling with increasing age, decreases in endothelial pressure sensitivity may manifest as a loss of functionality and responsiveness in aging.

Des-aspartate angiotensin I (DAA-I) reduces endothelial dysfunction in the aorta of the spontaneously hypertensive rat through inhibition of angiotensin II-induced oxidative stress

Des-aspartate angiotensin I (DAA-I), an endogenous nonapeptide, counteracts several effects of angiotensin II on vascular tone. The aim of this study was to investigate the acute protective effect of DAA-I on endothelial function in the spontaneously hypertensive rat (SHR) as well as its effect on angiotensin II-induced contractions and oxidative stress. Aortic rings were incubated with DAA-I (0.1μM) for 30min prior to the assessment of angiotensin II-induced contractions (0.1nM-10μM) in WKY and SHR aortas. Total nitrate and nitrite levels were assessed using a colorimetric method and reactive oxygen species (ROS) were measured by dihydroethidium (DHE) fluorescence and lucigenin-enhanced chemiluminescence. The effect of DAA-I was also assessed against endothelium-dependent and -independent relaxations to acetylcholine and sodium nitroprusside, respectively. Angiotensin II-induced contractions were significantly reduced by DAA-I, losartan and tempol. Incubation with ODQ (soluble guanylyl cyclase inhibitor) and removal of the endothelium prevented the reduction of angiotensin II-induced contractions by DAA-I. Total nitrate and nitrite levels were increased in DAA-I, losartan and tempol treated-SHR tissues while ROS level was reduced by DAA-I and the latter inhibitors. In addition, DAA-I significantly improved the impaired acetylcholine-induced relaxation in SHR aortas whilst sodium nitroprusside-induced endothelium-independent relaxation remained unaffected. The present findings indicate that improvement of endothelial function by DAA-I in the SHR aorta is mediated through endothelium-dependent release of nitric oxide and inhibition of angiotensin II-induced oxidative stress.

Vascular endothelial function is improved by oral glycine treatment in aged rats

Glycine has been used to reduce oxidative stress and proinflammatory mediators in some metabolic disorders; however, its effect on the vasculature has been poorly studied. The aim of this work was to explore the effect of glycine on endothelial dysfunction in aged rats. Aortic rings with intact or denuded endothelium were obtained from untreated or glycine-treated male Sprague-Dawley rats at 5 and 15 months of age. Concentration-response curves to phenylephrine (PHE) were obtained from aortic rings incubated with N(G)-nitro-l-arginine methyl ester (l-NAME), superoxide dismutase (SOD), indomethacin, SC-560, and NS-398. Aortic mRNA expression of endothelial nitric oxide synthase (eNOS), NADPH oxidase 4 (NOX-4), cyclooxygenase 1 (COX-1), cyclooxygenase 2 (COX-2), tumour necrosis factor (TNF)-α, and interleukin-1 β was measured by real time RT-PCR. The endothelial modulation of the contraction by PHE was decreased in aortic rings from aged rats. Glycine treatment improved this modulator effect and increased relaxation to acetylcholine. Glycine augmented the sensitivity for PHE in the presence of l-NAME and SOD. It also reduced the contraction by incubation with indomethacin, SC-560, and NS-398. Glycine increased the mRNA expression of eNOS and decreased the expression of COX-2 and TNF-α. Glycine improved the endothelium function in aged rats possibly by enhancing eNOS expression and reducing the role of superoxide anion and contractile prostanoids that increase the nitric oxide bioavailability.

Early co-expression of cyclooxygenase-2 and renin in the rat kidney cortex contributes to the development of N(G)-nitro-L-arginine methyl ester induced hypertension

We investigated the involvement of cyclooxygenase-2 (COX-2) and the renin-angiotensin system in N(G)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension. Male Wistar rats were treated with L-NAME (75.0 mg·(kg body mass)(-1)·day(-1), in their drinking water) for different durations (1-33 days). COX-2 and renin mRNA were measured using real-time PCR in the renal cortex, and prostanoids were assessed in the renal perfusate, whereas angiotensin II (Ang II) and Ang (1-7) were quantified in plasma. In some rats, nitric oxide synthase inhibition was carried out in conjunction with oral administration of captopril (30.0 mg·kg(-1)·day(-1)) or celecoxib (1.0 mg·kg(-1)·day(-1)) for 2 or 19 days. We found a parallel increase in renocortical COX-2 and renin mRNA starting at day 2 of treatment with L-NAME, and both peaked at 19-25 days. In addition, L-NAME increased renal 6-Keto-PGF(1α) (prostacyclin (PGI2) metabolite) and plasma Ang II from day 2, but reduced plasma Ang (1-7) at day 19. Captopril prevented the increase in blood pressure, which was associated with lower plasma Ang II and increased COX-2-derived 6-Keto-PGF(1α) at day 2 and plasma Ang (1-7) at day 19. Celecoxib partially prevented the increase in blood pressure; this effect was associated with a reduction in plasma Ang II. These findings indicate that renal COX-2 expression increased in parallel with renin expression, renal PGI2 synthesis, and plasma Ang II in L-NAME-induced hypertension.

Enhanced vasoconstriction to α1 adrenoceptor autoantibody in spontaneously hypertensive rats

Autoimmune activities have been implicated in the pathogenesis of hypertension. High levels of autoantibodies against the second extracellular loop of α1-adrenoceptor (α1-AR autoantibody, α1-AA) are found in patients with hypertension, and α1-AA could exert a α1-AR agonist-like vasoconstrictive effect. However, whether the vasoconstrictive effect of α1-AA is enhanced in hypertension is unknown. Using aortic rings of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, we observed the vasoconstrictive responses to α1-AA with phenylephrine (α1-AR agonist) as a positive control drug. Aortic nitrotyrosine levels were also measured by ELISA and immunohistochemistry. The results showed that the aortic constrictive responses to α1-AA and phenylephrine (both 1 nmol L(-1)-10 μmol L(-1)) were greater in SHR than in WKY rats. Endothelial denudation or L-NAME (a non-selective NOS inhibitor) (100 μmol L(-1)) increased α1-AA- or phenylephrine-induced vasoconstrictions both in SHR and WKY. However, selective iNOS inhibitor 1400 W (10 μmol L(-1)) enhanced the α1-AA-induced aortic constriction in WKY, but not in SHR. The aortic nitrotyrosine level was significantly higher in SHR than WKY, as shown by both ELISA and immunohistochemistry. These results indicate that the vasoconstrictive response to α1-AA is enhanced in SHR, and this altered responsiveness is due to endothelial dysfunction and decreased NO bioavailability. The study suggests an important role of α1-AR autoimmunity in the pathogenesis and management of hypertension especially in those harboring high α1-AA levels.

Pulmonary vasoreactivity in spontaneously hypertensive rats--effects of endothelin-1 and leptin

Background

Systemic hypertension may be associated with an increased pulmonary vascular resistance, which we hypothesized could be, at least in part, mediated by increased leptin.

Methods

Vascular reactivity to phenylephrine (1 μmol/L), endothelin-1 (10 nmol/L) and leptin (0.001–100 nmol/L) was evaluated in endothelium-intact and -denuded isolated thoracic aorta and pulmonary arteries from spontaneously hypertensive versus control Wistar rats. Arteries were sampled for pathobiological evaluation and lung tissue for morphometric evaluation.

Results

In control rats, endothelin-1 induced a higher level of contraction in the pulmonary artery than in the aorta. After phenylephrine or endothelin-1 precontraction, leptin relaxed intact pulmonary artery and aortic rings, while no response was observed in denuded arteries. Spontaneously hypertensive rats presented with increased reactivity to phenylephrine and endothelin-1 in endothelium-intact pulmonary arteries. After endothelin-1 precontraction, endothelium-dependent relaxation to leptin was impaired in pulmonary arteries from hypertensive rats. In both strains of rats, aortic segments were more responsive to leptin than pulmonary artery. In hypertensive rats, pulmonary arteries exhibited increased pulmonary artery medial thickness, associated with increased expressions of preproendothelin-1, endothelin-1 receptors type A and B, inducible nitric oxide synthase and decreased endothelial nitric oxide synthase, together with decreased leptin receptor and increased suppressor of cytokine signaling 3 expressions.

Conclusions

Altered pulmonary vascular reactivity in hypertension may be related to a loss of endothelial buffering of vasoconstriction and decreased leptin-induced vasodilation in conditions of increased endothelin-1.

New molecular mechanisms for cardiovascular disease: contribution of endothelium-derived hyperpolarizing factor in the regulation of vasoconstriction in peripheral resistance arteries

Endothelium regulates vascular tone via release of endothelium-derived relaxing factors (EDRF) including nitric oxide (NO), prostaglandin I₂ (PGI₂), and endothelium-derived hyperpolarizing factor (EDHF). The mesenteric vascular bed produces vascular resistance to develop blood pressure and regulate tissue blood flow that plays an important role in maintenance of systemic blood pressure. There is now strong evidence that in these small resistance arteries, EDHF plays a major role in the response to vasoactive substances and regulation of vascular tone. Pharmacological analysis to investigate the role of the vascular endothelium in the regulation of α₁-adrenoceptor agonist (methoxamine)-induced vasoconstriction in rat mesenteric vascular beds showed that vasoconstriction induced by continuous perfusion of methoxamine (7 µM), but not high KCl (60 mM), time-dependently decreased to 20% of the initial constriction. The time-dependent reduction of methoxamine-induced vasoconstriction was inhibited by endothelium removal, inhibitor of EDHF (30 mM KCl, K+-channel blockers), and gap-junction inhibitor, but not NO synthase inhibitor and cyclooxygenase inhibitor and ageing. These results suggest that vascular endothelium counteracts to normalize excess vasoconstriction of the mesenteric resistance arteries by releasing EDHF, which is associated with activation of multiple K+-channels and gap junction involvement and markedly decreases with ageing.

Endothelial modulation of agonist-induced vasoconstriction in mesenteric microcirculation

It is widely accepted that vascular endothelium regulates vasoconstriction via release of endothelium-derived relaxing factors (EDRF). The mesenteric circulation, which is the largest vascular bed, influences regulation of systemic blood pressure. However, the role of EDRF in the modulation of vascular tone in peripheral mesenteric circulation has not been extensively studied. Therefore, our recent studies investigated the role of the vascular endothelium in the regulation of methoxamine (alpha(1)-adrenoceptor agonist)-induced vasoconstriction and their age-related changes in rat mesenteric vascular beds. In mesenteric vascular beds with intact endothelium isolated from 8 week-old rats, the initial maximum vasoconstriction induced by continuous perfusion of methoxamine was time-dependently decreased during 3 hour-perfusion. Neither nitric oxide synthase inhibitor nor cyclooxygenase inhibitor altered this time-dependent reduction of methoxamine-induced vasoconstriction. Endothelium removal, K(+)-channel inhibitors and gap junction inhibitor significantly inhibited the time-dependent reduction of methoxamine-induced vasoconstriction. In the preparations with intact endothelium from 16 week-old rats, the time-dependent reduction of methoxamine-induced vasoconstriction disappeared. Furthermore, endothelium removal and treatment with cyclooxygenase inhibitor, thromboxane A(2) receptor antagonist or superoxide dismutase mimetic significantly reduced the methoxamine-induced vasoconstriction in the preparations from 16 week-old rats. These findings suggest that vascular endothelium acts to depress methoxamine-induced vasoconstriction by releasing endothelium-derived hyperpolarizing factor (EDHF), and dysfunction in this endothelial modulation develops with ageing.

Aging and total stenosis triggers differential responses of carotid and basilar arteries to endothelin-1 and phenylephrine

Our aim was to investigate the effects of ageing on the vascular contractility of carotid and basilar arteries from guinea-pigs, in a model of total stenosis. Moreover, we attempted to identify whether total stenosis of the left common carotid (stenosed) in adult guinea-pigs, would affect the contractions of contralateral carotid (intact) and basilar arteries to different vasoconstrictors. With this purpose, the left carotid was occluded with a silk thread at a position close to its origin. Vascular reactivity experiments using standard muscle bath were performed 7, 15, 30, and 90 days after carotid occlusion. Reactivity of carotid and basilar arteries to endothelin-1, phenylephrine and KCl was reduced with ageing in naive guinea-pigs. The endothelin-1 and KCl-induced contractions were unaltered in arteries from SHAM-operated animals. Moreover, phenylephrine-induced contractions were reduced in both carotids from 7 days SHAM-operated guinea-pigs, when compared to naive group. Stenosis induced progressive reduction in the contraction induced by endothelin-1, phenylephrine and KCl in the stenosed carotid, when compared to their respective age-matched naive and SHAM groups. Interestingly, an increased contractile-response to vasoconstrictor agents in all the contralateral carotids was observed. Stenosis (30 and 90 days) also induced an increase in the contractions induced by endothelin-1 in the basilar artery. Conversely, phenylephrine and KCl-induced contractions were reduced in basilar arteries 7, 15, 30 and 90 days after stenosis. These results showed that stenosis in adult guinea-pigs induce alterations of vascular reactivity in arteries distant from the site of injury. Thus, in spite of the common use of contralateral carotid as control, it must be aware of the potential alteration induced by stenosis in the vascular motility of such vessels. Additionally, it was verified a relationship between the period of stenosis and the alterations in the vascular reactivity to these vasoconstrictors.

Prostaglandins in action indispensable roles of cyclooxygenase-1 and -2 in endothelium-dependent contractions

Endothelium regulates local vascular tone by means of releasing relaxing and contracting factors, of which the latter have been found to be elevated in vascular pathogenesis of hypertension, diabetes, hypercholesterolemia, and aging. Endothelium-derived contracting factors (EDCFs) are mainly metabolites of arachidonic acid generated by cyclooxygenase (COX), as vasodilatations in patients with hypertension, metabolic diseases, or advancing age are improved by acute treatment with COX inhibitor indomethacin. COX is presented in two isoforms, COX-1 and COX-2, with the former regarded as constitutive and the latter mainly expressed upon induction. Experiments with animal models of vascular dysfunctions, however, reveal that both isoforms have similar capacity to participate in endothelium-dependent contractions, with augmented expression and activity. COX-derived prostaglandin (PG) H(2), PGF(2α), PGE(2), prostacyclin (PGI(2)), and thromboxane A(2) (TxA(2)) are the proposed EDCFs that mediate endothelium-dependent contractions via the activation of thromboxane-prostanoid (TP) receptor in various vascular beds from different species. Although COX inhibition seems to be a possible strategy in combating COX-associated vascular complications, the incidence of adverse cardiovascular effects of Vioxx has greatly antagonized this concept. Further review of COX inhibitors is required, especially toward the selectivity of coxibs and whether it directly inhibits prostacyclin synthase activity. Meanwhile, TP receptor antagonism may emerge as a therapeutic alternative to reverse prostanoid-mediated vascular dysregulations.

Age-related disappearance of the inhibitory effect of vascular endothelium on agonist-induced vasoconstriction in rat mesenteric vascular beds

We previously reported that endothelium-derived hyperpolarizing factor (EDHF)-mediated response time-dependently suppressed methoxamine-induced vasoconstriction in mesenteric vascular beds isolated from 8-week-old rats. We investigated age-related changes in endothelial regulation of methoxamine-induced vasoconstriction. Mesenteric vascular beds isolated from young (8-week-old) to adult (16-week-old) rats were perfused, and changes in perfusion pressure induced by continuous perfusion of methoxamine or high KCl (60 mM) were measured over 180 min. In young preparations with intact endothelium, methoxamine-induced vasoconstriction time-dependently decreased to 20% of the initial levels, while time-dependent reduction was not observed in adult preparations. High KCl-induced vasoconstriction in young and adult preparations did not show time-dependent reduction. Endothelium removal abolished time-dependent reduction of methoxamine-induced vasoconstriction in young preparations and significantly attenuated vasoconstriction in adult preparations. Indomethacin, seratrodast, or tempol but not catalase significantly reduced methoxamine-induced vasoconstriction in adult preparations with endothelium. A23187 (Ca(2+)-ionophore)-, but not acetylcholine-, induced endothelium-dependent vasodilation in the presence of N(G)-L-nitro arginine methyl ether in adult preparations was significantly smaller than that in young preparations. These findings suggest that the inhibitory effect of mesenteric vascular endothelium on methoxamine-induced vasoconstriction disappears with aging by reducing EDHF and increasing endothelium-derived contracting factors and reactive oxygen species.

Long-term portal hypertension increases the vasodilator response to acetylcholine in rat aorta: role of prostaglandin I2

In the present study, we have analysed both the effect of long-term portal hypertension on the vasomotor response to acetylcholine in rat aorta and the mechanism involved in this response. For this purpose, sham-operated rats and rats with pre-hepatic PH (portal hypertension; triple partial portal vein ligation) were used at 21 months after surgery. The participation of NO and COX (cyclo-oxygenase) derivatives in the vasodilator response elicited by acetylcholine after incubation with L-NAME (NG-nitro-L-arginine methyl ester), indomethacin, SC-560, NS-398, tranylcypromine and furegrelate, was analysed. NO, TXB2 (thromboxane B2) and 6-keto PGF1alpha (prostaglandin F1alpha) release were measured. In addition, SNP (sodium nitroprusside), U-46619, PGI2 and forskolin vasomotor responses were analysed. COX-1 and COX-2 expression was also determined. The acetylcholine-induced vasodilating response was higher in rats with PH. TXA2 and NO release, and SNP and U-46619 sensitivity were similar in both groups. PGI2 release was not modified by portal hypertension, but vasodilator responses to this prostanoid and to forskolin were higher in rats with PH. COX-1 and COX-2 expression remained unmodified by surgery. In conclusion, increased vasodilation to acetylcholine is maintained in long-term PH. Although the participation of endothelial NO remained unmodified, the COX-2 derivative PGI2 does participate through an increased vasodilator response.

Gene expression changes of prostanoid synthases in endothelial cells and prostanoid receptors in vascular smooth muscle cells caused by aging and hypertension

The present study was designed to assess whether or not changes in genomic expression of cyclooxygenases (COX-1, COX-2), endothelial nitric oxide synthase (eNOS), and prostanoid synthases in the endothelium and of prostanoid receptors in vascular smooth muscle contribute to the occurrence of endothelium-dependent contractions during aging and hypertension. Gene expression was quantified by real-time PCR using isolated endothelial cells and smooth muscle cells (SMC) from the aorta of Wistar-Kyoto and spontaneously hypertensive rats. Genes for all known prostanoid synthases and receptors were present in endothelial cells and SMC, respectively. Aging caused overexpression of eNOS, COX-1, COX-2, thromboxane synthase, hematopoietic-type prostaglandin D synthase, membrane prostaglandin E synthase-2, and prostaglandin F synthase in endothelial cells and COX-1 and prostaglandin E2 (EP)4 receptors in SMC. Hypertension augmented the expression of COX-1, prostacyclin synthase, thromboxane synthase, and hematopoietic-type prostaglandin D synthase in endothelial cells and prostaglandin D2 (DP), EP3, and EP4 receptors in SMC. The increase in genomic expression of endothelial COX-1 explains why in aging and hypertension the endothelium has greater propensity to release cyclooxygenase-derived vasoconstrictive prostanoids. The expression of prostacyclin synthase was by far the most abundant, explaining why the majority of the COX-1-derived endoperoxides are transformed into prostacyclin, substantiating the role of prostacyclin as an endothelium-derived contracting factor. The expression of thromboxane synthase was increased in the cells of aging or hypertensive rats, explaining why the prostanoid can contribute to endothelium-dependent contractions. It is uncertain whether the gene modifications caused by aging and hypertension directly contribute to endothelium-dependent contractions or rather to vascular aging and the vascular complications of the hypertensive process.

Aging alters mechanical and contractile properties of the Fisher 344/Nnia X Norway/Binia rat aorta

Vascular mechanical and contractile properties were compared in adult (6 months old) and very-aged (36 months old) Fischer 344/NNiaHSd X Brown Norway/BiNia (F344/NXBN) rats. Our previous work has indicated that aging is associated with aortic medial thickening. This morphological alteration was accompanied by a leftward shift in the aortic stress/strain curve indicating increased vessel stiffness in very-aged animals. Disruption of the endothelium as well as pretreatment of tissues with the nitric oxide (NO) donor sodium nitroprusside eliminated differences, suggesting a link between deficient endothelial NO release and reduced compliance in very-aged aortae. In addition, the Rho kinase inhibitor Y-27632 increased vessel compliance in both adult and very-aged tissues suggesting that the Rho cascade contributed to the stress/strain relationship. Maximal force developed in response to high potassium (K(+)) was reduced by approximately 70% in intact and endothelium-denuded aortae from very-aged rats. In contrast to contractile force development, calcium-dependent stress relaxation was increased in very-aged aorta. Finally, gel electrophoresis indicated a significantly higher tissue content of myosin heavy chain and a higher ratio of SM1/SM2 isoforms with aging. The results suggest multiple molecular changes with aging, which may be expected to alter vascular tissue function.

Effect of melatonin on vascular responses in aortic rings of aging rats

In old animals a marked reduction in endothelium-dependent relaxation occurs. Since there is evidence that the endothelial dysfunction associated with aging may be partly related to the local formation of reactive oxygen species, the purpose of this study was to examine the effect of the natural antioxidant melatonin (10(-5)mol/l) on in vitro contractility of aged aortic rings under conditions of increased oxidative stress (40 m mol/l glucose concentration in medium). Experiments were carried out in 18-20 months old, Wistar male rats, using adult (6-7 months old) animals as controls. A higher plasma lipid peroxidation was found in aged rats as compared to the younger ones. In a first experiment, dose-response curves for acetylcholine-induced relaxation of aortic rings were conducted. Analyzed as a main factor in a factorial ANOVA, age decreased and melatonin augmented the relaxing response to acetylcholine. melatonin's restoring effect on aortic ring relaxation was found in aged aortic rings only and was more pronounced in the presence of a high glucose medium. In a second experiment, the effect of melatonin on the contractility response to phenylephrine of intact or endothelium-denuded aortic rings obtained from aged or control rats was examined in normal or high glucose medium. A main factor analysis in the factorial ANOVA indicated that age and operation augmented, and melatonin decreased, aortic ring contractility response to phenylephrine. Melatonin's restoring effect on aortic contractility was seen in aged aortic rings. The effect of age or a high glucose medium on phenylephrine-induced contractility was more pronounced in the absence of an intact endothelium. Aging did not affect the relaxant response of intact or endothelium-denuded rings to sodium nitroprusside. The results support the improvement by melatonin of vascular response in aging rats, presumably via its antioxidant activity.