Differential contribution of endothelial function to vascular reactivity in conduit and resistance arteries from deoxycorticosterone-salt hypertensive rats

Nitric Oxide Donors as Potential Drugs for the Treatment of Vascular Diseases Due to Endothelium Dysfunction

Endothelial dysfunction and consequent vasoconstriction are a common condition in patients with hypertension and other cardiovascular diseases. Endothelial cells produce and release vasodilator substances that play a pivotal role in normal vascular tone. The mechanisms underlying endothelial dysfunction are multifactorial. However, enhanced reactive oxygen species (ROS) production and consequent vasoconstriction instead of endothelium-derived relaxant generation and consequent vasodilatation contribute to this dysfunction considerably. The main targets of the drugs that are currently used to treat vascular diseases concerning enzyme activities and protein functions that are impaired by endothelial nitric oxide synthase (eNOS) uncoupling and ROS production. Nitric oxide (NO) bioavailability can decrease due to deficient NO production by eNOS and/or NO release to vascular smooth muscle cells, which impairs endothelial function. Considering the NO cellular mechanisms, tackling the issue of eNOS uncoupling could avoid endothelial dysfunction: provision of the enzyme cofactor tetrahydrobiopterin (BH4) should elicit NO release from NO donors, to activate soluble guanylyl cyclase. This should increase cyclic guanosine-monophosphate (cGMP) generation and inhibit phosphodiesterases (especially PDE5) that selectively degrade cGMP. Consequently, protein kinase-G should be activated, and K+ channels should be phosphorylated and activated, which is crucial for cell membrane hyperpolarization and vasodilation and/or inhibition of ROS production. The present review summarizes the current concepts about the vascular cellular mechanisms that underlie endothelial dysfunction and which could be the target of drugs for the treatment of patients with cardiovascular disease.

Vascular Dysfunction in Horses with Endocrinopathic Laminitis

Endocrinopathic laminitis (EL) is a vascular condition of the equine hoof resulting in severe lameness with both welfare and economic implications. EL occurs in association with equine metabolic syndrome and equine Cushing’s disease. Vascular dysfunction, most commonly due to endothelial dysfunction, is associated with cardiovascular risk in people with metabolic syndrome and Cushing’s syndrome. We tested the hypothesis that horses with EL have vascular, specifically endothelial, dysfunction. Healthy horses (n = 6) and horses with EL (n = 6) destined for euthanasia were recruited. We studied vessels from the hooves (laminar artery, laminar vein) and the facial skin (facial skin arteries) by small vessel wire myography. The response to vasoconstrictors phenylephrine (10⁻⁹–10^-5M) and 5-hydroxytryptamine (5HT; 10⁻⁹–10^-5M) and the vasodilator acetylcholine (10⁻⁹–10^-5M) was determined. In comparison with healthy controls, acetylcholine-induced relaxation was dramatically reduced in all intact vessels from horses with EL (% relaxation of healthy laminar arteries 323.5 ± 94.1% v EL 90.8 ± 4.4%, P = 0.01, laminar veins 129.4 ± 14.8% v EL 71.2 ± 4.1%, P = 0.005 and facial skin arteries 182.0 ± 40.7% v EL 91.4 ± 4.5%, P = 0.01). In addition, contractile responses to phenylephrine and 5HT were increased in intact laminar veins from horses with EL compared with healthy horses; these differences were endothelium-independent. Sensitivity to phenylephrine was reduced in intact laminar arteries (P = 0.006) and veins (P = 0.009) from horses with EL. Horses with EL exhibit significant vascular dysfunction in laminar vessels and in facial skin arteries. The systemic nature of the abnormalities suggest this dysfunction is associated with the underlying endocrinopathy and not local changes to the hoof.

BAY 41-2272 Treatment Improves Acetylcholine-Induced Aortic Relaxation in L-NAME Hypertensive Rats

Hypertension, an emerging problem of recent era, and many pathophysiological factors are participating to produce the disease. Nitric oxide (NO) is an important constituent to ameliorate hypertensive condition. Inhibition of endogenous NO synthase by L-N^G-Nitroarginine methyl ester (L-NAME) was responsible for generating hypertension in rats. BAY 41-2272 (5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]-pyrimidin-4-ylamine), a soluble guanylyl cyclase activator, restricts rise of blood pressure and shows cardioprotective activity. The aim of the present study was to analyze effect of short-term BAY 41-2272 treatment on blood pressure and vascular function. Male Wistar rats were randomly divided into three groups such as control (group-A), hypertensive (group-B), and BAY 41-2272-treated hypertensive (group-C) rats. Normal saline was administered intramuscularly to control rats for last 3 days (days 40, 41, and 42) of total 42 days treatment, whereas rats of group-B and group-C were treated with L-NAME hydrochloride in drinking water at 50 mg/kg body weight daily for 42 days. Also, normal saline and BAY 41-2272 were administered for last 3 days at two different dosages at 1 and 3 mg/kg body weight/day intramuscularly to group-B and group-C rats, respectively. Administration of BAY 41-2272 for 3 days was not sufficient enough to decrease mean arterial pressure of hypertensive rats significantly. BAY at both the treatment dosages significantly ameliorate acetylcholine-induced maximal aortic relaxation compared with BAY-untreated hypertensive rats. Findings of the present study indicate that even shorter period of BAY 41-2272 treatment (3 days) improves vascular relaxation.

PGC-1α overexpression suppresses blood pressure elevation in DOCA-salt hypertensive mice

Increasing evidences have accumulated that endothelial dysfunction is involved in the pathogenesis of hypertension. Peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α) has been identified as an essential factor that protects against endothelial dysfunction in vascular pathologies. However, the functional role of PGC-1α in hypertension is not well understood. Using an adenovirus infection model, we tested the hypothesis that PGC-1α overexpression retards the progression of hypertension in deoxycorticosterone acetate (DOCA)-salt mice model through preservation of the function of endothelium. We first demonstrated that PGC-1α expression not only in conductance and resistance arteries but also in endothelial cells was decreased after DOCA-salt treatment. In PGC-1α adenovirus-infected mice, the elevation of blood pressure in DOCA-salt mice was attenuated, as determined using tail-cuff measurement. Furthermore, PGC-1α overexpression inhibited the decrease in nitric oxide (NO) generation and the increase in superoxide anion (O2 (-)) production in DOCA-salt-treated mice, in parallel with improved endothelium-dependent relaxation. Rather than affecting endothelial NO synthase (eNOS) total expression and phosphorylation, PGC-1α significantly inhibited eNOS uncoupling, as evidenced by increased eNOS homodimerization, BH4 levels, GTP-cyclohydrolase 1 (GTPCH1) and dihydrofolate reductase (DHFR) expression and heat-shock protein (Hsp)90-eNOS interaction. Our findings demonstrate that PGC-1α overexpression preserves eNOS coupling, enhances NO generation, improves endothelium-dependent relaxation and thus lowers blood pressure, suggesting that up-regulation of PGC-1α may be a novel strategy to prevent and treat hypertension.

Endothelium-derived Relaxing Factors of Small Resistance Arteries in Hypertension

Endothelium-derived relaxing factors (EDRFs), including nitric oxide (NO), prostacyclin (PGI₂), and endothelium-derived hyperpolarizing factor (EDHF), play pivotal roles in regulating vascular tone. Reduced EDRFs cause impaired endothelium-dependent vasorelaxation, or endothelial dysfunction. Impaired endothelium-dependent vasorelaxation in response to acetylcholine (ACh) is consistently observed in conduit vessels in human patients and experimental animal models of hypertension. Because small resistance arteries are known to produce more than one type of EDRF, the mechanism(s) mediating endothelium-dependent vasorelaxation in small resistance arteries may be different from that observed in conduit vessels under hypertensive conditions, where vasorelaxation is mainly dependent on NO. EDHF has been described as one of the principal mediators of endothelium-dependent vasorelaxation in small resistance arteries in normotensive animals. Furthermore, EDHF appears to become the predominant endothelium-dependent vasorelaxation pathway when the endothelial NO synthase (NOS3)/NO pathway is absent, as in NOS3-knockout mice, whereas some studies have shown that the EDHF pathway is dysfunctional in experimental models of hypertension. This article reviews our current knowledge regarding EDRFs in small arteries under normotensive and hypertensive conditions.

SFlt-1 elevates blood pressure by augmenting endothelin-1-mediated vasoconstriction in mice

Objective

Scavenging of vascular endothelial growth factor (VEGF) elevates blood pressure (BP) in patients receiving anti-angiogenic therapy. Similarly, inhibition of circulation VEGF by its soluble receptor fms-like tyrosine kinase-1 (sFlt-1) underlies BP elevation in pre-eclampsia. Both phenotypes are characterized by augmented production of endothelin-1 (ET-1), suggesting a role for ET-1 in anti-angiogenic hypertension. We aimed to assess the effect of VEGF inhibition on ET-1-induced contractility and downstream ET-1 signaling.

Approach and Results

Male C57BL/6N mice were treated with either sFlt-1 or vehicle and BP was assessed via tail-cuff. Mean arterial pressure of sFlt-1-treated mice markedly increased compared to vehicle-treated controls (N = 11–12, p<0.05). After sacrifice, carotid and mesenteric arteries were isolated for isometric tension measurements. ET-1-induced contractions were similar in mesenteric arteries of vehicle and sFlt-1-treated mice, but augmented in carotid segments of sFlt-1-treated mice compared to controls (N = 9–10, p<0.05). The increased contraction in carotid segments could be completely abrogated by the cyclooxygenase (COX) inhibitor indomethacin (N = 9–10, p<0.05), indicating heightened prostaglandin-mediated vasoconstriction. This was associated with a shift towards procontractile ET_B signaling in sFlt-1-treated mice, possibly explaining the increased ET-1-induced prostaglandin-mediated vasoconstriction. In line with the ex vivo findings, sFlt-1-induced BP elevation could be prevented in vivo by oral treatment with either a high-dose of the COX inhibitor aspirin (N = 7) or with picotamide (N = 9), a dual thromboxane A₂ synthase inhibitor and receptor antagonist.

Conclusions

VEGF inhibition augments the pressor response to ET-1. The cyclooxygenase-thromboxane signaling route downstream of ET-1 might be a possible target to prevent BP elevation during VEGF inhibition.

Pharmaceutical properties and toxicology of Dioclea grandiflora

CONTEXT

Since the beginning of civilization, herbal medicines have been an important source for human beings to treat their ailments. Despite the large number of synthetic remedies available in the market, the use of plants is seen as a great challenge in the search for new substances endowed with therapeutic properties. One example is Dioclea grandiflora Mart. ex Benth. (Leguminosae) employed in traditional medicine to treat prostate disorders and kidney stones.

OBJECTIVES

This work presents a brief overview of D. grandiflora, including a description of the plant, its chemical composition and pharmacological properties.

METHODS

This review gathers information available in the scientific literature compiled from databases such as Science Direct, PubMed, Dr. Dukes Phytochemical and Ethnobotany, Missouri Botanical Garden and The International Plant Names Index.

RESULTS

The information found in the literature showed that flavonoids are the major constituents of D. grandiflora that account for most of the pharmacological properties so far disclosed. Several studies have revealed that D. grandiflora possesses antinociceptive, cardiovascular, antioxidant and anti-inflammatory activities.

CONCLUSION

Research shows that D. grandiflora is a potential source of compounds pertaining medicinal applications. It provides an interesting subject in the search for new drugs of natural origin.

The essential oil of Citrus bergamia Risso induces vasorelaxation of the mouse aorta by activating K(+) channels and inhibiting Ca(2+) influx

OBJECTIVES

The aim of this study was to explore the effect of the essential oil of Citrus bergamia Risso (bergamot) on mouse blood vessels and to analyse the mechanism of this effect from a pharmacological perspective.

METHODS

We investigated the effect of bergamot essential oil (BEO) on vascular tonus during contraction of mouse aorta induced by prostaglandin F2α (PGF2α ) or noradrenaline (norepinephrine).

KEY FINDINGS

In mouse aortic rings, BEO (0.01, 0.1 and 0.2% v/v) reduced contraction in a dose-dependent manner, and relaxed the vascular tonus induced by PGF2α . No significant difference in the extent of vasorelaxation induced by 0.1% (v/v) BEO was evident when rings with intact endothelium and endothelium-denuded rings were compared. When aortic rings were suspended in a medium that was Ca(2+) -free but contained 80 mm KCl, addition of CaCl2 (1, 2.5 or 5 mm) induced contraction in a dose-dependent manner. However, addition of Ca(2+) after incubation of the rings with BEO strongly suppressed CaCl2 -induced contraction. Further, the K(+) -channel blocker tetraethylammonium chloride partially blocked BEO-induced vasorelaxation.

CONCLUSIONS

Our findings suggest that BEO may induce endothelium-independent vasorelaxation by regulating the vascular tone of smooth muscle. Activation of K(+) channels and inhibition of Ca(2+) influx may be involved in vasorelaxation of mouse aorta elicited by BEO.

Vasorelaxant effects of 1-nitro-2-phenylethane, the main constituent of the essential oil of Aniba canelilla, in superior mesenteric arteries from spontaneously hypertensive rats

The present study investigated the mechanisms underlying the vasorelaxant effects of the essential oil of Aniba canelilla (EOAC) and its main constituent 1-nitro-2-phenylethane (NP) in isolated superior mesenteric artery from spontaneously hypertensive rats (SHRs). At 0.1-1000 μg/mL, EOAC and NP relaxed SMA preparations pre-contracted with 75 mMKCl with IC(50) (geometric mean [95% confidence interval]) values of 294.19 [158.20-94.64] and 501.27 [378.60-624.00] μg/mL, respectively); or with phenylephrine (PHE) (IC(50)s=11.07 [6.40-15.68] and 7.91 [4.08-11.74) μg/mL, respectively). All these effects were reversible and remained unaltered by vascular endothelium removal. In preparations maintained under Ca(2+)-free conditions, EOAC and NP (both at 600 μg/mL) reduced the PHE-, but not the caffeine-induced contraction. In Ca(2+)-free and high K(+) (75 mM) medium, the contractions produced by CaCl(2) or BaCl(2) were reduced or even abolished by EOAC and NP at 100 and 600 μg/mL, respectively. EOAC and NP (both at 10-1000 μg/mL) also relaxed the contraction evoked by phorbol dibutyrate (IC(50)=52.66 [10.82-94.64] and 39.13 [31.55-46.72] μg/mL, respectively). It is concluded that NP has a myogenic endothelium-independent vasorelaxant effects and appears to be the active principle of the EOAC. Vasorelaxant effect induced by both EOAC and NP is preferential to receptor-activated pathways and it appears to occur intracellularly more than a superficial action restricted to the membrane environment such as a simple blocking activity on a given receptor or ion channel.

Knockout of the vascular endothelial glucocorticoid receptor abrogates dexamethasone-induced hypertension

BACKGROUND

Glucocorticoid-mediated hypertension is incompletely understood. Recent studies have suggested the primary mechanism of this form of hypertension may be through the effects of glucocorticoids on vascular tissues and not to excess sodium and water re-absorption as traditionally believed.

OBJECTIVE

The goal of this study was to better understand the role of the vasculature in the generation and maintenance of glucocorticoid-mediated hypertension.

METHODS

We created a mouse model with a tissue-specific knockout of the glucocorticoid receptor in the vascular endothelium.

RESULTS

We show that these mice are relatively resistant to dexamethasone-induced hypertension. After 1 week of dexamethasone treatment, control animals have a mean blood pressure (BP) increase of 13.1 mmHg, whereas knockout animals have only a 2.7 mmHg increase (P < 0.001). Interestingly, the knockout mice have slightly elevated baseline BP compared with the controls (112.2 ± 2.5 vs. 104.6 ± 1.2 mmHg, P = 0.04), a finding which is not entirely explained by our data. Furthermore, we demonstrate that the knockout resistance arterioles have a decreased contractile response to dexamethasone with only 6.6% contraction in knockout vessels compared with 13.4% contraction in control vessels (P = 0.034). Finally, we show that in contrast to control animals, the knockout animals are able to recover a significant portion of their normal circadian BP rhythm, suggesting that the vascular endothelial glucocorticoid receptor may function as a peripheral circadian clock.

CONCLUSION

Our study highlights the importance of the vascular endothelial glucocorticoid receptor in several fundamental physiologic processes, namely BP homeostasis and circadian rhythm.

Cardiovascular effects induced by Cymbopogon winterianus essential oil in rats: involvement of calcium channels and vagal pathway

OBJECTIVES

This study has investigated the cardiovascular effects of the Cymbopogon winterianus essential oil (EOCW) in rats. C. winterianus is a plant used in folk medicine for the treatment of hypertension.

METHODS

For the measurement of haemodynamic and ECG parameters, male Wistar rats under anaesthesia were cannulated in the abdominal aorta and lower vena cava and electrodes were subcutaneously implanted in their paws. For an in-vitro approach, the rats were killed and the superior mesenteric artery was removed and cut into rings (1-2 mm). These rings were then mounted in organ baths containing Tyrode's solution at 37 degrees C and gassed with carbogen.

KEY FINDINGS

In rats, EOCW (1-20 mg/kg, i.v.) induced dose-dependent hypotension and tachycardia. These effects were not affected by L-NAME or indometacin, but were partially reduced after atropine administration. EOCW (20 mg/kg only) also induced bradycardia-associated sinoatrial blockade, junctional rhythm, and first-degree atrioventricular block, which was abolished after atropine administration or vagotomy. In arterial rings, EOCW (0.1-3000 microg/ml) induced relaxation of phenylephrine tonus that was not affected by removal of the endothelium. These relaxations were similar to those observed in rings without endothelium precontracted with KCl 80 mm. EOCW was able to antagonize the CaCl(2) (30-300 mum) induced contractions in depolarizing solution (KCl 60 mm).

CONCLUSIONS

These results demonstrated that EOCW induced hypotension and vasorelaxation. These effects appeared to be mainly mediated by Ca(+2)-channel blocking. Furthermore, the higher dose of EOCW induced transient bradycardia and arrhythmias due to a cardiac muscarinic activation secondary to a vagal discharge.

Hypotensive and vasorelaxant effects of citronellol, a monoterpene alcohol, in rats

Citronellol is an essential oil constituent from the medicinal plants Cymbopogon citratus, Cymbopogon winterianus and Lippia alba which are thought to possess antihypertensive properties. Citronellol-induced cardiovascular effects were evaluated in this study. In rats, citronellol (1-20 mg/kg, i.v.) induced hypotension, which was not affected by pre-treatment with atropine, hexamethonium, N(omega)-nitro-L-arginine methyl ester hydrochloride or indomethacin, and tachycardia, which was only attenuated by pre-treatment with atropine and hexamethonium. These responses were less than those obtained for nifedipine, a reference drug. In intact rings of rat mesenteric artery pre-contracted with 10 microM phenylephrine, citronellol induced relaxations (pD(2) = 0.71 +/- 0.11; E(max) = 102 +/- 5%; n = 6) that were not affected by endothelium removal, after tetraethylamonium in rings without endothelium pre-contracted with KCl 80 mM. Citronellol strongly antagonized (maximal inhibition = 97 +/- 4%; n = 6) the contractions induced by CaCl(2) (10(-6) to 3 x 10(-3 )M) and did not induce additional effects on the maximal response of nifedipine (10 microM). Finally, citronellol inhibited the contractions induced by 10 microM phenylephrine or 20 mM caffeine. The present results suggest that citronellol lowers blood pressure by a direct effect on the vascular smooth muscle leading to vasodilation.

Complexation with beta-cyclodextrin confers oral activity on the flavonoid dioclein

Dioclein is a flavonoid reported to have many beneficial effects on the cardiovascular system such as vasorelaxant, hypotensive, antioxidant and antiarrythmogenic activities. However, use as pharmaceuticals is limited due to the lack of oral activity and low water solubility. In this work, intending to improve its oral activity, we performed a 1:1 inclusion complex (IC) between dioclein and beta-cyclodextrin (beta-CD). The IC was characterized by nuclear magnetic resonance and infrared spectroscopy and its vasodilator and hypotensive effects were evaluated in mice. The inclusion of dioclein in beta-CD increased the water solubility 44% compared to free dioclein. The IC (2.5mgkg(-1)) produced a higher and long lasting change in systolic blood pressure (SBP) after intraperitoneal administration compared to free dioclein. When given orally, free dioclein (10mgkg(-1)) showed no hypotensive effect while the IC induced a pronounced decrease in SBP. The in vitro vasodilator effect of dioclein was unchanged by its inclusion in beta-CD showing that the IC does not change the interaction between dioclein and its cellular targets. In conclusion, our results show that the new complex prepared by inclusion of dioclein in beta-CD improves the hypotensive effect of the flavonoid by increasing its bioavailability and enables dioclein to be effective after oral administration. The mechanism underling the increase in bioavailability is probably a consequence of a protective effect of beta-CD against in vivo biodegradation by enzymes and possibly increased water solubility.

Cardiovascular effects of the aqueous extract from Caesalpinia ferrea: involvement of ATP-sensitive potassium channels

Caesalpinia ferrea is a plant very used in the folk medicine for treatment of several diseases, such as diabetes. This study investigated the cardiovascular effects of the aqueous extract from stem bark of C. ferrea (AECF). In non-anesthetized rats, AECF (10, 20, 40, 60 and 80 mg/kg; i.v.) induced hypotension (-9+/-1;-12+/-1;-14+/-1; -20+/-3 and -51+/-6%; respectively) and tachycardia (6+/-1; 8+/-1; 12+/-2; 14+/-2 and 26+/-3%; respectively). Hypotension was not affected after atropine or L-NAME. Furthermore, AECF (40 mg/kg) induced atrioventricular block and extrasystoles, which was not affected after atropine. In intact rings of the rat mesenteric artery, AECF (0.001-30 mg/ml, n=6) induced relaxations of phenylephrine tonus (Emax=110+/-4%), which was not changed after the removal of endothelium (Emax=113+/-9%). In rings without endothelium pre-contracted with KCl 80 mM, phenylephrine plus KCl 20 mM or phenylephrine plus glibenclamide, the curve to AECF was significantly attenuated (Emax=24+/-4%, 70+/-5% and 62+/-7%, respectively, n=6), but was not affected in the presence of tetraethylammonium or 4-aminopyridine (Emax=125+/-15% and 114+/-7%, respectively, n=6). These results demonstrate that AECF induces hypotension associated to tachycardia; however, in dose of 40 mg/kg, AECF induces transient bradyarrhythmias. Furthermore, AECF induces vasodilatation in rat mesenteric artery which appears to be mediated by ATP-sensitive K+ channel openings.

Cardiovascular effects of Hyptis fruticosa essential oil in rats

In non-anesthetized normotensive rats, Hyptis fruticosa essential oil (HFEO, 5, 10, 20 and 40 mg/kg; i.v.) induced hypotension associated with tachycardia. In intact and isolated rings of rat superior mesenteric artery (control), HFEO (1-1000 microg/ml, n=6, cumulatively) induced concentration-dependent relaxations of tonus induced by 10 microM phenylephrine (Phe) (pD(2)=2.6+/-0.27; E(max)=64+/-8.3%). In denuded endothelium pre-contracted rings with Phe or K(+)-depolarizing solution (80 mM), the concentration-response curves to HFEO were not shifted (pD(2)=2.3+/-0.25 and 2.3+/-0.28, respectively), but their maximal responses were significantly (P<0.05 vs control) increased (E(max)=122.3+/-18.2% and 92+/-3.6%, respectively). HFEO was also capable of antagonizing the concentration-response curves to CaCl(2) (3 microM-30 mM) in a dose-dependent manner.

Cyclo-oxygenase-2, endothelium and aortic reactivity during deoxycorticosterone acetate salt-induced hypertension

OBJECTIVE

To test the hypothesis that the enhanced vascular responsiveness to norepinephrine that occurs during deoxycorticosterone acetate (DOCA)-salt induced hypertension is causally related to increased expression of cyclo-oxygenase (COX)-2 and oxidative stress, which diminishes the vasomodulatory influence of endothelium-derived nitric oxide.

METHODS

Four groups of age-matched, male Sprague-Dawley rats were studied: Sham (normotensive); DOCA-salt (hypertensive); DOCA-salt treated with manganese(III) tetra(4-benzoic acid) porphyrin chloride [MnTBAP, an antioxidant; 15 mg/kg intraperitoneally (i.p.) for 21 days]; DOCA-salt treated with {N-[2-(cyclohexyloxy)-4-nitrophenyl]-methane sulfonamide} (NS-398, a COX-2 selective blocker; 5 mg/kg i.p. for 7 days). Contraction and relaxation were measured with FT03 force transducers coupled to a Grass polygraph in aortic rings bathed with physiologic salt solution (37 degrees C) and bubbled with a 5%CO2/95%O2 gas mixture. Aortic sensitivities (pD2 values) to norepinephrine and serum isoprostanes (8-iso-prostaglandin F2alpha, a marker of oxidative stress) were measured for each experimental paradigm.

RESULTS

NS-398 significantly reduced maximal contractions in response to norepinephrine in aortic rings from Sham (44 +/- 3%) and DOCA-salt (96 +/- 2%) group rats. Expression of COX-2 protein increased significantly in vessels from DOCA-salt rats compared with those from Sham group rats. Treatment of DOCA-salt rats with either MnTBAP or NS-398 alleviated hypertension, normalized aortic pD2 values for norepinephrine and restored serum 8-isoprostane concentrations towards those observed in Sham group rats.

CONCLUSIONS

COX-2 expression increases during DOCA-salt hypertension, and mediates production of factors that enhance rat aortic contractility in response to norepinephrine. Our data also suggest a role for increased oxidative stress, which is at least in part dependent on enhanced COX-2 expression, in the mechanism(s) of enhanced aortic contractility in response to norepinephrine during DOCA-salt hypertension.

The antihypertensive and vasodilator effects of aqueous extract from Berberis vulgaris fruit on hypertensive rats

The aqueous extract from Berberis vulgaris fruit (B.V.) was tested to evaluate its antihypertensive effects on DOCA-induced hypertension in the rats. Hypertension was induced in male Sprague-Dawley rats (200-250 g) by DOCA-salt injection (20 mg/kg, twice weekly, for 5 weeks, s.c.) plus NaCl (1%) which was added to the animals' drinking water. Then 5 weeks later, the rats were anaesthetized with thiopental (30 mg/kg, i.p.) and the arterial blood pressure was measured. The mean arterial blood pressure and heart rate were 231 +/- 6.4 (mmHg) and 506 +/- 12 (beats/min), respectively. Administration of B.V. extracts significantly reduced the rat arterial blood pressure. In in vitro studies, rings of descending aorta were cut and mounted for isometric tension recording in an organ chamber containing Krebs solution. Mesenteric beds were also removed and perfused with Krebs solution. After 1 h of stabilization, preparations (aortic rings or mesenteric beds) were precontracted with phenylephrine (10(-5) M), then different concentrations of B.V. (0.4, 2 and 4 mg/mL) were added which caused a relaxation in these vessels. To investigate the mechanism of action of the extract, the tissues were incubated with either L-NAME (10(-5) M) or indomethacin (10(-5) M) for 20 min. In the aortic rings L-NAME pretreatment could only reduce the vasodilatory effects of a low concentration of B.V. (0.4 mg/mL), but indomethacin was without effect. In isolated perfused mesenteric beds preincubation with either L-NAME or indomethacin did not modify the vasodilator effects of the aqueous extract from B.V. fruit. The present results suggest that the antihypertensive and vasodilatory effects of B.V. fruit extract are mainly endothelial-independent and it may be used to treat hypertension, a status with endothelial dysfunction.

Restoration of normal vascular relaxation mechanisms in cerebral arteries by chromosomal substitution in consomic SS.13BN rats

This study sought to identify the mechanisms of vascular relaxation that are rescued in middle cerebral arteries (MCA) of SS.13BN consomic rats by substituting chromosome 13 containing the renin gene from Brown Norway (BN) rats into the Dahl salt-sensitive (SS) genetic background. Isolated MCA from SS rats exhibited an indomethacin-sensitive constriction in response to acetylcholine (ACh) and hypoxia. ACh-induced dilation was NO dependent and hypoxic dilations were cyclooxygenase (COX) dependent in BN and SS.13BN rats. In SS rats, hypoxic dilation was restored by indomethacin and abolished by inhibiting cytochrome P-450 epoxygenases, suggesting a role for epoxyeicosatrienoic acids. MCA from SS and SS.13BN rats constricted and MCA from BN rats dilated in response to the stable prostacyclin analog iloprost. MCA from SS.13BN and BN rats (but not SS rats) dilated in response to the prostaglandin E2 receptor agonist butaprost. Hypoxia increased prostacyclin release in cerebral arteries from all the strains, whereas thromboxane A2 production was reduced in BN rat vessels only. These data suggest that SS rats may be less sensitive to vasodilator prostaglandins and that normalization of renin-angiotensin system regulation causes a switch from production of COX-derived vasoconstrictor metabolites (in SS rats) toward NO-dependent relaxation in response to ACh- and prostaglandin-dependent dilation in response to hypoxia in SS.13(BN) rats.

Endothelial dysfunction in aortic rings and mesenteric beds isolated from deoxycorticosterone acetate hypertensive rats: possible involvement of protein kinase C

The main objectives of this study were to investigate the effects of deoxycorticosterone acetate (DOCA)-induced hypertension on the aortic and mesenteric vascular responses to vasodilator and vasoconstrictor agents and also to elucidate whether protein kinase C (PKC) was involved in these responses, by using chelerythrine and calphostin C, the inhibitors of protein kinase C. Hypertension was induced in male Sprague-Dawley rats (200-250 g) by DOCA-salt injection [20 mg/kg, twice weekly for 5 weeks, subcutaneously (s.c.)] and NaCl (1%) was added to their drinking water. Control rats received a saline injection (0.5 ml/kg, twice weekly for 5 weeks, s.c.), then the animals were anaesthetised [thiopental, 30 mg/kg, intraperitoneally (i.p.)] and the arterial blood pressure was measured. Mean arterial blood pressure in control and hypertensive rats were 98+/-7.5 and 163+/-3.5 mmHg, respectively (P<0.0001). In the in vitro studies, rings of descending aorta and mesenteric beds were precontracted with phenylephrine and then concentration-response curves to acetylcholine and sodium nitroprusside were constructed. In the tissue removed from hypertensive rats, the responses to acetylcholine, but not to sodium nitroprusside, were significantly reduced. However, addition of chelerythrine (10 microM) or calphostin C (100 nM) to the organ bath significantly restored these impaired responses. Our data suggest that protein kinase C plays a crucial role in the endothelial dysfunction induced by hypertension.

NOS 3 subcellular localization in the regulation of nitric oxide production

Endothelium-derived nitric oxide (NO) is a key signalling molecule in the maintenance of cardiovascular health. Endothelial NO synthase (NOS 3), which catalyses the formation of NO, is targeted to the plasma membrane by dual acylation. In vitro studies suggest that membrane localization of NOS 3 is an important regulatory element of NO production. Dysfunction of the vascular endothelium and a decrease in NO bioavailability is associated with the development and progression of a number of cardiovascular diseases, including hypertension. Our laboratory has previously published that in salt-dependent hypertension there is an altered localization of NOS 3, with an increase in cytosolic expression. These data have led us to question whether the increased cytosolic NOS 3 expression is a form of compensation for endothelial dysfunction in hypertension, or an indicator and contributing factor to endothelial dysfunction. This review will outline the importance of subcellular localization in the regulation of NOS 3 in vitro, the role of NOS 3 in endothelial dysfunction associated with salt-dependent hypertension, and the potential physiological consequences of altered NOS 3 localization in vivo.

Effects of berberine on angiotensin-converting enzyme and NO/cGMP system in vessels

The present study was designed to examine the relaxant and anticonstrictive effects of berberine in the isolated thoracic aorta in rats. Intravenous injection of berberine lowered the mean arterial pressure (MAP) of anesthesized rats in a dose-dependent manner. The angiotensin-converting enzyme (ACE) activities were inhibited significantly by the addition of berberine in a dose-dependent manner of which the IC50 value of berberine for ACE was 42 micrograms/ml (125 microM). In the endothelium-intact rings, angiotensin I-induced contraction was markedly attenuated by prior exposure of aortic rings to berberine. Treatment of the intact aortic rings with berberine (10 micrograms/ml) increased the NOx and cGMP productions relative to the vehicle-treated group. Berberine induced a dose-dependent relaxation in phenylephrine-precontracted aortic rings, but NG-nitro-L-arginine methyl ester (L-NAME)-pretreated intact aortic rings or functional removal of the endothelium attenuated the berberine-induced relaxation without an effect on maximum response. These results suggest that berberine has a hypotensive effect, at least in part, via the inhibition of ACE and direct release of NO/cGMP in the vascular tissues.

Early endothelial dysfunction following renal mass reduction in rats

BACKGROUND

Endothelial dysfunction has been previously described in severely hypertensive rats with renal mass reduction (RMR) receiving large dietary Na loads. Because hypertension and Na loading reduce endothelium-dependent vasodilation, the effect of renal failure per se is unclear.

METHODS

Responses to acetylcholine in noradrenaline-contracted isolated perfused mesenteric arteries were studied. Vessels were obtained from RMR rats kept on a normal diet, 3 and 10 days after surgery, and the results were compared with those from sham-operated rats (SN). The role of three putative mediators of endothelium-dependent vasodilation was assessed using: L-NAME (10(-4) mol L(-1)); indomethacin (INDO, 10(-5) mol L(-1)); and a mixture of charybdotoxin and apamin (C/A, both 10(-7) mol L(-1)), inhibitors of Ca-activated K-channels to mediate the effects of endothelium-derived hyperpolarizing factor (EDHF).

RESULTS

Response to acetylcholine but not that to nitroprusside (endothelium-independent) was decreased in RMR. L-NAME reduced further acetylcholine relaxations in SN but not in RMR. By contrary, INDO decreased acetylcholine vasodilation in RMR but had no effect in SN. C/A had similar effects in the SN and RMR rats. The levels of 6-keto prostaglandin F1alpha were elevated in the urine of the RMR rats and were perfusate from the RMR vessels.

CONCLUSION

Endothelial dysfunction occurs early after RMR, even when systolic blood pressure is only minimally elevated and Na intake is normal. This alteration may be because of decreased availability of nitric oxide, partially compensated by increased prostacyclin production.

Role of the endothelium in the vascular effects of vitamin C in rats

The present study was undertaken to determine whether vascular responsiveness and endothelial function were altered in rats after 8 weeks of vitamin C treatment. Thoracic aortae were isolated from control and vitamin C-treated rats and analysed for changes in vascular reactivity. Vitamin C treatment attenuated the contractile response of aortic rings to noradrenaline and KCl. Removal of the endothelium increased the sensitivity of control rings but did not alter the effect of vitamin C. Endothelium-dependent relaxation to acetylcholine was significantly (P<0.05) enhanced by vitamin C, but the endothelium-independent relaxation response to sodium nitroprusside was not affected by vitamin C. The results suggest that the endothelium is not involved in the reduction in vascular sensitivity to contractile agonists caused by vitamin C. In addition, the enhancement of endothelium-dependent relaxation may be due to protection of nitric oxide against inactivation by oxygen free radicals.

Vitamin C lowers blood pressure and alters vascular responsiveness in salt-induced hypertension

The present study was undertaken to investigate the effect of vitamin C treatment on blood pressure and vascular reactivity in salt-induced hypertension. Male Sprague-Dawley rats were fed a normal rat diet, a high-sodium (8% NaCl) diet, a normal rat diet plus vitamin C treament (100 mg x kg(-1) x day(-1)), or a high-sodium diet plus vitamin C treatment for 6 weeks. Salt loading significantly increased blood pressure, which was attenuated by vitamin C treatment. Aortic rings from the different groups were suspended for isometric-tension recording. The contractile response to noradrenaline was significantly increased in the salt-loaded rats. Vitamin C reduced the sensitivity of aortic rings to noradrenaline in rats on normal and high-sodium diets. In noradrenaline-precontracted rings, the relaxation response to acetylcholine, which was attenuated in the salt-loaded rats, was restored by vitamin C treatment. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME) abolished the enhanced response to acetylcholine caused by vitamin C. The results suggest that the antihypertensive effect of vitamin C is associated with a reduction in vascular sensitivity to noradrenaline and enhancement of endothelium-dependent relaxation due to increased nitric oxide bioavailability.

Effects of bulb of Fritillaria ussuriensis maxim. on angiotensin converting enzyme and vascular release of NO/cGMP in rats

The present study was designed to investigate whether the Bulbus Fritillaria shows a hypotensive effect via the angiotensin converting enzyme (ACE) inhibition and elicit NO/cGMP release in rat aortic rings. Intravenous injection of Bulbus Fritillaria water extract lowered the mean arterial pressure of anesthetized rats in a dose-dependent manner. The ACE activities were inhibited significantly by the additions of ethylacetate and butanol extracts from Bulbus Fritillaria, of which IC(50) values were 292 and 320 microg/ml, respectively. Moreover, angiotensin I-induced vasoconstriction was also strongly inhibited by the additions of ethylacetate and butanol extracts from Bulbus Fritillaria. In order to assess whether NO production was induced by Bulbus Fritillaria extracts, we directly measured NO and cGMP production levels from the aortic ring elicited by extracts of Bulbus Fritillaria. Our results showed that the hexane, butanol, and water extracts of Bulbus Fritillaria increased NO and cGMP productions in intact vascular tissue. These findings suggest that Bulbus Fritillaria extracts have a hypotensive effect in rats via the inhibition of ACE activity and direct release of NO/cGMP in the vascular tissue.

Role of ET-1 receptor binding and [Ca(2+)](i) in contraction of coronary arteries from DOCA-salt hypertensive rats

Hypertension is associated with an increase in coronary artery disease, but little is known about the regulation of coronary vascular tone by endothelin-1 (ET-1) in hypertension. The present study evaluated the mechanisms mediating altered contraction to ET-1 in coronary small arteries from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. DOCA-salt rats exhibited an increase in systolic blood pressure and plasma ET-1 levels compared with placebo rats. Contraction to ET-1 (1 x 10(-11) to 3 x 10(-8) M), measured in isolated coronary small arteries maintained at a constant intraluminal pressure of 40 mmHg, was largely reduced in vessels from DOCA-salt rats compared with placebo rats. To determine the role of endothelin receptor binding in the impaired contraction to ET-1, (125)I-labeled ET-1 receptor binding was measured in membranes isolated from coronary small arteries. Maximum binding (fmol/mg protein) and binding affinity were similar in coronary membranes from DOCA-salt rats compared with placebo rats. Changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) were measured in freshly dissociated coronary small artery smooth muscle cells loaded with fura 2. ET-1 (10(-9) M) produced a 30 +/- 9% increase in [Ca(2+)](i) in smooth muscle cells from placebo rats, but had no effect on cells from DOCA-salt rats (2 +/- 2%). In summary, the ET-1-induced coronary artery contraction and increase in [Ca(2+)](i) are impaired in DOCA-salt hypertensive rats, whereas endothelin receptor binding is not altered. These results suggest endothelin receptor uncoupling from signaling mechanisms and indicate that impaired [Ca(2+)](i) signaling contributes to the decrease in ET-1-induced contraction of coronary small arteries in DOCA-salt hypertensive rats.

Oxygen species in the microvascular environment: regulation of vascular tone and the development of hypertension

Derangements of the three endothelium-related vasodilator systems (prostaglandins, endothelium-derived hyperpolarizing factor(s) and nitric oxide) cause the endothelial dysfunction observed in hypertension. Free radical-induced nitric oxide degradation plays a crucial role in hypertension. An increase in superoxide producing enzymes such as NAD(P)H oxidase and xanthine oxidase has been demonstrated. Superoxide dismutase may correct endothelial dysfunction in vitro and superoxide dismutase mimetics can lower blood pressure in experimental animals. Antioxidant agents and xanthine oxidase-inhibiting compounds have been used in humans. In addition, the synthesis of vasoconstrictor peroxides derived from the activity of cyclooxygenase in the endothelium and the vascular smooth muscle is stimulated by the OH. radical. Hydrogen peroxide levels are augmented in hypertension, but its role is unclear because recent investigations have shown that this substance may act as a hyperpolarizing factor. It is thought that the therapeutic benefit of anti-hypertensive drugs, such as calcium antagonists and angiotensin-converting enzyme inhibitors, could be in part due to an inhibition of free radical production. A role of superoxide in the endothelial dysfunction and hypertension of chronic renal failure has also been suggested by recent animal experiments.

Novel mechanisms contributing to cerebral vascular dysfunction during chronic hypertension

Chronic hypertension is a major risk factor for numerous cardiovascular disorders and is strongly associated with stroke. Hypertension alters cerebral vascular structure and may have profound deleterious effects on cerebral vascular function, the underlying mechanisms of which are still not well understood. Recent findings have led to important developments in our understanding of novel areas of cerebral vascular biology. This review briefly examines new evidence for physiologic and pathologic roles of K(+) channels, the renin-angiotensin system and reactive oxygen species, and Rho and Rho-kinase in regulation of cerebral vascular tone.

Inhibition of neurogenic inflammation by the Amazonian herbal medicine sangre de grado

This study was designed to determine if the Amazonian medicinal sangre de grado, confers benefit by suppressing the activation of sensory afferent nerves.

METHODS

(i) vasorelaxation of rat mesenteric arteries in response to calcitonin gene-related peptide; (ii) rat paw edema in response to protease- activating peptide receptor 2-activating peptide; (iii) rat paw hyperalgesia in response to low-dose protease-activating peptide receptor 2-activating peptide or prostaglandin E2; (iv) gastric hyperemia in response luminal capsaicin; (v) a clinical trial of a sangre de grado balm in pest control workers. The parent botanical was fractionated for evaluation of potential active components. In preconstricted rat mesenteric arteries, highly diluted sangre de grado (1:10,000) caused a shift to the right of the calcitonin gene-related peptide dose-response curve (p < 0.01). Paw edema in response to protease-activating peptide receptor 2-activating peptide (500 microg) was reduced by as single topical administration sangre de grado balm (1% concentration, p < 0.01) for at least 6 h. Hyperalgesia induced by either low-dose protease-activating peptide receptor 2-activating peptide (50 microg) or prostaglandin E2 was prevented by sangre de grado balm. A fraction possessing analgesic and capsaicin antagonistic properties was isolated and high-performance liquid chromatography and gas chromatography-mass spectrometry analysis indicated that it was a proanthocyandin oligomer. In pest control workers, sangre de grado balm (Zangrado) was preferred over placebo, for the relief of itching, pain, discomfort, edema, and redness in response to wasps, fire ants, mosquitoes, bees, cuts, abrasions, and plant reactions. Subjects reported relief within minutes. We conclude that sangre de grado is a potent inhibitor of sensory afferent nerve mechanisms and supports its ethnomedical use for disorders characterized by neurogenic inflammation.

Effects of small doses of ouabain on the arterial blood pressure of anesthetized hypertensive and normotensive rats

Ouabain increases vascular resistance and may induce hypertension by inhibiting the Na+ pump. The effects of 0.18 and 18 microg/kg, and 1.8 mg/kg ouabain pretreatment on the phenylephrine (PHE; 0.1, 0.25 and 0.5 microg, in bolus)-evoked pressor responses were investigated using anesthetized normotensive (control and uninephrectomized) and hypertensive (1K1C and DOCA-salt treated) rats. Treatment with 18 microg/kg ouabain increased systolic and diastolic blood pressure in all groups studied. However, the magnitude of this increase was larger for the hypertensive 1K1C and DOCA-salt rats than for normotensive animals, while the pressor effect of 0.18 microg/kg ouabain was greater only in DOCA-salt rats. A very large dose (1.8 mg/kg) produced toxic effects on the normotensive control but not on uninephrectomized or 1K1C rats. Rat tail vascular beds were perfused to analyze the effects of 10 nM ouabain on the pressor response to PHE. In all animals, 10 nM ouabain increased the PHE pressor response, but this increase was larger in hypertensive DOCA-salt rats than in normotensive and 1K1C rats. Results suggested that a) increases in diastolic blood pressure induced by 18 microg/kg ouabain were larger in hypertensive than normotensive rats; b) in DOCA-salt rats, smaller ouabain doses had a stronger effect than in other groups; c) hypertensive and uninephrectomized rats were less sensitive to toxic doses of ouabain, and d) after treatment with 10 nM ouabain isolated tail vascular beds from DOCA-salt rats were more sensitive to the pressor effect of PHE than those from normotensive and 1K1C hypertensive rats. These data suggest that very small doses of ouabain, which might produce nanomolar plasma concentrations, enhance pressor reactivity in DOCA-salt hypertensive rats, supporting the idea that endogenous ouabain may contribute to the increase and maintenance of vascular tone in hypertension.

Pharmacological evidence for the activation of potassium channels as the mechanism involved in the hypotensive and vasorelaxant effect of dioclein in rat small resistance arteries

The hypotensive and vasorelaxant effect of dioclein in resistance mesenteric arteries was studied in intact animals and isolated vessels, respectively. In intact animals, initial bolus administration of dioclein (2.5 mg kg(-1)) produced transient hypotension accompanied by an increase in heart rate. Subsequent doses of dioclein (5 and 10 mg kg(-1)) produced hypotensive responses with no significant change in heart rate. N(G)-nitro-L-arginine methyl ester (L-NAME) did not affect the hypotensive response. In endothelium-containing or -denuded vessels pre-contracted with phenylephrine, dioclein (5 and 10 mg kg(-1) produced a concentration-dependent vasorelaxation (IC(50)=0.3+/-0.06 and 1.6+/-0.6 microM, respectively) which was not changed by 10 microM indomethacin. L-NAME (300 microM) produced a shift to the right. Dioclein was without effect on contraction of vessels induced by physiological salt solution (PSS) containing 50 mM KCl and the concentration dependence of dioclein's effect on phenylephrine induced contraction was shifted to the right in vessels bathed in PSS containing 25 mM KCl. Tetraethylammonium (10 mM) and BaCl(2) (1 mM) increased the IC(50) for dioclein-induced vasorelaxation without affecting the maximal response (E(max)). Charybdotoxin (100 nM), 4-aminopyridine (1 mM) and iberiotoxin (100 nM) increased the IC(50) and reduced the E(max). Apamin (1 microM) reduced the E(max) without affecting the IC(50). Dioclein produced a hyperpolarization in smooth muscle of mesenteric arteries with or without endothelium (7.7+/-1.4 mV and 12.3+/-3.6 mV, respectively). In conclusion dioclein lowered arterial pressure probably through a decrease in peripheral vascular resistance. The underling mechanism implicated in the vasorelaxant effect of dioclein appears to be the opening of K(Ca) and Kv channels and subsequent membrane hyperpolarization.

Arterial remodeling in chronic sinoaortic-denervated rats

The spontaneous variation of blood pressure is defined as "blood pressure variability" (BPV). The chronic sinoaortic-denervated (SAD) rat is a model of high BPV without sustained hypertension. Little is known about vascular remodeling in this model. In the present study, we examined blood pressure, vascular remodeling, and aortic angiotensin II concentration in chronic SAD rats in separate experiments. In experiment 1, intra-arterial blood pressure was continuously recorded in conscious unrestrained rats. The 16-week SAD rats had a significant increase in BPV and no change in the mean level of blood pressure over a 24-h period. In experiment 2, we measured structural changes of seven kinds of arteries by histologic method and computer image analysis and functional changes of thoracic aortas by isolated artery preparation. Structural remodeling after 16-week sinoaortic denervation was characterized by increase in wall thickness, wall area, and ratio of wall thickness to internal diameter, with different changes in internal diameter and external diameter in different arteries, indicating that arterial structural remodeling expresses itself mainly as vascular growth. This vascular growth might be caused by medial smooth muscle cell growth and collagen accumulation. Aortic contraction induced by norepinephrine was potentiated, whereas aortic relaxation induced by acetylcholine was attenuated after sinoaortic denervation. In experiment 3, plasma and aortic angiotensin II concentrations were determined by radioimmunoassay. The former remained unchanged, whereas the latter was significantly increased in 10-week SAD rats. It is concluded that in rats chronic sinoaortic denervation can produce vascular remodeling that might be related to increased BPV and an activated tissue renin-angiotensin system.

Altered coronary dilation in deoxycorticosterone acetate-salt hypertension

OBJECTIVE

To compare coronary dilation in uninephrectomized hypertensive deoxycorticosterone acetate (DOCA)-salt rats (HTRs), treated for 2 or 4 weeks, with age-matched uninephrectomized normotensive rats (NTRs). DESIGN AND METHODS Coronary perfusion pressure was recorded in isolated hearts perfused at a constant flow rate to evaluate coronary resistance.

RESULT

A decreased vasoconstriction due to NG-nitro-Larginine (NNLA, 30 pmol/I) in hearts from HTRs suggested a reduced basal nitric oxide (NO) release. In contrast, coronary vasodilation due to the NO donor, sodium nitroprusside (3 pmol/I), remained unaffected in 2-week HTRs, and was enhanced in 4-week HTRs. Cumulative dose-response curves to bradykinin induced an important vasodilation in NTRs, with a maximal response that remained unaffected in the presence of either NNLA (30 pmol/I), indomethacin (10 pmol/l) or the two combined. In contrast, hearts from HTRs showed a diminished maximal relaxation to bradykinin, suggesting an altered endothelium-dependent relaxation. The presence of NNLA or indomethacin had no effect on the weak relaxation observed in HTRs. However, NNLA and indomethacin combined unmasked an important relaxation due to bradykinin in HTRs. The addition of clotrimazole (1 pmol/I) to NNLA and indomethacin blunted the relaxation due to bradykinin in both NTRs and HTRs. Perfusion with superoxide dismutase (120 IU/ml) restored most of the coronary relaxation due to bradykinin in hearts from HTRs. Bradykinin-induced prostaglandin 12 (PGI2) and E2 (PGE2) production was unaffected by hypertension. No increase in thromboxane A2 (TXA2) due to bradykinin was detected. Finally, reduced reactivity to papaverine and forskolin was observed in hearts from HTRs.

CONCLUSION

DOCA-salt hypertension is associated with alterations in coronary reactivity. Basal NO formation appears to be reduced in HTRs, but the intact relaxation to exogenous NO suggests a preserved guanylate cyclase pathway. In addition, alteration in adenylate cyclase activity, and not in prostaglandin production, may explain the blunted cAMP-mediated responses in HTRs. The combined nitric-oxide synthase (NOS) and cyclo-oxygenase (COX) inhibition unmasked an endothelium-derived hyperpolarizing factor (EDHF) involvement in the coronary dilation due to bradykinin in hearts from HTRs, suggesting that endothelial NO and PGI2, although unable to induce coronary smooth-muscle relaxation, can inhibit EDHF production in HTRs. Impairment in the adenylate cyclase pathway and the suppression of NO by free radicals may explain the blunted vasodilation in DOCA-salt hypertension.

Impaired relaxation to acetylcholine in 2K-1C hypertensive rat aortas involves changes in membrane hyperpolarization instead of an abnormal contribution of endothelial factors

The contribution of endothelial factors and mechanisms underlying decreased acetylcholine-induced relaxation and endothelial inhibitory action on phenylephrine-induced contraction were evaluated in aortas of two-kidney, one-clip hypertensive (2K-1C) and normotensive (2K) rats. Relaxation induced by acetylcholine in 2K-1C precontracted by phenylephrine was lower [Maximum Effect (ME): 71.33+/-3.36%; pD(2): 7.050+/-0.03] than in 2K (ME: 95.26+/-1.59%; pD(2): 7.31+/-0.07). This response was abolished by N(G)-nitro-L-arginine (L-NNA) in 2K-1C, but was only reduced in 2K (ME: 29.21+/-9.28%). Indomethacin had no effect in 2K-1C, and slightly attenuated acetylcholine-induced relaxation in 2K. The combination of L-NNA and indomethacin almost abolished acetylcholine-induced relaxation in 2K-1C, while in 2K, the inhibition (ME: 56.61+/-8.95%) was lower than the effect of L-NNA alone. During the KCl-induced precontraction, 2K and 2K-1C aortas showed similar acetylcholine-induced relaxation (43.50+/-5.64% vs. 41.60+/-4.36%), which was abolished by L-NNA. The levels of cGMP produced in response to acetylcholine were not different between 2K and 2K-1C. The sensitivity to sodium nitroprusside was lower in phenylephrine-precontracted aortas from 2K-1C than 2K, as showed by the pD(2) values (7.72+/-0.20 vs. 8.59+/-0.17), and this difference was abolished in aortas precontracted by KCl. The membrane potential was less negative in 2K-1C than in 2K (-41.57+/-1.19 vs. -51.00+/-1.13 mV) and hyperpolarization induced by acetylcholine was lower in 2K-1C than in 2K aortas (6.00+/-0.66 vs. 13.27+/-1.61 mV). Phenylephrine-induced contraction in aortas with endothelium was similar in both groups, and increased by the endothelium removal. This increase was lower in 2K-1C (from 1.32+/-0.06 to 1.90+/-0.21 g) than 2K (from 1.49+/-0.07 to 2.83+/-0.18 g). L-NNA and the endothelium removal had similar effect in 2K-1C (1.85+/-0.18 g) and were lower in 2K (2.18+/-0.20 g). Indomethacin decreased phenylephrine-induced contraction only in 2K. In conclusion, our major finding was a selective defect in smooth muscle membrane hyperpolarization, which could explain the decreased relaxation to acetylcholine and the attenuated inhibitory effect of endothelium on the contractile function in 2K-1C aortas.

Attenuated coronary flow reserve and vascular remodeling in patients with hypertension and left ventricular hypertrophy

OBJECTIVES

The purpose of this study was to evaluate the association between hypertension and left ventricular hypertrophy (LVH) with both coronary vascular remodeling and endothelial function.

BACKGROUND

The association between endothelial and nonendothelial coronary flow reserve with vascular remodeling in patients with hypertension and LVH is still unclear.

METHODS

One hundred and eleven patients with normal or mildly diseased coronary arteries at angiography underwent intravascular ultrasound examination of the left anterior descending coronary artery. Patients were divided into three groups: group 1: n = 13, hypertensive patients with LVH; group 2: n = 30, hypertensive patients without LVH; group 3: n = 68, normotensive patients. Vessel and lumen area and atherosclerotic plaque area were evaluated. Vascular reactivity was examined using intracoronary adenosine and acetylcholine.

RESULTS

Vessel area in group 1 (with LVH) was significantly (p < 0.01) greater than that in group 2 (without LVH), whereas, vessel area in both groups 1 and 3 was similar (12.8 +/- 0.8 mm2, 10.7 +/- 0.4 mm2 and 11.5 +/- 0.3 mm2). Coronary blood flow at baseline for patients in group 1 (with LVH) was significantly greater than it was for patients in groups 2 and 3 (81.1 +/- 9.9 ml/min, 56.5 +/- 6.2 ml/min and 48.1 +/- 3.2 ml/min, both p < 0.05). In comparison with groups 2 and 3, the response to both acetylcholine and adenosine was significantly impaired in patients with LVH.

CONCLUSIONS

The current study demonstrates that hypertension with LVH is associated with both coronary vascular remodeling and attenuated endothelial and nonendothelial coronary flow reserve.

Coronary vascular reactivity is improved by endothelin A receptor blockade in DOCA-salt hypertensive rats

Endothelin-1 (ET-1) is thought to play an important role in the development of deoxycorticosterone acetate (DOCA)-salt hypertension. Because hypertension is associated with an increased incidence of coronary artery disease, this study was designed to determine if coronary vascular contraction to ET-1 is altered in DOCA-salt hypertensive rats and to determine the effect of chronic treatment of DOCA-salt rats with the selective ETA receptor antagonist A-127722. Male Sprague-Dawley rats were divided into four groups: DOCA, Placebo, DOCA + A-127722, and Placebo + A-127722. A-127722 was administered in drinking water at a concentration of 8 mg/100 ml. After 3 wk, mean arterial pressure (MAP) was significantly enhanced in DOCA-salt compared with Placebo rats. A-127722 significantly inhibited the increase in MAP. Contraction to ET-1 (10(-11) to 3 x 10(-8) M) was measured in isolated coronary and mesenteric small arteries (200-300 micron, intraluminal diameter) maintained at a constant intraluminal pressure of 40 mmHg and was significantly impaired in vessels from DOCA-salt compared with Placebo rats. Dose-dependent contractions to KCl were also inhibited in coronary, but only minimally impaired in mesenteric, arteries of DOCA-salt rats. Inhibition of nitric oxide synthase activity did not restore contraction to ET-1 in coronary small arteries. However contractions to ET-1 were enhanced in mesenteric small arteries. Chronic treatment with A-127722 significantly restored contraction to ET-1 in coronary, but not in mesenteric, arteries of DOCA-salt rats. Because ETA receptor blockade impairs the development of hypertension and improves coronary vascular reactivity, these data indicate that ET-1 plays an important role in coronary vascular dysfunction associated with DOCA-salt hypertension.

The contribution of nitric oxide to cardiovascular status and responses to vasodilators in conscious, hypertensive, transgenic ((mRen-2)27) rats

1. The aim of the study was to measure the regional haemodynamic responses to vasodilators, and the effects of nitric oxide (NO) synthase inhibition, in conscious, hypertensive, transgenic ((mRen-2)27) rats (TG rats) and normotensive, Hannover Sprague-Dawley (SD) rats. 2. The hypotensive response to acetylcholine was greater in TG than in SD rats, but the renal vasodilator responses were not different. 3. The responses to bradykinin were similar in the two strains, except that hindquarters vasodilatation occurred only in SD rats. 4. Salbutamol caused smaller renal and hindquarters vasodilatation in TG rats than in SD rats, and there was mesenteric vasodilatation only in the latter strain. 5. The hypotensive response to sodium nitroprusside was smaller, but the accompanying mesenteric vasodilatation was greater, in SD than in TG rats. 6. The contribution of NO to the vasodilator responses was taken as the difference between the responses in the presence of the NO synthase inhibitor, NG-nitro-L-arginine methylester (L-NAME), compared to those in the presence of a co-infusion of angiotensin II and vasopressin (to match the haemodynamic effects of L-NAME). 7. In TG rats, L-NAME caused a greater absolute pressor effect, but a smaller mesenteric vasoconstriction, than in SD rats. 8. L-NAME affected the vasodilator responses to all the challenges similarly in the two strains. 9. Collectively, the results provide no direct evidence for impaired NO-mediated vasodilator mechanisms in TG rats. It is feasible that the reduced hindquarters response to bradykinin and the reduced renal and hindquarters responses to salbutamol, in TG rats are due to abnormal beta2-adrenoceptor-mediated processes.

Heterogeneous vasomotor responses of coronary conduit and resistance vessels in hypertension

OBJECTIVES

The purpose of our study was to investigate the relation between conductance and resistance coronary vasomotor responsiveness in hypertensive patients without atherosclerosis.

BACKGROUND

Although similar in morphology, conduit and resistance coronary vessels differ importantly in size, function and local environment and appear to be differentially affected in certain disease processes, such as atherosclerosis and hypertension. However, little is known about the effect of hypertension on contiguous coronary conduit and resistance vessels in humans.

METHODS

Changes in coronary blood flow (a measure of resistance vessel reactivity) and coronary artery diameter (a measure of conduit vessel reactivity) were investigated in response to graded infusion of the endothelium-dependent agonist acetylcholine (ACh) in 98 patients with normal coronary arteries.

RESULTS

In 31 normotensive, euglycemic patients, conduit and resistance coronary artery responses to intracoronary infusion of ACh were significantly correlated (r = 0.73, p = 1 x 10[-6]), although eight patients (26%) had constriction of conduit but dilation of resistance arteries at peak effect. In 28 hypertensive patients without left ventricular hypertrophy (LVH), conduit and resistance artery responses to ACh remained significantly correlated (r = 0.5, p = 0.006), although 12 patients (43%) had discordant findings. Finally, in 39 hypertensive patients with LVH, conduit and resistance artery responses to ACh displayed the lowest correlation (r = 0.38, p = 0.02), with 22 patients (56%) demonstrating conduit artery constriction and resistance artery dilation.

CONCLUSIONS

Despite angiographically normal coronary arteries, heterogeneous vasomotor responses (dilation and constriction) were demonstrated in contiguous conduit and resistance arteries in normotensive and hypertensive patients referred for cardiac catheterization because of chest pain. In addition to more severe endothelial dysfunction among conduit and resistance arteries, a greater frequency of discordant conduit and resistance artery responses and resistance vessel constriction was found with increasing severity of hypertension. Our study suggests differing mechanisms of endothelium responsiveness to ACh among conduit and resistance coronary arteries.