Nitric oxide regulates local arterial distensibility in vivo

BACKGROUND

Arterial stiffness is an important determinant of cardiovascular risk. Several lines of evidence support a role for the endothelium in regulating arterial stiffness by release of vasoactive mediators. We hypothesized that nitric oxide (NO) acting locally regulates arterial stiffness in vivo, and the aim of this experiment was to test this hypothesis in an ovine hind-limb preparation.

METHODS AND RESULTS

All studies were conducted in anesthetized sheep. Pulse wave velocity (PWV) was calculated by the foot-to-foot methodology from 2 pressure waveforms recorded simultaneously with a high-fidelity dual pressure-sensing catheter placed in the common iliac artery. Intra-arterial infusion of N(G)-monomethyl-L-arginine (L-NMMA) increased iliac PWV significantly, by 3+/-2% (P<0.01). Infusion of acetylcholine and glyceryl trinitrate reduced PWV significantly, by 6+/-4% (P=0.03) and 5+/-2% (P<0.01), respectively. Only the effect of acetylcholine, however, was significantly inhibited during coinfusion of L-NMMA (P=0.03). There was no change in systemic arterial pressure throughout the studies. Importantly, infusion of L-NMMA or acetylcholine distal to the common iliac artery (via the sheath) did not affect PWV.

CONCLUSIONS

These results demonstrate, for the first time, that basal NO production influences large-artery distensibility. In addition, exogenous acetylcholine and glyceryl trinitrate both increase arterial distensibility, the former mainly through NO production. This may help explain why conditions that exhibit endothelial dysfunction are also associated with increased arterial stiffness. Therefore, reversal of endothelial dysfunction or drugs that are large-artery vasorelaxants may be effective in reducing large-artery stiffness in humans, and thus cardiovascular risk.

Potentiated angiogenic effect of scatter factor/hepatocyte growth factor via induction of vascular endothelial growth factor: the case for paracrine amplification of angiogenesis

BACKGROUND

Scatter factor/hepatocyte growth factor (SF/HGF) is a pleiotropic growth factor that stimulates proliferation and migration of endothelial cells (ECs) via the c-Met receptor, present on ECs as well as other cell types, including smooth muscle cells (SMCs). We studied the effects of recombinant human (rh) SF/HGF in vitro and in vivo in a rabbit model of hindlimb ischemia. We further compared these effects with those of recombinant human vascular endothelial growth factor (rhVEGF165), an EC-specific mitogen.

METHODS AND RESULTS

In vitro, rhSF/HGF and rhVEGF165 exhibited similar effects on proliferation and migration of ECs. When both cytokines were administered together, the result was an additive effect on EC proliferation and a synergistic effect on EC migration. Application of rhSF/HGF to cultures of human SMCs resulted in the induction of VEGF mRNA and protein. In vivo, administration of rhSF/HGF (500 microg x 3) was associated with significant improvements in collateral formation (P<.001) and regional blood flow (P<.0005) and with a significant reduction in muscle atrophy (P<.0001). These effects were significantly more pronounced than those of rhVEGF165 administered according to the same protocol (P<.05). Neither remote angiogenesis nor other pathological sequelae were observed with either rhSF/HGF or rhVEGF165.

CONCLUSIONS

The pleiotropic effects of certain growth factors may potentiate angiogenesis via a combination of direct effects on EC proliferation and migration and indirect effects that result in the generation of other potent EC mitogens from non-EC populations. The synergistic effects demonstrated when SF/HGF and VEGF are administered together in vitro may be reproduced in vivo by SF/HGF-induced upregulation of VEGF in vascular SMCs.

Pathological analysis of local delivery of paclitaxel via a polymer-coated stent

BACKGROUND

Paclitaxel can inhibit vascular smooth muscle proliferation in vitro, and early studies suggest that paclitaxel may be useful in preventing restenosis. Early and late intimal growth and local vascular pathological changes associated with paclitaxel delivered via stents have not been fully explored.

METHODS AND RESULTS

Localized drug delivery was accomplished with balloon-expandable stainless steel stents coated with a cross-linked biodegradable polymer, chondroitin sulfate and gelatin (CSG), containing various doses of paclitaxel. CSG-coated stents with paclitaxel (42.0, 20.2, 8.6, or 1.5 microgram of paclitaxel per stent), CSG-coated stents without paclitaxel, and uncoated stents (without paclitaxel or CSG) were deployed in the iliac arteries of New Zealand White rabbits, which were killed 28 days after implant. Mean neointimal thickness at stent strut sites was reduced 49% (P<0.0003) and 36% (P<0.007) with stents containing 42.0 and 20.2 microgram of paclitaxel per stent, respectively, versus CSG-coated stents without paclitaxel. However, histological findings suggested incomplete healing in the higher-dose (42.0 and 20.2 microgram) paclitaxel-containing stents consisting of persistent intimal fibrin deposition, intraintimal hemorrhage, and increased intimal and adventitial inflammation. Stents coated with CSG alone (without paclitaxel) had similar neointimal growth as uncoated stents. In a separate group of rabbits killed at 90 days, neointimal growth was no longer suppressed by CSG-coated stents containing 42.0 or 21.0 microgram of paclitaxel

CONCLUSIONS

CSG coating appears to be a promising medium for localized drug delivery. Paclitaxel polymer-coated stents reduce neointima formation but are associated with evidence of incomplete healing at 28 days. However, neointimal suppression was not maintained at 90 days.

Venous smooth muscle contains vasoconstrictor ETB-like receptors

Two endothelin (ET) receptor subtypes have been identified to date: the ETA receptor which preferentially binds ET-1 over ET-3, and the ETB receptor which is non-selective. This study characterized the ET receptor subtypes present in several vascular smooth muscle preparations using standard in vitro techniques. In all but one of the arteries tested, ET-3 was significantly less potent than ET-1. In contrast, the potency of ET-3 was very similar to that of ET-1 in all of the veins. The selective ETA receptor antagonist BQ-123 blunted the ET-1 contractions in rabbit carotid artery, but not in saphenous vein. The selective ETB receptor ligand sarafotoxin S6c contracted the rabbit saphenous vein, but not the carotid artery. These data suggest that vascular smooth muscle cells express ETA and ETB receptors. Stimulation of either receptor subtype can result in force development.

Endothelial control of arterial distensibility is impaired in chronic heart failure

BACKGROUND

Vascular tone is a determinant of conduit artery distensibility. The aim of this study was to establish whether endothelium-derived relaxing factor (EDRF) influences the distensibility of conduit arteries and whether endothelium-mediated increases in distensibility are impaired in chronic heart failure (CHF).

METHODS AND RESULTS

Conduit artery distensibility was measured by two methods in healthy subjects and in nine patients with CHF caused by dilated cardiomyopathy. In the first method, pulse-wave velocity (PWV) was measured in the right common iliac artery at rest and during local infusions of acetylcholine (10(-7) to 10(-5) mol/L) or adenosine (2 x 10(-7) to 2 x 10(-5) mol/L), with correction for systemic effects. Acetylcholine induced concentration-dependent local reductions of PWV in healthy subjects (-5%, -15%, and -26%) but not in CHF patients (3%, 1%, -4%, P < .01), whereas adenosine induced similar reductions of PWV in healthy subjects and CHF patients. In the second method, brachial artery diameter, blood flow, and blood pressure were measured noninvasively by high-resolution ultrasound, continuous-wave Doppler, and photoplethysmography during reactive hyperemia in the hand and after sublingual glyceryl trinitrate (GTN, 400 micrograms). Hyperemic flow, similar in healthy subjects and CHF patients, was associated with increases in diameter and distensibility in healthy subjects (8.8% and 18.4%, respectively) but not in CHF patients (0.3% and -4.5%), whereas GTN induced similar effects in healthy subjects and CHF patients.

CONCLUSIONS

These data indicate that conduit artery distensibility is increased by acetylcholine and increased blood flow in healthy subjects but not in CHF patients, whereas the effects of adenosine and GTN on distensibility are preserved in CHF patients. This implies that EDRF-mediated increases in distensibility are impaired in CHF patients, thus adding to cardiac work.

An endothelin receptor (ETA) antagonist isolated from Streptomyces misakiensis

A competitive endothelin (ET) antagonist, BE-18257B, was isolated from the fermentation products of Streptomyces misakiensis. It is a novel cyclic pentapeptide, cyclo(-D-Glu-L-Ala-allo-D-Ile-L-Leu-D-Trp-), and binds to ETA receptors (ET-1 selective) in cardiovascular tissues, but not to ETB receptors (equally sensitive to isopeptides of ET family) in kidney, adrenal gland and cerebellum tissues. BE-18257B also antagonizes ET-1-induced vasoconstriction in rabbit iliac artery and pressor action in rats. Thus it is a selective ETA antagonist and should provide a valuable tool for elucidation of the pharmacological and pathophysiological roles of ET-1.

Comparison of CI-976, an ACAT inhibitor, and selected lipid-lowering agents for antiatherosclerotic activity in iliac-femoral and thoracic aortic lesions. A biochemical, morphological, and morphometric evaluation

Due to the potential importance of acyl-coenzyme A:cholesterol O-acyltransferase (ACAT) in the generation of lipid-filled monocytes-macrophages, the ACAT inhibitor CI-976 (2,2-dimethyl-N-(2,4,6-trimethoxyphenyl)dodecanamide) was evaluated relative to selected lipid-lowering agents for their effect on atherosclerotic lesion regression and progression. Atherosclerotic lesions comparable in composition to human fatty streaks were induced by chronic endothelial denudation in the iliac-femoral artery of hypercholesterolemic New Zealand White rabbits before intervention, while naturally occurring fatty streaks developed in the thoracic aorta. CI-976 administered in a hypercholesterolemic diet at a dose that did not lower plasma cholesterol prevented the accumulation of monocytes-macrophages within the preestablished iliac-femoral lesion and reduced the foam cell area by 27-29% relative to the initiation of intervention. CI-976 also blunted the development of thoracic aortic fatty streak-like lesions and decreased the cholesteryl ester enrichment by 46%. CI-976 had no effect on plasma triglycerides and, more importantly, had no effect or decreased liver, iliac-femoral, and thoracic aortic free cholesterol content. Dietary intervention alone increased monocyte-macrophage involvement in the iliac-femoral lesion despite reductions in plasma, liver, and thoracic aortic cholesterol content. Conventional lipid-lowering therapy such as cholestyramine or cholestyramine/niacin required substantial decreases in plasma cholesterol levels to achieve comparable vascular changes. We conclude that inhibition of ACAT within the arterial wall by the potent and specific ACAT inhibitor CI-976, even in the absence of plasma cholesterol lowering, can result in the inhibition of atherosclerotic lesion progression and can enhance regression.

Endothelium-independent vasodilator effects of the flavonoid quercetin and its methylated metabolites in rat conductance and resistance arteries

The flavonoid quercetin is metabolized into isorhamnetin, tamarixetin, and kaempferol, the vascular effects of which are unknown. In the present study, the effects of quercetin and its metabolites were analyzed on isometric tension in isolated rat thoracic and abdominal aorta, in isolated intact and beta-escin-permeabilized iliac arteries, and on perfusion pressure in the isolated mesenteric resistance vascular bed. In noradrenaline-precontracted vessels, the four flavonoids produced a vasodilator effect, which was inversely correlated with the diameter of the vessel studied; i.e., quercetin, isorhamnetin, tamarixetin, and kaempferol were 5-, 25-, 4-, and 6-fold, respectively, more potent in the resistance mesenteric bed (-log IC(50) = 5.35 +/- 0.15, 5.89 +/- 0.11, 5.34 +/- 0.10, and 5.66 +/- 0.06, respectively) than in the thoracic aorta (-log IC(50) = 4.68 +/- 0.08, 4.61 +/- 0.08, 4.73 +/- 0.11, and 4.81 +/- 0.13, respectively; n = 4-6). The vasodilator responses of quercetin and isorhamnetin were not significantly modified after removal of the endothelium in the thoracic aorta or in the mesenteric bed. Furthermore, the guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 10(-6) M), the adenylate cyclase inhibitor SQ22536 [9-(tetrahydro-2-furanyl)-9H-purin-6-amine; 10(-6) M], KCl (40 mM), or ouabain (10(-3) M) had no effect on isorhamnetin-induced vasodilation in the mesenteric bed. In permeabilized iliac arteries stimulated with Ca(2+) (pCa of 5.9), isorhamnetin was also significantly more potent (-log IC(50) = 5.27 +/- 0.15) than quercetin (-log IC(50) = 4.56 +/- 0.15). In conclusion, quercetin and its metabolites showed vasodilator effects with selectivity toward the resistance vessels. These effects are not due to or modulated by endothelial factors and are unrelated to changes in cytosolic Ca(2+).

Oral everolimus inhibits in-stent neointimal growth

BACKGROUND

Rapamycin (sirolimus)-eluting stents are associated with reduced restenosis rates in animal studies and initial human trials. The present study evaluated whether orally administered everolimus (a macrolide of the same family as sirolimus) inhibits in-stent neointimal growth in rabbit iliac arteries.

METHODS AND RESULTS

New Zealand white rabbits were randomized to everolimus 1.5 mg/kg per day starting 3 days before stenting and reduced to 1 mg/kg per day from days 14 to 28 (group 1), everolimus 1.5 mg/kg given 1 day before stenting followed by 0.75 mg/kg per day for 28 days (group 2), or matching placebo for each group. Drugs were administered by oral gavage. Stents were deployed in both iliac arteries, and arteries were harvested 28 days after stenting. Group 1 everolimus-treated rabbits experienced weight loss and anorexia, which resolved after the everolimus dose was lowered on day 14. Group 2 animals were healthy for the duration of everolimus dosing. Both everolimus treatment groups significantly reduced in-stent neointimal growth (46% reduction and 42% reduction in intimal thickness in groups 1 and 2, respectively). In group 2 everolimus-treated animals, the neointima was healed or healing, characterized by stent struts covered by a thin neointima, overlying endothelial cells, and only small foci of fibrin. Scanning electron microscopy showed >80% stent surface endothelialization in group 2 everolimus-treated rabbits.

CONCLUSIONS

Oral everolimus suppresses in-stent neointimal growth in the rabbit iliac artery. At a dose of 1.5 mg/kg given 1 day before stenting followed by 0.75 mg/kg per day for 28 days, everolimus was well tolerated and was associated with significant neointimal healing.

Effect of antiplatelet therapy on restenosis after experimental angioplasty

Restenosis is recognized as a common complication of PTCA and can limit the long-term benefit of this procedure. To study the effect of antiplatelet agents in preventing restenosis, 25 New Zealand rabbits had bilateral iliac stenoses created by balloon deendothelialization and a 2% cholesterol diet for 6 weeks. After angiographic delineation of the iliac atherosclerosis, successful angioplasty was performed in all rabbits, with an average increase in luminal diameter of 0.9 mm (81%). Seven rabbits received aspirin (32 mg/day) plus dipyridamole (25 mg/day) and 9 received sulfinpyrazone (100 mg/day); 9 were given no antiplatelet drugs and served as controls. After 4 weeks of drug therapy and a continued atherogenic diet, angiography was repeated and the rabbits were killed for histologic examination. The angiographic luminal diameter was similar for these groups both before and immediately after angioplasty. However, the luminal diameter 4 weeks later was significantly larger in both the aspirin plus dipyridamole and the sulfinpyrazone groups compared with the control rabbits (1.3 +/- 0.6 and 1.8 +/- 0.5 mm vs 0.7 +/- 0.6 mm, respectively, p less than 0.05). Histologic examination revealed intraluminal clot in 4 of 9 control rabbits and in none of the drug-treated rabbits. Also, less intimal thickening was evident. In conclusion, aspirin plus dipyridamole and sulfinpyrazone inhibited angiographic restenosis after transluminal angioplasty in this experimental model. These findings support the use of antiplatelet agents in clinical angioplasty and suggest that platelet aggregation at the angioplasty site may promote restenosis.

Eplerenone suppresses constrictive remodeling and collagen accumulation after angioplasty in porcine coronary arteries

BACKGROUND

Coronary artery angioplasty triggers healing that causes constrictive remodeling. Because collagen accumulation correlates with constrictive remodeling and aldosterone has been implicated in collagen accumulation, we examined how aldosterone and the mineralocorticoid receptor antagonists spironolactone and eplerenone affect remodeling and collagen in porcine coronary and iliac arteries after angioplasty.

METHODS AND RESULTS

Twenty-four pigs were allocated into 4 treatment groups: oral eplerenone (100 mg/d), oral spironolactone (200 mg/d), subcutaneous aldosterone (400 microgram/d), or no treatment. Twenty-eight days after angioplasty of the coronary arteries, eplerenone increased total vessel area by 30% (P<0.05) and luminal area by nearly 60% (P<0.05) compared with the no-treatment group, without affecting neointima size. These effects were accompanied by a 65% reduction in neointimal and medial collagen density (both P<0.05). Spironolactone was less effective, and aldosterone tended to exert opposite effects on coronary artery structure after angioplasty. These effects were not observed in angioplastied iliac arteries.

CONCLUSIONS

Eplerenone attenuates constrictive remodeling after coronary artery angioplasty by mechanisms involving reduction in collagen accumulation, which thus appears to be an important contributor to constrictive remodeling of angioplastied coronary arteries.

Basal NO Locally Modulates Human Iliac Artery Function In Vivo

We demonstrated previously that endogenous NO influences large-artery distensibility in the ovine hindlimb. However, the role of basal NO in larger human conduit arteries is controversial. The aim of this study was to investigate whether basal production of NO, acting locally, influences iliac artery distensibility in humans. Distensibility was assessed by intra-arterial measurement of the pulse wave velocity. Eighteen subjects, free of significant coronary or iliac artery disease, were studied after diagnostic cardiac catheterization. Simultaneous pressure waveforms were recorded with a high-fidelity dual-pressure sensing catheter, placed in the common iliac artery during intra-arterial infusion of saline (baseline), glyceryl trinitrate (4 nmol/min), or N G -monomethyl- l -arginine (8 and 16 μmol/min). Drugs were infused proximally, via the catheter to perfuse the segment of artery under study, or distally, via the sheath, to control for any reflex changes in flow or sympathetic activation. Velocity was calculated using the foot-to-foot methodology. Six subjects received glyceryl trinitrate and 12 N G -monomethyl- l -arginine. There was no change in velocity after infusion of glyceryl trinitrate or N G -monomethyl- l -arginine via the sheath. However, infusion of glyceryl trinitrate via the catheter significantly reduced velocity by 31.43±5.80% (mean±SEM; P <0.01; P =0.02 for comparison). Likewise, infusion of the highest dose of N G -monomethyl- l -arginine via the catheter significantly increased velocity by 27.25±8.20% ( P =0.001; P =0.02 for comparison). Importantly, there was no change in mean arterial blood pressure throughout the studies. These data indicate that under resting conditions, local NO production modulates human iliac artery distensibility and that exogenous NO increases arterial distensibility.

Discrimination between ETA- and ETB-receptor-mediated effects of endothelin-1 and [Ala1,3,11,15]endothelin-1 by BQ-123 in the anaesthetized rat

1. The influence of BQ-123 (a selective ETA-receptor antagonist) on the haemodynamic response elicited by endothelin-1 (ET-1) and [Ala1,3,11,15]ET-1 (a selective ETB-receptor agonist) was studied in anaesthetized rats instrumented with ultrasonic Doppler flow probes on the carotid, coeliac, mesenteric, renal and iliac arteries. 2. BQ-123 alone (1.6 mumol kg-1, i.v.) induced a decrease in femoral mean arterial pressure (AP), accompanied by a systemic vasodilatation. The response was maximal after 3 min and then returned slowly to baseline. None of these effects was observed after a 0.016 mumol kg-1 dose of BQ-123. 3. ET-1 (1 nmol kg-1, i.v.) induced a biphasic response characterized by a transient initial decrease in AP accompanied by regional vasodilatation (mainly in the carotid and iliac beds) and by immediate mesenteric and renal vasoconstrictions. This was followed, within 1 min, by a marked and prolonged increase in AP accompanied by systemic vasoconstriction. Pretreatment with BQ-123 (1.6 mumol kg-1, i.v., 8 min before ET-1) increased and prolonged the vasodilator effect of ET-1 (mainly in the carotid, coeliac, mesenteric and iliac beds) and reduced its systemic vasoconstrictor effects with marked regional differences (the coeliac, mesenteric and renal beds being poorly affected). 4. [Ala1,3,11,15]ET-1 (3 nmol kg-1, i.v.) induced an initial and marked decrease in AP accompanied by regional vasodilatation (mainly in the carotid, coeliac and iliac beds) and by mesenteric and renal vasoconstrictions. This was followed, within 5 min, by a small increase in AP and systemic vasoconstriction. All these effects were dose-dependent. Pretreatment with BQ-123 (1.6 tmol kg'; 8 min before ET-1) did not modify the early effect of [Ala'3""5]ET-l, but abolished its secondary vasoconstrictor effect except in the mesenteric bed.5. This study demonstrates that pretreatment with BQ-123 not only reduced a large part of the sustained vasoconstrictor activity of ET-1, suggesting the involvement of ETA-receptors, but also enhanced the early vasodilator activity of ET-1 revealing a functional antagonism between the two effects. The vasodilator effect of [Ala1"3""l '5]ET-1 was not affected by BQ-123 and ET-1 induced a similar vasodilatation, that was potentiated by BQ-123, suggesting the involvement of ETB-receptors in this vasodilator response. Marked regional differences were however observed which might be partly related to different levels of functional antagonism between ETB- and ETA-mediated effects, but differences in receptor types, or subtypes, cannot be excluded, mainly in the mesenteric and renals beds.

Poly(vinyl alcohol)-graft-poly(lactide-co-glycolide) nanoparticles for local delivery of paclitaxel for restenosis treatment

Catheter-based local delivery of biodegradable nanoparticles (NP) with sustained release characteristics represents a therapeutic approach to reduce restenosis. Paclitaxel-loaded NP consisting of poly(vinyl alcohol)-graft-poly(lactide-co-glycolide) (PVA-g-PLGA) with varying PLGA chain length as well as poly(lactide-co-glycolide) (PLGA), were prepared by a solvent evaporation technique. NP of <180 nm in diameter characterized by photon correlation spectroscopy (PCS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) are spherical and show smooth surfaces. Yields typically range from 80 to 95% with encapsulation efficiencies between 77 and 87%. The extent of initial in vitro paclitaxel release was affected by the PVA-g-PLGA composition. Blank nanoparticles from PVA(300)-g-PLGA(30) and PVA(300)-g-PLGA(15) showed excellent biocompatibility in rabbit vascular smooth muscle cells (RbVSMC) at polymer concentrations of 0.37 mg/ml. Paclitaxel-loaded NP have an increased antiproliferative effect on cells in comparison to free drug. Confocal laser scanning microscopy of RbVSMC confirmed cellular uptake of nanoparticles composed of fluorescently labeled PVA(300)-g-PLGA(15) loaded with Oregon Green labeled paclitaxel. Cells showed a clearly increased fluorescence activity with a co-localization of paclitaxel and polymer nanoparticles during incubation with particle suspension. To evaluate the antirestenotic effect in vivo, paclitaxel-loaded nanoparticles were administered locally to the wall of balloon-injured rabbit iliac arteries using a porous balloon catheter. As a result a 50% reduction in neointimal area in vessel segments treated with paclitaxel-loaded nanoparticles compared to control vessel segments could be observed (local paclitaxel nanoparticle treated segments 0.80+/-0.19 mm(2), control segments 1.58+/-0.6 mm(2); p<0.05).

Adenosine A2a receptors increase arterial endothelial cell nitric oxide

BACKGROUND

Adenosine is a potent vasodilator of vascular smooth muscle. Endothelium-derived nitric oxide (NO) elicits vasodilation. We have previously reported that adenosine stimulates the production of NO from porcine carotid arterial endothelial cells (PCAEC) via a receptor-mediated mechanism. This study was to determine whether adenosine also enhances NO production from human arterial endothelium and to define the involvement of adenosine A1 and A2 receptors.

MATERIALS AND METHODS

Human iliac arterial endothelial cells (HIAEC) and PCAEC were harvested and cultured in dishes. NO production was evaluated with a NO electrode sensor which measured continuously real-time NO production.

RESULTS

NO content of the medium bathing HIAEC and PCAEC was significantly increased with adenosine (100 micromol/L). Ethylcarboxamidoadenosine (NECA), a nonselective adenosine receptor agonist, and carboxyethyl-phenethylamino-ethylcarboxamidoadenosine (CGS-21680), a selective adenosine A2a receptor agonist, increased NO production by HIAEC and PCAEC with respective EC50 values of 3.32 and 6.96 nmol/L for NECA and 30.97 and 29.47 nmol/L for CGS-21680. Chlorofuryl-triazolo-quinazolinamine (CGS-15943; 1 micromol/L), an adenosine A1 and A2 receptor antagonist, and aminofuryltriazolotriazinyl-aminoethylphenol (ZM-241385; 1 micromol/L), a selective adenosine A2a receptor antagonist, inhibited the effect of CGS-21680. Chlorocyclopentyl-adenosine (CCPA; 1 micromol/L), an adenosine A1 receptor agonist, significantly depressed NO production by both HIAEC and PCAEC: This effect was inhibited by cyclopentyl-dipropylxanthine (DPCPX), a selective adenosine A1 receptor antagonist.

CONCLUSIONS

The results demonstrate that adenosine A2a receptors increase, and adenosine A1 receptors decrease, the production of NO by human and porcine arterial endothelial cells.

Flow-induced arterial enlargement is inhibited by suppression of nitric oxide synthase activity in vivo

BACKGROUND

Acute flow-induced arterial dilation is mediated by nitric oxide (NO). The role of NO in chronic flow-induced adaptive enlargement is unknown. We assessed the role of NO in arterial adaptation to increased blood flow (BF).

METHODS

Iliac artery BF was increased in adult male rats by creating a left femoral arteriovenous fistula. Left iliac BF and diameter were measured, and wall shear stress was calculated. The effect of the NO synthase inhibitor N omega-nitro-L-arginine-methyl ester (L-NAME) was studied in arteriovenous fistula rats divided into three groups (group 1, vehicle, group 2, 0.5 mg/ml; group 3, 2 mg/ml) in drinking water. Arterial diameter, blood pressure, and medial cell density were assessed after 21 days. Left iliac cyclic guanosine monophosphate content was measured in an additional group of animals.

RESULTS

BF and wall shear stress in the left iliac artery increased fourfold immediately after arteriovenous fistula. Arterial enlargement was evident after 7 days, and wall shear stress normalized after 42 days. Flow-induced arterial enlargement was inhibited by both low- and high-dose L-NAME compared with control (analysis of variance p < 0.05). Blood pressure was elevated only in animals treated with high-dose L-NAME. Left iliac cyclic guanosine monophosphate content was lower in rats treated with L-NAME than in the control group (p < 0.05).

CONCLUSIONS

NO suppression by L-NAME inhibits flow-induced iliac artery enlargement in rats. This finding suggests that NO plays a role in flow-induced arterial remodeling.

Liposomal Alendronate Inhibits Systemic Innate Immunity and Reduces In-Stent Neointimal Hyperplasia in Rabbits

Background— Innate immunity is of major importance in vascular repair. The present study evaluated whether systemic and transient depletion of monocytes and macrophages with liposome-encapsulated bisphosphonates inhibits experimental in-stent neointimal formation.

Methods and Results— Rabbits fed on a hypercholesterolemic diet underwent bilateral iliac artery balloon denudation and stent deployment. Liposomal alendronate (3 or 6 mg/kg) was given concurrently with stenting. Monocyte counts were reduced by >90% 24 to 48 hours after a single injection of liposomal alendronate, returning to basal levels at 6 days. This treatment significantly reduced intimal area at 28 days, from 3.88±0.93 to 2.08±0.58 and 2.16±0.62 mm 2 . Lumen area was increased from 2.87±0.44 to 3.57±0.65 and 3.45±0.58 mm 2 , and arterial stenosis was reduced from 58±11% to 37±8% and 38±7% in controls, rabbits treated with 3 mg/kg, and rabbits treated with 6 mg/kg, respectively (mean±SD, n=8 rabbits/group, P <0.01 for all 3 parameters). No drug-related adverse effects were observed. Reduction in neointimal formation was associated with reduced arterial macrophage infiltration and proliferation at 6 days and with an equal reduction in intimal macrophage and smooth muscle cell content at 28 days after injury. Conversely, drug regimens ineffective in reducing monocyte levels did not inhibit neointimal formation.

Conclusions— Systemic transient depletion of monocytes and macrophages, by a single liposomal bisphosphonates injection concurrent with injury, reduces in-stent neointimal formation and arterial stenosis in hypercholesterolemic rabbits.

Nebivolol increases arterial distensibility in vivo

Arterial stiffness is a key determinant of cardiovascular risk in hypertensive patients. beta-Blockers appear to be less effective than other drugs in improving outcome in hypertensive patients, and a potential explanation may be that beta-blockers are less effective in reducing arterial stiffness. The aim of this study was to assess the direct effect of beta-blockade on pulse wave velocity (PWV), a robust measure of arterial distensibility, using a local, ovine, hind-limb model. In addition, we hypothesized that the vasodilating beta-blocker nebivolol, but not atenolol, would increase arterial distensibility in vivo. All studies were conducted in anesthetized sheep. PWV was recorded in vivo using a dual pressure-sensing catheter placed in the common iliac artery. Intraarterial infusion of nebivolol reduced PWV by 6+/-3% at the higher dose (P<0.001), but did not alter mean arterial pressure (change of -1+/-3 mm Hg, P=0.1). In contrast, atenolol had no effect on PWV (P=0.11) despite a small drop in mean pressure (change of -5+/-3 mm Hg, P<0.01). Infusion of glyceryl trinitrate led to a dose-dependent fall in PWV, and 2 nmol/min produced a similar reduction in PWV to the higher dose of nebivolol (500 nmol/min). The effect of nebivolol on PWV was significantly attenuated during coinfusion of N(G)-monomethyl-L-arginine (P=0.003) and also during coinfusion of butoxamine (P=0.02). These results demonstrate that nebivolol, but not atenolol, increases arterial distensibility. This effect of nebivolol is mediated through the release of NO via a beta2 adrenoceptor-dependent mechanism. Thus, nebivolol may be of benefit in conditions of increased large artery stiffness, such as isolated systolic hypertension.

Exercise attenuates alpha-adrenergic-receptor responsiveness in skeletal muscle vasculature

Attenuation of sympathetic vasoconstriction (sympatholysis) in working muscles during dynamic exercise is controversial. A potential mechanism is a reduction in alpha-adrenergic-receptor responsiveness. The purpose of this study was to examine alpha(1)- and alpha(2)-adrenergic-receptor-mediated vasoconstriction in resting and exercising skeletal muscle using intra-arterial infusions of selective agonists. Thirteen mongrel dogs were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs and a catheter in one femoral artery. The selective alpha(1)-adrenergic agonist (phenylephrine) or the selective alpha(2)-adrenergic agonist (clonidine) was infused as a bolus into the femoral artery catheter at rest and during mild and heavy exercise. Intra-arterial infusions of phenylephrine elicited reductions in vascular conductance of 76 +/- 4, 71 +/- 5, and 31 +/- 2% at rest, 3 miles/h, and 6 miles/h and 10% grade, respectively. Intra-arterial clonidine reduced vascular conductance by 81 +/- 5, 49 +/- 4, and 14 +/- 2%, respectively. The response to intra-arterial infusion of clonidine was unaffected by surgical sympathetic denervation. Agonist infusion did not affect either systemic blood pressure, heart rate, or blood flow in the contralateral iliac artery. alpha(1)-Adrenergic-receptor responsiveness was attenuated during heavy exercise. In contrast, alpha(2)-adrenergic-receptor responsiveness was attenuated even at a mild exercise intensity. These results suggest that the mechanism of exercise sympatholysis may involve reductions in postsynaptic alpha-adrenergic-receptor responsiveness.

Effects of halothane on left ventricular function and distribution of regional blood flow in dogs and primates

Left ventricular and regional vascular effects of halothane were assessed in dogs and primates in which coronary, mesenteric, renal, and iliac blood flows, arterial blood pressure, left ventricular diameter and pressure, dD/dt (i.e., the velocity of myocardial fiber shortening), and dP/dt were continuously measured in the control resting state, while the conscious animals were breathing O 2 , and during halothane-O 2 anesthesia maintained at 1% or at 2% for 90 minutes (separate experimental days). Halothane caused a concentration-dependent depression of myocardial contractility: (dP/dt)/P fell 68 ± 5% during 2% halothane anesthesia and left ventricular end-diastolic diameter rose. Halothane also caused a redistribution of regional blood flows. At a concentration of 1% halothane, the most intense vasodilatation occurred in the renal bed (renal resistance fell 46 ± 5%), but mesenteric resistance rose (42 ± 15%). With 1% halothane regional vascular resistances tended to rise with time, but with 2% halothane regional blood flows rose with time. A direct vasodilating action of halothane was observed following direct intra-arterial injection of the drug. Probably this action was responsible for the renal and iliac vasodilatations and for the opposition to the metabolically induced vasoconstriction in the coronary bed. Thus, the administration of the most commonly employed potent inhalation anesthetic, halothane, substantially alters myocardial contractility and regional blood flows and resistances. These effects are, in many instances, a function of the concentration of the anesthetic and the duration of its administration.

Local intramural delivery of L-arginine enhances nitric oxide generation and inhibits lesion formation after balloon angioplasty

BACKGROUND

Long-term oral administration of L-arginine has been shown to enhance production of nitric oxide (NO) and to reduce lesion formation. The goal of this study was to determine whether local intramural administration of L-arginine could enhance NO generation and reduce intimal thickening.

METHODS AND RESULTS

New Zealand White rabbits (n = 27) received a 1% cholesterol diet. For the short-term study, after 1 week of diet, both iliac arteries were balloon injured. Four weeks later, vasoreactivity was assessed angiographically during infusion of acetylcholine (Ach) before and after delivery of L-arginine or saline into the right or left iliac artery (800 mg/5 mL; 0.2 mL/min, 15 minutes) by use of a local drug-delivery balloon. Vessels were then harvested for measurements of NO. For the long-term study, after balloon injury, drugs were delivered as above into the iliac arteries. Two and 4 weeks after L-arginine delivery, vasoreactivity was determined. Subsequently, the iliac arteries were harvested for histomorphometric analysis and measurements of NO. In the short-term study, local delivery of L-arginine restored endothelium-dependent vasodilatation (Ach 10(-5) mol/L; L-arginine +35 +/- 10%; saline -14 +/- 5%; P < .001) and enhanced local production of nitrogen oxides (L-arginine 152 +/- 28; saline 78 +/- 12 nmol/L per milligram of tissue per hour; P < .04). In the long-term study, local administration of L-arginine enhanced vascular NO production as long as 1 week after the injury (L-arginine 394.4 +/- 141.6; saline 86.3 +/- 34.3 nmol/L per milligram of tissue per hour; P < .01) and reduced intimal thickening 4 weeks later (intima/ media ratio: L-arginine 0.56 +/- 0.1; saline 1.40 +/- 0.2; P < .001), largely due to suppression of macrophage accumulation.

CONCLUSIONS

A single intramural administration of L-arginine enhances vascular NO generation and inhibits lesion formation. Local augmentation of NO production at the site of balloon angioplasty may be a novel strategy to prevent restenosis.

Heterogeneity of the vasoconstrictor effect of vasopressin in septic shock*

OBJECTIVE

To determine whether pressor doses of vasopressin impair organ blood flow in endotoxic shock.

DESIGN

Graded doses of vasopressin or phenylephrine, starting at the clinically recommended doses for pressure support in septic shock, were intravenously infused during endotoxic shock.

SETTING

University hospital surgical research laboratory.

SUBJECTS

Twelve random-bred female Yorkshire pigs.

INTERVENTIONS

We measured mean arterial pressure, cardiac output, heart rate, pulmonary artery occlusion pressure, and carotid, mesenteric, renal, and iliac blood flows.

MEASUREMENTS AND MAIN RESULTS

Low doses of vasopressin (typically used in the clinical management of septic shock) raised arterial pressure by increasing systemic vascular resistance without a significant preferential effect in the circulations measured. However, moderately greater doses of vasopressin had a very heterogeneous vasoconstrictor action; although there was no significant vasoconstriction in the carotid and iliac circulations, mesenteric and renal blood flows decreased markedly. Furthermore, at pressor doses vasopressin improved cerebral perfusion.

CONCLUSIONS

The vasoconstrictor action of exogenous low-dose vasopressin in endotoxic shock does not impair blood flow to any of the vascular beds examined. However, moderately higher doses of vasopressin may induce ischemia in the mesenteric and renal circulations. The data indicate that the safe dose range for exogenous vasopressin in septic shock is narrow and support the current practice of fixed low-dose administration, generally 0.04 units/min and in no case exceeding 0.1 units/min.

Pharmacologic treatment of intimal hyperplasia after metallic stent placement in the peripheral arteries. An experimental study

RATIONALE AND OBJECTIVES

To evaluate the efficacy of oral administration of cilostazol, an antithrombotic agent, for the prevention of thrombotic occlusion and intimal hyperplasia after stenting.

METHODS

Single-bodied Z-stents were placed in the iliac arteries of 23 dogs. Before stenting, an embolizing coil was introduced into the right femoral artery to reduce blood flow in the right iliac artery. Eleven dogs were given cilostazol orally, and the other 12 were unmedicated as a control group. The dogs were killed at 4, 13, and 24 weeks.

RESULTS

Intraluminal narrowing due to thrombus was observed in 25% of dogs in the control group but in none of the dogs in the cilostazol group. The thickness of the neointima was significantly thinner in the cilostazol group than in the control group at 24 weeks on the noncoiled side (P < 0.05), and at 4 and 24 weeks on the coiled side (P < 0.01).

CONCLUSIONS

These results suggest that oral administration of cilostazol is an effective method of preventing thrombotic occlusion and intimal hyperplasia after stenting.

Sympathetic vasoconstriction in active skeletal muscles during dynamic exercise

Studies utilizing systemic administration of alpha-adrenergic antagonists have failed to demonstrate sympathetic vasoconstriction in working muscles during dynamic exercise. The purpose of this study was to examine the existence of active sympathetic vasoconstriction in working skeletal muscles by using selective intra-arterial blockade. Six mongrel dogs were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs and with a catheter in one femoral artery. All dogs ran on a motorized treadmill at three intensities on separate days. After 2 min, the selective alpha 1-adrenergic antagonist prazosin (0.1 mg) was infused as a bolus into the femoral artery catheter. At mild, moderate, and heavy workloads, there were immediate increases in iliac conductance of 76 +/- 7, 54 +/- 11, and 22 +/- 6% (mean +/- SE), respectively. Systemic blood pressure and blood flow in the contralateral iliac artery were unaffected. These results demonstrate that there is sympathetic vasoconstriction in active skeletal muscles even at high exercise intensities.

Cardiovascular responses to long-term blockade of nitric oxide synthesis

The goal of this study was to determine if there is a basal release of nitric oxide that affects long-term arterial pressure regulation in dogs. Studies were conducted over a 23-day period in eight conscious dogs with indwelling catheters. Nitric oxide synthesis was blocked by continuous intravenous infusion of nitro-L-arginine-methyl ester at 37.1 nmol/kg per minute for 11 days. Arterial pressure increased to 120 +/- 4% of control on the first day, decreased for a few days, and then increased to a maximum value of 122 +/- 6% of control on day 7. Bradycardia was sustained throughout the entire nitro-arginine period. Blockade of nitric oxide synthesis was evidenced by attenuated pressure and flow responses to systemic acetylcholine infusion. The pressor response to phenylephrine was increased for only 1 day, and the hypotensive effects of nitroprusside were enhanced. Also, the variability of arterial pressure was significantly increased during nitro-arginine. Sodium and water balances were positive the first day of nitro-arginine infusion but were unchanged for the entire nitro-arginine period. In conclusion, the data suggest that blockade of the basal release of nitric oxide in dogs causes an increase in the long-term level of arterial pressure without any sustained sodium or water retention.