Adventitial ablation technique that permits the assessment of adventitial-dependent contribution to microvascular contractile function

Resistance arteries have been implicated as a major contributing factor in the sequela of disease conditions such as hypertension and diabetes and, as such, are a major focus of cardiovascular research. The paracrine influence of the intimal endothelial layer of resistance arteries is well established. Considering the growing body of evidence substantiating a functionally relevant vascular adventitia, in this study we have established a technique that permits determination of the functional influence of the adventitial layer on resistance artery tone. Isolating adventitial-dependent function, analogous to isolating endothelial function, has potentially significant implications for studying the as yet unexplored role of the microvascular adventitial layer in modulating acute vascular contractile function.

The relationship between oxidised LDL, endothelial progenitor cells and coronary endothelial function in patients with CHD

Objective

The balance between coronary endothelial dysfunction and repair is influenced by many protective and deleterious factors circulating in the blood. We studied the relationship between oxidised low-density lipoprotein (oxLDL), circulating endothelial progenitor cells (EPCs) and coronary endothelial function in patients with stable coronary heart disease (CHD).

Methods

33 patients with stable CHD were studied. Plasma oxLDL was measured using ELISA, coronary endothelial function was assessed using intracoronary acetylcholine infusion and EPCs were quantified using flow cytometry for CD34⁺/KDR⁺ cells.

Results

Plasma oxLDL correlated positively with the number of EPCs in the blood (r=0.46, p=0.02). There was a positive correlation between the number of circulating EPCs and coronary endothelial function (r=0.42, p=0.04). There was no significant correlation between oxLDL and coronary endothelial function.

Conclusions

Plasma levels of oxLDL are associated with increased circulating EPCs in the blood of patients with CHD, which may reflect a host-repair response to endothelial injury. Patients with stable CHD had a high prevalence of coronary endothelial dysfunction, which was associated with lower numbers of circulating EPCs, suggesting a mechanistic link between endothelial dysfunction and the pathogenesis of atherosclerosis.

Perivascular mast cells regulate vein graft neointimal formation and remodeling

Objective. Emerging evidence suggests an important role for mast cells in vein graft failure. This study addressed the hypothesis that perivascular mast cells regulate in situ vascular inflammatory and proliferative responses and subsequent vein graft neointimal lesion formation, using an optimized local mast cell reconstitution method.

Methods and Results. Neointimal hyperplasia was induced by insertion of a vein graft into the right carotid artery in wild type and mast cell deficient Kit^{W−sh/W−sh} mice. In some experiments, mast cells were reconstituted systemically (tail vein injection of bone marrow-derived mast cells) or locally (directly into the right neck area) prior to vein grafting. Vein graft neointimal lesion formation was significantly (P < 0.05) reduced in Kit^{W−sh/W−sh} mice. Mast cell deficiency reduced the number of proliferating cells, and inhibited L-selectin, CCL2, M-CSF and MIP-3α expression in the vein grafts. Local but not systemic mast cell reconstitution restored a perivascular mast cell population that subsequently promoted neointimal formation in mast cell deficient mice.

Conclusion. Our data demonstrate that perivascular mast cells play a key role in promoting neointima formation by inducing local acute inflammatory and proliferative responses. These results suggest that ex vivo intraoperative targeting of mast cells may have therapeutic potential for the prevention of pathological vein graft remodeling.

Protective effects of nanoparticulate coenzyme Q10 and curcumin on inflammatory markers and lipid metabolism in streptozotocin-induced diabetic rats: a possible remedy to diabetic complications

Diabetes and its complications have been linked to increased levels of free radicals and systemic pro-inflammatory cytokines and to an altered lipid profile. Coenzyme Q10 and curcumin are potent antioxidants and anti-inflammatory agents but are underutilized clinically because of their poor bioavailability when administered orally. We have recently developed poly(D,L-lactic-co-glycolic acid)-based nanoparticles in which we have encapsulated coenzyme Q10 and curcumin to increase the oral bioavailability and therapeutic efficacy of the antioxidant molecules. These formulations when tested in streptozotocin-induced diabetic rats demonstrated protective effects on inflammatory markers as well as lipid metabolism. Coenzyme Q10 nanoparticulates reduced only C-reactive protein levels, whereas curcumin nanoparticles reduced levels of C-reactive protein, interleukin-6 and tumor necrosis factor-α. Administration of both nanoparticulates resulted in significant reductions of plasma triglycerides and total cholesterol and an increase in high-density lipoprotein cholesterol. Together, these data indicate the promise of coenzyme Q10 and curcumin in diabetes when delivered through nanoparticulate formulations.

Abstract 554: Rabbit Arteriovenous Fistula Model and Identification of a Therapeutic Agent to Increase Fistula Patency

An arteriovenous fistula (AVF) is a vein graft which is created to permit vascular access allowing haemodialysis to be performed in renal failure patients. AVF using native tissues is the preferred surgical option; however AVF are associated with failure rates as high as 50% at 6 months. Failure is principally due to vascular cell proliferation, leading to the development of neointima causing stenosis and impaired blood flow. The aims of this study were to 1) develop a rabbit model of AVF remodelling, 2) investigate the contribution of cannulation injury in AVF remodelling and 3) identify a potential therapeutic which could be delivered topically to reduce AVF stenosis.

The proposed model was an AVF created between the femoral artery and vein of a New Zealand white rabbit. Briefly, the fistula was fashioned by creating a side to side anastomosis, followed by occlusion of the distal vein. Over phase I of the study (days 1-28) maturation of the vein was evident by the presence of a pulsatile flow in the venous branch of the AVF, as well as a significant increase in venous blood velocity from 55.2± 6.0cm/s at day 10 to 68.4± 3.1cm/s by day 28 (p<0.05). A degree of medial/adventitial thickening was also evident at this time point. Rabbits were assigned to 3 groups for phase II of the study (days 29-56). The control group received no intervention, the injury group received cannulation to the AVF every 48-72 hrs, and the injury plus diclofenac group received the same frequency of injury and topical diclofenac (1.16% of diclofenac diethylammonium) twice a day, 5 days a week. In the control group, vein wall width increased significantly from 10.5± 0.9μM in the counter lateral vein to 16.6± 1.6μM in the AVF (p<0.05). Cannulation injury caused vein wall thickness to significantly increase to 46.8± 5.7μM (p<0.05). With diclofenac treatment, vein wall width decreased significantly to 15.8± 1.8μM (p<0.05).

These results show for the first time that cannulation injury significantly contributes to AVF remodelling in vivo . Topical treatment with diclofenac, which has anti-inflammatory as well as anti-proliferative properties, appears to reduce injury driven remodelling within AVF. Therefore, topical diclofenac could be used as a prophylactic treatment to reduce vascular stenosis in AVF.

Succinobucol-eluting stents increase neointimal thickening and peri-strut inflammation in a porcine coronary model

Objective

The aim of this study was to assess the efficacy of stent-based delivery of succinobucol alone and in combination with rapamycin in a porcine coronary model. Background: Current drugs and polymers used to coat coronary stents remain suboptimal in terms of long term efficacy and safety. Succinobucol is a novel derivative of probucol with improved antioxidant and anti-inflammatory properties.

Methods

Polymer-free Yukon stents were coated with 1% succinobucol (SucES), 2% rapamycin (RES), or 1% succinobucol plus 2% rapamycin solutions (SucRES) and compared with a bare metal stent (BMS).

Results

The in vivo release profile of SucES indicated drug release up to 28 days (60% drug released at 7 days); 41 stents (BMS, n = 11; SucES, n =10; RES, n = 10; SucRES, n = 10) were implanted in the coronary arteries of 17 pigs. After 28 days, mean neointimal thickness was 0.31 ± 0.14 mm for BMS, 0.51 ± 0.14 mm for SucES, 0.19 ± 0.11 mm for RES, and 0.36 ± 0.17 mm for SucRES (P < 0.05 for SucES vs. BMS). SucES increased inflammation and fibrin deposition compared with BMS (P < 0.05), whereas RES reduced inflammation compared with BMS (P < 0.05).

Conclusion

In this model, stent-based delivery of 1% succinobucol using a polymer-free stent platform increased neointimal formation and inflammation following coronary stenting. © 2012 Wiley Periodicals, Inc.

Abstract 317: Mast Cells Do Not Contribute to a Reduction in Vein Graft Neointima in the C-kit Mutant KitW-sh/w-sh Mice

Background: Recent evidence suggests mast cells are involved in the development of vascular diseases such as atherosclerosis. The presence of mast cells in vein grafts led us to hypothesise that mast cells may regulate the extent of vein graft neointima hyperplasia. In this study, we employed the Kit W-sh/W-sh mouse strain, a widely accepted mast cell deficient mouse model induced by a spontaneous inversion mutation in the transcriptional regulatory elements of the c-kit gene.

Methods: The vein graft surgery was performed by inserting the inferior thoracic vena cava from the donor mouse into the common carotid artery of the littermate recipient. Vein grafts were harvested at 4 weeks and fixed with 4% formaldehyde for histology. In some groups, Kit W-sh/W-sh mice were reconstituted with cultured mast cells either systemically or locally 9 weeks before vein graft surgery. For primary cell culture studies, aortic endothelial cells and smooth muscle cells were isolated by collagenase digestion method and cultured in standard conditions.

Results: Kit w-sh/w-sh vein grafts had a significant reduction (33%; p<0.05) in neointima area, compared to the wild type controls. The cellular composition of the Kit w-sh/w-sh neointima was similar to the wild type controls, most cells being smooth muscle alpha-actin positive. Neither the systemic nor local reconstitution of mast cells restored the neointima area to the wild type level. In the primary cell culture, Kit w-sh/w-sh vascular cells showed less migrating activity in the scratch wound healing test, which may account for the decrease in neointima formation.

Conlusion: This study suggests that it is not the deficiency of mast cells in the Kit W-sh/W-sh mice which accounts for the reduction in neointima formation in vein grafts. Other cell types affected by the c-kit mutation may be responsible for the altered neointima formation in Kit W-sh/W-sh mice.

The effect of reactive oxygen species on whole blood aggregation and the endothelial cell-platelet interaction in patients with coronary heart disease

Background

The effect of reactive oxygen species (ROS) on platelet function in coronary heart disease (CHD) is complex and poorly defined. Platelet aggregation studies in healthy volunteers have demonstrated contrasting results when platelets are exposed to ROS. We investigated the effect of ROS on whole blood aggregation (WBA) and the endothelial cell-platelet interaction in patients with CHD.

Methods and Results

ROS generated by xanthine and xanthine oxidase caused a concentration-dependent inhibition of WBA in blood from healthy donors and patients with CHD. In patients with CHD, 100 μM xanthine and 100 mU/ml xanthine oxidase inhibited WBA in response to 3 μg/ml collagen by 28.9% (95% CI 15.9%-41.8%, p < 0.001) and in response to 5 μM ADP by 36.0% (95% CI 9.6%-62.4%, p = 0.005). Using nitrotyrosine expression, platelets isolated from patients with CHD were found to be susceptible to peroxynitrite damage. The addition of 1 × 10⁵ cultured endothelial cells inhibited WBA in response to 3 μg/ml collagen by 31.2% (95% CI 12.2%-50.2%, p < 0.05) and in response to 5 μM ADP by 31.6% (95% CI 2.5-60.7%, p < 0.05). Addition of xanthine and xanthine oxidase did not alter this effect, however pre-treatment of endothelial cells with a nitric oxide synthase inhibitor (L-NAME) partly reversed the inhibition.

Conclusion

ROS inhibit WBA in blood from patients with CHD. Whilst endothelial cells also inhibit WBA, the effect is attenuated by L-NAME, suggesting that nitric oxide is likely to remain an important protective mechanism against thrombosis in CHD.

Tissue localization of nanoparticles is altered due to hypoxia resulting in poor efficacy of curcumin nanoparticles in pulmonary hypertension

The present study is an attempt to leverage therapeutic benefits of curcumin in pulmonary hypertension by encapsulating it in biodegradable poly(lactide-co-glycolic) acid nanoparticles. Pulmonary hypertension is induced in experimental animals by subjecting them to chronic hypoxic conditions. The ability of curcumin encapsulated nanoparticles to manage pulmonary hypertension is measured by right ventricular hypertrophy, haematocrit, vascular remodelling and target tissue levels of curcumin. Further, single oral dose tissue distribution of the nanoparticulate curcumin was also assessed under normoxic and hypoxic conditions. Orally administered nanoparticulate curcumin failed to offer any protection against hypoxia induced pulmonary hypertension as indicated by insignificant changes in right ventricular hypertrophy and vascular remodelling that are similar to untreated groups. A significant difference in the target tissue levels was observed between normoxic vs. hypoxic rats. The study suggests that hypoxia has a major role in the particle localization in lungs probably due to the altered blood flow, increased barrier properties of the lung vasculature and decreased endocytosis. The target tissue levels of curcumin under hypoxia are much lower to that achieved in normoxic rats probably due to difference in particle dynamics, resulting in the failure of treatment.

Tetrahydrobiopterin analogues with NO-dependent pulmonary vasodilator properties

Reduced NO levels due to the deficiency of tetrahydrobiopterin (BH(4)) contribute to impaired vasodilation in pulmonary hypertension. Due to the chemically unstable nature of BH(4), it was hypothesised that oxidatively stable analogues of BH(4) would be able to support NO synthesis to improve endothelial dysfunction in pulmonary hypertension. Two analogues of BH(4), namely 6-hydroxymethyl pterin (HMP) and 6-acetyl-7,7-dimethyl-7,8-dihydropterin (ADDP), were evaluated for vasodilator activity on precontracted rat pulmonary artery rings. ADDP was administered to pulmonary hypertensive rats, followed by measurement of pulmonary vascular resistance in perfused lungs and eNOS expression by immunohistochemistry. ADDP and HMP caused significant relaxation in vitro in rat pulmonary arteries depleted of BH(4) with a maximum relaxation at 0.3μM (both P<0.05). Vasodilator activity of ADDP and HMP was completely abolished following preincubation with the NO synthase inhibitor, L-NAME. ADDP and HMP did not alter relaxation induced by carbachol or spermine NONOate. BH(4) itself did not produce relaxation. In rats receiving ADDP 14.1mg/kg/day, pulmonary vasodilation induced by calcium ionophore A23187 was augmented and eNOS immunoreactivity was increased. In conclusion, ADDP and HMP are two analogues of BH(4), which can act as oxidatively stable alternatives to BH(4) in causing NO-mediated vasorelaxation. Chronic treatment with ADDP resulted in improvement of NO-mediated pulmonary artery dilation and enhanced expression of eNOS in the pulmonary vascular endothelium. Chemically stable analogues of BH(4) may be able to limit endothelial dysfunction in the pulmonary vasculature.

Inhibition of inducible nitric oxide synthase promotes vein graft neoadventitial inflammation and remodelling

BACKGROUND

Grafting veins into the arterial circulation causes endothelial damage and neointimal hyperplasia. However, the remodelling of vein grafts and the contribution of the endothelium is not well understood. Since nitric oxide (NO) has a crucial role in vascular function, we investigated the importance of NO synthases (NOSs) in vein graft re-endothelialization and remodelling in this study.

METHODS AND RESULTS

Mouse isogenic vena cava was grafted into the carotid artery. Progressive remodelling of the grafted veins was evidenced by re-endothelialization at 2 weeks and subsequent appearance of vasomotor function at 4 weeks. Pharmacological inhibition of inducible NOS (iNOS) with the specific inhibitor 1400W, administered between 2 and 4 weeks after grafting, when re-endothelialization was complete, resulted in neoadventitial inflammation, neoadventitial thickening and impaired functional remodelling.

CONCLUSION

Completion of re-endothelialization is pivotal in vein graft remodelling in the mouse and is associated with a series of changes in inflammation, proliferation and initiation of vascular functional remodelling. After re-endothelialization, iNOS upregulation may be an important mechanism to prevent secondary neoadventitial inflammation and preserve ongoing functional remodelling. iNOS activity could therefore be beneficial for long-term patency of the vein graft.

Peroxynitrite stimulates pulmonary artery endothelial and smooth muscle cell proliferation: involvement of ERK and PKC

BACKGROUND

There is evidence that peroxynitrite is generated in pulmonary hypertension and we have therefore investigated whether peroxynitrite can cause proliferation of pulmonary artery cells.

METHODS

Bovine pulmonary artery endothelial (PAEC) and smooth muscle cells (PASMC) were exposed to peroxynitrite solution or to the peroxynitrite generating compound, 3-morpholinosydnonimine (SIN-1). Vascular cell proliferation was determined by cell count and (3)H-thymidine incorporation. Protein biochemistry was by western blot analysis.

RESULTS

Transient exposure to peroxynitrite stimulated the proliferation of PASMC (peroxynitrite 0.2 nM-2 μM) and PAEC (peroxynitrite 0.2 μM). Peroxynitrite 0.2 μM stimulated DNA synthesis in PASMC cell by 200 ± 22% and in PAEC by 137 ± 4%. DNA synthesis in PAEC and PASMC was also stimulated by the peroxynitrite generator SIN-1 2 μM. Cell proliferation was accompanied by activation of ERK, which peaked at 15 min and remained elevated for 12 h in PASMC. However peroxynitrite at the concentrations used in this study did not activate the stress pathways p38 mitogen activated protein kinase (MAPK) or Jun N-terminal kinase (JNK). Peroxynitrite-induced proliferation and ERK phosphorylation in PASMC were abolished by the peroxynitrite scavenger ebselen 5 μM. Peroxynitrite-induced proliferation and extracellular signal-regulated kinase (ERK) phosphorylation in PASMC was prevented by selective inhibitors of MAP kinase kinase (MEK) (U0126 5 μM, PD98059 50 μM), Raf-1 (Raf-1 kinase inhibitor 10 μM), Ras (FPT II and FPT III 10 μM) and protein kinase C (PKC) (GF109203X 10 μM). Inhibition of EGF or PDGF receptor signaling using AG-1296, AG-1478 or imatinib prevented peroxynitrite-induced cell proliferation and ERK phosphorylation in PASMC.

CONCLUSION

Peroxynitrite can stimulate proliferation of pulmonary artery cells, involving ERK, PKC and EGF or PDGF receptors.

The sphingosine kinase inhibitor N,N-dimethylsphingosine inhibits neointimal hyperplasia

BACKGROUND AND PURPOSE

Sphingosine-1-phosphate and its receptors may be involved in vascular smooth muscle cell (VSMC) proliferation following vascular injury. Here, we evaluate the effect of d-erythro-N,N-dimethylsphingosine (DMS), a sphingosine kinase (SK) inhibitor, on VSMC proliferation, apoptosis and neointimal formation.

EXPERIMENTAL APPROACH

Growth responses in vitro to fetal calf serum (FCS) were measured by [(3)H]-thymidine incorporation and extracellular signal-regulated kinase-1/2 (ERK-1/2) activation in quiescent primary cultures of porcine VSMC in the presence and absence of various concentrations of the SK inhibitor DMS. In vivo treatment with DMS was delivered with a local endoluminal catheter, following balloon injury of coronary arteries. The artery intimal formation was investigated by angiography, myography and histomorphometry.

KEY RESULTS

In vitro experiments indicated that DMS induced a dose-dependent reduction in [(3)H]-thymidine incorporation and ERK-1/2 activation via a protein kinase C (PKC) independent mechanism with an IC(50) value of 12 +/- 6 and 15 +/- 10 microM respectively. DMS also reduced Akt signalling. Four weeks following in vivo delivery of DMS, complete functional endothelial regeneration was observed in all treatment groups, with significant reduction of intimal formation (vehicle 23.7 +/- 4.6% vs. DMS infusion 8.92 +/- 2.9%, P < 0.05).

CONCLUSIONS AND IMPLICATIONS

Taken together, these results demonstrate that local administration of the SK inhibitor, DMS, reduced neointimal formation, and this effect could involve inhibition of ERK-1/2 and Akt signalling, and modulation of smooth muscle growth.

Nitric oxide synthases in infants and children with pulmonary hypertension and congenital heart disease

Rationale

Nitric oxide is an important regulator of vascular tone in the pulmonary circulation. Surgical correction of congenital heart disease limits pulmonary hypertension to a brief period.

Objectives

The study has measured expression of endothelial (eNOS), inducible (iNOS), and neuronal nitric oxide synthase (nNOS) in the lungs from biopsies of infants with pulmonary hypertension secondary to cardiac abnormalities (n = 26), compared to a control group who did not have pulmonary or cardiac disease (n = 8).

Methods

eNOS, iNOS and nNOS were identified by immunohistochemistry and quantified in specific cell types.

Measurements and main results

Significant increases of eNOS and iNOS staining were found in pulmonary vascular endothelial cells of patients with congenital heart disease compared to control infants. These changes were confined to endothelial cells and not present in other cell types. Patients who strongly expressed eNOS also had strong expression of iNOS.

Conclusion

Upregulation of eNOS and iNOS occurs at an early stage of pulmonary hypertension, and may be a compensatory mechanism limiting the rise in pulmonary artery pressure.

Understanding organic nitrates--a vein hope?

The organic nitrate drugs, such as glyceryl trinitrate (GTN; nitroglycerin), are clinically effective in angina because of their dilator profile in veins and arteries. The exact mechanism of intracellular delivery of nitric oxide (NO), or another NO-containing species, from these compounds is not understood. However, mitochondrial aldehyde dehydrogenase (mtALDH) has recently been identified as an organic nitrate bioactivation enzyme. Nitrate tolerance, the loss of effect of organic nitrates over time, is caused by reduced bioactivation and/or generation of NO-scavenging oxygen-free radicals. In a recent issue of the British Journal of Pharmacology, Wenzl et al. show that guinea-pigs, deficient in ascorbate, also have impaired responsiveness to GTN, but nitrate tolerance was not due to ascorbate deficiency that exhibited divergent changes in mtALDH activity. Thus, the complex function of mtALDH appears to be the key to activation of GTN, the active NO species formed and the induction of tolerance that can limit clinical effectiveness of organic nitrate drugs.

Inhibition of p38 MAPK reverses hypoxia-induced pulmonary artery endothelial dysfunction

Hypoxia-induced endothelial dysfunction plays a crucial role in the pathogenesis of hypoxic pulmonary hypertension. p38 MAPK expression is increased in the pulmonary artery following hypoxic exposure. Recent evidence suggests that increased p38 MAPK activity is associated with endothelial dysfunction. However, the role of p38 MAPK activation in pulmonary artery endothelial dysfunction is not known. Sprague-Dawley rats were exposed to 2 wk hypobaric hypoxia, which resulted in the development of pulmonary hypertension and vascular remodeling. Endothelium-dependent relaxation of intrapulmonary vessels from hypoxic animals was impaired due to a reduced nitric oxide (NO) generation. This was despite increased endothelial NO synthase immunostaining and protein expression. Hypoxia exposure increased superoxide generation and p38 MAPK expression. The inhibition of p38 MAPK restored endothelium-dependent relaxation, increased bioavailable NO, and reduced superoxide production. In conclusion, the pharmacological inhibition of p38 MAPK was effective in increasing NO generation, reducing superoxide burden, and restoring hypoxia-induced endothelial dysfunction in rats with hypoxia-induced pulmonary hypertension. p38 MAPK may be a novel target for the treatment of pulmonary hypertension.

Inhibition of non-Ras protein farnesylation reduces in-stent restenosis

Ras has a key role in relation to cell proliferation, survival and migration and requires farnesylation for full activity. The effects of a Ras farnesyl transferase inhibitor, FPT III on human atherosclerotic vascular smooth muscle (VSM) cells proliferation and p42/p44 mitogen-activated protein kinase (p42/p44 MAPK) activity was measured. In addition the ability of FPT III to modify the development of neointimal growth was tested in cultured human arteries and in a rabbit model of in-stent restenosis. In human VSM cells FPT III (25 microM) inhibited FCS-stimulated cell proliferation through a ras-dependent mechanism (after 18 h exposure) and also a novel ras-independent mechanism (following 15 min exposure). FPT III incubation (18 h) inhibited platelet-derived growth factor (PDGF)-stimulated p42/p44 MAPK activation and p21 Ras membrane localization, whereas 15 min incubation had no effect on the activation of p42/p44 MAPK in response to PDGF (added at 18 h) or on membrane p21 Ras localization (measured at 18 h). In cultured human atherosclerotic arteries, the presence of 25 microM FPT III significantly reduced neointimal growth. In vivo, 15 min local infusion of 25 microM FPT III significantly reduced in-stent restenosis 28 days later without affecting vascular function in normal rabbit artery. This study demonstrates that brief administration of a farnesyl transferase inhibitor reduced in-stent restenosis in a rabbit model without deleterious effects on vascular function or endothelial regrowth. Acute application of FPT III was found to act through a novel mechanism to inhibit smooth muscle cell proliferation via a non-ras pathway, which may contribute to the prevention of in-stent restenosis.

Selective arterial dilatation by glyceryl trinitrate is not associated with nitric oxide formation in vitro

AIMS

Glyceryl trinitrate (GTN) is the most commonly used anti-anginal agent, yet its mechanism of action has still to be fully established. Release of nitric oxide (NO) and the selectivity of GTN in the venous system are believed to be crucial to this drug's anti-anginal action.

METHODS

Rat superior mesenteric arteries and renal veins were mounted in a wire myograph with an intraluminal NO microsensor.

RESULTS

In the superior mesenteric arteries, GTN (1 nM to 10 microM) produced a dose-dependent vasodilatation without NO release, except at concentrations supramaximal for relaxation. GTN was found to be markedly less potent in a wide range of veins tested, and lowering the oxygen concentrations in the myograph to that of the venous system did not improve the venodilator activity of GTN.

CONCLUSION

This is the first time that NO release from GTN has been monitored electrochemically in real time, simultaneously with vasodilatation. Unlike the endothelium-dependent vasodilator carbachol, NO could only be measured at concentrations of GTN that are supramaximal for relaxation. GTN was found to be arterioselective in vitro, even when oxygen levels were lowered to mimic those of the venous system in vivo.

Endothelial, inducible and neuronal nitric oxide synthase in congenital pulmonary lymphangiectasis

Abnormal growth and development of lymphatic pulmonary structures leads to severe hypoxia in congenital pulmonary lymphangiectasis (CPL). This case study aims to determine the cellular source and topographical distribution of the nitric oxide synthases in CPL. It studies the post mortem tissue of a term newborn with the clinical course and histological findings of CPL and three controls without pulmonary pathology. It was found that endothelial cells of pulmonary arteries and lymphatic structures stained significantly more for endothelial nitric oxide synthase protein in the CPL patient compared to the controls. The authors conclude that synthesis of endothelial nitric oxide synthase is upregulated in vascular and lymphatic endothelial cells in congenital pulmonary lymphangiectasis.

Locally administered antiproliferative drugs inhibit hypercontractility to serotonin in balloon-injured pig coronary artery

Although drugs such as sirolimus and paclitaxel are effective in reducing restenosis, their effects on vascular function are often overlooked. In this study, we have examined the effects of local delivery of several anti-restenotic drugs given in vivo after balloon injury on in vitro vascular contraction and relaxation 28 days after injury. Paclitaxel (50 microM), the farnesyl protein transferase inhibitor L744 (25 microM), sirolimus (25 microM) and Van 10/4 (decahydro-1,1,4,7-tetramethyl-1H-cycloprop[e]azulen-4-o-[2-(3-methylpent-2-enoyl)-fucopyranoside]; 25 microM) were delivered to porcine coronary arteries in vivo and the arteries removed 28 days later. Contractions to KCl and 5-hydroxytryptamine (5-HT) and relaxations to calcimycin and 3-morpholinosydnonimine (SIN-1) were measured in control (LCx) and balloon-injured (LAD) rings. In vehicle-infused coronary arteries, contraction to KCl and 5-HT was significantly enhanced 28 days after balloon injury, while the response to calcimycin had recovered fully, indicating endothelial regrowth. The response to SIN-1 was unchanged. None of the four drugs tested had any effect on the enhanced response to KCl 28 days after injury or on recovery of the calcimycin response. The hyper-responsiveness to 5-HT was eliminated by sirolimus, Van 10/4 and L744, but not paclitaxel. This study demonstrates that local drug infusion with structurally different antiproliferative drugs at the time of balloon angioplasty does not affect endothelial recovery and may in some cases prevent hyper-responsiveness to constrictor agents.

Location and function of VPAC1, VPAC2 and NPR-C receptors in VIP-induced vasodilation of porcine basilar arteries

Vasoactive intestinal peptide (VIP) is a vasodilator peptide present in cerebrovascular nerves. Vasoactive intestinal peptide can activate VPAC1, VPAC2 and the NPR-C receptor. This study sought to determine the receptors involved in VIP-induced vasodilation of porcine basilar arteries. Porcine basilar arteries contained the messenger ribonucleic acid of all three receptors. Immunocytochemical analysis of porcine basilar arteries revealed that the VPAC1 receptor is expressed on the endothelium, VPAC2 on the outer layers of the media and the NPR-C receptor throughout the artery, including nerves. Vasodilator responses to all receptor agonists showed that the receptors are functional. The vasodilator response to the VPAC1 receptor agonist was inhibited by L-NAME and abolished by endothelial denudation. Vasodilation induced by Ro-25-1553, the VPAC2 agonist, was unaffected by NOS inhibition or removal of the endothelium. Activation of the NPR-C receptor produced a vasodilation, which was susceptible to NOS inhibition and independent of endothelium. The vasodilator response to electrical stimulation at 20 Hz was attenuated by PG-99-465, the VPAC2 antagonist. This study shows that all known VIP receptors are involved in VIP-mediated vasodilation of porcine basilar arteries. The VPAC1 receptor is located on the endothelium and elicits vasodilation by generating nitric oxide (NO). The VPAC2 receptor is mainly expressed in the outer layers of the smooth muscle and induces vasodilation independently of NO in response to VIP released from intramural nerves. The NPR-C receptor produces NO-dependent vasodilation independently of the endothelium by stimulation of nNOS in intramural nerves.

PDGF-induced signaling in proliferating and differentiated vascular smooth muscle: Effects of altered intracellular Ca regulation

OBJECTIVE

Platelet-derived growth factor-BB (PDGF)-induced intracellular signaling is involved in phenotypic modulation of vascular smooth muscle (VSM). This study has examined the PDGF-induced Ca2+ increase and the resultant effect on signaling pathways in proliferative compared with fully differentiated VSM.

METHODS

PDGF-induced changes in Ca2+ were measured in portal vein (PV) myocytes from 2-4-day-old (proliferating), compared to 6-week-old (differentiated), Sprague Dawley rats. Phospholipase C (PLC)gamma expression and activation of extracellular signal-regulated kinase (ERK) 1/2 was determined by immunoblotting or confocal immunolabelling. Activation of the Ca(2+)-dependent transcription factor, nuclear factor of activated T-cells (NFATc), was assessed by electromobility shift assay.

RESULTS

PDGF increased the intracellular Ca2+ concentration in differentiated, but not in proliferating, PV myocytes. This is probably due to very low expression of PLC(gamma) in proliferating PV. In 6-week-old PV, PDGF stimulation induced nuclear translocation and activation of NFATc. PDGF did not induce NFATc activation in neonatal PV. PDGF-induced ERK1/2 activation was observed in both 2-4-day-old and 6-week-old PV. In 6-week-old PV, ERK1/2 activation was Ca(2+)-dependent and protein kinase C-dependent. However in 2-4-day-old PV, PDGF-induced ERK1/2 activation was via a Ca(2+)-independent, atypical protein kinase C. PLC(gamma) expression was also decreased in the neointima, compared to media, of balloon-injured rabbit subclavian arteries.

CONCLUSIONS

The regulation of PDGF-induced Ca2+ increases by PLC(gamma) expression in VSM may provide a mechanism for coordinating different signaling pathways leading to activation of specific transcription factors. This may play an important role in the phenotypic modulation of VSM.

TNFα increases the inflammatory response to vascular balloon injury without accelerating neointimal formation

There is now clear evidence for a contributory role of inflammatory processes to restenosis following vascular balloon injury and stent implantation. The aim of the present study was to study the effects of TNFalpha, administered locally in vivo immediately following balloon angioplasty, on the leukocyte adhesive response and extent of neointimal formation in a rabbit model of subclavian artery injury. Initial in vitro studies were performed with normal isolated artery rings to assess the vascular adhesive response to TNFalpha or IL-1beta. Pre-incubation with either cytokine prior to addition of (51)Cr-labelled leukocytes enhanced the adhesion of leukocytes to the artery in both a time- and concentration-dependent manner. Although both cytokines induced an increase in the expression of the adhesion molecules ICAM-1 and VCAM-1, only antibodies to ICAM-1 blocked the enhanced adhesion induced by the cytokines. In artery segments retrieved from rabbits that had previously undergone subclavian artery angioplasty either 24 h or 8 days previously, there was an injury-induced increase in adhesion of leukocytes assessed ex vivo. In segments obtained from rabbits that received a 15 min local infusion of TNFalpha (2 ng/min) to the injured artery immediately after the angioplasty procedure, leukocyte adhesion assessed ex vivo was further significantly enhanced. The pro-adhesive effect of TNFalpha was associated with an increased expression of both ICAM-1 and VCAM-1. However, TNFalpha administration did not alter the extent of neointimal formation observed 8 days after injury. These findings suggest that while TNFalpha may play a role following vascular injury, it does not act alone to induce neointimal formation. Thus anti-inflammatory strategies targeted at multiple cytokines may be more appropriate than targeting a single cytokine to reduce the response to vascular injury.

Induction of iNOS restricts functional activity of both eNOS and nNOS in pig cerebral artery

The aim of the study was to investigate the effect of iNOS expression on eNOS and nNOS functional activity in porcine cerebral arteries. iNOS was induced in pig basilar arteries using lipopolysaccharide (LPS). Arteries expressing iNOS generated NO and relaxed when challenged with L-arginine (30 microM), an effect that was reduced by treatment with dexamethasone (coincubated with LPS) and prevented by the iNOS inhibitor 1400 W (administered 10 min prior to precontraction). eNOS was activated by A23187 and was found to be impaired in arteries that had iNOS induced (A23187 1 microM relaxation: control 110+/-8%, LPS-treated 50+/-16% ; p<0.05, N=5-6). This was due mainly to reduced formation of NO by A23187 (NO concentration in response to A23187 1 microM: control 25+/-6 nM, LPS-treated 0.8+/-1.2 nM; p<0.001, N=5-6), in addition to a small reduction in the vasodilator response to the NO-donors NOC-22 and SIN-1. Cerebral vasodilation produced by stimulation of intramural nitrergic nerves was impaired in arteries that had iNOS induced, and this was reversed by 1400 W (control 23+/-4% relaxation, LPS-treated 11+/-1% relaxation, LPS plus 1400 W 10 microM treated 25+/-2% relaxation; p<0.01 for control versus LPS, N=6). It is concluded that the induction of iNOS in cerebral arteries reduces NO-mediated vasodilation initiated by eNOS and by nNOS, primarily by modulation of NO formation.

Correlation of changes in nitric oxide synthase, superoxide dismutase and nitrotyrosine with endothelial regeneration and neointimal hyperplasia in the balloon-injured rabbit subclavian artery

OBJECTIVES

Alterations in nitric oxide (NO) and superoxide production within the wall of injured vessels may modulate the development and eventual extent of neointima after balloon injury.

METHODS

In this study we have characterized a rabbit model of subclavian artery injury and have used immunocytochemistry to detect NO synthase (NOS) isoforms, Cu-Zn superoxide dismutase (SOD) and nitrotyrosine in the injured vessel from 2 h to 28 days after injury.

RESULTS

At 48 h after injury, when cellular proliferation that will ultimately form the neointima is commencing, there was upregulation of inducible NOS, Cu-Zn SOD and nitrotyrosine. Recovery of endothelial NOS occurred at 28 days after injury, when the neointima is stabilizing and cellular proliferation has slowed down. There was no increase in neuronal NOS at any time point studied.

CONCLUSIONS

NO may serve to limit the development of neointima while superoxide may attenuate the effect of NO by formation of peroxynitrite, detected as increased nitrotyrosine staining. Upregulation of Cu-Zn SOD would limit superoxide both at sites of inflammation in the vessel wall from 48 h and in the adventitia up to 28 days after injury. Very early intervention to protect NO may reduce neointimal size.

Effect of antiproliferative agents on vascular function in normal and in vitro balloon-injured porcine coronary arteries

Local infusion of antiproliferative agents following coronary balloon angioplasty is used in vivo. This study examined the effects of the antiproliferative agents paclitaxel (5-beta, 20-Epoxy-1,2-alpha,4,7-beta,10-beta,13-alpha-Hexahydroxy-Tax-11-en-9-one 4,10-Diacetate 2_Benzoate 13-Ester with (2R,3S)-N-Benzoyl-3-Phenylisoserine; 10 and 50 microM), farnesyl protein transferase inhibitor III (FPT III, (E,E)-2-[2-Oxo-2-[(3,7,11-trimethyl-2,6,10-dodecatrienyl) oxy] amino] ethyl] phosphonic acid, (2,2-dimethyl-1-oxopropoxy) methyl ester, sodium); 10 and 25 microM), perillyl alcohol (4-isopropenyl-cyclohexenecarbinol; 1 and 2 mM) and Van 10/4 (Decahydro-1,1,4,7-tetramethyl-1H-cycloprop[e]azulen-4-o-[2-(3-methylpent-2-enoyl)-fucopyranoside]; 10 and 25 microM) on normal and in vitro balloon-injured porcine coronary arteries. Short-term (30 min) incubation had no effect on contraction or relaxation. Overnight incubation with 25 microM Van 10/4-attenuated contraction while perillyl alcohol abolished contractility completely. Endothelium-dependent relaxation was significantly attenuated by the higher concentration of paclitaxel, FPT III and Van 10/4. Stretch injury significantly enhanced sensitivity to 3-morpholinosydnonimine (SIN-1) while attenuating relaxation to calcimycin. Drug incubation (15 min) had no effect on these responses. In conclusion, paclitaxel, FPT III and Van 10/4 have no detrimental effects on vascular function after short-term administration to normal or stretch-injured arteries.

Endothelial nitric oxide synthase (NOS) is upregulated in rapid progressive pulmonary hypertension of the newborn

OBJECTIVE

To provide evidence for the upregulation of endothelial nitric oxide synthase (eNOS) or inducible nitric oxide synthase (iNOS) in the assumed imbalance in the pathophysiology of rapid progressive pulmonary hypertension of the newborn (RPPHN), which is characterized by abnormal hypertrophy of the pulmonary arterioles and arteries leading to increased pulmonary vascular resistance. Furthermore, to determine the cellular source and topographic distribution of eNOS and iNOS.

MATERIAL AND METHODS

Lung biopsies were taken from two term neonates with clinical and echocardiographic evidence of RPPH and of three controls. Biopsies were obtained at an early stage of the disease as well as at post mortem and examined immunohistochemically for the presence of eNOS, iNOS and nitrotyrosine.

RESULTS

The endothelial cells of pulmonary arterioles stained significantly for eNOS protein in RPPHN patients. This was not the case in the control infants. There were no differences for nitrotyrosine or iNOS between RPPHN patients and controls.

CONCLUSION

Rapid progressive pulmonary hypertension of the newborn leads to compensatory induction of eNOS synthesis specifically in endothelial cells of the pulmonary arterioles. This mechanism of compensation can lead to delayed presentation of RPPHN during the late neonatal period. Exogenous inhaled nitric oxide therapy does not lead to suppression of the endogenous synthesis of nitric oxide.

Extracellular L-arginine is required for optimal NO synthesis by eNOS and iNOS in the rat mesenteric artery wall

1. The formation of NO from endothelial nitric oxide synthase (eNOS) in rat superior mesenteric artery rings was dependent on extracellular L-arginine, and was optimal at a concentration of L-arginine close to the plasma level (carbachol-stimulated NO: control 15.7+/-0.9, L-arginine 100 micro M 22.8+/-1.3 nM). 2. Enhancement of NO output by L-arginine was stereospecific, required the cationic amino-acid transporter and was dependent on caveolin. 3. Induction of inducible nitric oxide synthase (iNOS) impaired the stimulated NO synthesis from eNOS (100 nM carbachol-stimulated NO: control 5.7+/-0.6, iNOS 0.3+/-0.3 nM). 4. The interaction between iNOS and eNOS was reversed by the superoxide scavenger MnTMPyP. Impairment of eNOS by iNOS was also prevented by L-arginine 100 micro M administered simultaneously with carbachol, but not by L-arginine administered during incubation with lipopolysaccharide. 5. These data provide functional evidence that supplementing L-arginine from the extracellular medium optimises the formation of NO from eNOS and suggests that the impairment of eNOS by iNOS is caused by excess formation of superoxide by NO synthase, which can be prevented by L-arginine. These results provide an explanation for the observations that extracellular L-arginine can enhance endothelium function only when the endothelium is impaired or when iNOS has been induced.

The induction and detection in vitro of iNOS in the porcine basilar artery

The expression of iNOS in vascular tissues has an adverse effect on vascular responses to vasoconstrictors and NO-mediated vasodilators. The development of a simple method for detecting the iNOS expression by functional means would be extremely useful. Here we describe a method for inducing iNOS in the porcine basilar artery followed by the detection of iNOS protein by immunocytochemical means and the characterisation of functional responses to U46619 and L-arginine. Porcine basilar arteries were treated with LPS (1, 10 and 100 microg/ml) for between 5 and 18 h at 37 degrees C. Inducible NOS protein was expressed in a concentration-dependent manner in the endothelial and smooth muscle cells after 5 h and persisted for 18 h. Vessels treated with LPS showed a time-dependent reduction in contractile function in response to U46619 (10 nM) reaching significance at the 18-h time point. Moreover, a similar time-dependent increase in the vasodilator response to exogenously applied L-arginine (30 microM) was observed at both 5- and 18-h time points. These effects of LPS at the 18-h time point were prevented by the incubation of vessels with dexamethasone (100 microM) in addition to LPS. The vasodilator response to L-arginine was prevented with the incubation with and in the presence of the inhibitor of inducible NOS, 1400W (10 microM) in addition to LPS. These results show that iNOS protein can be expressed in porcine cerebral arteries and that the iNOS is functional. The assessment of contractile function and responses to L-arginine using single concentrations is a rapid and effective method for establishing whether functional iNOS is present in porcine cerebral arteries.

Validation of a technique to measure leukocyte adhesion to arterial segments: effects of drug treatments

Adhesion and transmigration of leukocytes into arterial walls occurs after vascular injury and may play a role in the development of atherosclerosis and restenosis. This protocol presents a simple, rapid method for quantifying leukocyte adhesion to artery segments ex vivo. The procedure involves isolating leukocytes from rabbit whole blood and labelling with the gamma-emitting isotope 51Cr. Labelled leukocytes are added to open rings of subclavian artery taken from the same rabbit. After gamma counting, percentage leukocyte adhesion can be calculated with reference to a sample containing a quantity of labelled leukocytes equivalent to that which was added to the artery. Leukocyte adhesion was increased by L-NAME, thrombin and increasing incubation time and decreased by low temperatures. In addition, leukocyte adhesion was found to be increased following a vascular stretch injury performed in vitro. This protocol offers a number of advantages: the rapidity of the leukocyte isolation and labelling; the small quantity of leukocytes required; the ability to use autologous leukocytes; the applicability to whole arteries and arteries injured in vitro or in vivo, allowing the effects of vascular injury on leukocyte adhesion to be studied.

Inflammation as a key event in the development of neointima following vascular balloon injury

1. The present review discusses the current evidence to implicate leucocytes as key players in the development of neointima in arteries that have been subjected to balloon angioplasty injury. 2. There is substantial clinical evidence that leucocytes are activated after angioplasty, as determined by increased plasma levels of both leucocyte granulation products and soluble leucocyte and endothelial cell adhesion molecules. 3. Experimental evidence to implicate leucocytes in neointimal formation comes from studies that demonstrate leucocyte accumulation occurs within the vascular wall soon after injury and that induction of leukopenia prevents neointimal formation. 4. The evidence implicating specific adhesion molecules and cytokines in the key events leading to neointimal formation is discussed.

Short-term local delivery of an inhibitor of Ras farnesyltransferase prevents neointima formation in vivo after porcine coronary balloon angioplasty

BACKGROUND

Mitogenic stimuli present at the site of coronary arterial balloon injury contribute to the progression and development of a restenotic lesion, many signaling through a common pathway involving the small G protein p21(ras). Our aim was to demonstrate in biochemical studies that farnesyl protein transferase inhibitor III (FPTIII) is an inhibitor of p21(ras) processing and that when it is given locally in vivo at the site of coronary balloon injury in a porcine model, it can inhibit neointima formation.

METHODS AND RESULTS

FPTIII (1 to 25 micromol/L) concentration-dependently reduced p21(ras) levels in porcine coronary artery smooth muscle cell membranes. FPTIII also prevented p42/p44 MAPK activation and DNA synthesis in response to platelet-derived growth factor in these cells at a concentration of 25 micromol/L. Application of 25 micromol/L FPTIII locally for 15 minutes to balloon-injured porcine coronary arteries in vivo prevented neointima formation assessed at 4 weeks, reduced proteoglycan deposition, and inhibited adventitial hypertrophy. Coronary arteries from FPTIII-treated pigs had no deterioration in contraction or in endothelium-dependent relaxation.

CONCLUSIONS

The study demonstrates in the pig that short-term local delivery of inhibitors of p21(ras)-dependent mitogenic signal transduction prevents restenosis after balloon angioplasty.

Inhibition by leukocyte depletion of neointima formation after balloon angioplasty in a rabbit model of restenosis

OBJECTIVE

The aim of the current study was to examine neointima formation in balloon injured left subclavian artery of rabbits subjected to two different methods of leukocyte depletion at the time of injury.

METHODS

Angioplasty of the left subclavian artery was performed in leukopenic male New Zealand White rabbits. Depletion of circulating leukocytes was induced by either mustine hydrochloride or an antibody against leukocyte common antigen (anti-LCA) before angioplasty. Left and right subclavian arteries were removed 28 days after injury for morphological analysis and measurement of neointimal size. At the same time, leukocytes were isolated from autologous rabbit blood for 51Cr-labelling for assessment of leukocyte adhesion to injured and non-injured artery segments.

RESULTS

Leukopenia decreased neointima formation in injured arteries (neointimal area was 0.09+/-0.03 mm(2) in mustine-treated arteries, n=8, vs. 0.56+/-0.07 mm(2) in control arteries, n=7; P<0.001 and 0.07+/-0.01 mm(2) in anti-LCA treated arteries, n=9, vs. 0.22+/-0.04 mm(2) in non immune serum-treated arteries, n=9; P<0.001). Adventitial fibrosis was also significantly (P<0.05) decreased by both leukopenic interventions. Neither medial nor adventitial area was modified in any of the groups. No differences in leukocyte adhesion were observed between injured and non-injured arteries in any of the experimental groups at the 28 day time point.

CONCLUSION

These results suggest that leukocytes play a major role in the development of two of the major characteristics of the response to balloon injury, namely formation of neointima and adventitial fibrosis, that currently limit the success of clinical angioplasty. Elucidation of the fine mechanisms involved in leukocyte-mediated injury may lead to the discovery of novel therapeutic targets for the prevention of restenosis.

A rapid, quantitative method for measuring leukocyte adhesion to normal and balloon-injured arteries in vitro

Many of the currently available techniques for quantifying leukocyte adhesion require monolayers of cells and are therefore unsuitable for use in ex vivo arterial tissue. Here we describe a rapid method to measure adhesion of leukocytes to intact artery strips and to determine the effect of artery injury on adhesiveness of leukocytes with and without activation. Leukocytes were isolated from rabbit blood, labelled with 51Cr, and added to the luminal face of the left and right subclavian arteries derived from the same animal. In some experiments the endothelium was removed before addition of leukocytes and in another series of experiments the artery was injured by inflating a balloon catheter within the lumen in vitro before leukocyte addition. After washing, the adhesion of labelled leukocytes was quantified by gamma counting. To determine localization of the leukocytes, some arteries were fixed in situ and examined microscopically, with confirmation of leukocyte identification by enzyme cytochemistry. The adhesion of leukocytes increased progressively during 60 min and was inhibited by reducing the temperature to 4 degrees C. Adhesion was increased by the nitric oxide synthase inhibitor L-NAME. Stretching the artery wall in vitro using a balloon catheter increased leukocyte adhesion within 1 h after injury. In contrast, this did not occur following simple arterial denudation. Histological examination of stained en face preparations and transverse sections of the subclavian arteries revealed loosely adherent granulocytic leukocytes on the endothelial surface. This technique is straightforward and allows accurate and rapid measurement of autologous leukocyte adhesion to normal and pathologically altered arteries ex vivo.

Accumulation of nitrotyrosine correlates with endothelial NO synthase in pulmonary resistance arteries during chronic hypoxia in the rat

Nitrotyrosine and eNOS were detected immunocytochemically using specific antibodies in paraffin sections of lung from rats subjected to hypoxia for 2, 7, or 14 days. The staining intensity for eNOS was enhanced in the endothelium of both resistance and conduit pulmonary arteries at 2 days. Staining intensity for eNOS remained elevated at 7 and 14 days in conduit arteries, whereas it progressively increased further in resistance arteries. Nitrotyrosine staining was elevated to a similar degree in endothelium and adjacent vascular smooth muscle. In resistance pulmonary arteries, there was a progressive increase in nitrotyrosine, which matched the increase in eNOS. In conduit pulmonary arteries, nitrotyrosine increased only after 14 days of hypoxia. The results suggest that in chronic hypoxia the up-regulation of eNOS leads to the formation of peroxynitrite which has access to both endothelium and vascular smooth muscle.

Reduction in libido and fertility of male rats by administration of the nitric oxide (NO) synthase inhibitor N-nitro-L-arginine methyl ester

The role of nitric oxide (NO) in libido and fertility of male rats was investigated by administration of the NO synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) (25 or 50 mg/kg/day). L-NAME caused marked reduction of precoital sexual behaviour, and a failure of most rats to mount or ejaculate during the test interval. In most matings that were successful, recovered spermatozoa were present in normal numbers. In mating experiments, L-NAME profoundly reduced the fertility of male rats. In those animals that did succeed in mating, the quantal pregnancy and the number of implants were reduced. After cessation of treatment with L-NAME, the fertility parameters returned close to normal. The inactive stereoisomer, D-NAME, caused none of the above effects when administered to rats. The results suggest that NO is essential for the expression of normal libido and fertility in male rats. It is likely that NO is required both in the male reproductive tract and in the brain.