The Effect of Sildenafil on Pulmonary Embolism-Induced Oxidative Stress and Pulmonary Hypertension

Oxidative stress in acute pulmonary embolism: emerging roles and therapeutic implications

Oxidative stress is an imbalance between the body's reactive oxygen species and antioxidant defense mechanisms. Oxidative stress is involved in the development of several cardiovascular diseases, such as pulmonary hypertension, atherosclerosis, and diabetes mellitus. A growing number of studies have suggested the potential role of oxidative stress in the pathogenesis of pulmonary embolism. Biomarkers of oxidative stress in pulmonary embolism have also been explored, such as matrix metalloproteinases, asymmetric dimethylarginine, and neutrophil/lymphocyte ratio. Here, we comprehensively summarize some oxidative stress mechanisms and biomarkers in the development of acute pulmonary embolism and summarize related treatments based on antioxidant stress to explore effective treatment strategies for acute pulmonary embolism.

Sildenafil: From angina to SARS-CoV-2

Sildenafil was first examined as an alternative to nitrates for the management of angina pectoris and hypertension and eventually developed into an oral therapeutic agent used for the treatment of erectile dysfunction. There are appropriate indicators that PDE5 inhibitors may also modify the detrimental consequences of the immune system over-stimulation, supplying a new chance for their use in SARS-CoV2 patients. The use of sildenafil for the management of SARS-CoV2 has been suggested based on its several mechanisms of action and therapeutic effects and on the clinical features of SARS-CoV2 which similar to those of other pathologies treated with the PDE5 inhibitors. Here we review fundamental highlights in the enhancement of sildenafil for numerous scientific disorders and consider practicable new uses for this versatile drug.

Changes in the Pulmonary Artery Wave Reflection in Dogs with Experimentally-Induced Acute Pulmonary Embolism and the Effect of Vasodilator

Simple Summary

Pulmonary hypertension (PH) remains a fatal disease, despite the advances in disease-specific therapies. This may be because the assessment of pulmonary hemodynamics in PH has not been established. Recently, several studies have reported that the pulmonary arterial wave reflection (PAWR) might influence the right ventricular afterload and could provide additional information regarding the severity and progression of PH. However, the pathophysiology of PAWR has some unclear points particularly in the case of acute pulmonary embolism (APE). The objective of this study was to investigate, for the first time, the characteristics of PAWR in a dog model of APE using dual-tipped sensor wire. From the result of the present study, after dogs developed PH by injections of dextran microsphere, PAWR was increased significantly along with the pulmonary vascular resistance (PVR) and reduced after vasodilator administration. In addition, PAWR was significantly correlated with PVR and right ventricular fractional area of change (FAC). These results indicating that PAWR may be useful as a new evaluation method in PH and may detect changes related to right ventricular afterload earlier than pulmonary artery pressure (PAP).

Abstract

Pulmonary hypertension (PH) is a complex syndrome that has been frequently diagnosed in dogs and humans and can be detected by Doppler echocardiography and invasive catheterization. Recently, PAWR attracts much attention as a noninvasive approach for the early detection of PH. The present study aims to investigate the PAWR changes in acute pulmonary embolism (APE) and highlight the response of PAWR variables to vasodilator therapy in dogs. For this purpose, anesthesia and catheterization were performed in 6 Beagle dogs. After that, APE was experimentally conducted by Dextran microsphere administration, followed by vasodilator (Nitroprusside; 1μg/kg/min/IV) administration. The hemodynamics, echocardiography, PVR and PAWR variables were evaluated at the baseline, after APE and after administration of nitroprusside. The result showed a significant increase in PVR, PAP, tricuspid regurgitation (TR) as well as PAWR variables following APE induction compared with the baseline (p < 0.05). Vasodilation caused by administration of nitroprusside reduced the mean atrial pressure, PVR and PAWR parameters. There were a significant correlation and linear regression between PAWR indices and PVR as well as right ventricular function parameters. In conclusion, PAWR is not only correlated with PVR but also the right ventricular function parameter, which indicates that PAWR may be useful as a new evaluation method in PH, considering that PAWR can assess both right ventricular afterload and right ventricular function.

Nitrite and tempol combination promotes synergic effects and alleviates right ventricular wall stress during acute pulmonary thromboembolism

INTRODUCTION

The mechanical obstruction and pulmonary vasoconstriction are major determinants of the sudden right ventricular (RV) afterload increases observed during acute pulmonary thromboembolism (APT). Vasodilators and antioxidants agents have been shown to mitigate pulmonary hypertension. We examined whether sodium nitrite and the antioxidant tempol combination could be advantageous in an APT sheep model.

METHODS

APT was induced in anesthetized sheep by autologous blood clots (250 mg/kg) into the right atrium. Thirty minutes after APT induction, the animals received a continuous infusion of tempol (1.0 mg/kg/min), increasing sodium nitrite infusion (5, 15, and 50 μmol/kg), or a simultaneous combination of both drugs. Saline was used as a control treatment. Hemodynamic measurements were carried out every 15 min. Also, whole blood nitrite and serum 8-isoprostanes levels were measured.

RESULTS

APT induced sustained pulmonary hypertension, increased dp/dt_max, and rate pressure product (RPP). Nitrite or tempol treatments attenuated these increases (P < 0.05). When both drugs were combined, we found a robust reduction in the RV RPP compared with the treatments alone (P < 0.05). The sole nitrite infusion increased blood nitrite concentrations by 35 ± 6 μM (P < 0.05), whereas the nitrite and tempol combination produced higher blood nitrite concentrations by approximately 54 ± 7 μM. Tempol or nitrite infusions, both alone or combined, blunted the increases in 8-isoprostane concentrations observed after APT.

CONCLUSIONS

Nitrite and tempol combination protects against APT-induced RV wall stress. The association of both drugs may offer an advantage to treat RV failure during severe APT.

Right ventricular adaptation in the critical phase after acute intermediate-risk pulmonary embolism

BACKGROUND

The haemodynamic response following acute, intermediate-risk pulmonary embolism is not well described. We aimed to describe the cardiovascular changes in the initial, critical phase 0-12 hours after acute pulmonary embolism in an in-vivo porcine model.

METHODS

Pigs were randomly allocated to pulmonary embolism (n = 6) or sham (n = 6). Pulmonary embolism was administered as autologous blood clots (20 × 1 cm) until doubling of mean pulmonary arterial pressure or mean pulmonary arterial pressure was greater than 34 mmHg. Sham animals received saline. Cardiopulmonary changes were evaluated for 12 hours after intervention by biventricular pressure-volume loop recordings, invasive pressure measurements, arterial and central venous blood gas analyses.

RESULTS

Mean pulmonary arterial pressure increased (P < 0.0001) and stayed elevated for 12 hours in the pulmonary embolism group compared to sham. Pulmonary vascular resistance and right ventricular arterial elastance (right ventricular afterload) were increased in the first 11 and 6 hours, respectively, after pulmonary embolism (P < 0.01 for both) compared to sham. Right ventricular ejection fraction was reduced (P < 0.01) for 8 hours, whereas a near-significant reduction in right ventricular stroke volume was observed (P = 0.06) for 4 hours in the pulmonary embolism group compared to sham. Right ventricular ventriculo-arterial coupling was reduced (P < 0.05) for 6 hours following acute pulmonary embolism despite increased right ventricular mechanical work in the pulmonary embolism group (P < 0.01) suggesting right ventricular failure.

CONCLUSIONS

In a porcine model of intermediate-risk pulmonary embolism, the increased right ventricular afterload caused initial right ventricular ventriculo-arterial uncoupling and dysfunction. After approximately 6 hours, the right ventricular afterload returned to pre-pulmonary embolism values and right ventricular function improved despite a sustained high pulmonary arterial pressure. These results suggest an initial critical and vulnerable phase of acute pulmonary embolism before haemodynamic adaptation.

Short-term effects of sildenafil in the treatment of dogs with pulmonary hypertension secondary to degenerative mitral valve disease

Background and Aim:

Pulmonary hypertension (PH) is a common complication of degenerative mitral valve disease (DMVD). Sildenafil, a phosphodiesterase-5 inhibitor, has effects in reducing pulmonary arterial pressure by selectively dilating pulmonary vessels. The study aimed to evaluate the effects of sildenafil in combination with conventional therapy in dogs with PH caused by DMVD.

Materials and Methods:

Fourteen dogs diagnosed with PH secondary to DMVD Stage C on conventional therapy were randomly assigned to placebo (n=7) and sildenafil (n=7) groups. On day 0, the recruited dogs underwent physical examinations, clinical score assessments, electrocardiography, systolic blood pressure measurements, blood collection, thoracic radiography, and echocardiography for baseline. The dogs then received a combination of conventional therapy with sildenafil or placebo every 8 h for 1 week. On day 7, all dogs underwent the baseline evaluations again.

Results:

The sildenafil group experienced a significant decrease in estimated systolic pulmonary artery pressure (sPAP) (p=0.043) from day 0 to day 7. Moreover, the total clinical scores were decreased in dogs treated with sildenafil relative to those who received the placebo (p=0.007); however, the lung scores were not different between before and after treatment with sildenafil.

Conclusion:

Sildenafil had a synergistic effect with conventional therapy in reducing the estimated sPAP and clinical scores in dogs with PH secondary to DMVD.

Pulmonary vasodilation in acute pulmonary embolism - a systematic review

Acute pulmonary embolism is the third most common cause of cardiovascular death. Pulmonary embolism increases right ventricular afterload, which causes right ventricular failure, circulatory collapse and death. Most treatments focus on removal of the mechanical obstruction caused by the embolism, but pulmonary vasoconstriction is a significant contributor to the increased right ventricular afterload and is often left untreated. Pulmonary thromboembolism causes mechanical obstruction of the pulmonary vasculature coupled with a complex interaction between humoral factors from the activated platelets, endothelial effects, reflexes and hypoxia to cause pulmonary vasoconstriction that worsens right ventricular afterload. Vasoconstrictors include serotonin, thromboxane, prostaglandins and endothelins, counterbalanced by vasodilators such as nitric oxide and prostacyclins. Exogenous administration of pulmonary vasodilators in acute pulmonary embolism seems attractive but all come with a risk of systemic vasodilation or worsening of pulmonary ventilation-perfusion mismatch. In animal models of acute pulmonary embolism, modulators of the nitric oxide-cyclic guanosine monophosphate-protein kinase G pathway, endothelin pathway and prostaglandin pathway have been investigated. But only a small number of clinical case reports and prospective clinical trials exist. The aim of this review is to give an overview of the causes of pulmonary embolism-induced pulmonary vasoconstriction and of experimental and human investigations of pulmonary vasodilation in acute pulmonary embolism.

Role of Phosphodiesterase-5 Inhibitors in Acute Right Ventricular Failure Due to Pulmonary Embolism

Patient: Male, 56

Final Diagnosis: Right heart failure due to pulmonary embolism

Symptoms: Syncope

Medication: —

Clinical Procedure: —

Specialty: Cardiology

Effect of a phosphodiesterase-5A (PDE5A) gene polymorphism on response to sildenafil therapy in canine pulmonary hypertension

Pulmonary hypertension (PH) is a common clinical condition associated with morbidity and mortality in both humans and dogs. Sildenafil, a phosphodiesterase-5 (PDE5) inhibitor causing accumulation of cGMP, is frequently used for treatment of PH. The authors previously reported a PDE5A:E90K polymorphism in dogs that results in lower basal cyclic guanosine monophosphate (cGMP) concentrations than in wild-type dogs, which could contribute to variability in the efficacy of sildenafil. In this study, response to sildenafil therapy was evaluated in dogs with PH by comparing echocardiographic parameters, quality-of-life (QOL) score, and plasma cGMP concentrations before and after sildenafil therapy. Overall, tricuspid regurgitation estimated systolic pressure gradient (PG) and QOL score were significantly improved after sildenafil therapy, and the plasma cGMP concentration was significantly decreased. Dogs that had a heterozygous PDE5A status had a significantly worse QOL score when compared to the wildtype group after sildenafil treatment. The simple and multiple regression analyses revealed a significant but weak prediction for the percent reduction in QOL score with sildenafil treatment by plasma cGMP level and by the PDE5A:E90K polymorphic status. This study showed that sildenafil treatment improved PH in dogs, and the PDE5A:E90K polymorphism blunted the efficacy of sildenafil in terms of QOL improvement.

Increasing complexity and interactions of oxidative stress in chronic respiratory diseases: An emerging need for novel drug delivery systems

Oxidative stress is intensely involved in enhancing the severity of various chronic respiratory diseases (CRDs) including asthma, chronic obstructive pulmonary disease (COPD), infections and lung cancer. Even though there are various existing anti-inflammatory therapies, which are not enough to control the inflammation caused due to various contributing factors such as anti-inflammatory genes and antioxidant enzymes. This leads to an urgent need of novel drug delivery systems to combat the oxidative stress. This review gives a brief insight into the biological factors involved in causing oxidative stress, one of the emerging hallmark feature in CRDs and particularly, highlighting recent trends in various novel drug delivery carriers including microparticles, microemulsions, microspheres, nanoparticles, liposomes, dendrimers, solid lipid nanocarriers etc which can help in combating the oxidative stress in CRDs and ultimately reducing the disease burden and improving the quality of life with CRDs patients. These carriers improve the pharmacokinetics and bioavailability to the target site. However, there is an urgent need for translational studies to validate the drug delivery carriers for clinical administration in the pulmonary clinic.

N-Acetylcysteine potentiates the haemodynamic-improving effect of sildenafil in a rabbit model of acute pulmonary thromboembolism via the p38 MAPK pathway

The current study aimed to investigate the effects of sildenafil and N-acetylcysteine (NAC) on the haemodynamics in a rabbit model of acute pulmonary thromboembolism (APT). We developed an APT model using healthy male China big-ear rabbits (2.7 ± 0.4 kg). The rabbits were divided into five groups subjected to various interventions. We recorded the haemodynamic parameters and assessed the oxidative stress and lipid peroxidation response in the groups. Additionally, we detected apoptosis-associated molecules, FoxO1, Bad and Bcl-2, in the lung tissue. Gelatine zymography was used to detect matrix metalloproteinase (MMP) activity in bronchoalveolar lavage (BLA). Pulmonary artery endothelial cells were isolated, and their apoptosis rates and MMP activity were assayed. N-acetylcysteine potentiated the haemodynamic-improving effect of sildenafil and significantly inhibited the oxidative stress response. N-acetylcysteine combined with sildenafil decreased MMP-2 and MMP-9 activity and NO consumption and inhibited apoptosis of pulmonary arterial endothelial cells. Moreover, NAC combined with sildenafil inhibited the expression of MCP-1 and p-p38 MAPK. Thus, NAC potentiates the haemodynamic-improving effect of sildenafil in a rabbit model of acute pulmonary thromboembolism via the MCP-1 and p38 MAPK signalling pathway. This study may provide a promising treatment method for APT.

Targeting Phosphodiesterase-5 by Vardenafil Improves Vascular Graft Function

OBJECTIVES

Ischaemia reperfusion (IR) injury occurs during vascular graft harvesting and implantation during vascular/cardiac surgery. Elevated intracellular cyclic guanosine monophosphate (cGMP) levels contribute to an effective endothelial protection in different pathophysiological conditions. The hypothesis that the phosphodiesterase-5 inhibitor vardenafil would protect vascular grafts against IR injury by upregulating the nitric oxide-cGMP pathway in the vessel wall of the bypass graft was investigated.

METHODS

Lewis rats (n = 6-7/group) were divided into Group 1, control; Group 2, donor rats received intravenous saline; Group 3, received intravenous vardenafil (30 μg/kg) 2 h before explantation. Whereas aortic arches of Group 1 were immediately mounted in an organ bath, aortic segments of Groups 2 and 3 were stored for 2 h in saline and transplanted into the abdominal aorta of the recipient. Two hours after transplantation, the implanted grafts were harvested. Endothelium dependent and independent vasorelaxations were investigated. TUNEL, CD-31, ICAM-1, VCAM-1, α-SMA, nitrotyrosine, dihydroethidium and cGMP immunochemistry were also performed.

RESULTS

Compared with the control, the saline group showed significantly attenuated endothelium dependent maximal relaxation (R_max) 2 h after reperfusion, which was significantly improved by vardenafil supplementation (R_max control, 91 ± 2%; saline 22 ± 2% vs. vardenafil 39 ± 4%, p < .001). Vardenafil pre-treatment significantly reduced DNA fragmentation (control 9 ± 1%, saline 66 ± 8% vs. vardenafil 13 ± 1%, p < .001), nitro-oxidative stress (control 0.8 ± 0.3, saline 7.6 ± 1.3 vs. vardenafil 3.8 ± 1, p = .036), reactive oxygen species level (vardenafil 36 ± 4, control 34 ± 2 vs. saline 43 ± 2, p = .049), prevented vascular smooth muscle cell damage (control 8.5 ± 0.7, saline 4.3 ± 0.6 vs. vardenafil 6.7 ± 0.6, p = .013), decreased ICAM-1 (control 4.1 ± 0.5, saline 7.0 ± 0.9 vs. vardenafil 4.4 ± 0.6, p = .031), and VCAM-1 score (control 4.4 ± 0.4, saline 7.3 ± 1.0 vs. vardenafil 5.2 ± 0.4, p = .046) and increased cGMP score in the aortic wall (control 11.2 ± 0.8, saline 6.5 ± 0.8 vs. vardenafil 8.9 ± 0.6, p = .016). The marker for endothelial integrity (CD-31) was also higher in the vardenafil group (control 74 ± 4%, saline 22 ± 2% vs. vardenafil 40 ± 3%, p = .008).

CONCLUSIONS

The results support the view that impairment of intracellular cGMP signalling plays a role in the pathogenesis of the endothelial dysfunction of an arterial graft after bypass surgery, which can effectively be prevented by vardenafil. Its clinical use as preconditioning drug could be a novel approach in vascular/cardiac surgery.

Sildenafil attenuates hepatocellular injury after liver ischemia reperfusion in rats: a preliminary study

We evaluated the role of sildenafil in a rat liver ischemia-reperfusion model. Forty male rats were randomly allocated in four groups. The sham group underwent midline laparotomy only. In the sildenafil group, sildenafil was administered intraperitoneally 60 minutes before sham laparotomy. In the ischemia-reperfusion (I/R) group, rats were subjected to 45 minutes of hepatic ischemia followed by 120 minutes of reperfusion, while in the sild+I/R group rats were subjected to a similar pattern of I/R after the administration of sildenafil, 60 minutes before ischemia. Two hours after reperfusion, serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured and histopathological examination of the lobes subjected to ischemia as well as TUNEL staining for apoptotic bodies was performed. Additionally, myeloperoxidase (MPO) activity and the expression of intercellular adhesion molecule-1 (ICAM-1) were analyzed. Serum markers of hepatocellular injury were significantly lower in the sild+I/R group, which also exhibited lower severity of histopathological lesions and fewer apoptotic bodies, as compared to the I/R group. The I/R group showed significantly higher MPO activity and higher expression of ICAM-1, as compared to the sild+I/R group. Use of sildenafil as a preconditioning agent in a rat model of liver I/R exerted a protective effect.

Plasma 15-F2t-isoprostane in idiopathic pulmonary arterial hypertension

BACKGROUND

15-F2t-isoprostane (15-F2t-IsoP), a prostaglandin F2-like compound, is widely recognized as a biomarker of chronic heart failure. This study investigated the potential role and prognostic significance of plasma 15-F2t-IsoP in patients with idiopathic pulmonary arterial hypertension (IPAH).

METHODS

Plasma 15-F2t-IsoP concentrations were determined in 80 consecutive IPAH patients at the time of their first right heart catheterization, and monitored for 30±12 months. The expression of 15-F2t-IsoP protein in autopsy lung samples was determined by immunohistochemical staining.

RESULTS

Plasma 15-F2t-IsoP concentrations were significantly increased in patients with IPAH compared with healthy controls (91 pg/ml vs. 30 pg/ml, respectively; P<0.001). Patients with baseline 15-F2t-IsoP concentrations≥97 pg/ml had a significantly lower survival rate than those with lower baseline concentrations (P<0.001). During follow-up, 15-F2t-IsoP concentrations in survivors decreased, whereas concentrations in non-surviving patients increased further (P<0.05). Elevated concentrations of 15-F2t-IsoP were correlated with a severity of WHO functional class, lower 6-minute walking distance and mixed venous oxygen saturation, higher mean right atrial pressure and brain natriuretic peptide. Multivariate analysis revealed that the plasma 15-F2t-IsoP concentration was an independent factor associated with mortality. Histological studies showed that the expression of 15-F2t-IsoP was up-regulated in remodeled pulmonary vessels.

CONCLUSIONS

An elevated plasma 15-F2t-IsoP concentration and a further increase during follow-up may be a risk factor for higher mortality in patients with IPAH.

Atorvastatin and sildenafil lower blood pressure and improve endothelial dysfunction, but only atorvastatin increases vascular stores of nitric oxide in hypertension

Nitric oxide (NO)-derived metabolites including the anion nitrite can recycle back to NO and thus complement NO formation independent of NO synthases. While nitrite is as a major vascular storage pool and source of NO, little is known about drugs that increase tissue nitrite concentrations. This study examined the effects of atorvastatin or sildenafil, or the combination, on vascular nitrite concentrations and on endothelial dysfunction in the 2 kidney-1 clip (2K1C) hypertension model. Sham-operated or 2K1C hypertensive rats were treated with vehicle, atorvastatin (50 mg/Kg), sildenafil (45 mg/Kg), or both for 8 weeks. Systolic blood pressure (SBP) was monitored weekly. Nitrite concentrations were assessed in the aortas and in plasma samples by ozone-based reductive chemiluminescence assay. Aortic rings were isolated to assess endothelium-dependent and independent relaxation. Aortic NADPH activity and ROS production were evaluated by luminescence and dihydroethidium, respectively, and plasma TBARS levels were measured. Aortic nitrotyrosine staining was evaluated to assess peroxynitrite formation. Atorvastatin and sildenafil, alone or combined, significantly lowered SBP by approximately 40 mmHg. Atorvastatin significantly increased vascular nitrite levels by 70% in hypertensive rats, whereas sildenafil had no effects. Both drugs significantly improved the vascular function, and decreased vascular NADPH activity, ROS, and nitrotyrosine levels. Lower plasma TBARS concentrations were found with both treatments. The combination of drugs showed no improved responses compared to each drug alone. These findings show evidence that atorvastatin, but not sildenafil, increases vascular NO stores, although both drugs exert antioxidant effects, improve endothelial function, and lower blood pressure in 2K1C hypertension.

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Nitrite recycles back to NO and complements NO formation independent of NO synthases.

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Little is known about drugs that increase tissue nitrite concentrations.

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Atorvastatin or sildenafil lowered blood pressure in renovascular hypertension.

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Both drugs exerted antioxidant effects and improved endothelial dysfunction.

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Only atorvastatin increased vascular nitrite levels by 70% in hypertensive rats.

Motion analysis of right ventricular dysfunction under mild or moderate pressure overload caused by acute pulmonary embolism

Acute pulmonary embolism (APE) is the third most common cause of death in the United States. Appearing as a sudden blockage in a major pulmonary artery, APE may cause mild, moderate or severe right ventricular (RV) overload. Although severe RV overload produces diagnostically obvious RV mechanical failure, little progress has been made in gaining a clinical and biophysical understanding of moderate and mild acute RV overload and its impact on RV functionality. In the research described here, we conducted a pilot study in pigs using echocardiography and observed the following abnormalities in RV functionality under acute mild or moderate RV overload: (i) occurrence of paradoxical septal motion with "waving" dynamics; (ii) decrease in local curvature of the septum (p < 0.01); (iii) lower positive correlation between movement of the RV free wall and movement of the septum (p < 0.05); (iv) slower rate of RV fractional area change (p < 0.05); and (v) decrease in movement stability, particularly in the middle of the septum (p < 0.05).

A comparison of the potential for acute cardiopulmonary adverse effects in dogs during continuous veno-venous hemofiltration with accusol 35 solution with and without induced calcium carbonate particles

BACKGROUND

Baxter received reports of visible precipitate, identified as calcium carbonate, forming during hemofiltration with Accusol 35 solution.

AIM

To evaluate the potential for acute cardiopulmonary adverse effects of Accusol 35 containing exaggerated calcium carbonate particles.

METHODS

Anesthetized dogs underwent continuous veno-venous hemofiltration (CVVH) with Accusol 35 containing visible and subvisible particles (≥10 µm) 36 times higher than the maximum concentration specified in the European Pharmacopoeia (P-Accusol), or Accusol 35 conforming to specification (Accusol). Select cardiovascular and blood gas parameters were evaluated during CVVH. Lung tissue samples were collected following CVVH.

RESULTS

No differences were observed in cardiovascular and blood gas parameters or lung histology between P-Accusol and Accusol.

CONCLUSION

Accusol 35 containing visible and subvisible particles (≥10 µm) 36 times higher than the maximum concentration specified in the European Pharmacopoeia resulted in no acute cardiopulmonary adverse effects compared with Accusol 35 containing no visible particles and subvisible particles within European Pharmacopoeia specification.

Addition of vardenafil into storage solution protects the endothelium in a hypoxia-reoxygenation model

OBJECTIVE

Based upon the well known protective effect of intracellular cyclic guanosine monophosphate (cGMP) accumulation, we tested the hypothesis that storage solution enriched with optimal concentration of the phosphodiestherase-5 inhibitor vardenafil could provide better protection of vascular grafts against reperfusion injury after long-term cold ischaemic storage.

METHODS

Isolated thoracic aorta obtained from rats underwent 24-h cold ischaemic preservation in physiological saline or vardenafil (10(-11) M)-supplemented saline solution. Reperfusion injury was simulated by hypochlorite (200 μM) exposure for 30 minutes. Endothelium-dependent vasorelaxation was assessed, and histopathological and molecular-biological examination of the aortic tissue were performed.

RESULTS

Compared with the control group, the saline group showed significantly attenuated endothelium-dependent maximal relaxation (Rmax) to acetylcholine after hypoxia-reoxygenation, which was significantly improved by vardenafil supplementation (Rmax control: 98 ± 1%; saline: 48 ± 6%; vardenafil: 75 ± 4%; p < .05). Vardenafil treatment significantly reduced DNA strand breaks (control: 10.6 ± 6.2%; saline: 72.5 ± 4.0%; vardenafil: 14.2 ± 5.2%; p < .05) and increased cGMP score in the aortic wall (control: 8.2 ± 0.6; saline: 4.5 ± 0.3; vardenafil: 6.7 ± 0.6; p < .05).

CONCLUSIONS

Our results support the view that impairment of intracellular cGMP signalling plays a role in the pathogenesis of the endothelial dysfunction induced by cold storage warm reperfusion, which can be effectively reversed by pharmacological phosphodiesterase-5 inhibition.

Vascular dysfunction induced by hypochlorite is improved by the selective phosphodiesterase-5-inhibitor vardenafil

Reactive oxygen species, such as hypochlorite induce oxidative stress, which impairs nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signalling and leads to vascular dysfunction. It has been proposed, that elevated cGMP-levels may contribute to an effective cytoprotection against oxidative stress. We investigated the effects of vardenafil, a selective inhibitor of the cGMP-degrading phosphodiesterase-5 enzyme on vascular dysfunction induced by hypochlorite. In organ bath experiments for isometric tension, we investigated the endothelium-dependent and endothelium-independent vasorelaxation of isolated rat aortic rings using cumulative concentrations of acetylcholine and sodium nitroprusside (SNP). Vascular dysfunction was induced by exposing rings to hypochlorite (100-400 µM). In the treatment groups, rats were pretreated with vardenafil (30 and 300 µg/kg i.v.). Immunohistochemical analysis was performed for the oxidative stress markers nitrotyrosine, poly(ADP-ribose) and for apoptosis inducing factor (AIF). Exposure to hypochlorite resulted in a marked impairment of acetylcholine-induced endothelium-dependent vasorelaxation of aortic rings. Pretreatment with vardenafil led to improved endothelial function as reflected by the higher maximal vasorelaxation (Rmax) to acetylcholine. Regarding endothelium-independent vasorelaxation, hypochlorite exposure led to a left-shift of SNP concentration-response curves in the vardenafil groups without any alterations of the Rmax. In the hypochlorite groups immunohistochemical analysis showed enhanced poly(ADP-ribose)-formation and nuclear translocation of AIF, which were prevented by vardenafil-pretreatment. Our results support the view that cytoprotective effects of PDE-5-inhibitors on the endothelium may underlie the improved endothelial function, however, a slight sensitisation of vascular smooth muscle to NO was also confirmed. PDE-5-inhibition may represent a potential therapy approach for treating vascular dysfunction induced by oxidative stress.

Beneficial effect of phosphodiesterase-5 inhibitor in experimental inflammatory bowel disease; molecular evidence for involvement of oxidative stress

ABSTRACT Inflammatory bowel disease (IBD) is a common and chronic gastrointestinal disorder characterized by intestinal inflammation and mucosal tissue damage. Reactive oxygen metabolites (ROMs) play a pathogenic role in IBD. We aimed to examine the protective effect of sildenafil, a cGMP phosphodiesterase inhibitor, in the experimental mouse model of IBD. Intrarectal instillation of acetic acid was used to induce IBD. Prednisolone was used as the standard drug for comparison. Sildenafil was used at doses of 0.75, 1.5, and 3 mg/kg. Biochemicals and macroscopic and microscopic examinations of colonic tissue were performed. Results indicated that activity of myeloperoxidase (MPO) and lipid peroxidation product (TBARS) markers of oxidative stress are increased in acetic acid-treated groups and are recovered by sildenafil pretreatment and prednisolone. Sildenafil- (1.5 and 3 mg/kg) and prednisolone-treated groups showed significantly lower score values of macroscopic and microscopic characters when compared to the acetic acid-treated group. The beneficial effect of sildenafil (3 mg/kg) was comparable to that of prednisolone. It is concluded that sildenafil is helpful in the management of IBD, which is presumably related to its strong antioxidative stress potential mediated through enhanced cGMP. Results of proper clinical trials will determine the possible efficacy of phosphodiesterase-5 inhibitors in human IBD.

Sildenafil stimulates the expression of gaseous monoxide-generating enzymes in vascular smooth muscle cells via distinct signaling pathways

Sildenafil is a cGMP-specific phosphodiesterase type 5 inhibitor that augments cGMP accumulation following the activation of soluble guanylate cyclase (sGC). In this study, we investigated whether sildenafil promotes the production of the sGC-stimulatory gases, carbon monoxide and nitric oxide, by stimulating the expression of the inducible isoforms of heme oxygenase (HO-1) and nitric oxide synthase (iNOS) in vascular smooth muscle cells (SMCs). Sildenafil increased HO-1 expression and potentiated cytokine-mediated expression of iNOS and NO synthesis by SMCs. The induction of HO-1 was unaffected by the sGC inhibitor 1H-(1,2,4)oxadiazolo[4,3-α]quinozalin-1-one (ODQ) or the protein kinase G inhibitor (8R,9S,11S)-(-)-2-methyl-9-methoxyl-9-methoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo(a,g)cyclocta9(cde)trinen-1-one (KT 5823). However, the sildenafil-mediated increase in HO-1 promoter activity was abolished by mutating the antioxidant responsive elements in the promoter or by overexpressing a dominant-negative mutant of NF-E2-related factor-2 (Nrf2). Furthermore, the induction of HO-1 by sildenafil was accompanied by an increase in reactive oxygen species (ROS) and blocked by N-acetyl-L-cysteine and rotenone. In contrast, the enhancement of cytokine-stimulated NO synthesis by sildenafil was prevented by ODQ and the protein kinase A inhibitor (9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo(1,2,3-fg:3',2',1'-kl)pyrrolo(3,4-i)(1,6)benzodiazocine-10-carboxylic acid hexyl ester (KT 5720) and duplicated by lipophilic analogs of cGMP. In conclusion, these studies demonstrate that sildenafil stimulates the expression of HO-1 and iNOS via the ROS-Nrf2 and sGC-cGMP pathway, respectively. The ability of sildenafil to block the catabolism of cGMP while stimulating the synthesis of sGC-stimulatory gaseous monoxides through the induction of HO-1 and iNOS provides a potent mechanism by which cGMP-dependent vascular actions of this drug are amplified.

Losartan exerts no protective effects against acute pulmonary embolism-induced hemodynamic changes

The acute obstruction of pulmonary vessels by venous thrombi is a critical condition named acute pulmonary embolism (APE). During massive APE, severe pulmonary hypertension may lead to death secondary to right heart failure and circulatory shock. APE-induced pulmonary hypertension is aggravated by active pulmonary vasoconstriction. While blocking the effects of some vasoconstrictors exerts beneficial effects, no previous study has examined whether angiotensin II receptor blockers protect against the hemodynamic changes associated with APE. We examined the effects exerted by losartan on APE-induced hemodynamic changes. Hemodynamic evaluations were performed in non-embolized lambs treated with saline (n = 4) and in lambs that were embolized with silicon microspheres and treated with losartan (30 mg/kg followed by 1 mg/kg/h, n = 5) or saline (n = 7) infusions. The plasma and lung angiotensin-converting enzyme (ACE) activity were assessed using a fluorometric method. APE increased mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance index (PVRI) by 21 ± 2 mmHg and 375 ± 20 dyn s cm⁻⁵ m⁻², respectively (P < 0.05). Losartan decreased MPAP significantly (by approximately 15%), without significant changes in PVRI and tended to decrease cardiac index (P > 0.05). Lung and plasma ACE activity were similar in both embolized and non-embolized animals. Our findings show evidence of lack of activation of the renin-angiotensin system during APE. The lack of significant effects of losartan on the pulmonary vascular resistance suggests that losartan does not protect against the hemodynamic changes found during APE.

Acute pulmonary embolism decreases adenosine plasma levels in anesthetized pigs

Adenosine plays a role in pulmonary arterial (PA) resistance due to its vasodilator properties. However, the behavior of adenosine plasma levels (APLs) during pulmonary embolism remains unknown. We investigated the effects of gradual pulmonary embolism on right ventricular (RV) contractility and PA coupling and on APLs in an piglet experimental model of RV failure. PA distal resistance by pressure-flow relationships and pulmonary vascular impedance were measured. RV contractility was determined by the end-systolic pressure-volume relationship (Ees), PA effective elastance by the end-diastolic to end-systolic relationship (Ea), and RV-PA coupling efficiency by the Ees/Ea ratio. APLs were measured before and during gradual pulmonary embolization. PA embolism increased PA resistance and elastance, increased Ea from 1.08 ± 0.15 to 5.62 ± 0.32 mmHg/mL, decreased Ees from 1.82 ± 0.10 to 1.20 ± 0.23 mmHg/mL, and decreased Ees/Ea from 1.69 ± 0.15 to 0.21 ± 0.07. APLs decreased from 2.7 ± 0.26 to 1.3 ± 0.12 μM in the systemic bed and from 4.03 ± 0.63 to 2.51 ± 0.58 μM in the pulmonary bed during embolism procedure. Pulmonary embolism worsens PA hemodynamics and RV-PA coupling. APLs were reduced, both in the systemic and in the pulmonary bed, leading then to pulmonary vasoconstriction.

Hemodynamic effects of inducible nitric oxide synthase inhibition combined with sildenafil during acute pulmonary embolism

While endogenous nitric oxide (NO) may be relevant to the beneficial hemodynamic effects produced by sildenafil during acute pulmonary embolism (APE), huge amounts of inducible NO synthase (iNOS)-derived NO may contribute to lung injury. We hypothesized that iNOS inhibition with S-methylisothiourea could attenuate APE-induced increases in oxidative stress and pulmonary hypertension and, therefore, could improve the beneficial hemodynamic and antioxidant effects produced by sildenafil during APE. Hemodynamic evaluations were performed in non-embolized dogs treated with saline (n=4), S-methylisothiourea (0.01 mg/kg followed by 0.5 mg/kg/h, n=4), sildenafil (0.3 mg/kg, n=4), or S-methylisothiourea followed by sildenafil (n=4), and in dogs that received the same drugs and were embolized with silicon microspheres (n=8 for each group). Plasma nitrite/nitrate (NOx) and thiobarbituric acid reactive substances (TBARS) concentrations were determined by Griess and a fluorometric assay, respectively. APE increased mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance index (PVRI) by 25±1.7 mm Hg and by 941±34 dyn s cm(-5) m(-2), respectively. S-methylisothiourea neither attenuated APE-induced pulmonary hypertension, nor enhanced the beneficial hemodynamic effects produced by sildenafil after APE (>50% reduction in pulmonary vascular resistance). While sildenafil produced no change in plasma NOx concentrations, S-methylisothiourea alone or combined with sildenafil blunted APE-induced increases in NOx concentrations. Both drugs, either alone or combined, produced antioxidant effects. In conclusion, although iNOS-derived NO may play a key role in APE-induced oxidative stress, our results suggest that the iNOS inhibitor S-methylisothiourea neither attenuates APE-induced pulmonary hypertension, nor enhances the beneficial hemodynamic effects produced by sildenafil.

A canine portal hypertension model induced by intra-portal administration of Sephadex microsphere

BACKGROUND AND AIM

Big animal models of portal hypertension are important for the research into this disease. The aim of this study was to establish a canine portal hypertension model by intra-portal administration of microspheres.

METHODS

Sixteen mongrel dogs were assigned to control group and experimental group randomly. The catheterization of portal vein was performed by laparotomy and the outer end of the catheter was fixed subcutaneously in the abdominal wall. The dogs of the experimental group were given intra-portal injections of microspheres at a five-day interval, six times in total. Portal hemodynamics, blood cell counting, liver and renal function test, portography, gastroscopy, liver, spleen and lung histological examination were taken to evaluate the model.

RESULTS

1, 2, 3 and 4 months after initial injection of microspheres, portal venous pressure rose from baseline 8.7 +/- 0.7 mmHg to 24.3 +/- 1.6, 20.6 +/- 2.1, 19.0 +/- 1.8 and 17.7 +/- 2.0 mmHg, respectively (P < 0.01). The diameter of portal vein increased from 7.6 +/- 0.3 to 8.6 +/- 0.3 mm, calculated portal resistance increased from 0.46 +/- 0.06 to 1.06 +/- 0.20 (mmHg/mL/min/kg body weight); velocity of portal blood flow decreased from 35.1 +/- 1.7 to 26.1 +/- 2.4 cm/s (P < 0.01, respectively). The animals of experimental group developed marked splenomegaly and profuse portosystemic collateral circulations with normal liver and renal function.

CONCLUSION

Repeated intra-portal administration of microspheres can induce stable and reproducible chronic portal hypertension in dogs with normal liver and renal functions. This model can meet multiple demands of both basic and clinical research of portal hypertension.

Circulating cell-free DNA levels in plasma increase with severity in experimental acute pulmonary thromboembolism

BACKGROUND

The diagnosis of acute pulmonary thromboembolism (APT) and its severity is challenging. No previous study has examined whether there is a linear relation between plasma DNA concentrations and the severity of APT. We examined this hypothesis in anesthetized dogs. We also examined the changes in plasma DNA concentrations in microspheres lung embolization and whether the therapy of APT with nitrite could modify APT-induced changes in plasma DNA concentrations. In vitro DNA release from blood clots was also studied.

METHODS

APT was induced with autologous blood clots (saline, 1, 3, or 5 ml/kg) injected into the right atrium. A group of dogs received 300 microm microspheres into the inferior vena cava to produce similar pulmonary hypertension. Another group of dogs received 6.75 micromol/kg nitrite after APT with blood clots of 5 ml/kg. Hemodynamic evaluations were carried out for 120 min. DNA was extracted from plasma samples using QIAamp DNA Blood Mini Kit and quantified using Quant-iT PicoGreen dsDNA detection kit at baseline and 120 min after APT.

RESULTS

APT produced dose-dependent increases in plasma DNA concentrations, which correlated positively with pulmonary vascular resistance (P=0.002, r=0.897) and with mean pulmonary arterial pressure (P=0.006, r=0.856). Conversely, lung embolization with microspheres produced no significant changes in plasma DNA concentrations. While nitrite attenuated APT-induced pulmonary hypertension, it produced no changes in plasma DNA concentrations. Blood clots released dose-dependent amounts of DNA in vitro.

CONCLUSIONS

Cell-free DNA concentrations increase in proportion to the severity of APT, probably as a result of increasing amounts of thrombi obstructing the pulmonary vessels.

Pharmacological activation of soluble guanylate cyclase protects the heart against ischemic injury

BACKGROUND

The role of the nitric oxide/cGMP/cGMP-dependent protein kinase G pathway in myocardial protection and preconditioning has been the object of intensive investigations. The novel soluble guanylate cyclase activator cinaciguat has been reported to elevate intracellular [cGMP] and activate the nitric oxide/cGMP/cGMP-dependent protein kinase G pathway in vivo. We investigated the effects of cinaciguat on myocardial infarction induced by isoproterenol in rats.

METHODS AND RESULTS

Rats were treated orally twice a day for 4 days with vehicle or cinaciguat (10 mg/kg). Isoproterenol (85 mg/kg) was injected subcutaneously 2 days after the first treatment at an interval of 24 hours for 2 days to produce myocardial infarction. After 17 hours, histopathological observations and left ventricular pressure-volume analysis to assess cardiac function with a Millar microtip pressure-volume conductance catheter were performed, and levels of biochemicals of the heart tissues were measured. Gene expression analysis was performed by quantitative real-time polymerase chain reaction. Isolated canine coronary arterial rings exposed to peroxynitrite were investigated for vasomotor function, and immunohistochemistry was performed for cGMP and nitrotyrosine. The present results show that cinaciguat treatment improves histopathological lesions, improves cardiac performance, improves impaired cardiac relaxation, reduces oxidative stress, ameliorates intracellular enzyme release, and decreases cyclooxygenase 2, transforming growth factor-beta, and beta-actin mRNA expression in experimentally induced myocardial infarction in rats. In vitro exposure of coronary arteries to peroxynitrite resulted in an impairment of endothelium-dependent vasorelaxation, increased nitro-oxidative stress, and reduced intracellular cGMP levels, which were all improved by cinaciguat. A cardioprotective effect of postischemic cinaciguat treatment was shown in a canine model of global ischemia/reperfusion.

CONCLUSIONS

Pharmacological soluble guanylate cyclase activation could be a novel approach for the prevention and treatment of ischemic heart disease.

The phosphodiesterase-5 inhibitor vardenafil improves cardiovascular dysfunction in experimental diabetes mellitus

BACKGROUND AND PURPOSE

Patients with diabetes mellitus exhibit generalized endothelial and cardiac dysfunction with decreased nitric oxide production. Elevated intracellular cyclic guanosine monophosphate (cGMP) levels contribute to an effective cardioprotection in different pathophysiological conditions. In this study, we investigated whether chronic treatment with the phosphodiesterase-5 inhibitor vardenafil could improve diabetic cardiovascular dysfunction by up-regulating the nitric oxide-cGMP pathway in the vessel wall and myocardium.

EXPERIMENTAL APPROACH

Diabetes was induced in young rats by a single intraperitoneal injection of streptozotocin (60 mg x kg(-1)). In the treatment group, vardenafil (10 mg x kg(-1) x day(-1)) was given orally for 8 weeks. Diabetic control animals received vehicle for the same time. Left ventricular pressure-volume relations were measured by using a microtip Millar pressure-volume conductance catheter, and indexes of contractility, such as the slope of end-systolic pressure-volume relationship (E(max)) and preload recruitable stroke work (PRSW), were calculated. In organ bath experiments for isometric tension with rings of isolated aortae, endothelium-dependent and independent vasorelaxation was investigated by using acetylcholine and sodium nitroprusside.

KEY RESULTS

When compared with the non-diabetic controls, diabetic rats showed increased myocardial and vascular transforming growth factor-beta1 expression, impaired left ventricular contractility (impairment of E(max) by 53%, PRSW by 40%; P < 0.05) and vascular dysfunction. Treatment with vardenafil resulted in higher cGMP levels, reduced transforming growth factor-beta1 expression, significantly improved cardiac function (improvement of E(max) by 95%, PRSW by 69%; P < 0.05) and greater vasorelaxation to acetylcholine and sodium nitroprusside in aortae from diabetic animals.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that impaired vascular cGMP signalling contributes to the development of diabetic vascular and cardiac dysfunction, which can be prevented by chronic phosphodiesterase-5 inhibition.

Sildenafil in Acute Pulmonary Embolism: Case Report and Review of Literature

We discuss the use of sildenafil in a patient who sustained a massive pulmonary embolism (PE). She remained haemodynamically unstable after thrombolysis, and needed large doses of inotropic support. She was treated with oral sildenafil at a dose of 75 mg three times a day which enabled weaning from inotropic support and clinical improvement.

Effects of selective phosphodiesterase-5-inhibition on myocardial contractility and reperfusion injury after heart transplantation

Recently, the infarct reducing and cardioprotective effects of phosphodiesterase-5-inhibitors were described. In this study, we investigated these effects on ischemia/reperfusion injury in a rat model of heart transplantation. Three groups were assigned for our study: a vardenafil preconditioning group, an ischemic control, and a nonischemic control. Hemodynamic parameters were significantly increased in the vardenafil group (Pmax: 82+/-4 vs. 110+/-12 vs. 127+/-13 mm Hg; dP/dtmax: 1740+/-116 vs. 3197+/-599 vs. 4397+/-602 mm Hg/sec; ischemic control vs. vardenafil vs. nonischemic control; P<0.05 vs. ischemic control). Furthermore, we recorded increased ATP levels and significantly less apoptosis in the treatment group after terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (apoptosis index: 27.23%+/-1.54% vs. 16.77%+/-1.42% vs. 18.86%+/-1.07%; ischemic control vs. vardenafil vs. nonischemic control; P<0.05 vs. ischemic control). Our current results support the concept that the cGMP-PKG-pathway plays an important role in ischemia/reperfusion injury. We could show that up-regulating this pathway has a preconditioning-like effect and can effectively reduce ischemia/reperfusion injury.

Molecular pathogenesis of pulmonary arterial hypertension

Recent investigations have suggested that it might be possible to reverse the pathology of pulmonary arterial hypertension (PAH), a disorder that can be rapidly progressive and fatal despite current treatments including i.v. prostacyclin. This review will address the cellular and molecular processes implicated in clinical, genetic, and experimental studies as underlying the pulmonary vascular abnormalities associated with PAH. Emerging treatments are aimed at inducing apoptosis of abnormal vascular cells that obstruct blood flow and at promoting regeneration of "lost" distal vasculature.

Pathobiology of pulmonary hypertension

A variety of conditions can lead to the development of pulmonary arterial hypertension (PAH). Current treatments can improve symptoms and reduce the severity of the hemodynamic abnormality, but most patients remain quite limited, and deterioration in their condition necessitates a lung transplant. This review discusses current experimental and clinical studies that investigate the pathobiology of PAH. An emerging theme is the consideration of ways in which one might reverse the advanced occlusive structural changes in the pulmonary circulation causing PAH. The current debate concerning the role of regeneration through stem cells is presented. This review also highlights investigations in a number of laboratories relating the pathobiology of PAH to mutations causing loss of function of bone morphogenetic protein receptor II in patients with familial PAH, as well as sporadic cases.

Dose-dependent beneficial hemodynamic effects of BAY 41-2272 in a canine model of acute pulmonary thromboembolism

The current therapy of acute pulmonary embolism is focused on removing the mechanical obstruction of the pulmonary vessels. However, accumulating evidence suggests that pulmonary vasoconstriction drives many of the hemodynamic changes found in this condition. We examined the effects of stimulation of soluble guanylate cyclase with BAY 41-2272 (5-Cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrim idin-4-ylamine) in an anesthetized dog model of acute pulmonary embolism. Hemodynamic and arterial blood gas evaluations were performed in non-embolized dogs treated with vehicle (N=5), and in embolized dogs (intravenous injections of microspheres) that received BAY 41-2272 intravenously in doses of 0.03, 0.1, 0.3, and 1 mg/kg/h or vehicle (1 ml/kg/h of 1.13% ethanol in saline, volume/volume). Plasma cGMP and thiobarbituric acid reactive substances concentrations were determined using a commercial enzyme immunoassay and a fluorometric method, respectively. The infusion of BAY 41-2272 resulted in a decrease in pulmonary artery pressure by approximately 29%, and in pulmonary vascular resistance by approximately 46% of the respective increases induced by lung embolization (both P<0.05). While the higher doses of BAY 41-2272 produced no additional effects on the pulmonary circulation, they caused significant arterial hypotension and reduction in systemic vascular resistance (both P<0.05). Although BAY 41-2272 increased cGMP concentrations (P<0.05), it did not affect the hypoxemia and the increased oxidative stress caused by lung embolization. These results suggest that stimulation of soluble guanylate cyclase with low (but not high) doses of BAY 41-2272 produces selective pulmonary vasodilation during acute pulmonary embolism. The dose-dependent systemic effects produced by BAY 41-2272, however, may limit its usefulness in larger doses.