Effects of BAY 41–2272, a soluble guanylate cyclase activator, on pulmonary vascular reactivity in the ovine fetus

Philippe Deruelle,1,2 Theresa R. Grover,1 Laurent Storme,3 and Steven H. Abman1

1Pediatric Heart Lung Center, University of Colorado School of Medicine, Denver, Colorado; 2Faculté de Médecine, Université de Lille II; and 3Hôpital Jeanne de Flandre, Centre Hospitalier Regional Universitaire de Lille, Lille, France

Submitted 2 November 2004 ; accepted in final form 10 December 2004


    ABSTRACT
 TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Nitric oxide (NO)-cGMP signaling plays a critical role during the transition of the pulmonary circulation at birth. BAY 41–2272 is a novel NO-independent direct stimulator of soluble guanylate cyclase that causes vasodilation in systemic and local circulations. However, the hemodynamic effects of BAY 41–2272 have not been studied in the perinatal pulmonary circulation. We hypothesized that BAY 41–2272 causes potent and sustained fetal pulmonary vasodilation. We performed surgery on 14 fetal lambs (125–130 days gestation; term = 147 days) and placed catheters in the main pulmonary artery, aorta, and left atrium to measure pressures. An ultrasonic flow transducer was placed on the left pulmonary artery (LPA) to measure blood flow, and a catheter was placed in the LPA for drug infusion. Pulmonary vascular resistance (PVR) was calculated as pulmonary artery pressure minus left atrial pressure divided by LPA blood flow. BAY 41–2272 caused dose-related increases in pulmonary blood flow up to threefold above baseline and reduced PVR by 75% (P < 0.01). Prolonged infusion of BAY 41–2272 caused sustained pulmonary vasodilation throughout the 120-min infusion period. The pulmonary vasodilator effect of BAY 41–2272 was not attenuated by N{omega}-nitro-L-arginine, a NO synthase inhibitor. In addition, compared with sildenafil, a phosphodiesterase 5 inhibitor, the pulmonary vasodilator response to BAY 41–2272 was more prolonged. We conclude that BAY 41–2272 causes potent and sustained fetal pulmonary vasodilation independent of NO release. We speculate that BAY 41–2272 may have therapeutic potential for pulmonary hypertension associated with failure to circulatory adaptation at birth, especially in the setting of impaired NO production.

physiology; lung; vasodilator


HIGH RESISTANCE AND LOW BLOOD flow characterize the normal fetal pulmonary circulation. Pulmonary vascular resistance (PVR) decreases dramatically during the normal transition from the fetal to neonatal circulation at birth. Mechanisms that explain the pulmonary vasodilatation at birth are incompletely understood but include alveolar ventilation (12), increase in PaO2 (9, 40), and the synthesis of vasoactive mediators such as nitric oxide (NO) (3, 10, 17). NO plays an important role in the regulation of the developing pulmonary circulation by modulation of basal pulmonary vascular tone and reactivity in the late-gestation fetus (3, 4, 10). The vasodilator action of several substances, such as acetylcholine, bradykinin, or ADP, and shear stress, is dependent, at least in part, on NO release (3, 4, 10, 20, 23, 32, 38). In addition, inhibition of NO synthase (NOS) attenuates the postnatal adaptation of the pulmonary circulation (3).

NO mediates vasodilatation by stimulating soluble guanylate cyclase (sGC) in vascular smooth muscle cells. sGC is a hemoprotein with a heterodimer of {alpha}- and {beta}-subunits (19). Enzyme activation by the binding of NO results in the conversion of guanosine triphosphate (GTP) to cGMP. cGMP modulates the activity of cGMP-dependent kinases, cGMP-regulated phosphodiesterases, and cGMP-regulated ion channels, which are involved in the regulation of many physiological functions (14). cGMP signaling is downregulated by phosphodiesterase 5 (PDE5) activity, which lowers intracellular cGMP content through degradation of cGMP to 5'-GMP (14).

In addition to NO, pharmacological agents have been developed to directly activate sGC. YC-1, a synthetic benzylindazole derivative, increases sGC activity in a NO-independent manner, enhances the sensivity of sGC toward NO, and inhibits PDE5 activity (14, 39). Recent studies showed that BAY 41–2272, a high-affinity YC-1 analog, caused marked vasodilation in the postnatal circulations (8, 13, 35, 36). However, the effects of direct activation of sGC in the perinatal lung are uncertain.

Persistent pulmonary hypertension of the newborn (PPHN) is a pathological condition related to endothelial injury and decrease in NO production (24). Although inhaled NO (iNO) is effective in treating newborns with PPHN, 30–40% of the patients do not respond to iNO and require ECMO therapy due to high PVR and hypoxemia (26, 30). These findings suggest that novel therapeutic strategies are still required to further improve outcomes in newborns with severe PPHN. Because BAY 41–2272 activates sGC in a NO-independent fashion, we hypothesized that BAY 41–2272 may be a potent pulmonary vasodilator in the fetal lung.

In addition, past studies of fetal pulmonary vasoreactivity have demonstrated that many endothelium-dependent vasodilator stimuli such as increased O2, shear stress, and pharmalogical agents cause only transient vasodilation (1, 2, 5, 6). In contrast, agonists that directly increase smooth muscle cell cGMP, such as atrial natriuretic peptide, 8-bromo-GMP, and iNO, cause sustained vasodilation (2, 18). Other studies suggest that a potent myogenic response exists in the fetal lung circulation, which is unmasked by NOS inhibition, and maintains high PVR in the normal fetus and in the setting of chronic intrauterine pulmonary hypertension (38). These findings led to the hypothesis that agonists that directly increase smooth muscle cell cGMP content, such as BAY 41–2272, may cause more potent and prolonged fetal pulmonary vasodilation and that the inability to sustain production of cGMP contributes to high PVR in the normal fetus.

To address this question, we examined the pulmonary hemodynamic response to BAY 41–2272 infusions and determined its mechanism of action in chronically prepared, late-gestation fetal lamb. We report that BAY 41–2272 is a potent pulmonary vasodilator in the fetus and speculate that this may be an effective strategy for the treatment of PPHN.


    METHODS
 TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Surgical Preparation

All procedures were reviewed and approved by the Animal Care and Use Committee at the University of Colorado Health Sciences Center (Denver, CO). Surgery was performed between 125 and 130 days gestation, according to previously published methods (5). Fourteen mixed-breed (Columbia-Rambouillet) pregnant ewes were fasted for 48 h before surgery. Ewes were sedated with intramuscular buprenex (0.6 mg) and intravenous ketamine (60 mg) and diazepam (10 mg) and intratracheally intubated. Ewes were anesthetized using inhaled isoflurane (2–3%) and remained sedated but breathed spontaneously throughout surgery. Under sterile conditions, the left forelimb of the fetal lamb was delivered through a uterine incision. A skin incision was made under the left forelimb after local infiltration with 1% lidocaine. Polyvinyl catheters were inserted into the axillary artery and advanced into the ascending aorta (Ao) and the superior vena cava. A left axillary to sternal thoracotomy exposed the heart and great arteries. Polyvinyl catheters were inserted into the left pulmonary artery (LPA), the main pulmonary artery (MPA), and left atrium (LA) by direct puncture and secured into position with purse-string sutures, as previously described. A 6-mm ultrasonic flow transducer (Transonic Systems, Ithaca, NY) was placed around the LPA to measure blood flow to the left lung (Qp). A catheter was placed in the amniotic cavity to serve as a pressure referent. The thoracotomy incision was closed in layers. The uteroplacental circulation was kept intact, and the fetus was gently replaced in the uterus. Ampicillin (500 mg) was added to the amniotic cavity before closure of the hysterotomy. The ewe was allowed to recover from surgery for 48 h before fetal drug administration and hemodynamic studies.

Physiological Measurements

The Ao, MPA, and LA catheters were connected to a computer-monitored pressure transducer and recorder (Biopac Systems, Santa Barbara, CA). Pressures were referenced to amniotic pressures, and the pressure transducer was calibrated with a mercury manometer. The flow transducer cable was attached to an internally calibrated flowmeter (Transonic Systems) for continuous measurements of LPA blood flow (QLPA). The absolute values of flow were determined from phasic blood flow signals as previously described (21). PVR in the left lung was calculated with the following equation: PVR (mmHg·ml–1·min–1) = (mean MPAP – mean LAP)/QLPA. Arterial blood gas tensions, pH, hemoglobin, oxygen saturation, and methemoglobin were measured from blood samples that were drawn from the Ao catheter and measured at 39.5°C with a blood gas analyzer and hemoximeter (model OSM-3, Radiometer, Copenhagen, Denmark).

Study Drugs

BAY 41–2272 (kindly provided by Dr. J.-P. Stasch, Bayer AG, Pharma Research, Wuppertal, Germany) was dissolved with 50% ethanol (1 vol ethanol and 1 vol saline) and diluted with saline to achieve the different concentration used in this study (100 µg, 500 µg, 1 mg, and 2.5 mg/ml).

N{omega}-nitro-L-arginine (L-NA; 10 mg, Sigma, St. Louis, MO) was dissolved in normal saline plus 2–3 drops 1 M HCl and titrated with 1 M NaOH to achieve a pH of 7.4 (1 ml final vol). The drug was infused into the LPA by an infusion pump set to deliver 10 mg for a 10-min period. L-NA was prepared immediately before drug administration, and the dose chosen was based on previous studies that have demonstrated effective blockade of NOS activity during acetylcholine and flow-induced vasodilation for at least 4 h (10).

Sildenafil (1 mg/ml, intravenous solution, Pfizer, Sandwich, UK) was diluted with normal saline for a final concentration of 0.1 mg/ml.

Experimental Design

Protocol 1: pulmonary hemodynamic effects of acute BAY 41–2272 infusion. The purpose of this protocol was to determine the effects of acute intrapulmonary administration of BAY 41–2272 on fetal pulmonary hemodynamics and the dosage needed for optimal response. After a 48-h recovery period after surgery, saline (0.1 ml/min) was first infused into the LPA catheter for at least 30 min and baseline hemodynamic measurements were recorded every 10 min for QLPA, MPAP, AoP, LAP, and heart rate (HR). After baseline measurements were stable for a 30-min period, BAY 41–2272 was infused at one of several doses in random order (100 µg, 500 µg, 1 mg, and 2.5 mg) into the LPA for 10 min. After each infusion, the catheter was subsequently flushed with saline (0.1 ml/min). Hemodynamic measurements were recorded for at least 30 min after the return to baseline values before the next drug infusion. As BAY 41–2272 was diluted in 50% ethanol, we studied the hemodynamic response to ethanol (1 ml, 50%) to ensure that the response cannot be related to the solvent. Arterial blood gas tensions were obtained before and after each study period.

Protocol 2: pulmonary hemodynamic effects of prolonged BAY 41–2272 infusion. The purpose of this protocol was to investigate the effects of prolonged BAY 41–2272 infusion on fetal pulmonary circulation. Saline (0.1 ml/min) was first infused into the LPA for at least 30 min. After 30 min of stable baseline measurements, BAY 41–2272 (1 mg/ml) was infused at 0.1 ml/min for 120 min into the LPA catheter (dose rate: 0.1 mg/min; total dose: 12 mg). Hemodynamic measurements were recorded every 10 min starting at the beginning of the infusion and continued for 60 min after drug infusion. Arterial blood gas tensions were obtained before, after 60 min of drug infusion, and at 30 min of the recovery period.

Protocol 3: pulmonary hemodynamic effects of BAY 41–2272 after NOS inhibition. The purpose of this protocol was to determine whether BAY 41–2272-induced pulmonary vasodilation was mediated through NO production. Protocol 2 was repeated after L-NA infusion. L-NA (10 mg over 10 min) was infused into the LPA catheter. The LPA catheter was then infused with saline for 20 min before starting the BAY 41–2272 infusion (1 mg/ml) at 0.1 ml/min for 120 min (dose rate: 0.1 mg/min; total dose: 12 mg). Hemodynamic measurements were recorded throughout the study period and 60 min after the Bay 41–2272 infusion was stopped.

Protocol 4: pulmonary hemodynamic effects of prolonged sildenafil infusion. The purpose of this protocol was to compare BAY 41–2272-induced pulmonary vasodilation to sildenafil, a selective inhibitor of cGMP-specific PDE5. Protocol 2 was repeated with sildenafil (0.1 mg/ml) infused into the LPA catheter at a constant rate of 0.1 ml/min. This dose of sildenafil was selected from previous studies that demonstrated a comparable change in pulmonary blood flow as obtained with BAY 41–2272.

Statistical Analysis

Data are presented as means ± SE. Statistical analysis was performed with the Statview software package (SAS Institute, Cary, NC). Statistical comparisons were made using factorial and repeated-measures analysis of variance and Fisher's protected least significant differences test. P < 0.05 was considered significant. In each experiment, n represents the number of different animals studied.


    RESULTS
 TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Protocol 1: Pulmonary Hemodynamic Effect of Acute BAY 41–2272 Infusion

BAY 41–2272 caused dose-related pulmonary vasodilation in the chronically prepared fetal lamb (Fig. 1). Brief infusion of BAY 41–2272 increased Qp and decreased PVR from baseline values at a threshold dose of 500 µg (P < 0.01, Fig. 1). At higher doses (1 and 2.5 mg), BAY 41–2272 progressively increased Qp and reduced PVR without altering blood gas tensions (P < 0.01). At 2.5 mg, BAY 41–2272 decreased MPA pressures and AoP and increased HR compared with baseline values and lower doses (P < 0.01, Fig. 1 and Table 1). Brief infusion of BAY 41–2272 did not alter blood gas tensions and LA pressures at the doses used in this study (Table 1).



View larger version (24K):
[in this window]
[in a new window]
 
Fig. 1. Dose-response effects of BAY 41–2272 on the fetal pulmonary circulation. Infusion of BAY 41–2272 (0.1–2.5 mg) caused dose-related vasodilation in the pulmonary circulation. At the highest dose studied, BAY 41–2272 reduced pulmonary and aortic pressures. Values are means ± SE (n = 4). *P < 0.01 compared with baseline value. PVR, pulmonary vascular resistance.

 

View this table:
[in this window]
[in a new window]
 
Table 1. Blood gases, AoPs, and HR after ethanol (50%, 1 ml) and BAY 41-2272 infused in the left pulmonary artery catheter for 10 min at 0.1 ml/min

 
Protocol 2: Pulmonary Hemodynamic Effects of Prolonged BAY 41–2272 Infusion

Prolonged (120 min) infusion of BAY 41–2272 caused sustained pulmonary vasodilation (Fig. 2). BAY 41–2272 infusion (0.1 mg/min) caused a nearly 3.5-fold rise in pulmonary blood flow (Qp: from 67 ± 8 to 242 ± 51 ml/min, P < 0.01; Fig. 2) and a 11% fall in MPA pressures (MPAP: from 46 ± 2 to 41 ± 2 mmHg, P < 0.05; Fig. 2). These changes resulted in a 75% fall in PVR (PVR: from 0.67 ± 0.06 to 0.17 ± 0.04 mmHg·ml–1·min–1, P < 0.01; Fig. 2). This vasodilator response was maximal 40 min after the beginning of the infusion and was sustained throughout the infusion period and persisted for 30 min after stopping drug infusion. Prolonged BAY 41–2272 infusion did not change arterial blood gas tensions but decreased AoP by 6% (P < 0.05; Table 2) and increased HR by 8% (not significant; Table 2).



View larger version (27K):
[in this window]
[in a new window]
 
Fig. 2. Pulmonary hemodynamic effects of prolonged infusion of BAY 41–2272. BAY 41–2272 (1 mg/ml at 0.1 mg/min, black rectangle) caused potent and sustained pulmonary vasodilation for the entire 120-min study period, which persisted for 30 min after termination of drug infusion. Values are expressed as means ± SE (n = 4). *P < 0.01 and §P < 0.05 compared with baseline value. PAP, pulmonary artery pressure.

 

View this table:
[in this window]
[in a new window]
 
Table 2. Blood gases, AoPs, and HR during baseline, after 60 min of drug infusion, and at 30 min of the recovery period for BAY 41-2272, BAY 41-2272 after L-NA pretreatment, and sildenafil infusions

 
Protocol 3: Pulmonary Hemodynamic Effects of BAY 41–2272 After NOS Inhibition

The response to BAY 41–2272 was not attenuated after NOS inhibition (Fig. 3). That is, after treatment with L-NA, which caused a marked rise in PVR, BAY 41–2272 still had potent and sustained vasodilator effects including a 247% increase in Qp (Qp: from 49.8 ± 6.5 to 196.5 ± 40.8 ml/min, P < 0.01; Fig. 3) and a 70% decrease in PVR (PVR: from 1.0 ± 0.28 to 0.28 ± 0.13 mmHg·ml–1·min–1, P < 0.01; Fig. 3A). Pretreatment with L-NA did not modify the effects of BAY 41–2272 on MPAP, AoP, and HR (Fig. 3B and Table 2). Blood gas tensions did not change during the study period (Table 2).



View larger version (40K):
[in this window]
[in a new window]
 
Fig. 3. A: effects of nitric oxide synthase (NOS) inhibition on the fetal pulmonary vasodilator response to BAY 41–2272 (1 mg/ml at 0.1 mg/min, black rectangle). N{omega}-nitro-L-arginine (L-NA; 10 mg/10 min, gray rectangle) increased PVR by 30% above baseline before BAY 41–2272 infusion and did not alter the pulmonary vasodilator effects of BAY 41–2272. Values are expressed as means ± SE (n = 4). *P < 0.01 compared with baseline value and post-L-NA treatment. §P < 0.05 compared with baseline value and post-L-NA treatment. {dagger}P < 0.01 and {ddagger}P < 0.05 compared with post-L-NA treatment. B: effect of NOS inhibition on BAY 41–2272-mediated vasodilation in the fetal lung. As shown, NOS inhibition did not attenuate the vasodilator response to BAY 41–2272.

 
Protocol 4: Pulmonary Hemodynamic Effects of Prolonged Sildenafil Infusion

To compare the effects of PDE5 inhibition with BAY 41–2272, we infused sildenafil, a selective PDE5 inhibitor (0.1 mg/ml), into the LPA for 120 min. At this dose, sildenafil infusion caused a nearly threefold rise in pulmonary blood flow (Qp: from 74 ± 4 to 210 ± 23 ml/min, P < 0.01; Fig. 4) and a 60% fall in PVR (PVR: from 0.63 ± 0.05 to 0.25 ± 0.05 mmHg·ml–1·min–1, P < 0.01; Fig. 4). The maximal response and the return to baseline values were, respectively, obtained 40 and 110 min after the beginning of the infusion. There was no effect of sildenafil on MPAP, AoP, HR, and arterial blood gas tensions (Table 2). Comparisons of the pulmonary vascular responses between BAY 41–2272 and sildenafil demonstrated that pulmonary vasodilatation was better sustained and more prolonged during BAY 41–2272 than during sildenafil infusion (Fig. 4).



View larger version (28K):
[in this window]
[in a new window]
 
Fig. 4. Comparison of the pulmonary vasodilator effects of prolonged infusions of BAY 41–2272 (n = 4) and sildenafil, a PDE5 inhibitor (n = 6). As shown, pulmonary vasodilatation was more prolonged during BAY 41–2272 than during sildenafil infusion. Values are expressed as means ± SE. *P < 0.05 between BAY 41–2272 and sildenafil infusions.

 

    DISCUSSION
 TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Although iNO is an effective therapy for hypoxemic newborns with severe pulmonary hypertension, responses are poor in up to 40% of patients. To determine whether a NO-independent activator of sGC can provide an alternate therapy, we studied the effects of BAY 41–2272 in the fetal lamb. We found that BAY 41–2272 markedly increased pulmonary blood flow by nearly 3.5-fold and reduced PVR by 75% and that the pulmonary vasodilator effect of BAY 41–2272 was not attenuated by NOS blockade. In addition, compared with sildenafil, a PDE5-selective inhibitor, the pulmonary vasodilator response of BAY 41–2272 was more sustained. These results support the hypothesis that direct activation of sGC by a NO-independent mechanism causes potent and sustained vasodilation in the developing lung. In addition, in contrast with many vasodilator stimuli, BAY 41–2272 causes potent and sustained pulmonary vasodilation in the fetus.

Our results are interesting because this is the first report describing the hemodynamic response to BAY 41–2272 in the developing pulmonary circulation. BAY 41–2272 directly stimulates sGC on a NO-independent but heme-dependent site (35). In vitro studies showed that BAY 41–2272 activates purified sGC up to 30-fold and is ~100-fold more potent than its analog YC-1 (35). After oral administration, BAY 41–2272 decreased blood pressure and improved mortality in hypertensive rats (35). Recently, in a model of acute pulmonary hypertension in juvenile lambs (mean weight = 19 ± 0.4 kg), Evgenov et al. (13) demonstrated that BAY 41–2272 is a potent pulmonary vasodilator. Although BAY 41–2272 induces a fall in blood pressure, the pulmonary effects were significantly greater than the systemic effects (13). In our study, BAY 41–2272 infusion caused potent and sustained falls in PVR but systemic effects were observed at higher doses and prolonged infusion.

The NO-cGMP cascade is one of the major physiological pathways in the fetal and neonatal pulmonary circulation. NO is produced during conversion of L-arginine to L-citrulline by the NOS in endothelial cells and activates sGC in vascular smooth muscle cells to release cGMP. Past studies showed that sGC is present and active early in the fetal lung (4, 17). Basal and stimulated NO release modulates pulmonary vasoregulation during late gestation. NOS antagonism increases PVR in near-term fetal lambs (3, 29). In addition, NOS inhibition selectively attenuates pulmonary vascular response to acetylcholine, oxygen, shear stress, and myogenic response (3, 10, 23, 38). At birth, pretreatment with L-NA reduces the fall in PVR and compromises the transition to neonatal circulation (3). Pathological conditions support the potential importance of NO and sGC in the regulation of the perinatal pulmonary circulation. Endothelial NOS and sGC activities and expression are altered in lamb models of persistent pulmonary hypertension and congenital diaphragmatic hernia (7, 27, 33, 41, 43, 44).

Stasch et al. (35) reported BAY 41–2272 as a NO-independent sGC activator without any PDE5 inhibitory activity. Our data agree with these findings as BAY 41–2272-induced vasodilation was not blocked by L-NA, suggesting a NO-independent mechanism. However, with higher doses, Mullershausen et al. (25) found that in addition to direct stimulation of sGC, BAY 41–2272 may have some PDE5 inhibitor effects as well. In addition, BAY 41–2272 may sensitize sGC to become more responsive to NO (25). For example, BAY 41–2272 augments and prolongs pulmonary vasodilation induced by iNO (13). Whether BAY 41–2272 at high doses can inhibit phosphodiesterase isoforms other than PDE5 is uncertain (22). In our study, the vasodilator effects of BAY 41–2272 were more sustained than those observed during treatment with the PDE5 inhibitor sildenafil. Further studies are needed to fully examine the mechanisms responsible for this response.

We found that BAY 41–2272 caused a prolonged and sustained vasodilation in the ovine fetal lung. This response is different from several endothelium-dependent agonists (acetylcholine, bradykinin, histamine, tolazoline, oxygen, or shear stress), which are unable to sustain vasodilation (1, 2, 5, 6). Conversely, direct stimulators of vascular smooth muscle cells such as 8-bromo-GMP, atrial natriuretic peptide, and iNO can produce a sustained pulmonary vasodilation (2, 18). Norepinephrine and estradiol, probably related to NO and lemakalin, a direct K+-ATP channel agonist, are also able to maintain a pulmonary vasorelaxant response, but the estradiol response occurred after 24–48 h of treatment (11, 16, 28). Nevertheless, in our findings, the BAY 41–2272 vasodilator response was greater than with these other agents. Mechanisms that sustain fetal pulmonary vasodilation are unknown but may include increased production of vasoconstrictors or PDE inhibition activity. BQ-123 and phosphoramidon, two endothelin-1 antagonists, augment and prolong the increase in flow during acute ductus arteriosus compression (15). Dipyridamole, a cGMP phosphodiesterase inhibitor, prolongs iNO-induced pulmonary vasodilation in the ovine transitional circulation (46). However, neither endothelin-1 blockade nor dypiridamole treatment completely inhibited this vasoconstrictor response in the fetal lung.

Increase cGMP production activates cGMP-dependent protein kinase (PKG). PKG induces the phosphorylation of phosphodiesterases that downregulate cGMP production. Inhibition of phosphodiesterases by a PDE5 inhibitor such as sildenafil enhances NO-induced vasorelaxation by increasing vascular smooth muscle cGMP concentration (14). Sildenafil causes vasodilation both in adult and neonatal pulmonary circulation (31, 34, 42, 45). Sildenafil may be useful in a newborn after cardiac surgery in association with iNO (37) and has been proposed for children with pulmonary hypertension. In our study, BAY 41–2272 infusion induced a more sustained pulmonary vasodilation than sildenafil infusion. This observation suggests that the therapeutic potential of BAY 41–2272 may be at least equivalent to sildenafil in the setting of severe pulmonary hypertension.

In conclusion, we found that BAY 41–2272 induces a potent and sustained vasorelaxant response in the fetal pulmonary circulation. The mechanism by which BAY 41–2272 causes pulmonary vasodilation is independent of NO release. The vasodilator response to BAY 41–2272 is greater and more sustained than the previously studied fetal pulmonary vasodilators. We speculate that BAY 41–2272 could improve conditions associated with failure to circulatory adaptation at birth. However, further investigations are necessary to evaluate and examine the systemic effects of BAY 41–2272 in these pathological conditions.


    GRANTS
 TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
This work was supported in part by National Institutes of Health Grants HL-68702 and HL-57144 to S. H. Abman, Bourse Lavoisier, Collège National des Gynécologues Obstétriciens Français, and Société Française de Médecine Périnatale (to P. Deruelle).


    ACKNOWLEDGMENTS
 
We thank Dr. J.-P. Stasch and Bayer Healthcare for providing the BAY 41–227 compound.


    FOOTNOTES
 

Address for reprint requests and other correspondence: S. H. Abman, Dept. of Pediatrics, B-395, Children's Hospital, 1056 E. 19th Ave., Denver, CO 80218-1088 (E-mail: steven.abman{at}uchsc.edu

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


    REFERENCES
 TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Abman SH and Accurso FJ. Acute effects of partial compression of ductus arteriosus on fetal pulmonary circulation. Am J Physiol Heart Circ Physiol 257: H626–H634, 1989.[Abstract/Free Full Text]
  2. Abman SH and Accurso FJ. Sustained fetal pulmonary vasodilation with prolonged atrial natriuretic factor and GMP infusions. Am J Physiol Heart Circ Physiol 260: H183–H192, 1991.[Abstract/Free Full Text]
  3. Abman SH, Chatfield BA, Hall SL, and McMurtry IF. Role of endothelium-derived relaxing factor during transition of pulmonary circulation at birth. Am J Physiol Heart Circ Physiol 259: H1921–H1927, 1990.[Abstract/Free Full Text]
  4. Abman SH, Chatfield BA, Rodman DM, Hall SL, and McMurtry IF. Maturational changes in endothelium-derived relaxing factor activity of ovine pulmonary arteries in vitro. Am J Physiol Lung Cell Mol Physiol 260: L280–L285, 1991.[Abstract/Free Full Text]
  5. Abman SH, Wilkening RB, Ward RM, and Accurso FJ. Adaptation of fetal pulmonary blood flow to local infusion of tolazoline. Pediatr Res 20: 1131–1135, 1986.[Abstract]
  6. Accurso FJ, Alpert B, Wilkening RB, Petersen RG, and Meschia G. Time-dependent response of fetal pulmonary blood flow to an increase in fetal oxygen tension. Respir Physiol 63: 43–52, 1986.[CrossRef][ISI][Medline]
  7. Black SM, Fineman JR, Steinhorn RH, Bristow J, and Soifer SJ. Increased endothelial NOS in lambs with increased pulmonary blood flow and pulmonary hypertension. Am J Physiol Heart Circ Physiol 275: H1643–H1651, 1998.[Abstract/Free Full Text]
  8. Boerrigter G, Costello-Boerrigter LC, Cataliotti A, Tsuruda T, Harty GJ, Lapp H, Stasch JP, and Burnett JC Jr. Cardiorenal and humoral properties of a novel direct soluble guanylate cyclase stimulator BAY 41–2272 in experimental congestive heart failure. Circulation 107: 686–689, 2003.[Abstract/Free Full Text]
  9. Cassin S, Dawes GS, Mott JC, Ross BB, and Strang LB. The vascular resistance of the fetal and newly ventilated lung of the lamb. J Physiol 171: 61–79, 1964.[ISI][Medline]
  10. Cornfield DN, Chatfield BA, McQueston JA, McMurtry IF, and Abman SH. Effects of birth-related stimuli on L-arginine-dependent pulmonary vasodilation in ovine fetus. Am J Physiol Heart Circ Physiol 262: H1474–H1481, 1992.[Abstract/Free Full Text]
  11. Cornfield DN, McQueston JA, McMurtry IF, Rodman DM, and Abman SH. Role of ATP-sensitive potassium channels in ovine fetal pulmonary vascular tone. Am J Physiol Heart Circ Physiol 263: H1363–H1368, 1992.[Abstract/Free Full Text]
  12. Dawes GS, Mott JC, Widdicombe JG, and Wyatt DG. Changes in the lungs of the newborn lamb. J Physiol 121: 141–162, 1953.[ISI][Medline]
  13. Evgenov OV, Ichinose F, Evgenov NV, Gnoth MJ, Falkowski GE, Chang Y, Bloch KD, and Zapol WM. Soluble guanylate cyclase activator reverses acute pulmonary hypertension and augments the pulmonary vasodilator response to inhaled nitric oxide in awake lambs. Circulation 110: 2253–2259, 2004.[Abstract/Free Full Text]
  14. Friebe A and Koesling D. Regulation of nitric oxide-sensitive guanylyl cyclase. Circ Res 93: 96–105, 2003.[Abstract/Free Full Text]
  15. Ivy DD, Kinsella JP, and Abman SH. Endothelin blockade augments pulmonary vasodilation in the ovine fetus. J Appl Physiol 81: 2481–2487, 1996.[Abstract/Free Full Text]
  16. Jaillard S, Houfflin-Debarge V, Riou Y, Rakza T, Klosowski S, Lequien P, and Storme L. Effects of catecholamines on the pulmonary circulation in the ovine fetus. Am J Physiol Regul Integr Comp Physiol 281: R607–R614, 2001.[Abstract/Free Full Text]
  17. Kinsella JP, Ivy DD, and Abman SH. Ontogeny of NO activity and response to inhaled NO in the developing ovine pulmonary circulation. Am J Physiol Heart Circ Physiol 267: H1955–H1961, 1994.[Abstract/Free Full Text]
  18. Kinsella JP, McQueston JA, Rosenberg AA, and Abman SH. Hemodynamic effects of exogenous nitric oxide in ovine transitional pulmonary circulation. Am J Physiol Heart Circ Physiol 263: H875–H880, 1992.[Abstract/Free Full Text]
  19. Koesling D and Friebe A. Soluble guanylyl cyclase: structure and regulation. Rev Physiol Biochem Pharmacol 135: 41–65, 1999.[Medline]
  20. Konduri GG and Mital S. Adenosine and ATP cause nitric oxide-dependent pulmonary vasodilation in fetal lambs. Biol Neonate 78: 220–229, 2000.[CrossRef][ISI][Medline]
  21. Lewis AB, Heymann MA, and Rudolph AM. Gestational changes in pulmonary vascular responses in fetal lambs in utero. Circ Res 39: 536–541, 1976.[Abstract]
  22. Mayer B and Koesling D. cGMP signalling beyond nitric oxide. Trends Pharmacol Sci 22: 546–548, 2001.[CrossRef][ISI][Medline]
  23. McQueston JA, Cornfield DN, McMurtry IF, and Abman SH. Effects of oxygen and exogenous L-arginine on EDRF activity in fetal pulmonary circulation. Am J Physiol Heart Circ Physiol 264: H865–H871, 1993.[Abstract/Free Full Text]
  24. McQueston JA, Kinsella JP, Ivy DD, McMurtry IF, and Abman SH. Chronic pulmonary hypertension in utero impairs endothelium-dependent vasodilation. Am J Physiol Heart Circ Physiol 268: H288–H294, 1995.[Abstract/Free Full Text]
  25. Mullershausen F, Russwurm M, Friebe A, and Koesling D. Inhibition of phosphodiesterase type 5 by the activator of nitric oxide-sensitive guanylyl cyclase BAY 41–2272. Circulation 109: 1711–1713, 2004.[Abstract/Free Full Text]
  26. Neonatal Inhaled Nitric Oxide Study Group. Inhaled nitric oxide in full-term and nearly full-term infants with hypoxic respiratory failure. The Neonatal Inhaled Nitric Oxide Study Group. N Engl J Med 336: 597–604, 1997.[Abstract/Free Full Text]
  27. North AJ, Moya FR, Mysore MR, Thomas VL, Wells LB, Wu LC, and Shaul PW. Pulmonary endothelial nitric oxide synthase gene expression is decreased in a rat model of congenital diaphragmatic hernia. Am J Respir Cell Mol Biol 13: 676–682, 1995.[Abstract]
  28. Parker TA, Kinsella JP, Galan HL, Le Cras TD, Richter GT, Markham NE, and Abman SH. Prolonged infusions of estradiol dilate the ovine fetal pulmonary circulation. Pediatr Res 47: 89–96, 2000.[Abstract/Free Full Text]
  29. Rairigh RL, Le Cras TD, Ivy DD, Kinsella JP, Richter G, Horan MP, Fan ID, and Abman SH. Role of inducible nitric oxide synthase in regulation of pulmonary vascular tone in the late gestation ovine fetus. J Clin Invest 101: 15–21, 1998.[Abstract/Free Full Text]
  30. Roberts JD, Polaner DM, Lang P, and Zapol WM. Inhaled nitric oxide in persistent pulmonary hypertension of the newborn. Lancet 340: 818–819, 1992.[CrossRef][ISI][Medline]
  31. Sastry BK, Narasimhan C, Reddy NK, and Raju BS. Clinical efficacy of sildenafil in primary pulmonary hypertension: a randomized, placebo-controlled, double-blind, crossover study. J Am Coll Cardiol 43: 1149–1153, 2004.[CrossRef][ISI][Medline]
  32. Shaul PW, Farrar MA, and Zellers TM. Oxygen modulates endothelium-derived relaxing factor production in fetal pulmonary arteries. Am J Physiol Heart Circ Physiol 262: H355–H364, 1992.[Abstract/Free Full Text]
  33. Shaul PW, Yuhanna IS, German Z, Chen Z, Steinhorn RH, and Morin FC III. Pulmonary endothelial NO synthase gene expression is decreased in fetal lambs with pulmonary hypertension. Am J Physiol Lung Cell Mol Physiol 272: L1005–L1012, 1997.[Abstract/Free Full Text]
  34. Shekerdemian LS, Ravn HB, and Penny DJ. Interaction between inhaled nitric oxide and intravenous sildenafil in a porcine model of meconium aspiration syndrome. Pediatr Res 55: 413–418, 2004.[Abstract/Free Full Text]
  35. Stasch JP, Becker EM, Alonso-Alija C, Apeler H, Dembowsky K, Feurer A, Gerzer R, Minuth T, Perzborn E, Pleiss U, Schroder H, Schroeder W, Stahl E, Steinke W, Straub A, and Schramm M. NO-independent regulatory site on soluble guanylate cyclase. Nature 410: 212–215, 2001.[CrossRef][ISI][Medline]
  36. Stasch JP, Schmidt P, Alonso-Alija C, Apeler H, Dembowsky K, Haerter M, Heil M, Minuth T, Perzborn E, Pleiss U, Schramm M, Schroeder W, Schroder H, Stahl E, Steinke W, and Wunder F. NO- and haem-independent activation of soluble guanylyl cyclase: molecular basis and cardiovascular implications of a new pharmacological principle. Br J Pharmacol 136: 773–783, 2002.[CrossRef][ISI][Medline]
  37. Stocker C, Penny DJ, Brizard CP, Cochrane AD, Soto R, and Shekerdemian LS. Intravenous sildenafil and inhaled nitric oxide: a randomised trial in infants after cardiac surgery. Intensive Care Med 29: 1996–2003, 2003.[CrossRef][ISI][Medline]
  38. Storme L, Rairigh RL, Parker TA, Kinsella JP, and Abman SH. In vivo evidence for a myogenic response in the fetal pulmonary circulation. Pediatr Res 45: 425–431, 1999.[Abstract]
  39. Straub A, Stasch JP, Alonso-Alija C, Benet-Buchholz J, Ducke B, Feurer A, and Furstner C. NO-independent stimulators of soluble guanylate cyclase. Bioorg Med Chem 11: 781–784, 2001.[CrossRef]
  40. Teitel DF, Iwamoto HS, and Rudolph AM. Effects of birth-related events on central blood flow patterns. Pediatr Res 22: 557–566, 1987.[Abstract]
  41. Thebaud B, Petit T, De Lagausie P, Dall'Ava-Santucci J, Mercier JC, and Dinh-Xuan AT. Altered guanylyl-cyclase activity in vitro of pulmonary arteries from fetal lambs with congenital diaphragmatic hernia. Am J Respir Cell Mol Biol 27: 42–47, 2002.[Abstract/Free Full Text]
  42. Travadi JN and Patole SK. Phosphodiesterase inhibitors for persistent pulmonary hypertension of the newborn: a review. Pediatr Pulmonol 36: 529–535, 2003.[CrossRef][ISI][Medline]
  43. Tzao C, Nickerson PA, Russell JA, Gugino SF, and Steinhorn RH. Pulmonary hypertension alters soluble guanylate cyclase activity and expression in pulmonary arteries isolated from fetal lambs. Pediatr Pulmonol 31: 97–105, 2001.[CrossRef][ISI][Medline]
  44. Villamor E, Le Cras TD, Horan MP, Halbower AC, Tuder RM, and Abman SH. Chronic intrauterine pulmonary hypertension impairs endothelial nitric oxide synthase in the ovine fetus. Am J Physiol Lung Cell Mol Physiol 272: L1013–L1020, 1997.[Abstract/Free Full Text]
  45. Weimann J, Ullrich R, Hromi J, Fujino Y, Clark MW, Bloch KD, and Zapol WM. Sildenafil is a pulmonary vasodilator in awake lambs with acute pulmonary hypertension. Anesthesiology 92: 1702–1712, 2000.[CrossRef][ISI][Medline]
  46. Ziegler JW, Ivy DD, Fox JJ, Kinsella JP, Clarke WR, and Abman SH. Dipyridamole, a cGMP phosphodiesterase inhibitor, causes pulmonary vasodilation in the ovine fetus. Am J Physiol Heart Circ Physiol 269: H473–H479, 1995.[Abstract/Free Full Text]