Paneth cell ontogeny in term and preterm ovine models

Introduction

Paneth cells are critically important to intestinal health, including protecting intestinal stem cells, shaping the intestinal microbiome, and regulating host immunity. Understanding Paneth cell biology in the immature intestine is often modeled in rodents with little information in larger mammals such as sheep. Previous studies have only established the distribution pattern of Paneth cells in healthy adult sheep. Our study aimed to examine the ontogeny, quantification, and localization of Paneth cells in fetal and newborn lambs at different gestational ages and with perinatal transient asphyxia. We hypothesized that ovine Paneth cell distribution at birth resembles the pattern seen in humans (highest concentrations in the ileum) and that ovine Paneth cell density is gestation-dependent.

Methods

Intestinal samples were obtained from 126-127 (preterm, with and without perinatal transient asphyxia) and 140-141 (term) days gestation sheep. Samples were quantified per crypt in at least 100 crypts per animal and confirmed as Paneth cells through in immunohistochemistry.

Results

Paneth cells had significantly higher density in the ileum compared to the jejunum and were absent in the colon.

Discussion

Exposure to perinatal transient asphyxia acutely decreased Paneth cell numbers. These novel data support the possibility of utilizing ovine models for understanding Paneth cell biology in the fetus and neonate.

Femoral Occlusion during Neonatal Cardiopulmonary Resuscitation Improves Outcomes in an Ovine Model of Perinatal Cardiac Arrest

BACKGROUND

The goal of chest compressions during neonatal resuscitation is to increase cerebral and coronary blood flow leading to the return of spontaneous circulation (ROSC). During chest compressions, bilateral femoral occlusion may increase afterload and promote carotid and coronary flow, an effect similar to epinephrine. Our objectives were to determine the impact of bilateral femoral occlusion during chest compressions on the incidence and timing of ROSC and hemodynamics.

METHODOLOGY

In this randomized study, 19 term fetal lambs in cardiac arrest were resuscitated based on the Neonatal Resuscitation Program guidelines and randomized into two groups: femoral occlusion or controls. Bilateral femoral arteries were occluded by applying pressure using two fingers during chest compressions.

RESULTS

Seventy percent (7/10) of the lambs in the femoral occlusion group achieved ROSC in 5 ± 2 min and three lambs (30%) did not receive epinephrine. ROSC was achieved in 44% (4/9) of the controls in 13 ± 6 min and all lambs received epinephrine. The femoral occlusion group had higher diastolic blood pressures, carotid and coronary blood flow.

CONCLUSION

Femoral occlusion resulted in faster and higher incidence of ROSC, most likely due to attaining increased diastolic pressures, coronary and carotid flow. This is a low-tech intervention that can be easily adapted in resource limited settings, with the potential to improve survival and neurodevelopmental outcomes.

Randomised trial of epinephrine dose and flush volume in term newborn lambs

OBJECTIVES

Neonatal resuscitation guidelines recommend 0.5-1 mL saline flush following 0.01-0.03 mg/kg of epinephrine via low umbilical venous catheter for persistent bradycardia despite effective positive pressure ventilation (PPV) and chest compressions (CC). We evaluated the effects of 1 mL vs 3 mL/kg flush volumes and 0.01 vs 0.03 mg/kg doses on return of spontaneous circulation (ROSC) and epinephrine pharmacokinetics in lambs with cardiac arrest.

DESIGN

Forty term lambs in cardiac arrest were randomised to receive 0.01 or 0.03 mg/kg epinephrine followed by 1 mL or 3 mL/kg flush after effective PPV and CC. Epinephrine (with 1 mL flush) was repeated every 3 min until ROSC or until 20 min. Haemodynamics, blood gases and plasma epinephrine concentrations were monitored.

RESULTS

Ten lambs had ROSC before epinephrine administration and 2 died during instrumentation. Among 28 lambs that received epinephrine, 2/6 in 0.01 mg/kg-1 mL flush, 3/6 in 0.01 mg/kg-3 mL/kg flush, 5/7 in 0.03 mg/kg-1 mL flush and 9/9 in 0.03 mg/kg-3 mL/kg flush achieved ROSC (p=0.02). ROSC was five times faster with 0.03 mg/kg epinephrine compared with 0.01 mg/kg (adjusted HR (95% CI) 5.08 (1.7 to 15.25)) and three times faster with 3 mL/kg flush compared with 1 mL flush (3.5 (1.27 to 9.71)). Plasma epinephrine concentrations were higher with 0.01 mg/kg-3 mL/kg flush (adjusted geometric mean ratio 6.0 (1.4 to 25.7)), 0.03 mg/kg-1 mL flush (11.3 (2.1 to 60.3)) and 0.03 mg/kg-3 mL/kg flush (11.0 (2.2 to 55.3)) compared with 0.01 mg/kg-1 mL flush.

CONCLUSIONS

0.03 mg/kg epinephrine dose with 3 mL/kg flush volume is associated with the highest ROSC rate, increases peak plasma epinephrine concentrations and hastens time to ROSC. Clinical trials evaluating optimal epinephrine dose and flush volume are warranted.

Optimal Oxygen Targets in Term Lambs with Meconium Aspiration Syndrome and Pulmonary Hypertension

Optimal oxygen saturation as measured by pulse oximetry (SpO2) in neonatal lung injury, such as meconium aspiration syndrome (MAS) and persistent pulmonary hypertension of newborn (PPHN), is not known. Our goal was to determine the SpO2 range in lambs with MAS and PPHN that results in the highest brain oxygen delivery (bDO2) and pulmonary blood flow (Qp) and the lowest pulmonary vascular resistance and oxidative stress. Meconium was instilled into endotracheal tubes in 25 near-term gestation lambs, and the umbilical cord was occluded to induce asphyxia and gasping, causing MAS and PPHN. Lambs were randomized into four groups and ventilated for 6 hours with fixed fraction of inspired oxygen (FiO2) = 1.0 irrespective of SpO2, and three groups had FiO2 titrated to keep preductal SpO2 between 85% and 89%, 90% and 94%, and 95% and 99%, respectively. Tissues were collected to measure nitric oxide synthase activity, 3-nitrotyrosine, and 8-isoprostanes. Throughout the 6-hour exposure period, lambs in the 95-99% SpO2 target group had the highest Qp, lowest pulmonary vascular resistance, and highest bDO2 but were exposed to higher FiO2 (0.5 ± 0.21 vs. 0.29 ± 0.17) with higher lung 3-nitrotyrosine (0.67 [interquartile range (IQR), 0.43-0.73] ng/mcg protein vs. 0.1 [IQR, 0.09-0.2] ng/mcg protein) and lower lung nitric oxide synthase activity (196 [IQR, 192-201] mMol nitrite/mg protein vs. 270 [IQR, 227-280] mMol nitrite/mg protein) compared with the 90-94% target group. Brain 3-nitrotyrosine was lower in the 85-89% target group, and brain/lung 8-isoprostane levels were not significantly different. In term lambs with MAS and PPHN, Qp and bDO2 through the first 6 hours are higher with target SpO2 in the 95-99% range. However, the 90-94% target range is associated with significantly lower FiO2 and lung oxidative stress. Clinical trials comparing the 90-94% versus the 95-99% SpO2 target range in term infants with PPHN are warranted.

In Vitro Consequences of Electronic-Cigarette Flavoring Exposure on the Immature Lung

Background: The developing lung is uniquely susceptible and may be at increased risk of injury with exposure to e-cigarette constituents. We hypothesize that cellular toxicity and airway and vascular responses with exposure to flavored refill solutions may be altered in the immature lung. Methods: Fetal, neonatal, and adult ovine pulmonary artery smooth muscle cells (PASMC) were exposed to popular flavored nicotine-free e-cigarette refill solutions (menthol, strawberry, tobacco, and vanilla) and unflavored solvents: propylene glycol (PG) or vegetable glycerin (VG). Viability was assessed by lactate dehydrogenase assay. Brochodilation and vasoreactivity were determined on isolated ovine bronchial rings (BR) and pulmonary arteries (PA). Results: Neither PG or VG impacted viability of immature or adult cells; however, exposure to menthol and strawberry flavored solutions increased cell death. Neonatal cells were uniquely susceptible to menthol flavoring-induced toxicity, and all four flavorings demonstrated lower lethal doses (LD50) in immature PASMC. Exposure to flavored solutions induced bronchodilation of neonatal BR, while only menthol induced airway relaxation in adults. In contrast, PG/VG and flavored solutions did not impact vasoreactivity with the exception of menthol-induced relaxation of adult PAs. Conclusion: The immature lung is uniquely susceptible to cellular toxicity and altered airway responses with exposure to common flavored e-cigarette solutions.

Bioavailability of endotracheal epinephrine in an ovine model of neonatal resuscitation

BACKGROUND

Distressed infants in the delivery room and those that have completed postnatal transition are both resuscitated according to established neonatal resuscitation guidelines, often with endotracheal (ET) epinephrine at the same dose. We hypothesized that ET epinephrine would have higher bioavailability in a post-transitional compared to transitioning newborn model due to absence of fetal lung liquid and intra-cardiac shunts.

METHODS

15 term fetal (transitioning newborn) and 6 postnatal lambs were asphyxiated by umbilical cord and ET tube occlusion respectively. Lambs were resuscitated after 5 min of asystole. ET epinephrine (0.1 mg/kg) was administered after 1 min of positive pressure ventilation (PPV) and chest compressions, and repeated 3 min later, followed by intravenous (IV) epinephrine (0.03 mg/kg) every 3 min until return of spontaneous circulation (ROSC). Serial plasma epinephrine concentrations were measured.

RESULTS

Peak plasma epinephrine concentrations were lower in transitioning newborns as compared to postnatal lambs: after a single ET dose (145.36 ± 135.5 ng/ml vs 553.54 ± 215 ng/ml, p < 0.01) and after two ET doses (443 ± 192.49 ng/ml vs 1406 ± 420.8 ng/ml, p < 0.01). The rates of ROSC with a single ET dose were similar in both groups (40% vs 50% in newborn and postnatal respectively, p > 0.99). There was a higher incidence of post-ROSC tachycardia and increased carotid blood flow in the postnatal group.

CONCLUSIONS

In the postnatal period, ET epinephrine at currently recommended doses resulted in higher peak epinephrine concentrations, post-ROSC tachycardia and cerebral reperfusion without significant differences in incidence of ROSC. Further studies evaluating the optimal dose of ET epinephrine during the postnatal period are warranted.

Effect of various inspired oxygen concentrations on pulmonary and systemic hemodynamics and oxygenation during resuscitation in a transitioning preterm model

BACKGROUND

The Neonatal Resuscitation Program recommends initial resuscitation of preterm infants with low oxygen (O₂) followed by titration to target preductal saturations (SpO₂). We studied the effect of resuscitation with titrated O₂ on gas exchange, pulmonary, and systemic hemodynamics.

METHODOLOGY

Twenty-nine preterm lambs (127 d gestation) were randomized to resuscitation with 21% O₂ (n = 7), 100% O₂ (n = 6), or initiation at 21% and titrated to target SpO₂ (n = 16). Seven healthy term control lambs were ventilated with 21% O₂.

RESULTS

Preductal SpO₂ achieved by titrating O₂ was within the desired range similar to term lambs in 21% O₂. Resuscitation of preterm lambs with 21% and 100% O₂ resulted in SpO₂ below and above the target, respectively. Ventilation of preterm lambs with 100% O₂ and term lambs with 21% O₂ effectively decreased pulmonary vascular resistance (PVR). In contrast, preterm lambs with 21% O₂ and titrated O₂ demonstrated significantly higher PVR than term lambs on 21% O₂.

CONCLUSION(S)

Initial resuscitation with 21% O₂ followed by titration of O₂ led to suboptimal pulmonary vascular transition at birth in preterm lambs. Ventilation with 100% O₂ in preterm lambs caused hyperoxia but reduced PVR similar to term lambs on 21% O₂. Studies evaluating the initiation of resuscitation at a higher O₂ concentration followed by titration based on SpO₂ in preterm neonates are needed.

Neonatal hyperoxia increases airway reactivity and inflammation in adult mice

BACKGROUND

Supplemental O₂ to treat bronchopulmonary dysplasia (BPD) in premature infants, is a major risk factor producing alteration in lung function, airway reactivity, and predisposition to respiratory infections. This study explores inflammatory and airway responses following neonatal hyperoxia in adult mice.

METHODS

Newborn mouse litters were randomized to 85% O₂ or room air (RA) on P3 for 12 days; mice were sacrificed either on P15 or at 15 weeks following recovery in RA. Airway hyper reactivity (AHR) was assessed in vivo (8 and 12 weeks) and in vitro (15 weeks) with methacholine; Lung and BAL were assayed for inflammatory mediators, cell counts, CD3 immunohistochemistry, and histopathology.

RESULTS

Hyperoxic mice had increased airway reactivity at baseline and following methacholine challenge in vivo (8 and 12 weeks); isolated tracheal rings had a significantly higher constriction response to methacholine in vitro compared to RA group. Inflammatory markers were higher at 2 weeks (MCP-1, IL-12, INF-γ) and at 15 weeks (LTB₄ , VEGF); Lipoxin-A₄ was lower in the hyperoxia group at both time points. Increased airway smooth muscle thickness and angiogenesis in the lung was seen at 15 weeks. Hyperoxic lungs exhibited alveolar simplification at 2 and 15 weeks. Absolute lymphocyte count was higher in lavage fluid with an increased CD3 cell count at 15 weeks suggesting persistent inflammation in adult mice following neonatal hyperoxia.

CONCLUSIONS

Exposure to hyperoxia in newborn mice increases long-term airway reactivity with persistent lung inflammation associated with a marked increase in lymphocytes, suggesting long-term consequences in adults. Pediatr Pulmonol. 2016;51:1131-1141. © 2016 Wiley Periodicals, Inc.

Neonatal resuscitation adhering to oxygen saturation guidelines in asphyxiated lambs with meconium aspiration

BACKGROUND

The Neonatal Resuscitation Program (NRP) recommends upper and lower limits of preductal saturations (SpO2) extrapolated from studies in infants resuscitated in room air. These limits have not been validated in asphyxia and lung disease.

METHODS

Seven control term lambs delivered by cesarean section were ventilated with 21% O2. Thirty lambs with asphyxia with meconium aspiration were randomly assigned to resuscitation with 21% O2 (n = 6), 100% O2 (n = 6), or initiation with 21% O2 followed by variable FIO2 to maintain NRP target SpO2 ranges (n = 18). Hemodynamic and ventilation parameters were recorded for 15 min.

RESULTS

Control lambs maintained preductal SpO2 near the lower limit of NRP target range. Asphyxiated lambs had low SpO2 (38 ± 2%), low arterial pH (6.99 ± 0.01), and high PaCO2 (96 ± 7 mm Hg) at birth. Resuscitation with 21% O2 resulted in SpO2 values below the target range with low pulmonary blood flow (Qp) compared to variable FIO2 group. The increase in PaO2 and Qp with variable FIO2 resuscitation was similar to control lambs.

CONCLUSION

Maintaining SpO2 as recommended by NRP by actively adjusting inspired O2 leads to effective oxygenation and higher Qp in asphyxiated lambs with lung disease. Our findings support the current NRP SpO2 guidelines for O2 supplementation during resuscitation of an asphyxiated neonate.

Fetal and postnatal ovine mesenteric vascular reactivity

BACKGROUND

Intestinal circulation and mesenteric arterial (MA) reactivity may play a role in preparing the fetus for enteral nutrition. We hypothesized that MA vasoreactivity changes with gestation and vasodilator pathways predominate in the postnatal period.

METHODS

Small distal MA rings (0.5-mm diameter) were isolated from fetal (116-d, 128-d, 134-d, and 141-d gestation, term ~ 147 d) and postnatal lambs. Vasoreactivity was evaluated using vasoconstrictors (norepinephrine (NE) after pretreatment with propranolol and endothelin-1(ET-1)) and vasodilators (NO donors A23187 and s-nitrosopenicillamine (SNAP)). Protein and mRNA assays for receptors and enzymes (endothelin receptor A, alpha-adrenergic receptor 1A (ADRA1A), endothelial NO synthase (eNOS), soluble guanylyl cyclase (sGC), and phosphodiesterase5 (PDE5)) were performed in mesenteric arteries.

RESULTS

MA constriction to NE and ET-1 peaked at 134 d. Relaxation to A23187 and SNAP was maximal after birth. Basal eNOS activity was low at 134 d. ADRA1A mRNA and protein increased significantly at 134 d and decreased postnatally. sGC and PDE5 protein increased from 134 to 141 d.

CONCLUSION

Mesenteric vasoconstriction predominates in late-preterm gestation (134 d; the postconceptional age with the highest incidence of necrotizing enterocolitis (NEC)) followed by a conversion to vasodilatory influences near the time of full-term birth. Perturbations in this ontogenic mechanism, including preterm birth, may be a risk factor for NEC.

Continuous End-Tidal Carbon Dioxide Monitoring during Resuscitation of Asphyxiated Term Lambs

BACKGROUND

The Neonatal Resuscitation Program (NRP) recommends close monitoring of oxygenation during the resuscitation of newborns using a pulse oximeter. However, there are no guidelines for monitoring carbon dioxide (CO2) to assess ventilation. Considering that cerebral blood flow (CBF) correlates directly with PaCO2, continuous capnography monitoring of end-tidal CO2 (ETCO2) may limit fluctuations in PaCO2 and, therefore, CBF during resuscitation of asphyxiated infants.

OBJECTIVE

To evaluate whether continuous monitoring of ETCO2 with capnography during resuscitation of asphyxiated term lambs with meconium aspiration will prevent fluctuations in PaCO2 and carotid arterial blood flow (CABF).

METHODS

Fifty-four asphyxiated term lambs with meconium aspiration syndrome were mechanically ventilated from birth to 60 min of age. Ventilatory parameters were adjusted based on clinical observation (chest excursion) and frequent arterial blood gas analysis in 24 lambs (control group) and 30 lambs (capnography group) received additional continuous ETCO2 monitoring. Left CABF was monitored. We aimed to maintain PaCO2 between 35 and 50 mm Hg and ETCO2 between 30 and 45 mm Hg.

RESULTS

There was a significant correlation between ETCO2 and PaCO2 (R = 0.7, p < 0.001), between PaCO2 and carotid flow (R = 0.52, p < 0.001) and between ETCO2 and carotid flow (R = 0.5, p < 0.001). PaCO2 and CABF during the first 60 min of age showed significantly higher fluctuation in the control group compared to the capnography group.

CONCLUSION

Continuous monitoring of ETCO2 using capnography with mechanical ventilation during and after resuscitation in asphyxiated term lambs with meconium aspiration limits fluctuations in PaCO2 and CABF and may potentially limit brain injury.

Mouse lung development and NOX1 induction during hyperoxia are developmentally regulated and mitochondrial ROS dependent

Animal models demonstrate that exposure to supraphysiological oxygen during the neonatal period compromises both lung and pulmonary vascular development, resulting in a phenotype comparable to bronchopulmonary dysplasia (BPD). Our prior work in murine models identified postnatal maturation of antioxidant enzyme capacities as well as developmental regulation of mitochondrial oxidative stress in hyperoxia. We hypothesize that consequences of hyperoxia may also be developmentally regulated and mitochondrial reactive oxygen species (ROS) dependent. To determine whether age of exposure impacts the effect of hyperoxia, neonatal mice were placed in 75% oxygen for 72 h at either postnatal day 0 (early postnatal) or day 4 (late postnatal). Mice exposed to early, but not late, postnatal hyperoxia demonstrated decreased alveolarization and septation, increased muscularization of resistance pulmonary arteries, and right ventricular hypertrophy (RVH) compared with normoxic controls. Treatment with a mitochondria-specific antioxidant, (2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl)triphenylphosphonium chloride (mitoTEMPO), during early postnatal hyperoxia protected against compromised alveolarization and RVH. In addition, early, but not late, postnatal hyperoxia resulted in induction of NOX1 expression that was mitochondrial ROS dependent. Because early, but not late, exposure resulted in compromised lung and cardiovascular development, we conclude that the consequences of hyperoxia are developmentally regulated and decrease with age. Attenuated disease in mitoTEMPO-treated mice implicates mitochondrial ROS in the pathophysiology of neonatal hyperoxic lung injury, with potential for amplification of ROS signaling through NOX1 induction. Furthermore, it suggests a potential role for targeted antioxidant therapy in the prevention or treatment of BPD.

Tracheal suctioning improves gas exchange but not hemodynamics in asphyxiated lambs with meconium aspiration

BACKGROUND

Current neonatal resuscitation guidelines recommend tracheal suctioning of nonvigorous neonates born through meconium-stained amniotic fluid.

METHODS

We evaluated the effect of tracheal suctioning at birth in 29 lambs with asphyxia induced by cord occlusion and meconium aspiration during gasping.

RESULTS

Tracheal suctioning at birth (n = 15) decreased amount of meconium in distal airways (53 ± 29 particles/mm(2) lung area) compared to no suction (499 ± 109 particles/mm(2); n = 14; P < 0.001). Three lambs in the suction group had cardiac arrest during suctioning, requiring chest compressions and epinephrine. Onset of ventilation was delayed in the suction group (146 ± 11 vs. 47 ± 3 s in no-suction group; P = 0.005). There was no difference in pulmonary blood flow, carotid blood flow, and pulmonary or systemic blood pressure between the two groups. Left atrial pressure was significantly higher in the suction group. Tracheal suctioning resulted in higher Pao2/FiO2 levels (122 ± 21 vs. 78 ± 10 mm Hg) and ventilator efficiency index (0.3 ± 0.05 vs.0.16 ± 0.03). Two lambs in the no-suction group required inhaled nitric oxide. Lung 3-nitrotyrosine levels were higher in the suction group (0.65 ± 0.03 ng/µg protein) compared with the no-suction group (0.47 ± 0.06).

CONCLUSION

Tracheal suctioning improves oxygenation and ventilation. Suctioning does not improve pulmonary/systemic hemodynamics or oxidative stress in an ovine model of acute meconium aspiration with asphyxia.

Packed red cell transfusions alter mesenteric arterial reactivity and nitric oxide pathway in preterm lambs

BACKGROUND

Cases of necrotizing enterocolitis occurring within 48 h of packed red blood cell (PRBC) transfusions are increasingly being described in observational studies. Transfusion-associated gut injury is speculated to result from an abnormal mesenteric vascular response to transfusion. However, the mechanism of disruption of the balance between mesenteric vasoconstriction and relaxation following transfusion is not known.

METHODS

Preterm lambs (n = 16, 134 d gestation; term: 145-147 d) were delivered and ventilated for 24 h. All the lambs received orogastric feeds with colostrum. In addition, 10 of these lambs received PRBC transfusions. Vasoreactivity was evaluated in isolated mesenteric arterial rings using norepinephrine and endothelin-1 as vasoconstrictors. Endothelium-dependent (A23187, a calcium ionophore) and endothelium-independent (SNAP) nitric oxide (NO) donors were used as vasorelaxants. Mesenteric arterial endothelial NO synthase (eNOS), soluble guanylyl cyclase (sGC), and phosphodiesterase 5 (PDE5) mRNA analyses and protein assays were performed.

RESULTS

Transfusion with PRBC significantly increased mesenteric vasoconstriction to norepinephrine and endothelin-1 and impaired relaxation to A23187 and SNAP. Mesenteric arterial eNOS protein decreased following PRBC transfusion. No significant changes were noted in sGC and PDE5 mRNA or protein assays.

CONCLUSION

PRBC transfusion in enterally fed preterm lambs promotes mesenteric vasoconstriction and impairs vasorelaxation by reducing mesenteric arterial eNOS.

Apocynin improves oxygenation and increases eNOS in persistent pulmonary hypertension of the newborn

NADPH oxidase is a major source of superoxide anions in the pulmonary arteries (PA). We previously reported that intratracheal SOD improves oxygenation and restores endothelial nitric oxide (NO) synthase (eNOS) function in lambs with persistent pulmonary hypertension of the newborn (PPHN). In this study, we determined the effects of the NADPH oxidase inhibitor apocynin on oxygenation, reactive oxygen species (ROS) levels, and NO signaling in PPHN lambs. PPHN was induced in lambs by antenatal ligation of the ductus arteriosus 9 days prior to delivery. Lambs were treated with vehicle or apocynin (3 mg/kg intratracheally) at birth and then ventilated with 100% O(2) for 24 h. A significant improvement in oxygenation was observed in apocynin-treated lambs after 24 h of ventilation. Contractility of isolated fifth-generation PA to norepinephrine was attenuated in apocynin-treated lambs. PA constrictions to NO synthase (NOS) inhibition with N-nitro-l-arginine were blunted in PPHN lambs; apocynin restored contractility to N-nitro-l-arginine, suggesting increased NOS activity. Intratracheal apocynin also enhanced PA relaxations to the eNOS activator A-23187 and to the NO donor S-nitrosyl-N-acetyl-penicillamine. Apocynin decreased the interaction between NADPH oxidase subunits p22(phox) and p47(phox) and decreased the expression of Nox2 and p22(phox) in ventilated PPHN lungs. These findings were associated with decreased superoxide and 3-nitrotyrosine levels in the PA of apocynin-treated PPHN lambs. eNOS protein expression, endothelial NO levels, and tetrahydrobiopterin-to-dihydrobiopterin ratios were significantly increased in PA from apocynin-treated lambs, although cGMP levels did not significantly increase and phosphodiesterase-5 activity did not significantly decrease. NADPH oxidase inhibition with apocynin may improve oxygenation, in part, by attenuating ROS-mediated vasoconstriction and by increasing NOS activity.

Hydrocortisone normalizes oxygenation and cGMP regulation in lambs with persistent pulmonary hypertension of the newborn

In the pulmonary vasculature, cGMP levels are regulated by soluble guanylate cyclase (sGC) and phosphodiesterase 5 (PDE5). We previously reported that lambs with persistent pulmonary hypertension of the newborn (PPHN) demonstrate increased reactive oxygen species (ROS) and altered sGC and PDE5 activity, with resultant decreased cGMP. The objective of this study was to evaluate the effects of hydrocortisone on pulmonary vascular function, ROS, and cGMP in the ovine ductal ligation model of PPHN. PPHN lambs were ventilated with 100% O(2) for 24 h. Six lambs received 5 mg/kg hydrocortisone every 8 h times three doses (PPHN-hiHC), five lambs received 3 mg/kg hydrocortisone followed by 1 mg·kg(-1)·dose(-1) times two doses (PPHN-loHC), and six lambs were ventilated with O(2) alone (PPHN). All groups were compared with healthy 1-day spontaneously breathing lambs (1DSB). O(2) ventilation of PPHN lambs decreased sGC activity, increased PDE5 activity, and increased ROS vs. 1DSB lambs. Both hydrocortisone doses significantly improved arterial-to-alveolar ratios relative to PPHN lambs, decreased PDE5 activity, and increased cGMP relative to PPHN lambs. High-dose hydrocortisone also increased sGC activity, decreased PDE5 expression, decreased ROS, and increased total vascular SOD activity vs. PPHN lambs. These data suggest that hydrocortisone treatment in clinically relevant doses improves oxygenation and decreases hyperoxia-induced changes in sGC and PDE5 activity, increasing cGMP levels. Hydrocortisone reduces ROS levels in part by increasing SOD activity in PPHN lambs ventilated with 100% O(2.) We speculate that hydrocortisone increases cGMP by direct effects on sGC and PDE5 expression and by attenuating abnormalities induced by oxidant stress.

Pulmonary hemodynamics and vascular reactivity in asphyxiated term lambs resuscitated with 21 and 100% oxygen

An increase in oxygen tension is an important factor in decreasing pulmonary vascular resistance (PVR) at birth. Birth asphyxia results in acidosis and increased PVR. We determined the effect of resuscitation with 21 vs. 100% O(2) on pulmonary hemodynamics, pulmonary arterial (PA) reactivity, and oxidant stress in a lamb model of in utero asphyxia. Term fetal lambs were acutely asphyxiated by intrauterine umbilical cord occlusion for 10 min resulting in acidosis (pH 6.96 ± 0.05 and Pco(2) 103 ± 5 Torr), bradycardia, systemic hypotension, and increased PVR. Lambs were treated with 30 min of resuscitation with 21% or 100% O(2) (n = 6 each). Pa(O(2)) was significantly elevated with 100% O(2) resuscitation compared with 21% O(2) (430 ± 38 vs. 64 ± 8 Torr), but changes in pH and Pa(CO(2)) were similar. The 100% O(2) induced greater increase in pulmonary blood flow and decrease in PVR at 1 min of life, but subsequent values were similar to 21% O(2) group between 2 and 30 min of life. Oxygen uptake from the lung and systemic oxygen extraction was similar between the two groups. Pulmonary arteries showed increased staining for superoxide anions and increased contractility to norepinephrine following resuscitation with 100% O(2). The increased PA contractility induced by 100% O(2) was reversed by scavenging superoxide anions with superoxide dismutase and catalase. We conclude that resuscitation of asphyxiated lambs with 100% O(2) increases Pa(O(2)) but does not improve lung oxygen uptake, decrease PVR at 30 min, or increase systemic oxygen extraction ratios. Furthermore, 100% O(2) also induces oxidative stress and increases PA contractility. These findings support the new neonatal resuscitation guidelines recommending 21% O(2) for initial resuscitation of asphyxiated neonates.

Mitochondrial oxidant stress increases PDE5 activity in persistent pulmonary hypertension of the newborn

In the pulmonary vasculature, phosphodiesterase-5 (PDE5) degrades cGMP and inhibits nitric oxide-mediated, cGMP-dependent vasorelaxation. We previously reported that ventilation with 100% O2 increased PDE5 activity in pulmonary arteries (PAs) of pulmonary hypertension lambs (PPHN) more than in control lambs. In the present study, PA smooth muscle cells (PASMCs) from PPHN lambs had increased basal PDE5 activity, decreased cGMP-responsiveness to NO, and increased mitochondrial matrix oxidant stress compared to control PASMC. Hyperoxia (24 h) increased PDE5 activity and mitochondrial matrix oxidant stress above baseline to a similar degree in PPHN and control PASMC. Mitochondrially targeted catalase decreased PDE5 activity at baseline and after hyperoxia in PPHN PASMC. Similarly, catalase treatment of PPHN lambs ventilated with 100% O2 decreased PDE5 activity and increased cGMP in PA. We conclude that baseline PDE5 activity and oxidative stress is increased in PPHN PASMC, and scavenging H2O2 is sufficient to block oxidant-mediated increases in PDE5 activity in PPHN.

SOD and inhaled nitric oxide normalize phosphodiesterase 5 expression and activity in neonatal lambs with persistent pulmonary hypertension

Phosphodiesterase 5 (PDE5) and soluble guanylate cyclase (sGC) are key regulators of cGMP and pulmonary vascular tone. We sought to determine the impact of mechanical ventilation with O(2) with or without inhaled nitric oxide (iNO) or recombinant human Cu/Zn SOD (rhSOD) on sGC, PDE5, and cGMP in the ovine ductal ligation model of persistent pulmonary hypertension of the newborn (PPHN). PPHN lambs were ventilated with 100% O(2) for 24 h alone or combined with either inhalation of 20 parts per million (ppm) iNO continuously or a single intratracheal dose of rhSOD (5 mg/kg). Ventilated PPHN lambs were compared with PPHN fetuses, control fetuses, and 1-day-old spontaneously breathing lambs (1DSB). In the small pulmonary arteries of 1DSB lambs, sGC expression increased, PDE5 expression decreased, and cGMP concentrations increased relative to fetal levels. In PPHN lambs ventilated with 100% O(2), sGC activity increased to levels comparable with 1DSB levels. However, PDE5 expression and activity increased, and cGMP levels remained at fetal levels. Addition of either iNO or rhSOD decreased PDE5 expression and activity in PPHN lambs and increased cGMP levels to levels comparable with 1DSB lambs. These data suggest that ventilation of PPHN lambs with 100% O(2) impairs cGMP-mediated vasodilation in part due to increased PDE5 expression and activity. The addition of either iNO or rhSOD normalized PDE5 and cGMP levels. Thus therapies designed to decrease PDE5 and increase cGMP, such as iNO and rhSOD, may prove useful in the treatment of PPHN in newborn infants.

Regulation of phosphodiesterase 3 in the pulmonary arteries during the perinatal period in sheep

The role of cAMP in the pulmonary vasculature during the transition from intrauterine to extrauterine life is poorly understood. We hypothesized that cAMP levels are regulated by alterations in phosphodiesterase 3 (PDE3), which hydrolyzes cAMP. PDE3 protein expression and hydrolytic activity were increased in the resistance pulmonary arteries (PA) from spontaneously breathing 1-d-old (1dSB) lambs relative to equivalent-gestation fetuses. This was accompanied by a decrease in steady-state cAMP. Ventilation with 21% O2 and 100% O2 for 24 h disrupted the normal transition, whereas ventilation with 100% O2 + inhaled NO (iNO) for 24 h restored both PDE3 activity and cAMP to 1dSB levels. Consistent with these findings, relaxation to milrinone, a PDE3 inhibitor, was greater in the PA isolated from 1dSB and 100% O2 + iNO lambs, relative to fetal, 21% O2, and 100% O2 lambs. In conclusion, PDE3 expression and activity in the PA dramatically increase after birth, with a concomitant decrease in steady-state cAMP. Ventilation with either 21% O2 or 100% O2 blunts this PDE3 increase, whereas iNO restores PDE3 activity to levels equivalent to 1dSB lambs. The vasodilatory effects of milrinone were most pronounced in vessels from lambs with the highest PDE3 activity, i.e., 1dSB and 100% O2 + iNO lambs. Thus, milrinone may be most beneficial when used in conjunction with iNO.

Oxygen concentration and pulmonary hemodynamics in newborn lambs with pulmonary hypertension

The effect of oxygen concentration on lowering pulmonary vascular resistance (PVR) during resuscitation in a model of persistent pulmonary hypertension of the newborn (PPHN) is not known. PPHN was induced in fetal lambs by ductal ligation 9 d before delivery. After delivery by cesarean section, resuscitation of PPHN lambs with 21%, 50%, or 100% O2 (n = 6 each) for 30 min produced similar decreases in PVR. Lambs were then ventilated with 50% O2 for 60 min and exposed to inhaled nitric oxide (iNO, 20 ppm). Initial resuscitation with 100% O2 significantly impaired the subsequent response to iNO compared with 21% O2 (42 +/- 9% vs 22 +/- 4% decrease from baseline PVR). Finally, each lamb was randomly and sequentially ventilated with 10%, 21%, 50%, or 100% O2. PVR decreased with increased concentrations of inhaled O2 up to 50%, there being no additional decrease in PVR with 100% O2. When PVR was correlated with Pao2, the maximal change in PVR was achieved at Pao2 values <60 mm Hg. We conclude that resuscitation with 100% O2 does not enhance pulmonary vasodilation compared with 21% and 50% O2, but impairs the subsequent response to iNO in PPHN lambs. Hypoxia increases PVR but hyperoxia does not confer significant additional pulmonary vasodilation in lambs with PPHN.

Superoxide dismutase restores eNOS expression and function in resistance pulmonary arteries from neonatal lambs with persistent pulmonary hypertension

Endothelial nitric oxide (NO) synthase (eNOS) expression and activity are decreased in fetal lambs with persistent pulmonary hypertension (PPHN). We sought to determine the impact of mechanical ventilation with O(2) with or without inhaled NO (iNO) or recombinant human SOD (rhSOD) on eNOS in the ductal ligation model of PPHN. PPHN lambs and age-matched controls were ventilated with 100% O(2) for 24 h alone or combined with 20 ppm iNO continuously or a single dose of rhSOD (5 mg/kg) given intratracheally at delivery. In 1-day spontaneously breathing lambs, eNOS expression in resistance pulmonary arteries increased relative to fetal levels. eNOS expression increased in control lambs ventilated with 100% O(2), but not in PPHN lambs. Addition of iNO or rhSOD increased eNOS expression and decreased generation of reactive oxygen species (ROS) in PPHN lambs relative to those ventilated with 100% O(2) alone. However, only rhSOD restored eNOS function, increased tetrahydrobiopterin (BH(4)), a critical cofactor for eNOS function, and restored GTP cyclohydrolase I expression in isolated vessels and lungs from PPHN lambs. These data suggest that ventilation of PPHN lambs with 100% O(2) increases ROS production, blunts postnatal increases in eNOS expression, and decreases available BH(4) in PPHN lambs. Although the addition of iNO or rhSOD diminished ROS production and increased eNOS expression, only rhSOD improved eNOS function and levels of available BH(4). Thus therapies designed to decrease oxidative stress and restore eNOS coupling, such as rhSOD, may prove useful in the treatment of PPHN in newborn infants.

Hyperoxia increases phosphodiesterase 5 expression and activity in ovine fetal pulmonary artery smooth muscle cells

In the pulmonary vasculature, cGMP concentrations are regulated in part by a cGMP-dependent phosphodiesterase (PDE), PDE5. Infants with persistent pulmonary hypertension of the newborn (PPHN) are often mechanically ventilated with high oxygen concentrations. The effects of hyperoxia on the developing pulmonary vasculature and PDE5 are largely unknown. Here, we demonstrate that exposure of fetal pulmonary artery smooth muscle cells (FPASMCs) to high levels of oxygen for 24 hours leads to decreased responsiveness to exogenous NO, as determined by a decreased intracellular cGMP response, increased PDE5 mRNA and protein expression, as well as increased PDE5 cGMP hydrolytic activity. We demonstrate that inhibition of PDE5 activity with sildenafil partially rescues cGMP responsiveness to exogenous NO. In FPASMCs, hyperoxia leads to increased oxidative stress without increasing cell death. Treatment of normoxic FPASMCs with H2O2 is sufficient to induce PDE5 expression and activity, suggesting that reactive oxygen species mediate the effects of hyperoxia in FPASMCs. In support of this mechanism, a chemical antioxidant, N-acetyl-cysteine, is sufficient to block the hyperoxia-mediated increase in PDE5 expression and activity and rescue cGMP responsiveness to exogenous NO. Finally, ventilation of healthy neonatal sheep with 100% O2 for 24 hours leads to increased PDE5 protein expression in the resistance pulmonary arteries and increased PDE5 activity in whole lung extracts. These data suggest that PDE5 expression and activity play a critical role in modulating neonatal pulmonary vascular tone in response to common clinical treatments for PPHN, such as oxygen and inhaled NO.

Pulmonary hemodynamics in neonatal lambs resuscitated with 21%, 50%, and 100% oxygen

The effect of resuscitation with varying levels of O2 on pulmonary hemodynamics at birth is not well known. We hypothesized that the decrease in pulmonary vascular resistance (PVR) and subsequent response to pulmonary vasoconstrictors and vasodilators will differ following resuscitation with 21%, 50%, or 100% O2 for 30 min at birth in normal term lambs. Lambs at 141 d gestation were delivered by cesarean section and ventilated with 21% (21% Res; n=6), 50% (50% Res; n=6), or 100% 02 (100% Res; n=7) for 30 min followed by ventilation with 21% O2 in all three groups. A greater decrease in PVR was seen with 50% and 100% O2 ventilation than with 21% O2 (0.21 +/- 0.02, 0.21 +/- 0.02, and 0.34 +/- 0.05 mm Hg/mL/min/kg, respectively). Subsequent pulmonary vasoconstriction to hypoxia (10% O2) and the thromboxane,analog U46619 (0.5 and 1 mcirog/kg/min) was similar in all three groups. After inducing a stable elevation in PVR with U46619, impaired pulmonary vasodilation to inhaled NO (59 +/- 4, 65 +/- 4, and 74 +/- 5% of baseline PVR with 21, 50, and 100%Res, respectively) and acetylcholine infusion (67 +/- 8, 75 +/- 6, and 87 +/- 4% of baseline PVR with 21, 50, and 100%Res, respectively) and rebound pulmonary hypertension following their withdrawal were observed in the 100%Res group. We conclude that, while ventilation with 100% O2 at birth results in a greater initial decrease in PVR, subsequent pulmonary vasodilation to NO/acetylcholine is impaired.

The role of nitric oxide synthase-derived reactive oxygen species in the altered relaxation of pulmonary arteries from lambs with increased pulmonary blood flow

Congenital cardiac defects associated with increased pulmonary blood flow (Q(p)) produce pulmonary hypertension. We have previously reported attenuated endothelium-dependent relaxations in pulmonary arteries (PA) isolated from lambs with increased Q(p) and pulmonary hypertension. To better characterize the vascular alterations in the nitric oxide-superoxide system, 12 fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt). Twin lambs served as controls. PA were isolated from these lambs at 4-6 wk of age. Electron paramagnetic resonance spectroscopy on fourth-generation PA showed significantly increased superoxide anion generation in shunt PA that were decreased to control levels following inhibition of nitric oxide synthase (NOS) with 2-ethyl-2-thiopseudourea. Preconstricted fifth-generation PA rings were relaxed with a NOS agonist (A-23187), a nitric oxide donor [S-nitrosyl amino penicillamine (SNAP)], polyethylene glycol-conjugated superoxide dismutase (PEG-SOD), or H(2)O(2). A-23187-, PEG-SOD-, and H(2)O(2)-mediated relaxations were impaired in shunt PA compared with controls. Pretreatment with PEG-SOD significantly enhanced the relaxation response to A-23187 and SNAP in shunt but not control PA. Inhibition of NOS with nitro-L-arginine or scavenging superoxide anions with tiron enhanced relaxation to SNAP and inhibited relaxation to PEG-SOD in shunt PA. Pretreatment with catalase inhibited relaxation of shunt PA to A-23187, SOD, and H(2)O(2). We conclude that NOS catalyzes the production of superoxide anions in shunt PA. PEG-SOD relaxes shunt PA by converting these anions to H(2)O(2), a pulmonary vasodilator. The redox environment, influenced by the balance between production and scavenging of ROS, may have important consequences on pulmonary vascular reactivity in the setting of increased Q(p).

Functional tissue-engineered blood vessels from bone marrow progenitor cells

OBJECTIVE

Stem cells have significant potential for development of cell-based therapeutics for cardiovascular tissue regeneration.

METHODS

We developed a novel method for isolating smooth muscle cells (SMC) from ovine bone marrow using a tissue-specific promoter and fluorescence-activated cell sorting.

RESULTS

As compared to vascular SMC, bone marrow-derived smooth muscle progenitor cells (BM-SMPC) exhibited similar morphology, showed higher proliferation potential and expressed several SMC markers including alpha-actin, calponin, myosin heavy chain, smoothelin, caldesmon and SM22. When embedded in fibrin hydrogels, BM-SMPC contracted the matrix and displayed receptor- and non-receptor-mediated contractility, indicating that BM-SMPC can generate force in response to vasoreactive agonists. We also prepared tissue-engineered blood vessels from BM-SMPC and BM-derived endothelial cells and implanted them into the jugular veins of lambs. As early as five weeks post-implantation, grafted tissues displayed a confluent endothelial layer overlaying the medial layer in which BM-SMPC were aligned circumferentially and synthesized significant amounts of collagen. In contrast to previous results with vascular SMC, BM-SMPC synthesized high amounts of elastin that was organized in a fibrillar network very similar to that of native vessels.

CONCLUSIONS

Our results suggest that BM-SMPC may be useful in studying SMC differentiation and have high potential for development of cell therapies for the treatment of cardiovascular disease.

Superoxide dismutase improves oxygenation and reduces oxidation in neonatal pulmonary hypertension

RATIONALE

Hyperoxic ventilation in the management of persistent pulmonary hypertension of the newborn (PPHN) can result in the formation of reactive oxygen species, such as superoxide anions, which can inactivate nitric oxide (NO) and cause vasoconstriction and oxidation.

OBJECTIVE

To compare the effect of intratracheal recombinant human superoxide dismutase (rhSOD) and/or inhaled NO (iNO) on systemic oxygenation, contractility of pulmonary arteries (PAs), and lung reactive oxygen species (isoprostane, 3-nitrotyrosine) levels in neonatal lambs with PPHN.

METHODS

Six newborn lambs with PPHN (induced by antenatal ductal ligation) were killed at birth. Twenty-six PPHN lambs were ventilated for 24 h with 100% O(2) alone (n = 6) or O(2) combined with rhSOD (5 mg/kg intratracheally) at birth (n = 4), rhSOD at 4 h of age (n = 5), iNO (20 ppm, n = 5), or rhSOD + iNO (n = 6). Contraction responses of fifth-generation PAs to norepinephrine and KCl, lung isoprostane levels, and 3-nitrotyrosine fluorescent intensity were measured.

RESULTS

Systemic oxygenation was impaired in PPHN lambs and significantly improved (up to threefold) in both rhSOD groups with or without iNO. Oxygenation improved more rapidly with the combination of rhSOD + iNO compared with either intervention alone. Norepinephrine- and KCl-induced contractions and lung isoprostane levels were significantly increased by 100% O(2) compared with nonventilated newborn lambs with PPHN. Both rhSOD and iNO mitigated the increased PA contraction response and lung isoprostane levels. Intratracheal rhSOD decreased the enhanced lung 3-nitrotyrosine fluorescence observed with iNO therapy.

CONCLUSION

Intratracheal rhSOD and/or iNO rapidly increase oxygenation and reduce both vasoconstriction and oxidation in newborn lambs with PPHN. This has important implications for clinical trials of rhSOD and iNO in newborn infants with PPHN.

Adjacent bronchus attenuates pulmonary arterial contractility

Bronchus-derived relaxing factor (BrDRF) decreases contractility of newborn rat pulmonary arteries (PA) and is dependent on nitric oxide (NO) synthesis. In vivo, this factor appears to gain access via the adventitial side of the PA. However, the adventitia has been reported to be a barrier to NO. We studied the effect of an adjacent bronchus on PA contractility to norepinephrine in nine juvenile lambs in the presence and absence of inhibitors of the NO pathway (LNA, ODQ, and Rp-8-Br-PET-cGMPS), cytochrome P-450 inhibitor (17-ODYA), perivascular nerve activity blocker (TTX), and superoxide scavenger (tiron), and following disruption of bronchial epithelium. We also evaluated whether BrDRF was effective on both the endothelial and/or adventitial side of PA. Fifth-generation PA rings with and without an attached bronchus were contracted in standard baths with norepinephrine. PA were dissected, cut open, and placed in a sided chamber in which adventitial and endothelial sides of the PA were exposed to unattached bronchus separately. Norepinephrine (10−8 to 10−5 M) contractions were expressed as a fraction of maximal KCl (118 mM) contractions. Norepinephrine contractions were significantly reduced by the presence of an attached bronchus, an effect reversed by pretreatment with LNA, ODQ, and Rp-8-Br-PET-cGMPS, and removal of bronchial epithelium. Unattached bronchus in the bath perfusing the adventitial side was effective in inhibiting the contractile response in PA. NO gas relaxed PA when administered on the endothelial side only. We speculate that BrDRF is a diffusible factor that crosses the adventitia and stimulates production of NO within the PA.

Ovine bronchial-derived relaxing factor: changes with development and hyperoxic ventilation

Recent studies suggest that a bronchial-derived relaxing factor (BrDRF) decreases the contractility of newborn, but not fetal, rat pulmonary arteries (PAs) by a nitric oxide (NO)-mediated mechanism. We studied the effect of an adjacent bronchus on PA contractility to norepinephrine (NE) in late-gestation fetal (n = 7), neonatal (1 day old, n = 9), ventilated neonatal (24-h ventilation from birth with 100% oxygen, n = 9), and adult sheep (n = 6) in the presence and absence of the NO synthase inhibitor N(omega)-nitro-l-arginine (l-NNA). The sheep were anesthetized and killed, and fifth-generation PA rings with and without an attached adjacent bronchus (PA+Br) were contracted in standard tissue baths with NE (10(-8)-10(-6) M). NE contractions were expressed as fraction of KCl (118 mM) contraction and as grams of contraction force. NE contractions were significantly diminished by the presence of an attached bronchus in the neonatal and ventilated neonatal and adult, but not fetal, lambs. Hyperoxic ventilation markedly increased NE contractions in PA and PA+Br. l-NNA significantly enhanced NE contractions in PA+Br in postnatal but not in fetal lambs. Pretreatment with l-NNA abolished the difference between NE contractions in PA and PA+Br in neonatal but not in hyperoxic ventilated neonatal lambs. We conclude that there is a BrDRF that is developmentally regulated and has vascular activity postnatally but not during fetal life. The effect of BrDRF is predominantly mediated by NO in air-breathing neonatal lambs but may involve a second non-NO mediator following hyperoxic ventilation. We speculate that BrDRF may have an important role in postnatal changes in pulmonary arterial reactivity.

Pulmonary arterial contractility in neonatal lambs increases with 100% oxygen resuscitation

The optimal Fi(O2) during neonatal resuscitation is a subject of controversy. The effect of exposure to high levels of inspired oxygen on pulmonary arterial (PA) contractility is not known. We studied differences in PA vasoreactivity in term lambs initially ventilated with 21% or 100% oxygen, followed by continued ventilation using oxygen as needed for 24 h, or ventilated with 100% oxygen for 24 h and room air breathing 1-d-old lambs. Term lambs were delivered by cesarean section, intubated, and ventilated with 21% (21%Res) or 100% oxygen (100%Res) for the first 30 min of life. Subsequently, the ventilator Fi(O2) was adjusted to maintain a Pa(O2) between 45 and 65 mm Hg for 24 h. Five lambs were ventilated continuously with 100% oxygen (100%24h). Six spontaneously breathing newborn lambs (RA Spont) were studied for comparison. Lambs were killed at 24 h of life and PA rings were isolated and contracted with norepinephrine (NE) and KCl and some were relaxed with A23187 and SNAP in tissue baths. NE and KCl induced contractions were highest in PA isolated from 100%24h lambs, and were significantly higher in 100%Res lambs than PA from 21%Res lambs. Contraction responses in PA from RA Spont lambs were similar to 21%Res lambs. Relaxations to A23187 and SNAP were similar among all ventilated groups. PA contractility to NE and KCl is increased following both brief (30 min) and prolonged (24 h) exposure to 100% oxygen during mechanical ventilation. In contrast, normoxic resuscitation and ventilation do not increase PA contractility.

C-type natriuretic peptide system in fetal ovine pulmonary vasculature

C-type natriuretic peptide (CNP) is a recently described endothelium-derived relaxing factor. CNP relaxes vascular smooth muscle and inhibits smooth muscle proliferation by binding to natriuretic peptide receptor (NPR) type B (NPR-B) and producing cGMP. Lung parenchyma and fifth-generation pulmonary arteries (PA) and veins (PV) were isolated from late-gestation fetal lambs. All three types of NPR mRNA were detected in PA and PV by RT-PCR. CNP and NPR-B immunostaining was positive in pulmonary vascular endothelium and medial smooth muscle. CNP concentration-response curves of PA and PV were compared with those of atrial natriuretic peptide (ANP) by use of standard tissue bath techniques. CNP relaxed PV significantly better than PA. ANP relaxed PA and PV equally, but ANP relaxed PA significantly better than CNP. Pretreating PA and PV with natriuretic peptide receptor blocker (HS-142-1) or cGMP-dependent protein kinase inhibitor Rp-beta-phenyl-1- N2-etheno-8-bromoguanosine 3',5'-cyclic monophosphorothionate significantly inhibited the CNP relaxation response, indicating that the response was mediated through the NPR-cGMP pathway. We conclude that CNP is important in mediating pulmonary venous tone in the fetus.

Pulmonary hypertension alters soluble guanylate cyclase activity and expression in pulmonary arteries isolated from fetal lambs

The nitric oxide (NO)-guanosine 3',5'-cyclic monophosphate (cGMP) signaling pathway plays an important role in the pulmonary vascular transition at birth. We studied pulmonary arteries and veins isolated from normal late-gestation fetal lambs and from fetal lambs with persistent pulmonary hypertension (PPHN) following prenatal ligation of the ductus arteriosus. We additionally used double immunolabeling and immunoblot analysis to determine relative vascular contents of endothelial nitric oxide synthase (NOS-III) and soluble guanylate cyclase (sGC). Cyclic GMP content and sGC activity were significantly lower in arteries from hypertensive lambs than controls. A rank order for contents of both soluble guanylate cyclase and NOS-III was observed by both immunolabeling and immunoblotting: Control vein = Hypertensive vein > Control artery > Hypertensive artery. Our data demonstrate that the relative expression of sGC correlates well with the relative expression of NOS-III, and indicate the potential importance of soluble guanylate cyclase in the regulation of the perinatal pulmonary circulation. These data may help us understand vascular mechanisms producing PPHN, as well as patterns of response to exogenous NO.

Altered endothelium-dependent relaxations in lambs with high pulmonary blood flow and pulmonary hypertension

Congenital heart disease associated with increased pulmonary blood flow produces pulmonary hypertension. To characterize vascular alterations in the nitric oxide (NO)-cGMP cascade induced by increased pulmonary blood flow and pulmonary hypertension, 10 fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt). When the lambs were 4-6 wk of age, we assessed responses of pulmonary arteries (PAs) and pulmonary veins (PVs) isolated from lungs of control and shunted lambs. PVs from control and shunted lambs relaxed similarly to exogenous NO (S-nitrosyl-acetyl-penicillamine), to NO produced endogenously (zaprinast and A-23187), and to cGMP (atrial natriuretic peptide). In contrast, relaxations to A-23187 and zaprinast were blunted in PAs isolated from shunted lambs relative to controls. Inhibitors of NO synthase (NOS) and soluble guanylate cyclase constricted control but not shunt PAs, indicating reduced basal NOS activity in shunt PAs. Pretreatment of shunt PAs with the substrates L-arginine and sepiapterin, a precursor for tetrahydrobiopterin synthesis, did not augment A-23187 relaxations. However, pretreatment with superoxide dismutase and catalase significantly enhanced A-23187 relaxations in shunt PAs. We conclude that increased pulmonary blood flow induces an impairment of endothelium-dependent relaxation that is selective to PAs. The impaired relaxation may be mediated in part by excess superoxide production.

cGMP inhibition of endothelin-stimulated inositol phosphate production in the fetal lamb pulmonary artery

Endothelin-1 (ET-1) stimulates inositol phosphate production in vascular smooth muscle. In the present study, interactions between cyclic GMP (cGMP), cyclic AMP (cAMP) and ET-1 in fetal lamb pulmonary arteries were investigated using phosphoinositide hydrolysis studies and tissue bath techniques. ET-1 was found to be a potent vasoconstrictor of these vessels, with an EC50 of 15.8 nM. ET-1 stimulated total inositol phosphate (IP) production; basal IP production was 68 cpm/mg vs. 247 cm/mg with 1 microM ET-1. 8-bromo-cGMP (2 mM) significantly increased the threshold of ET-1 concentration for pulmonary artery contraction, but had no effect on IP production. Zaprinast (a selective type V phosphodiesterase inhibitor, 60 microM) did not affect ET-1-induced contractility or IP production. IBMX (0.5 mM), a non-specific phosphodiesterase inhibitor, inhibited the potent and maximal effects of ET-1 in arterial contraction and decreased ET-1-stimulated IP production by 49%, while forskolin had a lesser effect in the tissue bath and no effect on IP production. Thus, 8-bromo-cGMP and IBMX alter the contractile effects of ET-1 in the fetal pulmonary artery and IBMX also inhibits inositol phosphate production. The cross-talk mechanisms of these agents require further investigation.

Endothelium-dependent relaxations to adenosine in juvenile rabbit pulmonary arteries and veins

We studied the actions of adenosine and its analogues 5'-(N-ethylcarboxamido)-adenosine (NECA) and N6-cyclohexyladenosine (CHA) in pulmonary vessels isolated from juvenile rabbits. Pulmonary arteries relaxed in a concentration-dependent fashion to all three compounds. Pretreatment with the methylxanthine 8-p-sulfophenyltheophylline shifted the concentration-response curves to adenosine and NECA rightward, indicating that the vasodilator effects were mediated by the adenosine receptor. The order of potency of adenosine compounds was NECA > adenosine > CHA, indicating that the A2-receptor mediates relaxations to adenosine in rabbit pulmonary arteries. Endothelium rubbing attenuated relaxations to adenosine at concentrations of < or = 3 x 10(-7) M and to all NECA concentrations. Inhibition of nitric oxide synthase with NG-nitro-L-arginine (L-NNA) similarly attenuated relaxations at concentrations of < or = 3 x 10(-7) M for adenosine and < or = 3 x 10(-8) M for NECA. With the use of the same methods, a substantial endothelial contribution was additionally observed in pulmonary veins to the vasodilator effects of NECA. We conclude that adenosine, and the more specific A2-receptor agonist NECA, dilate pulmonary arteries and veins isolated from young rabbits via a mechanism that is partially dependent on endothelium-derived nitric oxide.

Developmental differences in endothelium-dependent responses in isolated ovine pulmonary arteries and veins

Despite evidence for an important role for endothelium-derived relaxing factor (EDRF) in transitional circulation, previous in vitro studies of newborn pulmonary arteries have demonstrated diminished EDRF activity when compared with arteries from older animals. We studied pulmonary arteries and veins isolated from early newborn and juvenile sheep using standard tissue bath techniques. Incubation of vessels with the nitric oxide synthase inhibitor N omega-nitro-L-arginine (L-NNA) constricted veins but not arteries from both age groups. Further studies using preconstricted vessels revealed that arteries relaxed to acetylcholine (ACh), with significantly greater responses observed in juvenile arteries. Veins from both age groups contracted to ACh. Pretreatment with prostaglandin inhibitors (indomethacin and SQ 29,548) diminished ACh relaxations in pulmonary arteries from both age groups, greatly enhanced relaxations to ACh in newborn pulmonary veins, and depressed contractions in juvenile pulmonary veins. Removal of endothelium mechanically or functionally with prostaglandin inhibitors and L-NNA eliminated relaxations to ACh in pulmonary arteries from both age groups and resulted in contractions in veins. We conclude that isolated pulmonary veins from newborn sheep exhibit both baseline and stimulated release of EDRF, and we speculate that these venous responses may be important in the transitional pulmonary circulation.

Characterization and mechanisms of H2O2-induced contractions of pulmonary arteries

We studied H2O2-induced contractions of isolated rabbit intrapulmonary arteries mounted in standard tissue baths. All vessels were pretreated with a thromboxane A2/prostaglandin H2 receptor antagonist, SQ 29,548, to block immediate transient contractions to H2O2 and to isolate slowly developing sustained contractions. When exposed to H2O2 (0.1, 0.2, 0.3, 0.6, and 1.0 mM) for 30 min, vessels contracted in (0.1, 0.2, 0.3, 0.6, and 1.0 mM) for 30 min, vessels contracted in a concentration-dependent fashion between 0.1 and 0.3 mM H2O2; contractions at 0.6 and 1.0 mM H2O2 were not significantly different from those at 0.3 mM H2O2. During recovery (90 min) from H2O2 exposures, baseline tension was significantly greater, but active tension (10 microM phenylephrine) was significantly less for vessels previously exposed to 0.6 and 1.0 mM H2O2. Contractions to 0.3 mM H2O2 were not blunted by the following interventions: 1) endothelium rubbing, 2) incubation in Ca(2+)-free 100 microM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) Krebs-Ringer solution, 3) incubation in the Ca(2+)-free solution and depletion of ryanodine (20 microM)-sensitive Ca(2+) stores, or 4) pretreatment with the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-3-methyl-piperazine (20 microM). However, contractions were depressed by approximately 50% when vessels were pretreated with the phospholipase C/serine esterase inhibitor 2-nitro-4-carboxy-phenyl-N,N-diphenylcarbamate (50 microM). These results suggest that slow-developing contractions to H2O2 are concentration dependent and may result, in part, from activation of a serine esterase(s) and/or phospholipase C.

Cleft lip and dermatoglyphic asymmetry

We have shown that fibrin-based small-diameter tissue-engineered blood vessels (TEVs) exhibited considerable mechanical strength and could withstand implantation in the jugular veins of lambs, where they remained patent for 15 weeks. The microtopology of fibrin matrix is influenced by the concentration of fibrinogen and calcium, whereas fibrinolysis and matrix remodeling are affected by the presence of the fibrinolytic inhibitor aprotinin. Here we report the effects of these components on two key properties of TEVs, namely mechanical strength and vasoreactivity. We found that high concentrations of fibrinogen or calcium decreased significantly both strength and reactivity. Surprisingly, aprotinin increased mechanical strength but decreased vascular reactivity in a dose-dependent manner. Transforming growth factor beta(1) (TGF-beta(1)) and insulin had a moderate effect on mechanical strength but significantly enhanced reactivity, through receptor- and non-receptor- mediated pathways. In addition, the combination of TGF-beta(1), insulin, and aprotinin resulted in significant improvement of both properties. Our data suggest that the microtopology of fibrin matrix and the rates of fibrinolysis and extracellular matrix synthesis may affect the properties of TEVs significantly. They also indicate that biomaterial and culture parameters may have differential effects on mechanical properties versus vascular reactivity and, therefore, engineering blood vessels under conditions that maximize tissue strength may not always result in optimal function. Instead, strength and reactivity must be used in concert for more accurate evaluation of tissue-engineered vascular constructs.