Huamei Wang

Effects of Prostacyclin and Milrinone on Pulmonary Hemodynamics in Newborn Lambs With Persistent Pulmonary Hypertension Induced by Ductal Ligation

Prostacyclin (PGI2) stimulates adenyl cyclase to synthesize cAMP within the vascular smooth muscle resulting in vasodilatation. Milrinone inhibits cAMP clearance by phosphodiesterase type III. We studied the dose response of pulmonary and systemic hemodynamics to intratracheal (IT) PGI2 in newborn lambs with pulmonary hypertension (PH) and whether intravenous milrinone potentiate these effects. IT-PGI2 at varying doses was administered to lambs with PH induced by prenatal ductal ligation. IT-PGI2 doses were repeated in the presence of intravenous milrinone (bolus—100 μg/kg followed by infusion at 1 μg/kg/min). Increasing doses of IT-PGI2 significantly decreased mean pulmonary arterial pressures (PAP) and pulmonary vascular resistance (PVR) and increased pulmonary blood flow (PBF). Intravenous milrinone by itself produced a significant reduction in PVR and a significant increase in PBF. Intravenous milrinone significantly shortened the onset, prolonged the duration and degree of pulmonary vasodilation produced by PGI2. We conclude that intravenous milrinone potentiates the pulmonary vasodilator effects of PGI2 at lower doses.

Exposure to Supplemental Oxygen Downregulates Antioxidant Enzymes and Increases Pulmonary Arterial Contractility in Premature Lambs

Background: The optimal oxygen concentration for the resuscitation of premature infants remains controversial. Objectives: We studied the effects of 21 versus 100% oxygen at initial resuscitation and also the effects of 24-hour exposure to 100% oxygen on arterial blood gases, oxidant lung injury, activities of lung antioxidant enzymes (AOEs) and isolated pulmonary artery (PA) contractility in preterm newborn lambs. Methods: Preterm lambs at 128 days’ gestation (term = 145 days) were delivered and ventilated with 21 (RAR; n = 5) or 100% oxygen (OXR; n = 5) for the first 30 min of life. Subsequently, FiO2 was adjusted to maintain an arterial PO2 (PaO2) between 45 and 70 mm Hg for 24 h. A third group of lambs was mechanically ventilated with 100% oxygen for 24 h (OX24; n = 5). Results: Oxidized glutathione levels in whole blood correlated highly with PaO2. Reduced to oxidized glutathione ratio was significantly different between the groups, the ratio increasing with decreasing oxygen exposure. The OX24 group had significantly higher activities of lipid hydroperoxide and myeloperoxidase and significantly lower activities of superoxide dismutase, catalase and glutathione peroxidase in the lung at 24 h. Activities of AOEs correlated inversely with alveolar PO2. PA contractility to norepinephrine and KCl was greater with increasing oxygen exposure. Pretreatment with superoxide dismutase and catalase significantly reduced PA contractility in the OXR and OX24 groups, but not in the RAR group. Conclusions: We conclude that ventilated premature lambs are unable to appropriately increase AOE activity in response to hyperoxia and that increasing exposure to oxygen aggravates systemic oxidant stress, oxidant lung injury and pulmonary arterial contractility in these lambs.

Exposure to supplemental oxygen and its effects on oxidative stress and antioxidant enzyme activity in term newborn lambs.

The optimal oxygen concentration for the resuscitation of term infants remains controversial. We studied the effects of 21 versus 100% oxygen immediately after birth, and also exposure for 24 h to 100% oxygen, on oxidant lung injury and lung antioxidant enzyme (AOE) activities in term newborn lambs. Lambs at 139 d gestation were delivered and ventilated with 21% (RAR) or 100% (OXR) for 30 min. A third group of newborn lambs were ventilated with 100% O2 for 24 h (OX24). Oxidized glutathione levels in whole blood were significantly different among the groups with lower values in the RAR group, and these values correlated highly with partial pressure of arterial oxygen (Pao2). The reduced to oxidized glutathione ratio was significantly different among the groups, the ratio decreasing with increasing oxygen exposure. Lipid hydroperoxide (LPO) activity was significantly higher in the OXR and OX24 groups. AOE activity was higher in the whole lung and in red cell lysate in the OX24 group. Increased myeloperoxidase (MPO) activity, percent neutrophils, and proteins in lung lavage suggested inflammation in the OX24 group after maximal oxygen exposure. We conclude that even relatively brief exposure of the lung to 100% oxygen increases systemic oxidative stress and lung oxidant injury in ventilated term newborn lambs.

Ductus venosus flow velocity in newborn lambs during increased pulmonary artery pressure

The aim of the present study was to assess with ultrasound the ductus venosus flow velocity in newborn lambs with increasing pulmonary artery pressures and to evaluate whether this is a useful method to detect elevated pulmonary artery pressure. The ductus venosus flow velocity was studied with pulsed-wave Doppler echocardiography in nine newborn lambs ≤30 h old. The lambs were anesthetized, mechanically ventilated, and instrumented to measure mean airway pressure and pulmonary artery and arterial blood pressures. A vascular occluder was placed around the main pulmonary artery. With mean pressures ranging from 20 to 50 mm Hg in the pulmonary artery, the ductus venosus flow velocity was examined. In seven lambs, the mean portal pressure and central venous pressure were also measured. With a stepwise increase in the pulmonary artery pressure, the minimum ductus venosus flow velocity during atrial systole decreased to a reversed flow, and the duration of this reversed flow component increased. The systolic forward peak flow velocity signal also gradually decreased. No changes were detected in the mean central venous or in the portal pressure with increasing pulmonary artery pressure or changes in ductus venosus flow. The flow velocity in the ductus venosus, which is higher than in other precordial veins, shows a reduction and even reversal of the nadir and an increase of the duration of reversed flow during atrial systole as a response to increased pulmonary artery pressure. Thus, Doppler ultrasound of the ductus venosus flow velocity may be a useful noninvasive diagnostic supplement to detect pulmonary hypertension of the newborn.

Long-Term Effects of Neonatal Hyperoxia in Adult Mice: NEONATAL HYPEROXIA & LONG-TERM EFFECTS IN MICE

The outcomes of premature infants have improved greatly; however, the health risks in adulthood are still relatively unclear. Bronchopulmonary dysplasia (BPD) in premature infants is a major risk factor for alteration in lung function and predisposition to respiratory morbidity, and is associated with hyperoxia. The study explores the effect of neonatal hyperoxia on organ systems in adult mice. Newborn mouse litters were randomized to 85%O2 or room air (RA) on P3 for 12 days; mice were sacrificed at P3, P7, P15, 3 months and 9 months. Lungs were assessed by histopathology, radial alveolar count, mean linear intercept, and α‐Smooth muscle actin immunohistochemistry. Aortic assessment included histology, wall thickness, elastin, and collagen content. Glomerular histology and nephron number were assessed in the kidneys. Hyperoxia‐exposed mice had progressive alveolar simplification and poor weight gain over time. Greater thickness of pulmonary arterioles by 3 months and a higher Fulton index by 9 months suggest worsening pulmonary hypertension. Aortic wall thickness to lumen ratio was greater with a lower aortic elastin‐to‐collagen ratio suggesting long‐term effects of neonatal hyperoxia. Hyperoxia‐exposed mice at 9 months had smaller glomeruli as indicated by glomerular diameter and volume. Prolonged neonatal hyperoxia during the critical period of development induces irreversible lung damage, pulmonary hypertension and structural changes in the kidneys and aorta in adult mice. This could have implications for chronic adult diseases following exposure to high levels of oxygen in the newborn period. Anat Rec, 301:717–726, 2018.

Adaptive immune responses are altered in adult mice following neonatal hyperoxia

Premature infants with bronchopulmonary dysplasia (BPD), are at risk for frequent respiratory infections and reduced pulmonary function. We studied whether neonatal hyperoxia disrupts adaptive immune responses in adult mice, contributing to higher respiratory‐related morbidities seen in these infants. Newborn mice litters were randomized at 3 days to 85% O2 or room air (RA) for 12 days. Whole lung mRNA was isolated in both the groups at 2 weeks and 3 months. Gene expression for T‐cell and B‐cell adaptive immune response was performed by real‐time PCR and qRT‐PCR; protein expression (p21, IL4, IL10, IL27, cd4) was performed by enzyme immunoassay along with p21 immunohistochemistry. Hyperoxia increased expression of p21 and decreased expression of 19 genes representing T/B‐cell activation by ≥ fourfold; three of them significantly (Rag1, Cd1d1, Cd28) compared to the RA group at 2 weeks. Despite RA recovery, the expression of IFNγ, IL27, and CD40 was significantly reduced at 3 months in the hyperoxia group. Expression of p21 was significantly higher and IL27 protein lower at 2 weeks following hyperoxia. Adult mice exposed to neonatal hyperoxia had lower IL4 and IL10 in the lung at 3 months. Adaptive immune responses are developmentally regulated and neonatal hyperoxia suppresses expression of genes involved in T‐/B‐cell activation with continued alterations in gene expression at 3 months. Dysfunction of adaptive immune responses increases the risk for susceptibility to infection in premature infants.

Nfib hemizygous mice are protected from hyperoxic lung injury and death

Nuclear Factor I (Nfi) genes encode transcription factors essential for the development of organ systems including the lung. Nfib null mice die at birth with immature lungs. Nfib hemizygous mice have reduced lung maturation with decreased survival. We therefore hypothesized that these mice would be more sensitive to lung injury and would have lower survival to hyperoxia. Adult Nfib hemizygous mice and their wild‐type (Wt) littermates were exposed to 100% O2 for 89, 80, 72 and 66 h for survival studies with lung outcome measurements at 66 h. Nfib hemizygous and Wt controls were also studied in RA at 66 h. Cell counts and cytokines were measured in bronchoalveolar lavage (BAL); lung sections examined by histopathology; lung angiogenic and oxidative stress gene expression assessed by real‐time PCR. Unexpectedly, Nfib hemizygous mice (0/14–0%) had significantly lower mortality compared to Wt mice (10/22–45%) at 80 h of hyperoxia (P < 0.003). LD50 was 80 h in the Wt group versus 89 h in the hemizygous group. There were no differences in BAL cell counts between the groups. Among the cytokines studied, MIP‐2 was significantly lower in hemizygous mice exposed to hyperoxia. New vessel formation, edema, congestion, and alveolar hemorrhage were noted on histopathology at 72 and 80 h in wild‐type mice. Nfib hemizygous lungs had significant downregulation of genes involved in redox signaling and inflammatory pathways. Adult Nfib hemizygous mice are relatively resistant to hyperoxia compared to wild‐type littermates. Mechanisms contributing to this resistance are not clear; however, transcription factors such as Nfib may regulate cell survival and play a role in modulating postnatal lung development.

Natriuretic peptide C receptor in the developing sheep lung: role in perinatal transition

BackgroundAt birth, the release of surfactant from alveolar type II cells (ATIIs) is stimulated by increased activity of the beta-adrenergic/adenylyl cyclase/cyclic 3′-5′ adenosine monophosphate-signaling cascade. Atrial natriuretic peptide (ANP) stimulates surfactant secretion through natriuretic peptide receptor A (NPR-A). ANP inhibits adenylyl cyclase activity through its binding to NPR-C. We wished to further understand the role of the NPR-C in perinatal transition.MethodsWe studied ATII expression of NPR-C in fetal and newborn sheep using immunohistochemistry, and surfactant secretion in isolated ATIIs by measuring 3[H] choline release into the media.ResultsANP induced surfactant secretion, and, at higher doses, it inhibits the stimulatory effect of the secretagogue terbutaline. ATII NPR-C expression decreased significantly after birth. Premature delivery also markedly decreased ANP and NPR-C in ATIIs. Co-incubation of terbutaline (10−4 M) with ANP (10−6 M) significantly decreased 3[H] choline release from isolated newborn ATII cells when compared with terbutaline alone; this inhibitory effect was mimicked by the specific NPR-C agonist, C-ANP (10−10 M).ConclusionANP may act as an important epithelial-derived inhibitor of surfactant release in the fetal lung, and downregulation of ANP and NPR-C following birth may sensitize ATII cells to the effects of circulating catecholamines, thus facilitating surfactant secretion.

598 Effects of Catalytic Antioxidant Mntbap on Pulmonary Angiogenic and Oxidative Gene Expression to Hyperoxia in Newborn Mice

Background Development of lung injury during prolonged O2 exposure is a complex process, associated with changes in expression of a number of genes important in the adaptive response to hyperoxia. MnTBAP is a compound with strong antioxidant properties. Objective To study the effects of MnTBAP on angiogenic and oxidative gene expression in C57BL6 neonatal mice following hyperoxia. Design and methods: Newborn mice litters were randomized on postnatal day 4 to hyperoxia (> 95% O2)(OX) or room air (RA) for 72 hrs during which they received MnTBAP (MN) 10mg/kg or saline (SL) daily by IP injection for 3 days and then were sacrificed. Whole lung angiogenic and oxidative gene expression profiling (84 related genes for each) was done by real-time, reverse transcription, quantitative PCR (n=4). Data was processed and analyzed using SA Biosciences PCR array data analysis web portal. Results Hyperoxia significantly upregulated peroxiredoxin 6 expression compared to room air exposed newborn mice. Treatment with MnTBAP downregulated the expression of myeloperoxidase and Prdx6-rs1. Hyperoxia downregulated the expression of angiogenic genes such as angiopoietin 1 & 2, TGF 1, TGF 3 and HGF; MnTBAP treatment during the hyperoxia exposure reversed this effect and these genes were upregulated. Conclusions The catalytic antioxidant MnTBAP reversed the effects of hyperoxia on angiogenic gene expression in newborn mice. The protective effects of antioxidants in newborn hyperoxia models need to be studied further to provide additional understanding of the management of bronchopulmonary dysplasia.