L-citrulline attenuates lipopolysaccharide-induced inflammatory lung injury in neonatal rats

BACKGROUND

Prenatal or postnatal lung inflammation and oxidative stress disrupt alveolo-vascular development leading to bronchopulmonary dysplasia (BPD) with and without pulmonary hypertension. L-citrulline (L-CIT), a nonessential amino acid, alleviates inflammatory and hyperoxic lung injury in preclinical models of BPD. L-CIT modulates signaling pathways mediating inflammation, oxidative stress, and mitochondrial biogenesis-processes operative in the development of BPD. We hypothesize that L-CIT will attenuate lipopolysaccharide (LPS)-induced inflammation and oxidative stress in our rat model of neonatal lung injury.

METHODS

Newborn rats during the saccular stage of lung development were used to investigate the effect of L-CIT on LPS-induced lung histopathology and pathways involved in inflammatory, antioxidative processes, and mitochondrial biogenesis in lungs in vivo, and in primary culture of pulmonary artery smooth muscle cells, in vitro.

RESULTS

L-CIT protected the newborn rat lung from LPS-induced: lung histopathology, ROS production, NFκB nuclear translocation, and upregulation of gene and protein expression of inflammatory cytokines (IL-1β, IL-8, MCP-1α, and TNF-α). L-CIT maintained mitochondrial morphology, increased protein levels of PGC-1α, NRF1, and TFAM (transcription factors involved in mitochondrial biogenesis), and induced SIRT1, SIRT3, and superoxide dismutases protein expression.

CONCLUSION

L-CIT may be efficacious in decreasing early lung inflammation and oxidative stress mitigating progression to BPD.

IMPACT

The nonessential amino acid L-citrulline (L-CIT) mitigated lipopolysaccharide (LPS)-induced lung injury in the early stage of lung development in the newborn rat. This is the first study describing the effect of L-CIT on the signaling pathways operative in bronchopulmonary dysplasia (BPD) in a preclinical inflammatory model of newborn lung injury. If our findings translate to premature infants, L-CIT could decrease inflammation, oxidative stress and preserve mitochondrial health in the lung of premature infants at risk for BPD.

Maturational effect of leptin on CO2 chemosensitivity in newborn rats

BACKGROUND

Leptin augments central CO2 chemosensitivity and stabilizes breathing in adults. Premature infants have unstable breathing and low leptin levels. Leptin receptors are on CO2 sensitive neurons in the Nucleus Tractus Solitarius (NTS) and locus coeruleus (LC). We hypothesized that exogenous leptin improves hypercapnic respiratory response in newborn rats by improving central CO2 chemosensitivity.

METHODS

In rats at postnatal day (p)4 and p21, hyperoxic and hypercapnic ventilatory responses, and pSTAT and SOCS3 protein expression in the hypothalamus, NTS and LC were measured before and after treatment with exogenous leptin (6 µg/g).

RESULTS

Exogenous leptin increased the hypercapnic response in p21 but not in p4 rats (P ≤ 0.001). At p4, leptin increased pSTAT expression only in the LC, and SOCS3 expression in the NTS and LC; while at p21 pSTAT and SOCS3 levels were higher in the hypothalamus, NTS, and LC (P ≤ 0.05).

CONCLUSIONS

We describe the developmental profile of the effect of exogenous leptin on CO2 chemosensitivity. Exogenous leptin does not augment central CO2 sensitivity during the first week of life in newborn rats. The translational implication of these findings is that low plasma leptin levels in premature infants may not be contributing to respiratory instability.

IMPACT

Exogenous leptin does not augment CO2 sensitivity during the first week of life in newborn rats, similar to the developmental period when feeding behavior is resistant to leptin. Exogenous leptin increases CO2 chemosensitivity in newborn rats after the 3rd week of life and upregulates the expression of pSTAT and SOC3 in the hypothalamus, NTS and LC. Low plasma leptin levels in premature infants are unlikely contributors to respiratory instability via decreased CO2 sensitivity in premature infants. Thus, it is highly unlikely that exogenous leptin would alter this response.

Impact of the Addition of a Centrifugal Pump in a Preterm Miniature Pig Model of the Artificial Placenta

The recent demonstration of normal development of preterm sheep in an artificial extrauterine environment has renewed interest in artificial placenta (AP) systems as a potential treatment strategy for extremely preterm human infants. However, the feasibility of translating this technology to the human preterm infant remains unknown. Here we report the support of 13 preterm fetal pigs delivered at 102 ± 4 days (d) gestation, weighing 616 ± 139 g with a circuit consisting of an oxygenator and a centrifugal pump, comparing these results with our previously reported pumpless circuit (n = 12; 98 ± 4 days; 743 ± 350 g). The umbilical vessels were cannulated, and fetuses were supported for 46.4 ± 46.8 h using the pumped AP versus 11 ± 13 h on the pumpless AP circuit. Upon initiation of AP support on the pumped system, we observed supraphysiologic circuit flows, tachycardia, and hypertension, while animals maintained on a pumpless AP circuit exhibited subphysiologic flows. On the pumped AP circuit, there was a progressive decline in umbilical vein (UV) flow and oxygen delivery. We conclude that the addition of a centrifugal pump to the AP circuit improves survival of preterm pigs by augmenting UV flow through the reduction of right ventricular afterload. However, we continued to observe the development of heart failure within a matter of days.

Adiponectin and the regulation of gastric content volume in the newborn rat

BACKGROUND

Oral intake is dependent on the gastric ability to accommodate the food bolus. Comparatively, neonates have a smaller gastric capacity than adults and this may limit the volume of their milk intake. Yet, we previously reported that the newborn rat gastric milk volume is greatest after birth and, when normalized to body weight, decreases with postnatal age. Such age-dependent changes are not the result of intake differences, but greater gastric accommodation and reduced emptying rate.

AIM

Hypothesizing that breastmilk-derived adiponectin is the factor regulating gastric accommodation in neonates, we comparatively evaluated its effects on the rat fundic muscle tone at different postnatal ages.

METHODS

In freshly dispersed smooth muscle cells (SMC), we measured the adiponectin effect on the carbachol-induced length changes.

RESULTS

Adiponectin significantly reduced the carbachol-stimulated SMC shortening independently of age. In the presence of the inhibitor iberiotoxin, the adiponectin effect on SMC shortening was suppressed, suggesting that it is mediated via large-conductance Ca²⁺ sensitive K⁺ channel activation. Lastly, we comparatively measured the newborn rat gastric milk curd adiponectin content in one- and two-week-old rats and found a 50% lower value in the latter.

CONCLUSION

Adiponectin, a major component of breastmilk, downregulates fundic smooth muscle contraction potential, thus facilitating gastric volume accommodation. This rodent’s adaptive response maximizes breastmilk intake volume after birth.

Clinical and echocardiography predictors of response to inhaled nitric oxide in hypoxemic term and near-term neonates

Approximately 40% of hypoxemic term/near-term neonates are nonresponders to inhaled nitric oxide (iNO). Phenotypic characterization of patients less likely to respond may improve diagnostic precision and therapeutic decisions. We conducted a retrospective cohort study of neonates born ≥35 weeks gestation with hypoxemia who received iNO in the first 72 h of life and classified them into responders and nonresponders according to changes in the fraction of inspired oxygen, saturations and/or arterial partial pressure of oxygen after 1 h of administration. Comprehensive targeted neonatal echocardiography (TnECHO) data were collected when performed up to 6 h prior or 24 h after iNO initiation. Descriptive statistics, univariate analysis, and binary logistic regression were used to compare the groups. There were 183 patients included (63% responders) and TnECHO was performed in 54 infants. The presence of lung disease, and particularly meconium aspiration syndrome (p = .004), was associated with nonresponse to iNO. Nonresponders were characterized by a higher need for rescue high-frequency ventilation (p < .001), longer duration of mechanical ventilation (p < .001), and need for oxygen support (p = .003). Pulmonary hypertension documented on TnECHO was present in 96.3% of the patients but there was no difference in frequency or severity of pulmonary hypertension, or rates of low cardiac output between the groups. Moderate-to-severe right ventricular systolic dysfunction (p > .05) and lower left ventricular strain (p < .05) were more likely in the nonresponder group. In summary, response to iNO is influenced by lung disease, choice of ventilation strategy, and perhaps underlying cardiovascular physiology. Prospective pre- and post-iNO echocardiography data may provide novel physiologic insights.

Necrotising enterocolitis in newborns receiving diazoxide

BACKGROUND

Frequent and severe gastrointestinal disturbances have been reported with the use of diazoxide in adults and older children. However, no studies have investigated the incidence of necrotising enterocolitis (NEC) in diazoxide-exposed newborns.

OBJECTIVE

To evaluate a possible association between diazoxide treatment for neonatal hypoglycaemia and the occurrence of NEC.

DESIGN

Multicentre retrospective cohort study.

SETTING

Three tertiary neonatal intensive care units in Toronto, Canada.

PATIENTS

All patients treated with diazoxide for persistent hypoglycaemia between July 2012 and June 2017 were included. Overall incidence of NEC during those years on the participating units was obtained for comparison from the Canadian Neonatal Network database.

MAIN OUTCOME

Incidence of NEC after diazoxide exposure.

RESULTS

Fifty-five neonates were exposed to diazoxide during the study period. Eighteen patients (33%) showed signs of feeding intolerance, and 7 developed NEC (13%). A diagnosis of NEC was more prevalent in the diazoxide-exposed, as compared with non-exposed infants of similar gestational age (OR 5.07, 95% CI 2.27 to 11.27; p<0.001), and greatest among infants born at 33-36 weeks' gestation (OR 13.76, 95% CI 3.77 to 50.23; p<0.001). All but one of the neonates diagnosed with NEC developed the disease within 7 days from initiation of diazoxide treatment.

CONCLUSION

The present data suggest a possible association between diazoxide exposure and the development of NEC in neonates. Further evaluation of the diazoxide-associated risk of NEC in neonates treated for persistent hypoglycaemia is warranted.

Achieving sustained extrauterine life: Challenges of an artificial placenta in fetal pigs as a model of the preterm human fetus

Artificial placenta (AP) technology aims to maintain fetal circulation, while promoting the physiologic development of organs. Recent reports of experiments performed in sheep indicate the intrauterine environment can be recreated through the cannulation of umbilical vessels, replacement of the placenta with a low-resistance membrane oxygenator, and incubation of the fetus in fluid. However, it remains to be seen whether animal fetuses similar in size to the extremely preterm human infant that have been proposed as a potential target for this technology can be supported in this way. Preterm Yucatan miniature piglets are similar in size to extremely preterm human infants and share similar umbilical cord anatomy, raising the possibility to serve as a good model to investigate the AP. To characterize fetal cardiovascular physiology, the carotid artery (n = 24) was cannulated in utero and umbilical vein (UV) and umbilical artery were sampled. Fetal UV flow was measured by MRI (n = 16). Piglets were delivered at 98 ± 4 days gestation (term = 115 days), cannulated, and supported on the AP (n = 12) for 684 ± 228 min (range 195-3077 min). UV flow was subphysiologic (p = .002), while heart rate was elevated on the AP compared with in utero controls (p = .0007). We observed an inverse relationship between heart rate and UV flow (r2  = .4527; p < .001) with progressive right ventricular enlargement that was associated with reduced contractility and ultimately hydrops and circulatory collapse. We attribute this to excessive afterload imposed by supraphysiologic circuit resistance and augmented sympathetic activity. We conclude that short-term support of the preterm piglet on the AP is feasible, although we have not been able to attain normal fetal physiology. In the future, we propose to investigate the feasibility of an AP circuit that incorporates a centrifugal pump in our miniature pig model.

Recombinant adiponectin protects the newborn rat lung from lipopolysaccharide-induced inflammatory injury

Preterm infants are at high risk for developing bronchopulmonary dysplasia and pulmonary hypertension from inflammatory lung injury. In adult models, adiponectin (APN)—an adipocyte‐derived hormone—protects the lung from inflammatory injury and pulmonary vascular remodeling. Cord blood APN levels in premature infants born < 26 weeks gestation are 5% of the level in infants born at term. We previously reported the expression profile of APN and its receptors in neonatal rat lung homogenates during the first 3 weeks of postnatal development. Here, we characterize the expression profile of APN and its receptors in specific lung cells and the effects of exogenous recombinant APN (rAPN) on lipopolysaccharide‐(LPS)‐induced cytokine and chemokine production in total lung homogenates and specific lung cells. In vitro, rAPN added to primary cultures of pulmonary artery smooth muscle cells attenuated the expression of LPS‐induced pro‐inflammatory cytokines while increasing the expression of anti‐inflammatory cytokines. In vivo, intraperitoneal rAPN (2 mg/kg), given 4 hr prior to intrapharyngeal administration of LPS (5 mg/kg) to newborn rats at postnatal day 4, significantly reduced gene and protein expression of the pro‐inflammatory cytokine IL‐1ß and reduced protein expression of the chemokines monocyte chemoattractant protein (MCP‐1) and macrophage inflammatory protein‐1 alpha (MIP‐1α) in the lung. LPS‐induced histopathological changes in the lung were also decreased. Moreover, rAPN given 20 hr after intrapharyngeal LPS had a similar effect on lung inflammation. These findings suggest a role for APN in protecting the lung from inflammation during early stages of lung development.

A novel role for milrinone in neonatal acute limb ischaemia: successful conservative treatment of thrombotic arterial occlusion without thrombolysis

Acute neonatal limb ischaemia (NLI) is most frequently an iatrogenic complication, however, may also occur in utero due to thromboembolism. There is no widely accepted protocol for treatment of NLI and limited evidence to guide management. Thrombolysis and surgical management have been attempted, though both are associated with significant morbidities. Milrinone is a phosphodiesterase-3 inhibitor used for its vasodilatory effects on the systemic and pulmonary vasculature. There is also emerging evidence for benefit of milrinone in ameliorating ischaemia-reperfusion injury. The authors present a case report of a term infant with spontaneous perinatal acute limb ischaemia secondary to near-completely occlusive thrombosis of the right subclavian artery. The infant was successfully managed conservatively with milrinone without requirement for thrombolysis or surgical intervention. Milrinone represents a novel treatment option for neonates with acute limb ischaemia and consideration of a trial of milrinone prior to higher risk treatment options is warranted in this patient group.

Neonatal coning secondary to hypoxic ischaemic encephalopathy: A case study and literature review

Introduction

Brain herniation is an extremely rare complication of hypoxic ischaemic encephalopathy (HIE) in the neonatal period with only a single report described. We report a 2-day-old term infant with severe HIE, who developed diffuse brain oedema and herniation.

Case presentation and description

A term female infant delivered by vacuum, required therapeutic hypothermia for severe encephalopathy. At 36 hours of age, a marked change in neurological status was noted with signs of brainstem involvement. A head Computed Tomography Scan showed uncal and tonsillar herniation.

Conclusion

Vigilance in monitoring neonatal neurological status during therapeutic hypothermia is imperative for early brain herniation detection.

Gavage Feed Volume Determines the Gastric Emptying Rate in Preterm Infants

OBJECTIVE

Feeding intolerance, manifesting as increased gastric residual, is a common finding in preterm neonates. Little is known about the regulation of gastric emptying early in life and the extent to which this plays a role in the preterm infants' feeding tolerance. The goal of this study was to evaluate clinically stable 28- to 32-week gestation neonates during the first 4 weeks of life and noninvasively determine their gastric emptying rate.

STUDY DESIGN

Ultrasound measurements of gastric milk content volume were obtained from 25 neonates immediately after, 30 and/or 60 minutes following routine gavage feeds. The content emptying rate was calculated from the gastric volume data.

RESULTS

Gastric emptying rate was not postnatal age-dependent, was significantly higher at 30 minutes, whenever compared with 60-minute postfeed and directly proportional to the feed volume. At any postnatal age, the gastric emptying rate was at least 6-fold greater, when comparing the lowest and highest average stomach content volumes.

CONCLUSIONS

The gastric emptying rate of preterm infants is content volume-dependent and unrelated to the postnatal age. Given the present findings, further investigation on the gastric residual of preterm infants receiving larger than currently administered feed volumes at the initiation of enteral nutrition, is warranted.

New Ventilator Strategies: High-Frequency Oscillatory Ventilation Combined with Volume Guarantee

High-frequency oscillatory ventilation (HFOV) has been proposed as an alternative method of invasive ventilation in immature infants to prevent ventilator lung injury. To better control the size of the high-frequency tidal volume and to prevent large tidal volumes, a new strategy of controlling the tidal volume during HFOV (VThf) has been developed, HFOV-volume guarantee (VG). Data from preclinical, neonatal animal studies in normal and surfactant-depleted lungs have demonstrated the feasibility of this technique to directly control the VThf in the normal compliance and low compliance situations. Different I:E ratios also can modify the effect of CO₂ washout during HFOV combined with VG in a different way as without the VG modality. Finally, clinical use of this technique in newborn infants has demonstrated the possibility of using very high frequency combined with constant very low VThf to decrease the risk of lung trauma related to the ventilator.

The newborn rat gastric emptying rate is volume and not developmentally dependent

BACKGROUND

Gastric residuals are a common finding in enterally fed preterm neonates and traditionally thought to reflect immaturity-related delayed gastric emptying. Adult human data suggest that the meal volume regulate the gastric emptying rate, but early in life, this has not been adequately evaluated. The goal of this study was to study the rat postnatal changes in gastric emptying rate and the strain-induced effect on muscle contraction. We hypothesized that the stomach content volume and not developmental factors determines the newborn gastric emptying rate, via the Rho-kinase 2 (ROCK-2) pathway.

METHODS

Gastric volume and emptying rate measurements were obtained by ultrasound at different postprandial times and the wall strain-dependent changes in muscle contraction were evaluated ex vivo.

KEY RESULTS

The newborn rat gastric emptying rate was unrelated to postnatal age, maximal 30 min postprandial, and directly proportional to content volume. In vitro measurements showed that the agonist-induced gastric muscle contraction was directly proportional to the stomach wall strain. These changes were mediated via upregulation of ROCK-2 activity.

CONCLUSIONS & INFERENCES

The newborn rat gastric emptying rate is not developmentally regulated, but dependent on the content volume via wall strain-induced ROCK-2 activation. Further clinical studies addressing the content volume effect on the rate of gastric emptying are warranted, to enhance feeding tolerance in preterm neonates.

Chronic Intermittent Hypoxia in Premature Infants: The Link Between Low Fat Stores, Adiponectin Receptor Signaling and Lung Injury

Premature infants have chronic intermittent hypoxia (CIH) that increases morbidity, and the youngest and the smallest premature infants are at the greatest risk. The combination of lung injury from inflammation/oxidative stress causing low functional residual capacity combined with frequent short apneas leads to CIH. Adiponectin (APN) is an adipose-derived adipokine that protects the lung from inflammation and oxidative stress. Premature and small for gestational age (SGA) infants have minimal body fat and low levels of circulating APN. To begin to understand the potential role of APN in lung protection during lung development, we characterized the developmental profile of APN and APN receptors (AdipoR1 and AdipoR2) protein and mRNA expression in the newborn rat lung at fetal day (FD) 19, and postnatal days (PD) 1, 4, 7, 10, 14, 21, and 28. Protein levels in lung homogenates were measured by western blot analyses; relative mRNA expression was detected by quantitative PCR (qPCR); and serum high molecular weight (HMW) APN was measured using enzyme-linked immunosorbent assay (ELISA). Results: APN protein and mRNA levels were lowest at FD19 and PD1, increased 2.2-fold at PD4, decreased at PD10, and then increased again at PD21. AdipoR1 protein and mRNA levels peaked at PD1, followed by a threefold drop by PD4, and remained low until PD21. AdipoR2 protein and mRNA levels also peaked at PD1, but remained high at PD4, followed by a 1.7-fold drop by PD10 that remained low by PD21. Serum APN levels detected by ELISA did not differ from PD4 to PD28. To date, this is the first report characterizing APN and APN receptor protein and mRNA expression in the rat lung during development. The developmental stage of the newborn rat lung models that of the premature human infant; both are in the saccular stage of lung development. In the newborn rat lung, alveolarization begins at PD4, peaks at PD10, and ends at PD21. Importantly, we found that AdipoR1 receptor protein and mRNA expression is lowest during lung alveolarization (PD4 to PD21). Thus, we speculate that low levels of AdipoR1 during lung alveolarization contributes to the increased susceptibility to developing acute lung edema and chronic lung injury such as bronchopulmonary dysplasia (BPD) in premature human infants.

Tetrahydrobiopterin (BH4) deficiency is associated with augmented inflammation and microvascular degeneration in the retina

Background

Tetrahydrobiopterin (BH4) is an essential cofactor in multiple metabolic processes and plays an essential role in maintaining the inflammatory and neurovascular homeostasis. In this study, we have investigated the deleterious effects of BH4 deficiency on retinal vasculature during development.

Methods

hph-1 mice, which display deficiency in BH4 synthesis, were used to characterize the inflammatory effects and the integrity of retinal microvasculature. BH4 levels in retinas from hph-1 and wild type (WT) mice were measured by LC-MS/MS. Retinal microvascular area and microglial cells number were quantified in hph-1 and WT mice at different ages. Retinal expression of pro-inflammatory, anti-angiogenic, and neuronal-derived factors was analyzed by qPCR. BH4 supplementation was evaluated in vitro, ex-vivo, and in vivo models.

Results

Our findings demonstrated that BH4 levels in the retina from hph-1 mice were significantly lower by ~ 90% at all ages analyzed compared to WT mice. Juvenile hph-1 mice showed iris atrophy, persistent fetal vasculature, significant increase in the number of microglial cells (p < 0.01), as well as a marked degeneration of the retinal microvasculature. Retinal microvascular alterations in juvenile hph-1 mice were associated with a decreased expression in Norrin (0.2-fold) and its receptor Frizzled-4 (FZD4; 0.51-fold), as well as with an augmented expression of pro-inflammatory factors such as IL-6 (3.2-fold), NRLP-3 (4.4-fold), IL-1β (8.6-fold), and the anti-angiogenic factor thrombospondin-1 (TSP-1; 17.5-fold). We found that TSP-1 derived from activated microglial cells is a factor responsible of inducing microvascular degeneration, but BH4 supplementation markedly prevented hyperoxia-induced microglial activation in vitro and microvascular injury in an ex-vivo model of microvascular angiogenesis and an in vivo model of oxygen-induced retinopathy (OIR).

Conclusion

Our findings reveal that BH4 is a key cofactor in regulating the expression of inflammatory and anti-angiogenic factors that play an important function in the maintenance of retinal microvasculature.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-0955-x) contains supplementary material, which is available to authorized users.

Intestinal microbiota as a tetrahydrobiopterin exogenous source in hph-1 mice

Tetrahydrobiopterin (BH4) is a cofactor of a number of regulatory enzymes. Although there are no known BH4 exogenous sources, the tissue content of this biopterin increases with age in GTP cyclohydrolase 1-deficient hyperphenylalaninemia-1 (hph-1) mice. Since certain bacteria are known to generate BH4, we hypothesize that generation of this biopterin by the intestinal microbiota contributes to its tissue increase in hph-1 adult mice. The goal of this study was to comparatively evaluate hph-1 mice and wild-type C57Bl/6 controls for the presence of intestinal BH4-producing bacteria. Newborn and adult mice fecal material was screened for 6-pyruvoyltetrahydropterin synthase (PTPS-2) an enzyme only present in BH4-generating bacteria. Adult, but not newborn, wild-type control and hph-1 mouse fecal material contained PTPS-2 mRNA indicative of the presence of BH4-generating bacteria. Utilizing chemostat-cultured human fecal bacteria, we identified the PTPS-2-producing bacteria as belonging to the Actinobacteria phylum. We further confirmed that at least two PTPS-2-producing species, Aldercreutzia equolifaciens and Microbacterium schleiferi, generate BH4 and are present in hph-1 fecal material. In conclusion, intestinal Actinobacteria generate BH4. This finding has important translational significance, since manipulation of the intestinal flora in individuals with congenital biopterin deficiency may allow for an increase in total body BH4 content.

Effect of the I/E ratio on CO2 removal during high-frequency oscillatory ventilation with volume guarantee in a neonatal animal model of RDS

The objective of this study was to analyze the effect of I/E ratio on carbon dioxide (CO2) elimination during high-frequency oscillatory ventilation (HFOV) combined with volume guarantee (VG). Five 2-day-old piglets were studied before and after a bronchoalveolar lavage (BAL). The effect of an I/E ratio of 1:1 and 1:2 with (VG-ON) and without VG (VG-OFF) on PaCO2, as well as delta and mean airway pressures at the airway opening (∆Phf-ao, mPaw-ao) and at the tracheal level (∆Phf-t, mPaw-t) were evaluated at frequencies of 5, 8, 11, and 14 Hz. With the VG-ON, PaCO2 was significant lower with the I/E ratio of 1:2 at 5 Hz compared with the 1:1. mPaw-t was higher than mPaw-ao, with 1:1 I/E ratio, and on VG-ON, this difference was statistically significant.

CONCLUSION

"In this animal study and with this ventilator, the I/E ratio of 1:1 compared to 1:2 in HFOV and VG-ON did not produce a higher CO2 lavage as when HFOV was used without the VG modality. Even more, a lower PaCO2 was found when using the lower frequency and 1:2 ratio compared to 1:1. So in contrast to non-VG HFOV mode, using a fixed tidal volume, no significant changes on CO2 elimination are observed during HFOV when the I/E ratios of 1:1 and 1:2 are compared at different frequencies."

WHAT IS KNOWN

•The tidal volume on HFOV is determinant in CO 2 removal, and this is generated by delta pressure and the length of the inspiratory time. What is New: •HFOV combined with VG, an I/E ratio of 1:2 is more effective to remove CO 2 , and this is not related to the tidal volume.

Gastric and pyloric sphincter muscle function and the developmental-dependent regulation of gastric content emptying in the rat

Feeding intolerance is a common issue in the care of preterm neonates. The condition manifests as delayed emptying of gastric contents and represents a therapeutic challenge, since the factors accounting for its manifestations are unknown. The main goal of this study was to comparatively investigate the age-related function of rat gastric and pyloric smooth muscle and their putative regulators. We hypothesized that a reduced gastric muscle contraction potential early in life contributes to the delayed gastric emptying of the newborn. Newborn and adult rat gastric (fundus) and pyloric sphincter tissues were comparatively studied in vitro. Shortening of the tissue-specific dissociated smooth muscle cell was evaluated, and expression of the key regulatory proteins Rho-associated kinase 2 and myosin light chain kinase was determined. Gastric and pyloric smooth muscle cell shortening was significantly greater in the adult than the respective newborn counterpart. Expression of myosin light chain kinase and Rho-associated kinase 2 was developmentally regulated and increased with age. Pyloric sphincter muscle expresses a higher neuronal nitric oxide synthase and phosphorylated vasodilator-stimulated phosphoprotein content in newborn than adult tissue. Compared with later in life, the newborn rat gastropyloric muscle has a Ca(2+)-related reduced potential for contraction and the pyloric sphincter relaxation-dependent modulators are overexpressed. To the extent that these rodent data can be extrapolated to humans, the delayed gastric emptying in the newborn reflects reduced stomach muscle contraction potential, as opposed to increased pyloric sphincter tone.

Maternal-pup interaction disturbances induce long-lasting changes in the newborn rat pulmonary vasculature

The factors accounting for the pathological maintenance of a high pulmonary vascular (PV) resistance postnatally remain elusive, but neonatal stressors may play a role in this process. Cross-fostering in the immediate neonatal period is associated with adult-onset vascular and behavioral changes, likely triggered by early-in-life stressors. In hypothesizing that fostering newborn rats induces long-lasting PV changes, we evaluated them at 14 days of age during adulthood and compared the findings with animals raised by their biological mothers. Fostering resulted in reduced maternal-pup contact time when compared with control newborns. At 2 wk of age, fostered rats exhibited reduced pulmonary arterial endothelium-dependent relaxation secondary to downregulation of tissue endothelial nitric oxide synthase expression and tetrahydrobiopterin deficiency-induced uncoupling. These changes were associated with neonatal onset-increased ANG II receptor type 1 expression, PV remodeling, and right ventricular hypertrophy that persisted into adulthood. The pulmonary arteries of adult-fostered rats exhibited a higher contraction dose response to ANG II and thromboxane A2, the latter of which was abrogated by the oxidant scavenger Tempol. In conclusion, fostering-induced neonatal stress induces long-standing PV changes modulated via the renin-angiotensin system.

Neonatal nasal intermittent positive pressure ventilation efficacy and lung pressure transmission

OBJECTIVE

The objective of this study was to evaluate carbon dioxide (CO2) clearance, delivered pressures and tidal volume (VT) during neonatal nasal intermittent positive pressure ventilation (NIPPV) with two commonly used interfaces.

STUDY DESIGN

A neonatal lung model, with either short binasal prongs (SBP) or a small caliber nasal cannula (RAM) interface, was tested over a range of clinically relevant settings. A fixed amount of CO2 was infused and the fraction remaining in the lung 100 s postinfusion was measured. Pressure transmission to the lung and VT was measured at the level of the trachea.

RESULT

CO2 elimination was directly proportional to the inspiratory pressure during NIPPV. At peak pressures of 22 to 34 cm H2O, CO2 clearance was greater (P<0.001) with SBP as compared with RAM. Relative to the set ventilator parameters, a substantial pressure dampening effect was documented at the lung level, which was significantly lower with RAM when compared with SBP (2.8% (0.2) versus 11.9% (1.5), P<0.0001). CO2 elimination was dependent on VT and effective despite only a small fraction of physiological VT (maximum delivered VT%: SBP 15.5 (0.7) versus RAM 6.1 (1.4), P<0.0001).

CONCLUSION

NIPPV promotes CO2 elimination even at low transmitted airway pressures, but less effective with RAM as compared with SBP. CO2 elimination despite small VT suggests that NIPPV may depend on a non-conventional gas-exchange mechanism.

Caffeine impairs gastrointestinal function in newborn rats

BACKGROUND

Feeding intolerance is commonly documented in premature infants. Caffeine is routinely utilized for apnea of prematurity treatment and known to reduce the lower esophageal sphincter (LES) muscle tone, but the caffeine effect on the newborn gastrointestinal function is unknown. We hypothesized that caffeine impairs esophageal and gastrointestinal motor function. As such, we investigated the drug effect on the tissue's mechanical properties and the newborn rat's in vivo gastric emptying rate.

METHODS

The effects of caffeine on LES, gastric fundal and antrum, as well as ileal and colonic muscle force potential and relaxation response, were measured in newborn and adult rats. The caffeine-induced (10 mg/kg i.p.) newborn gastric emptying rate changes were evaluated following 3 h of fasting.

RESULTS

Caffeine relaxed the precontracted LES and fundal muscle (P < 0.01), reduced the gastric and intestinal muscle contraction (P < 0.01), and delayed the pups' gastric emptying time (P < 0.01). The caffeine-induced muscle relaxant effect was independent of age and mediated via ryanodine receptors.

CONCLUSION

Caffeine administration to newborn rats at a dose comparable to the one therapeutically used for preterm neonates impairs LES and gastrointestinal motor function. Further clinical investigation on the possible contribution of caffeine to neonatal feeding intolerance is warranted.

In vivo ultrasound assessment of gastric emptying in newborn mice

OBJECTIVES

The aim of the present study was to develop an ultrasonographic approach to comparatively assess gastric emptying in newborn wild-type and guanosine triphosphate cyclohydrolase knockout hph-1 mice, because we previously reported gastroparesis early in life in this strain.

METHODS

Stomach transverse, anteroposterior, and longitudinal ultrasonographic measurements were obtained with a 40-MHz transducer in pups immediately after maternal separation and 4 hours later. A conventional equation was used and the predicted values validated by obtaining postmortem gastric content volume measurements. Wild-type and hph-1 mice gastric emptying rates were comparatively evaluated at 1 to 3 and 5 to 8 days of age, respectively.

RESULTS

The ultrasound equation closely predicted the newborn stomach content volumes with a correlation coefficient (R) of 0.93 and 0.81 (P < 0.01) for measurements obtained on full stomach and after 4 hours of fasting, respectively. In wild-type mice, gastric emptying was age dependent and associated with a greater residual volume at 1 to 3 days (65% ± 7%), as compared with 5- to 8-day-old pups (33% ± 4%; P  < 0.01), after fasting. In contrast, an equal duration of fasting resulted in a significantly greater residual gastric content volume in 5- to 8-day-old hph-1 mice (68%  ± 7%; P < 0.01), as compared with same-age wild-type mice.

CONCLUSIONS

Ultrasonography offers a sensitive and accurate estimate of gastric content volume in newborn mice. In wild-type newborn mice, gastric emptying rate is age dependent and significantly reduced in the immediate postnatal period. The newborn hph-1 mice have a significantly higher gastric residual volume, as compared with wild-type same-age animals.

Use of noninvasive high-frequency ventilation in the neonatal intensive care unit: a retrospective review

OBJECTIVE

The aim of the article is to review the effectiveness of neonatal noninvasive high-frequency ventilation (NIHFV) in preventing endotracheal mechanical ventilation.

STUDY DESIGN

Retrospective case series including all 79 instances of NIHFV use at four participating centers between July 2010 and September 2012.

RESULTS

In 73% of cases, NIHFV was used as rescue after another noninvasive mode, and prophylactically (postextubation) in the remainder. In 58% of cases, infants transitioned to another noninvasive mode, without requiring intubation. There were significant reductions in the mean (SD) number of apneas, bradycardias, or desaturations (over 6 hours) (3.2 [0.4] vs. 1.2 [0.3]; p < 0.001), FiO2 (48 [3] vs. 40 [2]%; p < 0.001) and CO2 levels (74 [6] vs. 62 [4] mm Hg; p = 0.025] with NIHFV. No NIHFV-related complications were noted.

CONCLUSIONS

NIHFV is a promising NIV mode that may help prevent or delay intubation and deserves further clinical research.

Arginase inhibition prevents bleomycin-induced pulmonary hypertension, vascular remodeling, and collagen deposition in neonatal rat lungs

Arginase is an enzyme that limits substrate L-arginine bioavailability for the production of nitric oxide by the nitric oxide synthases and produces L-ornithine, which is a precursor for collagen formation and tissue remodeling. We studied the pulmonary vascular effects of arginase inhibition in an established model of repeated systemic bleomycin sulfate administration in neonatal rats that results in pulmonary hypertension and lung injury mimicking the characteristics typical of bronchopulmonary dysplasia. We report that arginase expression is increased in the lungs of bleomycin-exposed neonatal rats and that treatment with the arginase inhibitor amino-2-borono-6-hexanoic acid prevented the bleomycin-induced development of pulmonary hypertension and deposition of collagen. Arginase inhibition resulted in increased L-arginine and L-arginine bioavailability and increased pulmonary nitric oxide production. Arginase inhibition also normalized the expression of inducible nitric oxide synthase, and reduced bleomycin-induced nitrative stress while having no effect on bleomycin-induced inflammation. Our data suggest that arginase is a promising target for therapeutic interventions in neonates aimed at preventing lung vascular remodeling and pulmonary hypertension.

Infantile hypertrophic pyloric stenosis (IHPS): a study of its pathophysiology utilizing the newborn hph-1 mouse model of the disease

Infantile hypertrophic pyloric stenosis (IHPS) is a common disease of unknown etiology. The tetrahydrobiopterin (BH4)-deficient hyperphenylalaninemia-1 (hph-1) newborn mouse has a similar phenotype to the human condition. For hph-1 and wild-type control animals, pyloric tissue agonist-induced contractile properties, reactive oxygen species (ROS) generation, cGMP, neuronal nitric oxide synthase (nNOS) content, and Rho-associated protein kinase 2 (ROCK-2) expression and activity were evaluated. Primary pyloric smooth muscle cells from wild-type newborn animals were utilized to evaluate the effect of BH4 deficiency. One-week-old hph-1 mice exhibited a fourfold increase (P < 0.01) in the pyloric sphincter muscle contraction magnitude but similar relaxation values when compared with wild-type animals. The pyloric tissue nNOS expression and cGMP content were decreased, whereas the rate of nNOS uncoupling increased (P < 0.01) in 1-wk-old hph-1 mice when compared with wild-type animals. These changes were associated with increased pyloric tissue ROS generation and elevated ROCK-2 expression/activity (P < 0.05). At 1-3 days of age and during adulthood, the gastric emptying rate of the hph-1 mice was not altered, and there were no genotype differences in pyloric tissue ROS generation, nNOS expression, or ROCK-2 activity. BH4 inhibition in pyloric smooth muscle cells resulted in increased ROS generation (P < 0.01) and ROCK-2 activity (P < 0.05). Oxidative stress upregulated ROCK-2 activity in pyloric tissue, but no changes were observed in newborn fundal tissue in vitro. We conclude that ROS-induced upregulation of ROCK-2 expression accounts for the increased pyloric sphincter tone and nNOS downregulation in the newborn hph-1 mice. The role of ROCK-2 activation in the pathogenesis of IHPS warrants further study.

Physiologic characterization of inflammatory arthritis in a rabbit model with BOLD and DCE MRI at 1.5 Tesla

OBJECTIVE

Our aim was to test the feasibility of blood oxygen level dependent magnetic resonance imaging (BOLD MRI) and dynamic contrast-enhanced (DCE) MRI to monitor periarticular hypoxic/inflammatory changes over time in a juvenile rabbit model of arthritis.

METHODS

We examined arthritic and contralateral nonarthritic knees of 21 juvenile rabbits at baseline and days 1,14, and 28 after induction of arthritis by unilateral intra-articular injection of carrageenin with BOLD and DCE MRI at 1.5 Tesla (T). Nine noninjected rabbits served as controls. Associations between BOLD and DCE-MRI and corresponding intra-articular oxygen pressure (PO2) and blood flow [blood perfusion units (BPU)] (polarographic probes, reference standards) or clinical-histological data were measured by correlation coefficients.

RESULTS

Percentage BOLD MRI change obtained in contralateral knees correlated moderately with BPU on day 0 (r = -0.51, p = 0.02) and excellently on day 28 (r = -0.84, p = 0.03). A moderate correlation was observed between peak enhancement DCE MRI (day 1) and BPU measurements in arthritic knees (r = 0.49, p = 0.04). In acute arthritis, BOLD and DCE MRI highly correlated (r = 0.89, p = 0.04; r = 1.0, p < 0.0001) with histological scores in arthritic knees.

CONCLUSION

The proposed techniques are feasible to perform at 1.5 T, and they hold potential as surrogate measures to monitor hypoxic and inflammatory changes over time in arthritis at higher-strength MRI fields.

KEY POINTS

• BOLD and DCE MRI detect interval perisynovial changes in a rabbit knee • BOLD and DCE MRI act as surrogate markers of physiologic changes in arthritis • BOLD MRI signal represents oxygen extraction compared with intra-articular PO 2 • DCE MRI measurements estimate physiologic periarticular vascular properties • In rabbit knees with acute arthritis, BOLD/DCE MRI highly correlated with histological scores.

Pantoprazole decreases gastroesophageal muscle tone in newborn rats via rho-kinase inhibition

Proton pump inhibitors reduce gastric acid secretion and are commonly utilized in the management of gastroesophageal reflux disease across all ages. Yet a decrease in lower esophageal sphincter tone has been reported in vitro in rats through an unknown mechanism; however, their effect on the gastroesophageal muscle tone early in life was never studied. Hypothesizing that proton pump inhibitors also reduce gastroesophageal muscle contraction in newborn and juvenile rats, we evaluated the in vitro effect of pantoprazole on gastric and lower esophageal sphincter muscle tissue. Electrical field stimulation and carbachol-induced force were significantly (P < 0.01) reduced in the presence of pantoprazole, whereas the drug had no effect on the neuromuscular-dependent relaxation. When administered in vivo, pantoprazole (9 mg/kg) significantly (P < 0.01) reduced gastric emptying time at both ages. To ascertain the signal transduction pathway responsible for the reduction in muscle contraction, we evaluated the tissue ROCK-2 and CPI-17 activity. Pantoprazole reduced myosin light chain phosphatase MYPT-1, but not CPI-17 phosphorylation of gastric and lower esophageal sphincter tissue, strongly suggesting that it is a ROCK-2 inhibitor. To the extent that these findings can be extrapolated to human neonates, the use of pantoprazole may impair gastric and lower sphincter muscle tone and thus paradoxically exacerbate esophageal reflux. Further studies addressing the effect of proton pump inhibitors on gastroesophageal muscle contraction are warranted to justify its therapeutic use in gastroesophageal reflux disease.

Metoclopramide does not increase gastric muscle contractility in newborn rats

Feeding intolerance resulting from delayed gastric emptying is common in premature neonates. Metoclopramide (MCP), the most frequently used prokinetic drug in neonates, enhances gastric muscle contractility through inhibition of dopamine receptors. Although its therapeutic benefit is established in adults, limited data are available to support its clinical use in infants. Hypothesizing that developmentally dependent differences are present, we comparatively evaluated the effect of MCP on fundus muscle contractility in newborn, juvenile, and adult rats. The muscle strips were either contracted with electrical field stimulation (EFS) to induce cholinergic nerve-mediated acetylcholine release or carbachol, a cholinergic agonist acting directly on the muscarinic receptor. Although in adult rats MCP increased EFS-induced contraction by 294 ± 122% of control (P < 0.01), no significant effect was observed in newborn fundic muscle. MCP had no effect on the magnitude of the carbachol-induced and/or bethanechol-induced gastric muscle contraction at any age. In response to dopamine, an 80.7 ± 5.3% relaxation of adult fundic muscle was observed, compared with only a 8.4 ± 8.7% response in newborn tissue (P < 0.01). Dopamine D2 receptor expression was scant in neonates and significantly increased in adult gastric tissue (P < 0.01). In conclusion, the lack of MCP effect on the newborn fundic muscle contraction potential relates to developmental differences in dopamine D2 receptor expression. To the extent that these novel data can be extrapolated to neonates, the therapeutic value of MCP as a prokinetic agent early in life requires further evaluation.

Newborn rat response to single vs. combined cGMP-dependent pulmonary vasodilators

Inhaled nitric oxide (NO) and other cGMP- or cAMP-dependent pulmonary vasodilators are often used in combination for the treatment of the persistent pulmonary hypertension of the newborn syndrome. There is in vitro evidence to indicate that NO downregulate the pulmonary vascular response to cGMP-dependent agonists raising concern as to whether a synergistic effect is observed when employing a combined strategy in newborns. Hypothesizing that a synergistic effect is absent, we evaluated newborn and juvenile rat pulmonary arteries to determine the individual and combined vasodilatory effect of cGMP- and cAMP-dependent agonists. In precontracted near-resistance pulmonary arteries, the addition of sildenafil reduced vasorelaxation response to NO donor S-nitroso-N-acetyl penicillamine (SNAP). A similar decrease in SNAP-induced vasodilation was observed in arteries pretreated with BAY 41-2272 (10(-9) M), a soluble guanylate cyclase stimulator cGMP, and its downstream protein kinase activator. cGMP also reduced the vasorelaxant response to the cAMP-dependent forskolin. Inhibition of endogenous vascular NO generation enhanced SNAP-induced relaxation. The present data suggest that the mechanism involved in the cGMP desensitization to other relaxant agonists involves downregulation of the small heat shock protein HSP20 and is evident in rat pulmonary and systemic vascular smooth muscle cells. In newborn rats with chronic hypoxia-induced pulmonary hypertension, the combination of sildenafil and inhaled NO resulted in a lesser reduction in pulmonary vascular resistance compared with their individual effect. These data suggest that clinical exposure to one cGMP-dependent pulmonary vasodilator may affect the response to other cGMP- or cAMP-mediated agonists.

Tetrahydrobiopterin deficiency induces gastroparesis in newborn mice

Pyloric stenosis, the most common infant gastrointestinal disease, has no known etiology and clinically presents as abnormal gastric emptying with evidence of pyloric muscle hypertrophy. Whether abnormalities in gastric muscle contraction and/or relaxation have a role in this condition is poorly known, but gastroparesis is commonly observed in association with delayed gastric emptying in adults. Therefore, we evaluated the tetrahydrobiopterin (BH4)-deficient newborn mouse model of this disease (hph-1) and hypothesized that their gastric muscle properties are impaired, when compared with wild-type control animals. In vitro studies evaluating the age-dependent gastric fundus muscle contraction and relaxation potential were conducted. Compared with wild-type mice, the hph-1 stomach content/body weight ratio was significantly increased in newborn but not juvenile or adult animals, confirming abnormal gastric emptying. Gastric tissue neuronal nitric oxide synthase (nNOS) protein expression was upregulated in both newborn and adult hph-1 mice, but in the former there was evidence of enzyme uncoupling and higher tissue superoxide generation when compared with same age-matched animals. As opposed to the lack of strain differences in the U46619-induced force, the newborn hph-1 gastric muscle carbachol-induced contraction and nNOS-dependent relaxation were significantly reduced (P < 0.01). These group differences were not present in juvenile or adult mice. Preincubation with BH4 significantly enhanced the newborn hph-1, but not wild-type, gastric muscle contraction. In conclusion, changes compatible with gastroparesis are present in the newborn mouse model of pyloric stenosis. The role of BH4 deficiency and possibly associated gastroparesis in the pathogenesis of infantile pyloric stenosis warrants further investigation.

Prolonging in utero-like oxygenation after birth diminishes oxidative stress in the lung and brain of mice pups

Background

Fetal-to-neonatal transition is associated with oxidative stress. In preterm infants, immaturity of the antioxidant system favours supplemental oxygen-derived morbidity and mortality.

Objectives

To assess if prolonging in utero-like oxygenation during the fetal-to-neonatal transition limits oxidative stress in the lung and brain, improving postnatal adaptation of mice pups.

Material and methods

Inspiratory oxygen fraction (FiO₂) in pregnant mice was reduced from 21% (room air) to 14% (hypoxia) 8–12 h prior to delivery and reset to 21% 6–8 h after birth. The control group was kept at 21% during the procedure. Reduced (GSH) and oxidized (GSSG) glutathione and its precursors [γ-glutamyl cysteine (γ-GC) and L-cysteine (CySH)] content and expression of several redox-sensitive genes were evaluated in newborn lung and brain tissue 1 (P1) and 7 (P7) days after birth.

Results

As compared with control animals, the GSH/GSSG ratio was increased in the hypoxic group at P1 and P7 in the lung, and at P7 in the brain. In the hypoxic group a significant increase in the mRNA levels of NAD(P)H:quinone oxidoreductase 1 (noq1), Sulfiredoxin 1 (srnx1) and Glutathione Peroxidase 1 (gpx) was found in lung tissue at P1, as well as a significant increase in gpx in brain tissue at P7.

Conclusions

Delaying the increase in tissue oxygenation to occur after birth reduces short-and-long-term oxidative stress in the lung. Similar yet more subtle effects were found in the brain. Apparently, the fetal-to-neonatal transition under hypoxic conditions appears to have protective qualities.

•

The present study describes a mouse model meant to study redox biology of the fetal-to-neonatal transition under hypoxia.

•

Lung protection against oxidative stress was induced at day 1 after birth.

•

Improvement in lung and brain redox environments 7 days after birth was observed.

•

Changes detected in lung and brain were subtle, however significant, under physiologic conditions.

•

The applicability of our model under pathophysiologic conditions (e.g. postnatal hyperoxia) should be tested.

Persistent pulmonary hypertension of the newborn: recent advances in pathophysiology and treatment

OBJECTIVES

Although recognized for decades, little is known about the etiology, physiopathology, and prevention of persistent pulmonary hypertension of the newborn (PPHN), and its treatment remains a major challenge for neonatologists. In this review, the clinical features and physiopathology of the syndrome will be addressed, as well as its general and specific treatments.

DATA SOURCE

A review was carried out in PubMed, Cochrane Library, and MRei consult databases, searching for articles related to the syndrome and published between 1995 and 2011.

DATA SYNTHESIS

Risk factors and the physiopathological mechanisms of the syndrome are discussed. The clinical presentation depends on the different factors involved. These are related to the etiology and physiopathology of the different forms of the disease. In addition to the measures used to allow for the decrease in pulmonary vascular resistance after birth, in some instances pulmonary vasodilators will be required. Although inhaled nitric oxide has proved effective, other vasodilators have been recently used, but clinical evidence is still lacking to demonstrate their benefits in the treatment of PPHN.

CONCLUSIONS

Despite recent technological advances and new physiopathological knowledge of this disease, mortality associated with PPHN remains at 10%. More clinical research and evidence-based experimental results are needed to prevent, treat, and reduce the morbidity/mortality associated with this neonatal syndrome.

Lipid hydroperoxide formation regulates postnatal rat lung cell apoptosis and alveologenesis

An acute increase in oxygen tension after birth imposes an oxidative stress upon the lung. We hypothesized that the resultant increase in reactive oxygen species, specifically lipid hydroperoxides, would trigger postnatal alveologenesis and physiological lung cell apoptosis in the neonatal rat. Neonatal rats were either untreated or treated daily with subcutaneous vehicle or diphenyl phenyl diamine, a scavenger of lipid hydroperoxides and inhibitor of lipid peroxidation, from day 1 to 6 of life. Alveolar formation and physiological lung cell apoptosis were assessed by morphometry, immunohistochemistry, and Western blot analyses on day 7 samples. Substitution experiments were conducted using the prototypic lipid hydroperoxide t-butylhydroperoxide. At a minimum effective dose of 15μg/g body wt, treatment with diphenyl phenyl diamine resulted in a significant increase in tissue fraction and mean linear intercept and significant reductions in small peripheral blood vessels, secondary crest formation, lung and secondary crest cell DNA synthesis, and estimated alveolar number. Decreased numbers of apoptotic type II pneumocytes and mesenchymal cells, and decreased contents of proapoptotic cleaved caspase-3 and -7 and cytoplasmic cytochrome c, and an increase in antiapoptotic Bcl-xL were found in lungs treated with diphenyl phenyl diamine. A prevention of selected changes induced by diphenyl phenyl diamine was observed with concurrent treatment with intraperitoneal t-butylhydroperoxide, at a minimally effective dose of 187μg/g body wt. We conclude that oxidative stress after birth induces lipid hydroperoxide formation, which, in turn, triggers postnatal alveologenesis and physiological lung cell apoptosis in the neonatal rat.

Nasal high-frequency oscillation for lung carbon dioxide clearance in the newborn

BACKGROUND

Noninvasive ventilation has been used increasingly in recent years to minimize the duration of endotracheal mechanical ventilation in neonates due to its association with lung injury. Nasal high-frequency oscillation (nHFO) is a relatively new noninvasive modality but evidence for its use is limited.

OBJECTIVE

The goal of this study was to compare the CO2 clearance efficacy of nHFO and noninvasive positive pressure ventilation (NIPPV) in a neonatal lung model.

DESIGN/METHODS

A newborn mannequin with dimensions and anatomy similar to a term infant was utilized. It was connected to a commercially available neonatal mechanical ventilator using a manufacturer-provided nasal adaptor. Various modes of noninvasive ventilation were compared as CO2 clearance was measured at the oropharynx by an end-tidal CO2 analyzer following the addition of a known amount of CO2 into the lung. Measurements were obtained at two different lung compliances using nHFO and compared with nCMV and nasal continuous positive airway pressure (nCPAP) as a control. Pressures near the nasal adaptor and the larynx were simultaneously measured with in-line pressure transducers.

RESULTS

Whereas no CO2 elimination was observed under nCPAP, its clearance with nHFO was 3-fold greater as compared to NIPPV. On nHFO, CO2 clearance was inversely proportional to frequency and maximal at 6 and 8 Hz. At a lower lung compliance, CO2 clearance was significantly higher at 6 Hz as compared to 10 Hz. During nHFO set to deliver a MAP of 10.0, we documented pressures of 7.2 ± 0.3 at the nasal adaptor and only 2.3 ± 0.3 cm H2O at the larynx.

CONCLUSIONS

Nasal HFO is effective and superior to NIPPV at lung CO2 elimination in a newborn mannequin model. The use of nHFO as the preferred mode of noninvasive ventilation warrants further clinical studies.

Sex-dependent changes in the pulmonary vasoconstriction potential of newborn rats following short-term oxygen exposure

BACKGROUND

Chronic exposure to supplemental oxygen (O(2)) induces lung damage and mortality in a sex-dependent manner. The effect of short-term hyperoxia on the newborn pulmonary vasculature is unknown but is, however, of clinical significance in the neonatal resuscitation context. We hypothesize that short-term hyperoxia has a sex-dependent effect on the pulmonary vasculature.

METHODS

Following 1-h 100% O(2) exposure, the pulmonary arteries and lung tissues of newborn rats were evaluated.

RESULTS

Superoxide dismutase 3 (SOD3) expression in female pups' lungs was increased as compared with that in the lungs of male pups. As compared with air-treated pups, the response of male pups to thromboxane was increased by O(2), whereas the opposite effect was documented in the vessels of female pups. The enhanced force of hyperoxia-exposed arteries of the male pups was suppressed with superoxide or peroxynitrite scavengers, and increased lung SOD activity and hydrogen peroxide content were seen in female, but not in male, rats. Hyperoxia induced an increase in lung tissue oxidative products and Rho-kinase (ROCK) activity in male, but not in female, pups.

CONCLUSION

A lower lung SOD content and failure to upregulate SOD activity facilitates peroxynitrite generation and ROCK activation in hyperoxia-exposed males, predisposing them to pulmonary vasoconstriction. These observations, if relevant to humans, may explain the increased mortality and higher incidence of pulmonary hypertension in male neonates.

Sustained therapeutic hypercapnia attenuates pulmonary arterial Rho-kinase activity and ameliorates chronic hypoxic pulmonary hypertension in juvenile rats

Sustained therapeutic hypercapnia prevents pulmonary hypertension in experimental animals, but its rescue effects on established disease have not been studied. Therapies that inhibit Rho-kinase (ROCK) and/or augment nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling can reverse or prevent progression of chronic pulmonary hypertension. Our objective in the present study was to determine whether sustained rescue treatment with inhaled CO2 (therapeutic hypercapnia) would improve structural and functional changes of chronic hypoxic pulmonary hypertension. Spontaneously breathing pups were exposed to normoxia (21% O2) or hypoxia (13% O2) from postnatal days 1–21 with or without 7% CO2 (PaCO2 elevated by ∼25 mmHg) or 10% CO2 (PaCO2 elevated by ∼40 mmHg) from days 14 to 21. Compared with hypoxia alone, animals exposed to hypoxia and 10% CO2 had significantly ( P < 0.05) decreased pulmonary vascular resistance, right-ventricular systolic pressure, right-ventricular hypertrophy, and medial wall thickness of pulmonary resistance arteries as well as decreased lung phosphodiesterase (PDE) V, RhoA, and ROCK activity. Rescue treatment with 10% CO2, or treatment with a ROCK inhibitor (15 mg/kg ip Y-27632 twice daily from days 14 to 21), also increased pulmonary arterial endothelial nitric oxide synthase and lung NO content. In contrast, cGMP content and cGMP-dependent protein kinase (PKG) activity were increased by exposure to 10% CO2, but not by ROCK inhibition with Y-27632. In vitro exposure of pulmonary artery smooth muscle cells to hypercapnia suppressed serum-induced ROCK activity, which was prevented by inhibition of PKG with Rp-8-Br-PET-cGMPS. We conclude that sustained hypercapnia dose-dependently inhibited ROCK activity, augmented NO-cGMP-PKG signaling, and led to partial improvements in the hemodynamic and structural abnormalities of chronic hypoxic PHT in juvenile rats. Increased PKG content and activity appears to play a major upstream role in CO2-induced suppression of ROCK activity in pulmonary arterial smooth muscle.