Changes in the nitric oxide pathway of the pulmonary vasculature after exposure to hypoxia in swine model of neonatal pulmonary vascular disease.

Neonatal pulmonary vascular disease (PVD) is increasingly recognized as a disease that complicates the cardiopulmonary adaptations after birth and predisposes to long-term cardiopulmonary disease. There is growing evidence that PVD is associated with disruptions in the nitric oxide (NO)-cGMP-phosphodiesterase 5 (PDE5) pathway. Examination of the functionality of different parts of this pathway is required for better understanding of the pathogenesis of neonatal PVD. For this purpose, the role of the NO-cGMP-PDE5 pathway in regulation of pulmonary vascular function was investigated in vivo, both at rest and during exercise, and in isolated pulmonary small arteries in vitro, in a neonatal swine model with hypoxia-induced PVD. Endothelium-dependent vasodilatation was impaired in piglets with hypoxia-induced PVD both in vivo at rest and in vitro. Moreover, the responsiveness to the NO-donor SNP was reduced in hypoxia-exposed piglets in vivo, while the relaxation to SNP and 8-bromo-cyclicGMP in vitro were unaltered. Finally, PDE5 inhibition-induced pulmonary vasodilatation was impaired in hypoxia-exposed piglets both in vitro and in vivo at rest. During exercise, however, the pulmonary vasodilator effect of PDE5 inhibition was significantly larger in hypoxia-exposed as compared to normoxia-exposed piglets. In conclusion, the impaired endothelium-dependent vasodilatation in piglets with hypoxia-induced PVD was accompanied by reduced responsiveness to NO, potentially caused by altered sensitivity and/or activity of soluble guanylyl cyclase (sGC), resulting in an impaired cGMP production. Our findings in a newborn animal model for neonatal PVD suggests that sGC stimulators/activators may be a novel treatment strategy to alleviate neonatal PVD.

Structural and functional changes of the pulmonary vasculature after hypoxia exposure in the neonatal period: a new swine model of pulmonary vascular disease.

Pulmonary vascular disease (PVD) represents an underestimated and increasing clinical burden not only in the neonatal period but also later in life, when exercise tolerance is decreased. Animal models performing long-term followup after a perinatal insult are lacking. This study aimed to develop and characterize a neonatal swine model with hypoxia-induced PVD during long-term followup after reexposure to normoxia and to investigate the exercise response in this model. Piglets were exposed to a normoxic ( n = 10) or hypoxic environment ( n = 9) for 4 wk. Neonatal hypoxia exposure resulted in pulmonary hypertension. Mean pulmonary artery pressure was elevated 1 day after reexposure to normoxia (30.2 ± 3.3 vs. 14.3 ± 0.9 mmHg) and remained significantly higher in the second week (32.8 ± 3.8 vs. 21.4 ± 1.2 mmHg), accompanied by decreased exercise tolerance. Exercise resulted in a trend toward an exaggerated increase of pulmonary artery pressure in hypoxia-exposed animals ( week 6, P = 0.086). Although pulmonary hypertension was transient, thickening of pulmonary arterioles was found at the end of followup. Furthermore, right ventricular dilation, lower right ventricular fractional area change ( week 8, 40.0 ± 2.7% vs. 29.5 ± 4.7%), and tricuspid annular plane systolic excursion ( week 8, 27.0 ± 2.5 vs. 22.9 ± 2.1 mm) persisted during followup. Male animals showed more severe PVD than female animals. In conclusion, we developed a neonatal swine model that allows examination of the long-term sequelae of damage to the developing neonatal lung, the course of the disease and the effect of therapy on long-term outcome. NEW & NOTEWORTHY The swine model of neonatal pulmonary vascular disease developed in the present study is the first that allows exercise testing and examination of long-term sequelae of a perinatal hypoxic insult, the course of the disease, and the effect of therapy on long-term outcome.

Oxidative injury of the pulmonary circulation in the perinatal period: Short- and long-term consequences for the human cardiopulmonary system.

Development of the pulmonary circulation is a complex process with a spatial pattern that is tightly controlled. This process is vulnerable for disruption by various events in the prenatal and early postnatal periods. Disruption of normal pulmonary vascular development leads to abnormal structure and function of the lung vasculature, causing neonatal pulmonary vascular diseases. Premature babies are especially at risk of the development of these diseases, including persistent pulmonary hypertension and bronchopulmonary dysplasia. Reactive oxygen species play a key role in the pathogenesis of neonatal pulmonary vascular diseases and can be caused by hyperoxia, mechanical ventilation, hypoxia, and inflammation. Besides the well-established short-term consequences, exposure of the developing lung to injurious stimuli in the perinatal period, including oxidative stress, may also contribute to the development of pulmonary vascular diseases later in life, through so-called "fetal or perinatal programming." Because of these long-term consequences, it is important to develop a follow-up program tailored to adolescent survivors of neonatal pulmonary vascular diseases, aimed at early detection of adult pulmonary vascular diseases, and thereby opening the possibility of early intervention and interfering with disease progression. This review focuses on pathophysiologic events in the perinatal period that have been shown to disrupt human normal pulmonary vascular development, leading to neonatal pulmonary vascular diseases that can extend even into adulthood. This knowledge may be particularly important for ex-premature adults who are at risk of the long-term consequences of pulmonary vascular diseases, thereby contributing disproportionately to the burden of adult cardiovascular disease in the future.

Sex differences in pulmonary vascular control: focus on the nitric oxide pathway.

Although the incidence of pulmonary hypertension is higher in females, the severity and prognosis of pulmonary vascular disease in both neonates and adults have been shown to be worse in male subjects. Studies of sex differences in pulmonary hypertension have mainly focused on the role of sex hormones. However, the contribution of sex differences in terms of vascular signaling pathways regulating pulmonary vascular function remains incompletely understood. Consequently, we investigated pulmonary vascular function of male and female swine in vivo, both at rest and during exercise, and in isolated small pulmonary arteries in vitro, with a particular focus on the NO-cGMP-PDE5 pathway. Pulmonary hemodynamics at rest and during exercise were virtually identical in male and female swine. Moreover, NO synthase inhibition resulted in a similar degree of pulmonary vasoconstriction in male and female swine. However, NO synthase inhibition blunted bradykinin-induced vasodilation in pulmonary small arteries to a greater extent in male than in female swine. PDE5 inhibition resulted in a similar degree of vasodilation in male and female swine at rest, while during exercise there was a trend towards a larger effect in male swine. In small pulmonary arteries, PDE5 inhibition failed to augment bradykinin-induced vasodilation in either sex. Finally, in the presence of NO synthase inhibition, the pulmonary vasodilator effect of PDE5 inhibition was significantly larger in female swine both in vivo and in vitro. In conclusion, the present study demonstrated significant sex differences in the regulation of pulmonary vascular tone, which may contribute to understanding sex differences in incidence, treatment response, and prognosis of pulmonary vascular disease.

The Effect of Maternal Milk on Tolerance and Growth in Premature Infants: A Hypothesis-generating Study.

OBJECTIVE: Early growth rates and feeding advancement rates of preterm infants are thought to influence later health. Feeding advancement is often difficult because of feeding intolerance. Exclusive human milk feeding improves tolerance, but can result in a lower weight gain rate. The addition of human milk fortifier has advantages for growth, but there are concerns that it may nullify the beneficial effect of human milk on tolerance. Therefore, the objective of the present study was to evaluate the relation between the amount of fortified human milk or formula and feeding tolerance and growth in preterm infants. METHODS: Patients (n = 174) participating in the TOL trial and born with a gestational age 30 weeks or younger were divided into tertiles according to the amount of human milk received during feeding advancement. Data on feeding tolerance during the advancement phase of enteral nutrition and anthropometrics were analysed. RESULTS: The infants (n = 59) receiving the lowest percentage of their enteral intake as human milk (0%-57%) had the lowest amount of gastric residuals (P = 0.034) compared with the other 2 tertiles. Time to reach full enteral feeding and other tolerance parameters were not different among the groups. There was no dose response effect of the amount of human milk consumed on growth. CONCLUSIONS: In preterm infants, an association between type of feeding (human milk vs infant formula) and time to achieve full enteral feeding or short-term growth was not found. Future prospective trials are needed to verify our results and focus on means to improve tolerance further.

Surgical Placement of Catheters for Long-term Cardiovascular Exercise Testing in Swine.

This protocol describes the surgical procedure to chronically instrument swine and the procedure to exercise swine on a motor-driven treadmill. Early cardiopulmonary dysfunction is difficult to diagnose, particularly in animal models, as cardiopulmonary function is often measured invasively, requiring anesthesia. As many anesthetic agents are cardiodepressive, subtle changes in cardiovascular function may be masked. In contrast, chronic instrumentation allows for measurement of cardiopulmonary function in the awake state, so that measurements can be obtained under quiet resting conditions, without the effects of anesthesia and acute surgical trauma. Furthermore, when animals are properly trained, measurements can also be obtained during graded treadmill exercise. Flow probes are placed around the aorta or pulmonary artery for measurement of cardiac output and around the left anterior descending coronary artery for measurement of coronary blood flow. Fluid-filled catheters are implanted in the aorta, pulmonary artery, left atrium, left ventricle and right ventricle for pressure measurement and blood sampling. In addition, a 20 G catheter is positioned in the anterior interventricular vein to allow coronary venous blood sampling. After a week of recovery, swine are placed on a motor-driven treadmill, the catheters are connected to pressure and flow meters, and swine are subjected to a five-stage progressive exercise protocol, with each stage lasting 3 min. Hemodynamic signals are continuously recorded and blood samples are taken during the last 30 sec of each exercise stage. The major advantage of studying chronically instrumented animals is that it allows serial assessment of cardiopulmonary function, not only at rest but also during physical stress such as exercise. Moreover, cardiopulmonary function can be assessed repeatedly during disease development and during chronic treatment, thereby increasing statistical power and hence limiting the number of animals required for a study.

UM206, a selective Frizzled antagonist, attenuates adverse remodeling after myocardial infarction in swine.

Modulation of Wnt/Frizzled signaling with UM206 reduced infarct expansion and prevented heart failure development in mice, an effect that was accompanied by increased myofibroblast presence in the infarct, suggesting that Wnt/Frizzled signaling has a key role in cardiac remodeling following myocardial infarction (MI). This study investigated the effects of modulation of Wnt/Frizzled signaling with UM206 in a swine model of reperfused MI. For this purpose, seven swine with MI were treated with continuous infusion of UM206 for 5 weeks. Six control swine were treated with vehicle. Another eight swine were sham-operated. Cardiac function was determined by echo in awake swine. Infarct mass was estimated at baseline by heart-specific fatty acid-binding protein ELISA and at follow-up using planimetry. Components of Wnt/Frizzled signaling, myofibroblast presence, and extracellular matrix were measured at follow-up with qPCR and/or histology. Results show that UM206 treatment resulted in a significant decrease in infarct mass compared with baseline (-41±10%), whereas infarct mass remained stable in the Control-MI group (+3±17%). Progressive dilation of the left ventricle occurred in the Control-MI group between 3 and 5 weeks after MI, while adverse remodeling was halted in the UM206-treated group. mRNA expression for Frizzled-4 and the Frizzled co-receptor LRP5 was increased in UM206-treated swine as compared with Control-MI swine. Myofibroblast presence was significantly lower in infarcted tissue of the UM206-treated animals (1.53±0.43% vs 3.38±0.61%) at 5 weeks follow-up. This study demonstrates that UM206 treatment attenuates adverse remodeling in a swine model of reperfused MI, indicating that Wnt/Frizzled signaling is a promising target to improve infarct healing and limit post-MI remodeling.

Intermittent Bolus or Semicontinuous Feeding for Preterm Infants?

OBJECTIVES: The aim of the present study was to assess the clinical benefits and risks of semicontinuous (CON) versus intermittent nasogastric tube feeding in low-birth-weight infants. METHODS: Infants with a birth weight <1750 g and gestational age <32 weeks were stratified according to birth weight and assigned to either CON or intermittent bolus (BOL) feeding. The primary endpoint was days to full enteral feeding (defined as 120 mL(-1) · kg(-1) · day(-1)). We also collected data on feeding tolerance, weight gain, respiratory support, and complications (sepsis, necrotising enterocolitis, and death). RESULTS: There was no difference between the 2 groups (CON n = 121, BOL n = 125) in days to reach full enteral feeding--7 (5-10) versus 6 (5-8) days, respectively, with a difference 1 (-0.05 to 2.1). Mean daily gastric residual volumes, however, were significantly lower in the BOL group (4.8 vs 3.9 mL/day, difference 0.9 mL/day [0.1-1.7]), as was the total number of patients with feeding interruptions (76 vs 59, difference 16% [3%-28%]). CONCLUSIONS: Bolus and continuous feeding are equally suitable feeding strategies for preterm neonates. BOL feeding, however, may be preferable.

[A neonate with umbilical cord bleeding]. / Een neonaat met een navelstompbloeding.

A 7-day-old neonate was admitted to our neonatal ward for umbilical stump bleeding. His medical history included hyperbilirubinaemia due to cephalic haematoma. Only after the administration of fresh frozen plasma, the bleeding stopped, suggesting coagulation factor deficiency. Elaborate coagulation tests showed factor XIII-deficiency.