Vasa vasorum hypoperfusion is responsible for medial hypoxia and anatomic remodeling in the newborn lamb ductus arteriosus

Using omics to breathe new life into our understanding of the ductus arteriosus oxygen response

The ductus arteriosus (DA) connects the aorta to the pulmonary artery (PA), directing placentally oxygenated blood away from the developing lungs. High pulmonary vascular resistance and low systemic vascular resistance facilitate shunting of blood in utero from the pulmonary to the systemic circulation through the widely patent DA, thereby optimizing fetal oxygen (O₂) delivery. With the transition from fetal (hypoxia) to neonatal (normoxia) oxygen conditions, the DA constricts while the PA dilates. This process often fails in prematurity, promoting congenital heart disease. Impaired O₂-responsivness in the DA promotes persistent ductus arteriosus (PDA), the most common form of congenital heart disease. Knowledge of DA oxygen sensing has greatly advanced in the past few decades, however we still lack a complete understanding of the sensing mechanism. The genomic revolution of the past two decades has facilitated unprecedented discovery in every biological system. This review will demonstrate how multiomic integration of data generated from the DA can breathe new life into our understanding of the DA's oxygen response.

Impact of early screening echocardiography and targeted PDA treatment on neonatal outcomes in "22-23" week and "24-26" infants

The hemodynamically significant patent ductus arteriosus (hsPDA) is a controversial topic in neonatology, particularly among neonates at the earliest gestational ages of 22+0-23+6 weeks. There is little, to no data on the natural history or impact of the PDA in extremely preterm babies. In addition, these high-risk patients have typically been excluded from randomized clinical trials of PDA treatment. In this work, we present the impact of early hemodynamic screening (HS) of a cohort of patients born 22+0-23+6 weeks gestation who either were diagnosed with hsPDA or died in the first postnatal week as compared to a historical control (HC) cohort. We also report a comparator population of 24+0-26+6 weeks gestation. All patients in the HS epoch were evaluated between 12-18h postnatal age and treated based on disease physiology whereas the HC patients underwent echocardiography at the discretion of the clinical team. We demonstrate a two-fold reduction in the composite primary outcome of death prior to 36 weeks or severe BPD and report a lower incidence of severe intraventricular hemorrhage (n=5, 7% vs n=27, 27%), necrotizing enterocolitis (n=1, 1% vs n=11, 11%) and first-week vasopressor use (n=7, 11% vs n=40, 39%) in the HS cohort. HS was also associated with an increase in survival free of severe morbidity from the already high rate of 50% to 73% among neonates <24 weeks gestation. We present a biophysiological rationale behind the potential modulator role of hsPDA on these outcomes and review the physiology relevant to neonates born at these extremely preterm gestations. These data highlight the need for further interrogation of the biological impact of hsPDA and impact of early echocardiography directed therapy in infants born less than 24 weeks gestation.

Management of cardiac dysfunction in neonates with pulmonary hypertension and the role of the ductus arteriosus

Pulmonary hypertension in the neonate is associated with cardiopulmonary disturbances and neurodevelopment morbidity. The patent ductus arteriosus is a persistent fetal shunt that can be pathologic vs supportive in the setting of neonatal pulmonary hypertension. Understanding the underlying pathophysiology of pulmonary hypertension and the cardiopulmonary effects of various phenotypes can guide management in this vulnerable population. In this narrative, we will summarize the physiologic principles of pulmonary hypertension, the impact of the patent ductus arteriosus on various phenotypes, and the utility of serial targeted neonatal echocardiography to individualize clinical assessment and management.

On vasa vasorum: A history of advances in understanding the vessels of vessels

The vasa vasorum are a vital microvascular network supporting the outer wall of larger blood vessels. Although these dynamic microvessels have been studied for centuries, the importance and impact of their functions in vascular health and disease are not yet fully realized. There is now rich knowledge regarding what local progenitor cell populations comprise and cohabitate with the vasa vasorum and how they might contribute to physiological and pathological changes in the network or its expansion via angiogenesis or vasculogenesis. Evidence of whether vasa vasorum remodeling incites or governs disease progression or is a consequence of cardiovascular pathologies remains limited. Recent advances in vasa vasorum imaging for understanding cardiovascular disease severity and pathophysiology open the door for theranostic opportunities. Approaches that strive to control angiogenesis and vasculogenesis potentiate mitigation of vasa vasorum-mediated contributions to cardiovascular diseases and emerging diseases involving the microcirculation.

Spontaneous Closure of the Arterial Duct after Transcatheter Closure Attempt in Preterm Infants

(1) Background: Transcatheter closure of the patent arterial duct (TCPDA) in preterm infants is an emerging procedure. Patent arterial duct (PDA) spontaneous closure after failed TCPDA attempts is seen but reasons and outcomes are not reported; (2) Methods: We retrospectively included all premature infants <2 kg with abandoned TCPDA procedures from our institutional database between September 2017 and August 2021. Patients’ data and outcomes were reviewed; (3) Results: The procedure was aborted in 14/130 patients referred for TCPDA. Two patients had spasmed PDA upon arrival in the catheterization laboratory and had no intervention. One patient had ductal spasm after guidewire cross. Four patients had unsuitable PDA size/shape for closure. In seven patients, device closure was not possible without causing obstruction on adjacent vessels. Among the 12 patients with attempted TCPDA, five had surgery on a median of 3 days after TCPDA and seven had a spontaneous PDA closure within a median of 3 days after the procedure. Only the shape of the PDA differed between the surgical ligation group (short and conical) and spontaneous closure group (F-type); (4) Conclusions: In the case of TCPDA failure, mechanically induced spontaneous closure may occur early after the procedure. Surgical ligation should be postponed when clinically tolerated.

Patent ductus arteriosus: From pharmacology to surgery

Patent ductus arteriosus (PDA) may be found in 0.1-0.2% of term infants, but the average incidence is at least five-fold higher in premature infants, correlating inversely with birth weight and gestational age. While not all patients with a PDA require treatment, the deleterious effects of persistent left-to-right shunting across the ductus can have important short- and long-term consequences. Medical and interventional approaches to PDA closure have evolved greatly in the past decade and add to the decision-making pathways. This article summarizes the pathophysiology of PDA and characterizes the medical, surgical and endovascular treatment approaches.

The molecular mechanisms of oxygen-sensing in human ductus arteriosus smooth muscle cells: A comprehensive transcriptome profile reveals a central role for mitochondria

The ductus arteriosus (DA) connects the fetal pulmonary artery and aorta, diverting placentally oxygenated blood from the developing lungs to the systemic circulation. The DA constricts in response to increases in oxygen (O2) with the first breaths, resulting in functional DA closure, with anatomic closure occurring within the first days of life. Failure of DA closure results in persistent patent ductus arteriosus (PDA), a common complication of extreme preterm birth. The DA's response to O2, though modulated by the endothelium, is intrinsic to the DA smooth muscle cells (DASMC). DA constriction is mediated by mitochondrial-derived reactive oxygen species, which increase in proportion to arterial partial pressure of oxygen (PaO2). The resulting redox changes inhibit voltage-gated potassium channels (Kv) leading to cell depolarization, calcium influx and DASMC constriction. To date, there has not been an unbiased assessment of the human DA O2-sensors using transcriptomics, nor are there known molecular mechanisms which characterize DA closure. DASMCs were isolated from DAs obtained from 10 term infants at the time of congenital heart surgery. Cells were purified by flow cytometry, negatively sorting using CD90 and CD31 to eliminate fibroblasts or endothelial cells, respectively. The purity of the DASMC population was confirmed by positive staining for α-smooth muscle actin, smoothelin B and caldesmon. Cells were grown for 96 h in hypoxia (2.5% O2) or normoxia (19% O2) and confocal imaging with Cal-520 was used to determine oxygen responsiveness. An oxygen-induced increase in intracellular calcium of 18.1% ± 4.4% and SMC constriction (-27% ± 1.5% shortening) occurred in all cell lines within five minutes. RNA sequencing of the cells grown in hypoxia and normoxia revealed significant regulation of 1344 genes (corrected p < 0.05). We examined these genes using Gene Ontology (GO). This unbiased assessment of altered gene expression indicated significant enrichment of the following GOterms: mitochondria, cellular respiration and transcription. The top regulated biologic process was generation of precursor metabolites and energy. The top regulated cellular component was mitochondrial matrix. The top regulated molecular function was transcription coactivator activity. Multiple members of the NADH-ubiquinone oxidoreductase (NDUF) family are upregulated in human DASMC (hDASMC) following normoxia. Several of our differentially regulated transcripts are encoded by genes that have been associated with genetic syndromes that have an increased incidence of PDA (Crebb binding protein and Histone Acetyltransferase P300). This first examination of the effects of O2 on human DA transcriptomics supports a putative role for mitochondria as oxygen sensors.

Patent Ductus Arteriosus of the Preterm Infant

Postnatal ductal closure is stimulated by rising oxygen tension and withdrawal of vasodilatory mediators (prostaglandins, nitric oxide, adenosine) and by vasoconstrictors (endothelin-1, catecholamines, contractile prostanoids), ion channels, calcium flux, platelets, morphologic maturity, and a favorable genetic predisposition. A persistently patent ductus arteriosus (PDA) in preterm infants can have clinical consequences. Decreasing pulmonary vascular resistance, especially in extremely low gestational age newborns, increases left-to-right shunting through the ductus and increases pulmonary blood flow further, leading to interstitial pulmonary edema and volume load to the left heart. Potential consequences of left-to-right shunting via a hemodynamically significant patent ductus arteriosus (hsPDA) include increased risk for prolonged ventilation, bronchopulmonary dysplasia, necrotizing enterocolitis or focal intestinal perforation, intraventricular hemorrhage, and death. In the last decade, there has been a trend toward less aggressive treatment of PDA in preterm infants. However, there is a subgroup of infants who will likely benefit from intervention, be it pharmacologic, interventional, or surgical: (1) prophylactic intravenous indomethacin in highly selected extremely low gestational age newborns with PDA (<26 + 0/7 weeks' gestation, <750 g birth weight), (2) early targeted therapy of PDA in selected preterm infants at particular high risk for PDA-associated complications, and (3) PDA ligation, catheter intervention, or oral paracetamol may be considered as rescue options for hsPDA closure. The impact of catheter-based closure of hsPDA on clinical outcomes should be determined in future prospective studies. Finally, we provide a novel treatment algorithm for PDA in preterm infants that integrates the several treatment modalities in a staged approach.

Molecular and Mechanical Mechanisms Regulating Ductus Arteriosus Closure in Preterm Infants

Failure of ductus arteriosus closure after preterm birth is associated with significant morbidities. Ductal closure requires and is regulated by a complex interplay of molecular and mechanical mechanisms with underlying genetic factors. In utero patency of the ductus is maintained by low oxygen tension, high levels of prostaglandins, nitric oxide and carbon monoxide. After birth, ductal closure occurs first by functional closure, followed by anatomical remodeling. High oxygen tension and decreased prostaglandin levels mediated by numerous factors including potassium channels, endothelin-1, isoprostanes lead to the contraction of the ductus. Bradykinin and corticosteroids also induce ductal constriction by attenuating the sensitivity of the ductus to PGE2. Smooth muscle cells of the ductus can sense oxygen through a mitochondrial network by the role of Rho-kinase pathway which ends up with increased intracellular calcium levels and contraction of myosin light chains. Anatomical closure of the ductus is also complex with various mechanisms such as migration and proliferation of smooth muscle cells, extracellular matrix production, endothelial cell proliferation which mediate cushion formation with the interaction of blood cells. Regulation of vessel walls is affected by retinoic acid, TGF-β1, notch signaling, hyaluronan, fibronectin, chondroitin sulfate, elastin, and vascular endothelial cell growth factor (VEGF). Formation of the platelet plug facilitates luminal remodeling by the obstruction of the constricted ductal lumen. Vasa vasorum are more pronounced in the term ductus but are less active in the preterm ductus. More than 100 genes are effective in the prostaglandin pathway or in vascular smooth muscle development and structure may affect the patency of ductus. Hemodynamic changes after birth including fluid load and flow characteristics as well as shear forces within the ductus also stimulate closure. Current pharmacological treatment for the closure of a patent ductus is based on the blockage of the prostaglandin pathway mainly through COX or POX inhibition, albeit with some limitations and side effects. Further research for new agents aiming ductal closure should focus on a clear understanding of vascular biology of the ductus.

Transcription box‑3 protects human umbilical vein endothelial cells in a high‑glucose environment through sirtuin 1/AKT signaling

The increasing burden of diabetes in low and middle-income countries is attributable to both genetic and epigenetic factors. Environmental- and lifestyle-associated changes are also considered to be important contributors to this disease. The resultant co-morbidities arising from micro-and macrovascular changes in diabetes are difficult to manage and are an economic burden. However, very little is known about the molecular mechanisms that drive this phenotype. The present study aimed to investigate the role of sirtuin 1 (SIRT1)- and transcription box-3 (TBX-3)-mediated regulation of endothelial dysfunction, given the significance of SIRT1 in glucose metabolism and the role of TBX-3 in the maintenance of cellular proliferation, senescence and apoptosis. Following the recruitment of adult patients with and without diabetes, both SIRT1 and TBX-3 expression was confirmed to be present in the sera of the patients with diabetes and the patients without diabetes; however, both SIRT1 and TBX-3 expression levels were higher in the sera of the patients with diabetes. Human umbilical vein endothelial cells (HUVECs) were further used for in vitro studies. Using TBX-3 and SIRT1 knockdown models, the cellular responses to proliferation, migration, invasion and tube formation were investigated using an MTS, cell cycle analysis, wound healing, Transwell and tube formation assay, respectively. Western blotting was also used to determine the downstream signaling pathways involved. The genetic knockdown of TBX-3 in hyperglycemic conditions significantly decreased the cellular proliferation, migration, invasion and angiogenesis of HUVECs. It was subsequently identified that TBX-3 mediated its effects through the activation of AKT and vascular endothelial growth factor (VEGF) signaling. However, the genetic knockdown of SIRT1 in the presence of TBX-3 overexpression and glucose failed to activate the AKT and VEGF signaling pathways. In conclusion, the results of the present study suggested that SIRT1 may positively regulate TBX-3 in endothelial cells, therefore, SIRT1 and/or TBX-3 may serve as potential novel biomarkers for disease progression.

Patent ductus arteriosus in preterm infants: is early transcatheter closure a paradigm shift?

The optimal management approach of the patent ductus arteriosus (PDA) in premature infants remains uncertain owing the lack of evidence for long-term benefits and the limited analyses of the complications of medical and surgical interventions to date. In recent years, devices suitable to plug the PDA of premature infants (including extremely low birthweight, <1000 g) have become available and several trials have demonstrated successful and safe transcatheter PDA closure (TCPC) in this population. Whether TCPC represents a paradigm shift in PDA management that will result in improved short- and long-term outcomes, less bronchopulmonary dysplasia, improved neurodevelopment, or better long term renal function remains to be seen. Careful rigorous study of the potential benefits of TCPC in this highly vulnerable population in the context of well-designed adequately powered trials is needed prior to widespread adoption of this approach.

Understanding the pathobiology in patent ductus arteriosus in prematurity-beyond prostaglandins and oxygen

The ductus arteriosus (DA) is probably the most intriguing vessel in postnatal hemodynamic transition. DA patency in utero is an active state, in which prostaglandin E₂ (PGE₂) and nitric monoxide (NO), play an important role. Since the DA gets programmed for postnatal closure as gestation advances, in preterm infants the DA frequently remains patent (PDA). PGE₂ exposure programs functional postnatal closure by inducing gene expression of ion channels and phosphodiesterases and anatomical closure by inducing intimal thickening. Postnatally, oxygen inhibits potassium and activates calcium channels, which ultimately leads to a rise in intracellular calcium concentration consequently inducing phosphorylation of the myosin light chain and thereby vasoconstriction of the DA. Since ion channel expression is lower in preterm infants, oxygen induced functional vasoconstriction is attenuated in comparison with full term newborns. Furthermore, the preterm DA is more sensitive to both PGE₂ and NO compared to the term DA pushing the balance toward less constriction. In this review we explain the physiology of DA patency in utero and subsequent postnatal functional closure. We will focus on the pathobiology of PDA in preterm infants and the (un)intended effect of antenatal exposure to medication on both fetal and neonatal DA vascular tone.

Platelet Counts and Patent Ductus Arteriosus in Preterm Infants: A Systematic Review and Meta-Analysis

BACKGROUND

Several cohort studies have shown an association between low platelet counts in the first day(s) of life and patent ductus arteriosus (PDA) in preterm infants. However, these results have not been confirmed by other studies.

OBJECTIVE

To perform a meta-analysis of all the studies addressing the relationship between platelet counts in the first day(s) of life and PDA in preterm infants.

METHODS

PubMed/MEDLINE and EMBASE were searched from their inception until December 2014. Results from 11 cohort studies involving 3,479 preterm infants (gestational age <32 weeks) were pooled using random-effects modeling.

RESULTS

Meta-analysis showed a significant positive association between PDA and platelet counts <150 × 10(9)/l [6 studies, risk ratio (RR) = 1.215, 95% CI: 1.027-1.436], between PDA and platelet counts <100 × 10(9)/l (5 studies, RR = 1.255, 95% CI: 1.034-1.525), and between significant PDA (SPDA) and platelet counts <100 × 10(9)/l (5 studies, RR = 1.254, 95% CI: 1.021-1.540). The association between SPDA and platelet counts <150 × 10(9)/l was not statistically significant (6 studies, RR = 1.289, 95% CI: 0.925-1.795). Pooled standard differences in mean platelet counts between infants with and without PDA/SPDA were not statistically different.

CONCLUSION

This meta-analysis reveals a marginal but significant association between low platelet counts in the first day(s) of life and PDA/SPDA in very preterm infants. This association needs to be confirmed in prospective studies.

Role of dynamin-related protein 1 (Drp1)-mediated mitochondrial fission in oxygen sensing and constriction of the ductus arteriosus

RATIONALE

Closure of the ductus arteriosus (DA) is essential for the transition from fetal to neonatal patterns of circulation. Initial PO2-dependent vasoconstriction causes functional DA closure within minutes. Within days a fibrogenic, proliferative mechanism causes anatomic closure. Though modulated by endothelial-derived vasodilators and constrictors, O2 sensing is intrinsic to ductal smooth muscle cells and oxygen-induced DA constriction persists in the absence of endothelium, endothelin, and cyclooxygenase mediators. O2 increases mitochondrial-derived H2O2, which constricts ductal smooth muscle cells by raising intracellular calcium and activating rho kinase. However, the mechanism by which oxygen changes mitochondrial function is unknown.

OBJECTIVE

The purpose of this study was to determine whether mitochondrial fission is crucial for O2-induced DA constriction and closure.

METHODS AND RESULTS

Using DA harvested from 30 term infants during correction of congenital heart disease, as well as DA from term rabbits, we demonstrate that mitochondrial fission is crucial for O2-induced constriction and closure. O2 rapidly (<5 minutes) causes mitochondrial fission by a cyclin-dependent kinase- mediated phosphorylation of dynamin-related protein 1 (Drp1) at serine 616. Fission triggers a metabolic shift in the ductal smooth muscle cells that activates pyruvate dehydrogenase and increases mitochondrial H2O2 production. Subsequently, fission increases complex I activity. Mitochondrial-targeted catalase overexpression eliminates PO2-induced increases in mitochondrial-derived H2O2 and cytosolic calcium. The small molecule Drp1 inhibitor, Mdivi-1, and siDRP1 yield concordant results, inhibiting O2-induced constriction (without altering the response to phenylephrine or KCl) and preventing O2-induced increases in oxidative metabolism, cytosolic calcium, and ductal smooth muscle cells proliferation. Prolonged Drp1 inhibition reduces DA closure in a tissue culture model.

CONCLUSIONS

Mitochondrial fission is an obligatory, early step in mammalian O2 sensing and offers a promising target for modulating DA patency.

Bioluminescence imaging of energy depletion in vascular pathology: patent ductus arteriosus and atherosclerosis

The artery wall may develop energy depletion due to insufficient nutritional supply. However, until recently it has not been possible to validate this hypothesis because no available technology has allowed assessment of energy metabolism with sufficient spatial resolution. We use high resolution bioluminescence metabolic imaging to study energy metabolism in two mechanistically different vascular pathologies: patent ductus arteriosus and atherosclerosis. Physiological energy depletion in postnatally constricting ductus arteriosus promotes permanent closure. Insufficient ductus energy depletion, common in preterm infants, is associated with persistent patent ductus arteriosus, a condition with significantly increased morbidity and mortality. In contrast, in atherosclerosis, energy depletion in the macrophage-rich lesion core promotes cell death contributing to lesion instability and disease progression.

Mechanisms for ductus arteriosus closure

Closure of the ductus arteriosus at birth is a complex phenomenon being conditioned by antenatal events and progressing in preprogrammed steps. Functional at first, narrowing of the vessel is determined by 2 overlapping processes--removal of the prostaglandin E(2)-based relaxation sustaining prenatal patency and activation of a constrictor mechanism by the natural rise in blood oxygen tension. Two schemes have been proposed for oxygen action--one involving a cytochrome P450 hemoprotein (sensor)/endothelin-1 (effector) complex and the other a set of voltage-gated K(+) channels. These proposals, however, are not mutually exclusive. Structural closure follows the constriction through a remodeling process initiated antenatally with the development of intimal cushions and completed postnatally by a host of humoral and mechanical stimuli. Research in this area has already provided clinical applications. Nevertheless, management of premature infants with persistent ductus remains troublesome and calls for an alternative approach to the prostaglandin E(2) inhibitors now in use. Studies in progress on the oxygen-sensing system may lead to a definitive solution for this problem.

Pre-clinical Implants of the Levitronix PediVAS® Pediatric Ventricular Assist Device - Strategy for Regulatory Approval

The PediVAS blood pump is a magnetically levitated centrifugal pump designed for pediatric bridge-to-decision or bridge-to-recovery in pediatric patients from 3-20kg in weight. In preparation for submission of an investigational device exemption (IDE) application, we completed a final six-animal series of pre-clinical studies. The studies were conducted under controlled conditions as prescribed by the recently released FDA guidance document for animal studies for cardiovascular devices. Three 30-day chronic left ventricular support studies were completed in a juvenile lamb model to demonstrate the safety and hemocompatibility of the PediVAS pump. Three additional 8-hour acute biventricular support studies were performed to demonstrate the feasibility of this approach from a hemodynamic and systems standpoint. It is estimated that 50% of pediatric patients who require left ventricular support also require right ventricular support. All studies were successfully completed without complications, device malfunctions, or adverse events. End-organ function was normal for the chronic studies. We noted small surface lesions on one kidney from each chronic study as well as the presence of ring thrombus on connectors, as expected for these types of studies in animal models. The strategy and challenges imposed by performing a controlled cardiovascular device study in a juvenile lamb model are discussed. We believe that these successful implants demonstrate safety and performance for the PediVAS device for support of an IDE application to initiate human clinical trials and provide a roadmap for other researchers.

Relationship between circulating platelet counts and ductus arteriosus patency after indomethacin treatment

OBJECTIVE

To determine whether low platelet counts are related to the incidence of patent ductus arteriosus (PDA) after indomethacin treatment in preterm human infants.

STUDY DESIGN

Multivariable logistic regression modeling was used for a cohort of 497 infants, who received indomethacin (within 15 hours of birth).

RESULTS

Platelet counts were not related to the incidence of permanent closure after indomethacin constriction. There was a relationship between platelet counts and the initial degree of constriction; however, this relationship appeared to be primarily influenced by the high end of the platelet distribution curve. PDA incidence was similar in infants with platelet counts < 50 × 10⁹/L and those with platelet counts above this range. Only when platelet counts were consistently >230 ×10⁹/L was there a decrease in PDA incidence.

CONCLUSION

In contrast to the evidence in mice, low circulating platelet counts do not affect permanent ductus closure (or ductus reopening) in human preterm infants.

Comparative functional structure of the olfactory mucosa in the domestic dog and sheep

Olfactory acuity differs among animal species depending on age and dependence on smell. However, the attendant functional anatomy has not been elucidated. We sought to determine the functional structure of the olfactory mucosa in suckling and adult dog and sheep. Mucosal samples harvested from ethmoturbinates were analyzed qualitatively and quantitatively. In both species, the olfactory mucosa comprised olfactory, supporting and basal cells, and a lamina propria containing bundles of olfactory cell axons, Bowman's glands and vascular elements. The olfactory cells terminated apically with an expanded knob, from which cilia projected in a radial fashion from its base and in form of a tuft from its apex in the dog and the sheep respectively. Olfactory cilia per knob were more numerous in the dog (19 ± 3) compared to the sheep (7 ± 2) (p<0.05). In the dog, axonal bundles exhibited one to two centrally located capillaries and the bundles were of greater diameters (73.3 ± 10.3 μm) than those of the sheep (50.6 ± 6.8 μm), which had no capillaries. From suckling to adulthood in the dog, the packing density of the olfactory and supporting cells increased by 22.5% and 12.6% respectively. Surprisingly in the sheep, the density of the olfactory cells decreased by 26.2% while that of the supportive cells showed no change. Overall epithelial thickness reached 72.5 ± 2.9 μm in the dog and 56.8 ± 3.1 μm in the sheep. These observations suggest that the mucosa is better structurally refined during maturation in the dog than in the sheep.

Morphological and functional alterations of the ductus arteriosus in a chicken model of hypoxia-induced fetal growth retardation

The hypoxic conditions in which children with intrauterine growth retardation (IUGR) develop are hypothesized to alter the development of the ductus arteriosus (DA). We aimed to evaluate the effects of in ovo hypoxia on chicken DA morphometry and reactivity. Hypoxia (15% O2 from day 6 to 19 of the 21-d incubation period) produced a reduction in the body mass of the 19-d fetuses and a shortening of right and left DAs. However, ductal lumen and media cross-sectional areas were not affected by hypoxia. The ductal contractions induced by oxygen, KCl, H2O2, 4-aminopyridine, and endothelin-1 were similar in control and hypoxic fetuses. In contrast, the DAs from the hypoxic fetuses showed increased contractile responses to norepinephrine and phenylephrine and impaired relaxations to acetylcholine, sodium nitroprusside, and isoproterenol. The relaxations induced by 8-Br-cGMP, forskolin, Y-27632, and hydroxyfasudil were not altered by chronic hypoxia. In conclusion, chronic in ovo hypoxia-induced growth retardation in fetal chickens and altered the response of the DA to adrenergic agonists and to endothelium-dependent and -independent relaxing agents. Our observations support the concept that prolonged patency of the DA in infants with IUGR may be partially related with hypoxia-induced changes in local vascular mechanisms.

Insufficient intimal thickening and scarcity of cell deaths may play a significant role in the pathogenesis of the persistently patent ductus arteriosus in the preterm infant

BACKGROUND

Functional closure and subsequent remodeling of the ductus arteriosus (DA) are essential for postnatal adaptation. Very preterm infants often fail to accomplish this process spontaneously. Histologic studies on human DA have shown that the closing ductus exhibits progressive intimal thickening and cell death of muscle media, which was verified by recent animal studies.

AIMS

To analyze the histologic findings of preterm infants' DA in relation to their clinical parameters and to investigate the histologic difference between preterm and term DAs.

METHODS

Histology of 14 preterm DAs and 13 term DAs obtained from surgery was analyzed. We examined hematoxylin and eosin staining and van Gieson staining for the elastic tissue. Cell death was determined with the in situ apoptosis detection technique.

RESULTS

The histologic findings of preterm DAs showed apparent correlations with clinical parameters, especially birth weight. Preterm DA histology was significantly different from that of term DAs in the extent and degree of intimal thickening. Cytolytic necrosis where TUNEL-positive cell deaths were prominent was observed mainly in term DAs.

CONCLUSIONS

The results of this study indicate that insufficient intimal thickening and scarcity of cell deaths in the DA may play a significant role in the pathogenesis of the persistently patent DA in preterm infants.

Morphological changes in the chicken ductus arteriosi during closure at hatching

The chicken embryo has two functioning ductus arteriosi (DA) during development. These blood vessels connect the pulmonary arteries to the descending aorta providing a right-to-left shunt of blood away from the nonrespiring lungs and to the systemic circuit and chorioallanotic membrane. The DA consists of two distinct tissue types along its length, a muscular proximal portion and an elastic distal portion. During hatching, the DA must close for proper separation of systemic and pulmonary circulation. We examined the morphological changes of the chicken DA before, during, and after hatching. Occlusion of the proximal DA began during external pipping and was complete at hatching. Anatomical remodeling began as early as external pipping with fragmentation of the internal elastic lamina and smooth muscle actin appearing in the neointimal zone. By day 2 posthatch, the proximal DA lumen was fully occluded by endothelial cells and smooth muscle actin positive cells. In contrast, the distal DA was not fully occluded by day 2 posthatch. Increases in Po(2) of the blood serves as the main stimulus for closure of the mammalian DA. The responsiveness of the chicken proximal DA to oxygen increased during hatching, peaking during external pipping. This peak correlated with an increase in blood gas Po(2) and the initial occlusion of the vessel. The distal portion remained unresponsive to oxygen throughout hatching. In conclusion, the chicken DA begins to close during external pipping when arterial Po(2) increases and vessel tone is most sensitive to oxygen.

Risk factors for persistent ductus arteriosus patency during indomethacin treatment

OBJECTIVE

To test the hypothesis that patent ductus arteriosus that fail to close with prostaglandin inhibition may be regulated by mechanisms that act independently of prostaglandin production.

STUDY DESIGN

We examined a cohort of 446 infants who were treated with indomethacin (within 15 hours of birth) to inhibit prostaglandin production. We used multiple logistic regression modeling to determine which perinatal/neonatal variables were most closely associated with the persistence of ductus patency in the presence of diminished prostaglandin production.

RESULTS

We identified 4 variables (immature gestational age, lack of exposure to antenatal betamethasone, severity of respiratory distress, and Caucasian race) that were significantly and independently associated with the degree of ductus patency.

CONCLUSION

Gestational age, antenatal glucocorticoid exposure, respiratory distress, and race are independent risk factors that appear to affect ductus closure even when indomethacin has been used to inhibit prostaglandin production. Future studies of these risk factors may identify new potential targets for patent ductus arteriosus treatment.

Patent ductus arteriosus: an overview

Patent ductus arteriosus (PDA) is one of the most common congenital heart defects, accounting for 5%-10% of all congenital heart disease in term infants. The occurrence of PDA is inversely related to gestational age and weight, with an even greater incidence in preterm infants. The maintenance of ductal patency is essential for the normal development of the fetus. In the neonate, however, persistent patency of the ductus arteriosus (DA) is associated with significant morbidity and mortality. Normally, at birth, the DA constricts, resulting in intraluminal ischemic hypoxia, which eventually leads to closure and remodeling of the ductus. PDA in term infants is usually associated with a functional defect, whereas in preterm infants it is associated with immaturity. Normal physiologic mechanisms contributing to closure - oxygen tension and decreased prostaglandins-are altered in prematurity. Clinical signs of ductal patency include murmur, tachycardia, bounding peripheral pulses, and congestive heart failure and associated symptoms. Symptoms are not always present; therefore, diagnostic imaging is critical if a PDA is suspected on clinical grounds. Three management strategies are currently available for PDA: fluid restriction and diuretics (as clinically appropriate), medical intervention, and surgical ligation. Pharmacologic closure can be achieved via administration of intravenous indomethacin or ibuprofen lysine. While both agents have shown similar efficacy, ibuprofen lysine has demonstrated an improved safety profile, particularly in terms of renal effects, compared to indomethacin.

Patent ductus arteriosus: an overview

Patent ductus arteriosus (PDA) is one of the most common congenital heart defects, accounting for 5%-10% of all congenital heart disease in term infants. The occurrence of PDA is inversely related to gestational age and weight, with an even greater incidence in preterm infants. The maintenance of ductal patency is essential for the normal development of the fetus. In the neonate, however, persistent patency of the ductus arteriosus (DA) is associated with significant morbidity and mortality. Normally, at birth, the DA constricts, resulting in intraluminal ischemic hypoxia, which eventually leads to closure and remodeling of the ductus. PDA in term infants is usually associated with a functional defect, whereas in preterm infants it is associated with immaturity. Normal physiologic mechanisms contributing to closure - oxygen tension and decreased prostaglandins-are altered in prematurity. Clinical signs of ductal patency include murmur, tachycardia, bounding peripheral pulses, and congestive heart failure and associated symptoms. Symptoms are not always present; therefore, diagnostic imaging is critical if a PDA is suspected on clinical grounds. Three management strategies are currently available for PDA: fluid restriction and diuretics (as clinically appropriate), medical intervention, and surgical ligation. Pharmacologic closure can be achieved via administration of intravenous indomethacin or ibuprofen lysine. While both agents have shown similar efficacy, ibuprofen lysine has demonstrated an improved safety profile, particularly in terms of renal effects, compared to indomethacin.

Persistent ductus arteriosus in the Brown-Norway inbred rat strain

Persistent ductus arteriosus (PDA) is a common cardiovascular anomaly in children caused by the pathologic persistence of the left sixth pharyngeal arch artery. The inbred Brown-Norway (BN) rat presents with increased vascular fragility due to an aortic elastin deficit resulting from decreased elastin synthesis. The strikingly high prevalence of PDA in BN rats in a pilot study led us to investigate this vascular anomaly in 12 adolescent BN rats. In all BN rats, a PDA was observed macroscopically, whereas a ligamentum arteriosum was found in adult controls. The macroscopic appearance of the PDA was tubular (n = 2), stenotic (n = 8), or diverticular (n = 2). The PDA had the structure of a muscular artery with intimal thickening. In the normal closing ductus of the neonatal controls, the media consisted of layers of smooth muscle cells (SMCs) intermingled with layers of elastin. The intima was thin and poor in elastin. By contrast, the media of PDA in BN rats elastin lamellae were absent and the intima contained many elastic fibers. The abnormal distribution of elastin in the PDA of BN rats suggests that impaired elastin metabolism is related to the persistence of the ductus and implicates a genetically determined factor that may link the PDA with aortic fragility.

Inhibition of cyclooxygenase isoforms in late- but not midgestation decreases contractility of the ductus arteriosus and prevents postnatal closure in mice

Use of cyclooxygenase (COX) inhibitors to delay preterm birth is complicated by in utero constriction of the ductus arteriosus and delayed postnatal closure. Delayed postnatal closure has been attributed to loss of vasa vasorum flow and ductus wall ischemia resulting from constriction in utero. We used the murine ductus (which does not depend on vasa vasorum flow) to determine whether delayed postnatal closure may be because of mechanisms independent of in utero constriction. Acute inhibition of both COX isoforms constricted the fetal ductus on days 18 and 19 (term) but not earlier in gestation; COX-2 inhibition constricted the fetal ductus more than COX-1 inhibition. In contrast, mice exposed to prolonged inhibition of COX-1, COX-2, or both COX isoforms (starting on day 15, when the ductus does not respond to the inhibitors) had no contractile response to the inhibitors on days 18 or 19. Newborn mice closed their ductus within 4 h of birth. Prolonged COX inhibition on days 11-14 of gestation had no effect on newborn ductal closure; however, prolonged COX inhibition on days 15-19 resulted in delayed ductus closure despite exposure to 80% oxygen after birth. Similarly, targeted deletion of COX-2 alone, or COX-1/COX-2 together, impaired postnatal ductus closure. Nitric oxide inhibition did not prevent the delay in ductus closure. These data show that impaired postnatal ductus closure is not the result of in utero ductus constriction or upregulation of nitric oxide synthesis. They are consistent with a novel role for prostaglandins in ductus arteriosus contractile development.

Mechanisms regulating the ductus arteriosus

A patent ductus arteriosus (PDA) results in increased pulmonary blood flow and redistribution of flow to other organs. Several co-morbidities (i.e., necrotizing enterocolitis, intracranial hemorrhage, pulmonary edema/hemorrhage, bronchopulmonary dysplasia, and retinopathy) are associated with the presence of a PDA, but whether or not a PDA is responsible for their development is still unclear. In this review, comparative physiology between the full term and preterm newborn and the barriers preventing the necessary cascade of events leading to permanent constriction of the PDA are reviewed.

Postnatal constriction, ATP depletion, and cell death in the mature and immature ductus arteriosus

After birth, constriction of the full-term ductus arteriosus induces oxygen, glucose and ATP depletion, cell death, and anatomic remodeling of the ductus wall. The immature ductus frequently fails to develop the same degree of constriction or anatomic remodeling after birth. In addition, the immature ductus loses its ability to respond to vasoconstrictive agents, like oxygen or indomethacin, with increasing postnatal age. We examined the effects of premature delivery and postnatal constriction on the immature baboon ductus arteriosus. By 6 days after birth, surrogate markers of hypoxia (HIF1alpha/VEGF mRNA) and cell death [dUTP nick-end labeling (TUNEL)-staining] increased, while glucose and ATP concentrations (bioluminescence imaging) decreased in the immature ductus. TUNEL-staining was significantly related to the degree of glucose and ATP depletion. Glucose and ATP depletion were directly related to the degree of ductus constriction; while TUNEL-staining was logarithmically related to the degree of ductus constriction. Extensive cell death (>15% TUNEL-positive cells) occurred only when there was no Doppler flow through the ductus lumen. In contrast, HIF1alpha/VEGF expression and ATP concentrations were significantly altered even when the immature ductus remained open after birth. Decreased ATP concentrations produced decreased oxygen-induced contractile responses in the immature ductus. We hypothesize that ATP depletion in the persistently patent immature newborn ductus is insufficient to induce cell death and remodeling but sufficient to decrease its ability to constrict after birth. This may explain its decreasing contractile response to oxygen, indomethacin, and other contractile agents with increasing postnatal age.

ATP depletion and cell death in the neonatal lamb ductus arteriosus

Postnatal constriction of the full-term ductus arteriosus produces cell death and remodeling of the ductus wall. Using a bioluminescence imaging technique, we found that after birth, the lamb ductus develops ATP, glucose, and glycogen depletion in addition to hypoxia. In vitro studies showed that cell death correlates best with ATP depletion and is most marked when both glucose and oxygen are severely depleted; in addition, the degree of ATP depletion found in vivo is sufficient to account for the extensive degree of cell death that occurs after birth. Under hypoxic conditions, the immature ductus is more capable of preserving its ATP supply than the mature ductus as a result of increased glucose availability, glycogen stores, and glucose utilization. However, the immature ductus is just as susceptible as the mature ductus to ATP depletion when glucose supplies are restricted. The extensive degree of cell death that occurs in the newborn ductus after birth is associated primarily with ATP depletion. The increased glycolytic capacity of the immature ductus may enable it to tolerate episodes of hypoxia and nutrient shortage, making it more resistant to developing postnatal cell death and permanent closure.

Patency of the preterm fetal ductus arteriosus is regulated by endothelial nitric oxide synthase and is independent of vasa vasorum in the mouse

Patency of the fetal ductus arteriosus (DA) is maintained in an environment of low relative oxygen tension and a preponderance of vasodilating forces. In addition to prostaglandins, nitric oxide (NO), a potent vasodilator in the pulmonary and systemic vasculatures, has been implicated in regulation of the fetal DA. To further define the contribution of NO to DA patency, the expression and function of NO synthase (NOS) isoforms were examined in the mouse DA on days 17–19 of pregnancy and after birth. Our results show that endothelial NOS (eNOS) is the predominant isoform expressed in the mouse DA and is localized in the DA endothelium by in situ hybridization. Despite rapid constriction of the DA after birth, eNOS expression levels were unchanged throughout the fetal and postnatal period. Pharmacological inhibition of prostaglandin vs. NO synthesis in vivo showed that the preterm fetal DA on day 16 is more sensitive to NOS inhibition than the mature fetal DA on day 19, whereas prostaglandin inhibition results in marked DA constriction on day 19 but minimal effects on the day 16 DA. Combined prostaglandin and NO inhibition caused additional DA constriction on day 16. The contribution of vasa vasorum to DA regulation was also examined. Immunoreactive platelet endothelial cell adhesion molecule and lacZ tagged FLK1 localized to DA endothelial cells but revealed the absence of vasa vasorum within the DA wall. Similarly, there was no evidence of vasa vasorum by vascular casting. These studies indicate that eNOS is the primary source of NO in the mouse DA and that vasomotor tone of the preterm fetal mouse DA is regulated by eNOS-derived NO and is potentiated by prostaglandins. In contrast to other species, mechanisms for DA patency and closure appear to be independent of any contribution of the vasa vasorum.

Persistent Doppler flow predicts lack of response to multiple courses of indomethacin in premature infants with recurrent patent ductus arteriosus

OBJECTIVE

Although indomethacin produces ductus arteriosus constriction in extremely premature newborns, a recurrent symptomatic patent ductus arteriosus (PDA) frequently develops after the initial course of indomethacin. Currently, there is little information available to determine the effectiveness of a second course of indomethacin in producing permanent ductus closure. The objective of this study was to determine the rate of permanent ductus closure after a second course of indomethacin for a recurrent, symptomatic PDA and to identify the factors associated with permanent ductus closure.

METHODS

We identified 32 infants (<28 weeks' gestational age) 1) whose ductus was considered to be clinically closed after an initial course of indomethacin and 2) who subsequently developed a symptomatic PDA and received a second course of indomethacin. Clinical variables were evaluated for their association with failure of the second course (defined as surgical ligation after the second course for recurrence of a hemodynamically significant PDA). Data were analyzed by chi(2) analysis, Fisher's exact test, and the Mann-Whitney rank sum test.

RESULTS

After the second course of indomethacin, 56% (18 of 32) of the infants had persistent or recurrent PDA-related symptoms that were considered to be hemodynamically significant. The only significant predictor of failure of the second indomethacin course was the demonstration (by Doppler echocardiogram) of persistent ductus flow within 24 hours of completing the initial indomethacin course. All of the 9 newborns with persistent Doppler ductus flow after the initial indomethacin course failed the second course of indomethacin. In contrast, only 39% (9 of 23) of newborns with absent Doppler flow after the initial indomethacin course failed the second course of indomethacin.

CONCLUSIONS

Newborns who are <28 weeks' gestational age and develop a recurrent, symptomatic PDA after completion of an initial indomethacin course rarely respond to multiple courses of indomethacin if there was persistent Doppler evidence of ductus flow after completion of the initial course. Additional indomethacin treatment is unlikely to produce permanent ductus closure.

Effects of hypoxia, hypoglycemia, and muscle shortening on cell death in the sheep ductus arteriosus

After birth, constriction of the full-term ductus arteriosus produces ischemic hypoxia, caspase activation, DNA fragmentation (>70% of cell nuclei are positive by the terminal deoxynucleotidyl transferase nick-end labeling [TUNEL] technique), and permanent ductus closure. In contrast, the preterm ductus frequently fails to develop these changes. We used the TUNEL technique to examine rings of fetal ductus arteriosus (incubated for 24 h at different oxygen and glucose concentrations) to determine the roles of 1) constriction and shortening, 2) hypoxia, and 3) hypoglycemia in producing cell death. Under controlled conditions, late-gestation ductus rings had a low rate of TUNEL-positive staining (0.6 +/- 0.9%) that did not change during muscle shortening. Although hypoxia (6.9 +/- 3.5%) and hypoglycemia (2.4 +/- 1.9%) increased the incidence of TUNEL-positive staining, only the combination of hypoxia-plus-hypoglycemia increased the incidence to the range found in vivo (83 +/- 9.5%). The combination of hypoxia-plus-hypoglycemia was associated with an oligonucleosomal pattern of DNA fragmentation. Under the same experimental conditions, the preterm ductus was capable of developing a similar degree of TUNEL-positive staining as found at term. Although caspase-3 and caspase-7 were activated in rings exposed to hypoxia-plus-hypoglycemia, a nonselective caspase inhibitor, Z-VAD.FMK (which inhibited caspase-3 and caspase-7 cleavage in the rings), did not diminish the degree of TUNEL-positive staining. We hypothesize that the preterm ductus is capable of developing an extensive degree of cell death, if it can develop the same degree of hypoxia and hypoglycemia found in the full-term newborn ductus. We also hypothesize that cell death in the ductus wall may involve pathways that are not dependent on caspase-3 or -7 activation.