Chronic in utero cyclooxygenase inhibition alters PGE2-regulated ductus arteriosus contractile pathways and prevents postnatal closure

The impact of cyclooxygenase inhibitor use on urinary prostaglandin metabolites in preterm infants

BACKGROUND

There is limited evidence on the association between the clinical course of patent ductus arteriosus (PDA) and prostaglandin (PG) metabolites. This study aimed to determine the influence of PDA treatment on urinary PG metabolite excretion in very-low-birth-weight (VLBW) infants.

METHODS

Urine samples were collected from 25 VLBW infants at 1, 3, and 7 days of age. Infants were separated into two groups: a PDA-treated group that received a cyclooxygenase-2 (COX) inhibitor (n = 12) and a control group that did not receive a COX inhibitor during the first 7 days after birth (n = 13). Urinary PG metabolite tetranor prostaglandin E2 metabolite (t-PGEM) and tetranor prostaglandin D2 metabolite (t-PGDM) levels were analyzed using liquid chromatography-tandem mass spectrometry.

RESULTS

Urinary t-PGEM excretion levels were not significantly different between the groups at 1, 3, and 7 days of age. Urinary t-PGDM excretion levels at 1 day of age were higher in PDA-treated infants than in control infants (median [interquartile range]: 5.5 [2.6, 12.2] versus 2.1 [1.0, 3.9] ng/mg creatinine; p = 0.017); however, among PDA-treated infants, the levels were significantly lower at 3 and 7 days than at 1 day of age (5.5 [2.6, 12.2] versus 3.4 [1.7, 4.5] and 4.0 [1.7, 5.3] ng/mg creatinine, respectively; p < 0.05). The urinary t-PGDM excretion level in the control group did not significantly differ among the time points.

CONCLUSION

PDA and COX inhibitor administration affected PG metabolism in VLBW infants. Our results indicated that urinary t-PGDM excretion was significantly associated with PDA-treatment in preterm infants.

A novel role for PGE2-EP4 in the developmental programming of the mouse ductus arteriosus: consequences for vessel maturation and function

The ductus arteriosus (DA) is a vascular shunt that allows oxygenated blood to bypass the developing lungs in utero. Fetal DA patency requires vasodilatory signaling via the prostaglandin E2 (PGE2) receptor EP4. However, in humans and mice, disrupted PGE2-EP4 signaling in utero causes unexpected patency of the DA (PDA) after birth, suggesting another role for EP4 during development. We used EP4-knockout (KO) mice and acute versus chronic pharmacological approaches to investigate EP4 signaling in DA development and function. Expression analyses identified EP4 as the primary EP receptor in the DA from midgestation to term; inhibitor studies verified EP4 as the primary dilator during this period. Chronic antagonism recapitulated the EP4 KO phenotype and revealed a narrow developmental window when EP4 stimulation is required for postnatal DA closure. Myography studies indicate that despite reduced contractile properties, the EP4 KO DA maintains an intact oxygen response. In newborns, hyperoxia constricted the EP4 KO DA but survival was not improved, and permanent remodeling was disrupted. Vasomotion and increased nitric oxide (NO) sensitivity in the EP4 KO DA suggest incomplete DA development. Analysis of DA maturity markers confirmed a partially immature EP4 KO DA phenotype. Together, our data suggest that EP4 signaling in late gestation plays a key developmental role in establishing a functional term DA. When disrupted in EP4 KO mice, the postnatal DA exhibits signaling and contractile properties characteristic of an immature DA, including impairments in the first, muscular phase of DA closure, in addition to known abnormalities in the second permanent remodeling phase.NEW & NOTEWORTHY EP4 is the primary EP receptor in the ductus arteriosus (DA) and is critical during late gestation for its development and eventual closure. The "paradoxical" patent DA (PDA) phenotype of EP4-knockout mice arises from a combination of impaired contractile potential, altered signaling properties, and a failure to remodel associated with an underdeveloped immature vessel. These findings provide new mechanistic insights into women who receive NSAIDs to treat preterm labor, whose infants have unexplained PDA.

Mouse models of patent ductus arteriosus (PDA) and their relevance for human PDA

The ductus arteriosus (DA) is a unique fetal vascular shunt, which allows blood to bypass the developing lungs in utero. After birth, changes in complex signaling pathways lead to constriction and permanent closure of the DA. The persistent patency of the DA (PDA) is a common disorder in preterm infants, yet the underlying causes of PDA are not fully defined. Although limits on the availability of human DA tissues prevent comprehensive studies on the mechanisms of DA function, mouse models have been developed that reveal critical pathways in DA regulation. Over 20 different transgenic models of PDA in mice have been described, with implications for human DA biology. Similarly, we enumerate 224 human single-gene syndromes that are associated with PDA, including a small subset that consistently feature PDA as a prominent phenotype. Comparison and functional analyses of these genes provide insight into DA development and identify key regulatory pathways that may serve as potential therapeutic targets for the management of PDA.

Effects of astragalus polysaccharide on intestinal inflammatory damage in goslings infected with gosling plague

1. This study explored the effects of Astragalus membranaceus polysaccharide (APS) on intestinal inflammatory damage of goslings infected with parvovirus ('gosling plague').2. A total of 90 healthy goslings were randomly divided into three groups; control, infected or APS treated, respectively. Goslings in the infection and APS treatment groups were inoculated with 0.3 ml allantoic fluid containing goose parvovirus (ELD₅₀ = 1 × 10³/0.3 ml) by intramuscular injection and the control group were injected with saline (0.3 ml) twice a day for 15 days.3. Blood serum and the jejunum were collected at 5, 10 and 15 days after the start of the experiment to detect the activities of SOD and GSH-Px, levels of MDA, sIgA, IL-1β, IL-6 and TNF-α, the mRNA expression of IL-1β, IL-6, LITAF, NF-κB, COX-2 and PGE2, pathological damage in the jejunum and serum IgG, IgM, C3, C4, IFN-γ levels.4. After APS treatment, SOD and GSH-Px activities increased, MDA content decreased; sIgA, IL-1β, IL-6 and TNF-α protein content, and IL-1β, IL-6, LITAF, NF-κB, COX-2 and PGE2 mRNA expression decreased in the jejunal tissue, serum IgG, IgM, C3, C4, IFN-γ significantly increased and pathological damage of jejunum significantly improved.5. In conclusion, APS reduced intestinal inflammatory damage in goslings infected with parvovirus by improving the immune and antioxidant functions of goslings.

Role of Tissue-Type Plasminogen Activator in Remodeling of the Ductus Arteriosus

Vascular remodeling (e.g., intimal thickening) is necessary for complete closure of the ductus arteriosus (DA). Smooth muscle cells are reported to contribute to DA remodeling. In contrast, the contribution of endothelial cells remains largely unknown. Recent data showed that tissue-type plasminogen activator (t-PA) was highly expressed in the endothelial cells of rat and human DA. It is well known that t-PA is an activator of the blood fibrinolytic system, but t-PA-induced localized proteolysis has been reported to play an important role in vascular development. We found that t-PA-induced plasminogen-plasmin conversion promoted matrix metalloproteinase-2 activation in endothelial cells of rat DA. Gelatinase activity was noted at the internal elastic laminae (IEL) of rat and human DA on in situ gelatin zymography. The in vivo injection of plasminogen to pre-term rats increased gelatinase activation, IEL disruption, and the subsequent intimal thickening formation in the pre-term rat DA. Human DA results partly supported the rat DA findings, suggesting that t-PA-mediated DA remodeling may also be present in the human DA. Current pharmacotherapy for patent DA (PDA) mainly focuses on increasing vascular constriction. Elucidating the molecular mechanisms of DA remodeling may help to expand the range of therapeutic strategies for PDA.

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.

Effects of antenatal betamethasone on preterm human and mouse ductus arteriosus: comparison with baboon data

BACKGROUND

Although studies involving preterm infants ≤34 weeks gestation report a decreased incidence of patent ductus arteriosus after antenatal betamethasone, studies involving younger gestation infants report conflicting results.

METHODS

We used preterm baboons, mice, and humans (≤276/7 weeks gestation) to examine betamethasone's effects on ductus gene expression and constriction both in vitro and in vivo.

RESULTS

In mice, betamethasone increased the sensitivity of the premature ductus to the contractile effects of oxygen without altering the effects of other contractile or vasodilatory stimuli. Betamethasone's effects on oxygen sensitivity could be eliminated by inhibiting endogenous prostaglandin/nitric oxide signaling. In mice and baboons, betamethasone increased the expression of several developmentally regulated genes that mediate oxygen-induced constriction (K+ channels) and inhibit vasodilator signaling (phosphodiesterases). In human infants, betamethasone increased the rate of ductus constriction at all gestational ages. However, in infants born ≤256/7 weeks gestation, betamethasone's contractile effects were only apparent when prostaglandin signaling was inhibited, whereas at 26-27 weeks gestation, betamethasone's contractile effects were apparent even in the absence of prostaglandin inhibitors.

CONCLUSIONS

We speculate that betamethasone's contractile effects may be mediated through genes that are developmentally regulated. This could explain why betamethasone's effects vary according to the infant's developmental age at birth.

Novel drug targets for ductus arteriosus manipulation: Looking beyond prostaglandins

Forty years ago, non-steroidal anti-inflammatory drugs were first reported to decrease systemic prostaglandin levels and promote ductus arteriosus (DA) closure. And yet, prolonged patency of the DA (PDA) remains a significant clinical problem, complicated by imperfect therapies and wide variations in treatment strategy. There are few pharmacology-based tools available for treating PDA (indomethacin, ibuprofen, and acetaminophen), or for maintaining DA patency (PGE₁) as is needed to facilitate corrective surgery for ductus-dependent congenital heart defects. Unfortunately, all of these treatments are inefficient and are associated with concerning adverse effects. This review highlights novel potential DA drug targets that may expand our therapeutic repertoire beyond the prostaglandin pathway.

Effects of Advancing Gestation and Non-Caucasian Race on Ductus Arteriosus Gene Expression

OBJECTIVE

To identify genes affected by advancing gestation and racial/ethnic origin in human ductus arteriosus (DA).

STUDY DESIGN

We collected 3 sets of DA tissue (n = 93, n = 89, n = 91; total = 273 fetuses) from second trimester pregnancies. We examined four genes, with DNA polymorphisms that distribute along racial lines, to identify "Caucasian" and "non-Caucasian" DA. We used real time polymerase chain reaction to measure RNA expression of 48 candidate genes involved in functional closure of the DA, and used multivariable regression analyses to examine the relationships between advancing gestation, "non-Caucasian" race, and gene expression.

RESULTS

Mature gestation and non-Caucasian race are significant predictors for identifying infants who will close their patent DA when treated with indomethacin. Advancing gestation consistently altered gene expression in pathways involved with oxygen-induced constriction (eg, calcium-channels, potassium-channels, and endothelin signaling), contractile protein maturation, tissue remodeling, and prostaglandin and nitric oxide signaling in all 3 tissue sets. None of the pathways involved with oxygen-induced constriction appeared to be altered in "non-Caucasian" DA. Two genes, SLCO2A1 and NOS3, (involved with prostaglandin reuptake/metabolism and nitric oxide production, respectively) were consistently decreased in "non-Caucasian" DA.

CONCLUSIONS

Prostaglandins and nitric oxide are the most important vasodilators opposing DA closure. Indomethacin inhibits prostaglandin production, but not nitric oxide production. Because decreased SLCO2A1 and NOS3 expression can lead to increased prostaglandin and decreased nitric oxide concentrations, we speculate that prostaglandin-mediated vasodilation may play a more dominant role in maintaining the "non-Caucasian" patent DA, making it more likely to close when inhibited by indomethacin.

Prostaglandin E-mediated molecular mechanisms driving remodeling of the ductus arteriosus

The ductus arteriosus (DA), a fetal arterial connection between the pulmonary arteries and aorta, normally closes after birth. Persistent DA patency usually has life-threatening consequences. In certain DA-dependent congenital heart diseases, however, patient survival depends on maintaining DA patency. Complete closure of the DA involves both functional closure, induced by muscle contraction, and anatomical closure, achieved through morphological and molecular remodeling. Anatomical closure of the DA is associated with the formation of intimal thickening, which is characterized by deposition of extracellular matrix in the subendothelial region, sparse elastic fiber formation, and migration of medial smooth muscle cells into the subendothelial space. In addition, fetal molecular remodeling that is suitable for postnatal muscle contraction has been observed in the DA. After the second trimester, high concentration of prostaglandin E2 (PGE2) causes the DA to dilate through the remainder of the fetal period. Emerging evidence from studies using pharmacological approaches and genetically modified mice suggests that, in addition to its vasodilatory effect, this chronic exposure to PGE2 promotes DA-specific anatomical and molecular remodeling through EP4, one of four receptor subtypes for PGE2. Signals that are downstream of PGE2-EP4, such as cyclic AMP (cAMP)-protein kinase A (PKA), exchange protein activated by cAMP (Epac), phospholipase C, and Wnt/β-catenin, may be involved in the regulation of intimal thickening, elastogenesis, and contraction-related genes. Understanding the physiological role of PGE2 in DA remodeling could enable more effective regulation of PDA, both in isolation and in the context of congenital cardiac anomalies.

Characterization of transcription factor AP-2 β mutations involved in familial isolated patent ductus arteriosus suggests haploinsufficiency

BACKGROUND

Patent ductus arteriosus (PDA) is one of the most common congenital heart defects. Transcription factor AP-2 beta (TFAP2B) mutations are associated with the Char syndrome, a disorder associated with PDA, and with facial and fingers abnormalities. Recently, we identified two TFAP2B mutations in two families without Char syndrome phenotype, c.601+5G>A and c.435_438delCCGG, and these TFAP2B mutations were associated with familial isolated PDA. The aim of this study was to identify the effects of these mutations on TFAP2B function.

METHODS

Plasmids containing the wild-type or mutated TFAP2B were constructed and transfected in cells. Plasmids containing the TFAP2B coactivator, Cpb/p300-interacting transactivator 2 (CITED2), was also transfected. TFAP2B expression was detected by luciferase expression and by Western blot analysis.

RESULTS

These mutations resulted in loss of transactivation function, which could not be improved by Cpb/p300-interacting transactivator 2. The c.601+5G>A mutated gene did not express any protein, whereas the c.435_438delCCGG mutation did not impact the transactivation function activated by the wild-type TFAP2B.

CONCLUSIONS

These results suggest that a haploinsufficiency effect of TFAP2B could be involved in familial isolated PDA.

Association of amino acids with common complications of prematurity

BACKGROUND

Tandem mass spectrometry has been proposed as a method of diagnosing or predicting the development of common complex neonatal diseases. Our objective was to identify metabolites associated with common complications of prematurity.

METHODS

We performed a retrospective analysis of medical data and metabolite measurements from routine neonatal screening on 689 preterm (<37 wk of gestational age) neonates.

RESULTS

We observed higher levels of phenylalanine (PHE) in infants with respiratory distress syndrome (RDS; P = 1.7 × 10(-5)), the only association that was significant after correction for multiple testing. We found suggestive significance (P < 0.001) of higher essential amino acids in infants with patent ductus arteriosus (PDA). Functionality of these findings was explored in the ductus arteriosus (DA) isolated from term and preterm mouse pups. None of the amino acids had a direct vasodilatory effect on the isolated DA.

CONCLUSION

We found that newborns with RDS had higher levels of PHE that may be a result of impaired PHE hydroxylase activity. We also detected marginally higher levels of all measured essential amino acids in infants with PDA. We did not find dilation of the mouse ductus for these metabolites, indicating that instead of potentially causing PDA, they are probably serving as markers of catabolism.

Low-dose thromboxane A2 receptor stimulation promotes closure of the rat ductus arteriosus with minimal adverse effects

BACKGROUND

Patent ductus arteriosus (PDA) is a common life-threatening complication among premature infants. Although cyclooxygenase inhibitors are frequently used to treat PDA, as they inhibit the synthesis of prostaglandin E(2), the most potent vasodilator in the ductus arteriosus (DA), their efficacy is often limited. As thromboxane A(2) (TXA(2)) induces vascular contraction via the TXA(2) receptor (TP), we hypothesized that TP stimulation would promote DA closure.

METHOD

To measure the inner diameter of the vessels, a rapid whole-body freezing method was used.

RESULTS

Injection of the selective TP agonists U46619 and I-BOP constricted the fetal DA at embryonic day 19 (e19) and e21 in a dose-dependent manner. Of note, U46619 also exerted a vasoconstrictive effect on two different types of postnatal PDA models: premature PDA and hypoxia-induced PDA. We also found that U46619 constricted the ex vivo DA ring to a greater extent than it constricted the ex vivo aorta. Furthermore, we found that U46619 at lower concentrations (up to 0.05 mg/g of body weight) had a minimal vasoconstrictive effect on other vessels and did not induce microthrombosis in the pulmonary capillary arteries.

CONCLUSION

Low-dose TP stimulation constricts the DA with minimal adverse effects at least in rat neonates and our results could point to an alternative potent vasoconstrictor for PDA.

Omental grafting: a cell-based therapy for blood vessel repair

Clinicians regularly transplant omental pedicles to repair a wide variety of injured tissues, but the basic mechanism underlying this efficacious procedure is not understood. One possibility that has not been addressed is the ability of omentum to directly contribute regenerative cells to injured tissues. We hypothesized that if omental progenitor cells could be mobilized to incorporate into damaged tissue, the power of this therapy would be greatly expanded. Labelled omental grafts were transplanted into a murine carotid artery injury model. Selected grafts were treated with thymosin β4 (Tβ4) prior to transplantation to investigate the effects of chemical potentiation on healing. We found treatment of grafts with Tβ4-induced progenitor cells to fully integrate into the wall of injured vessels and differentiate into vascular smooth muscle. Myographic studies determined that arteries receiving Tβ4-stimulated grafts were functionally indistinguishable from uninjured controls. Concurrent in vitro analyses showed that Tβ4 promoted proliferation, migration and trans-differentiation of cells via AKT signalling. This study is the first to demonstrate that omentum can provide progenitor cells for repair, thus revealing a novel and naturally occurring source of vascular smooth muscle for use in cell-based therapies. Furthermore, our data show that this system can be optimized with inducing factors, highlighting a more powerful therapeutic potential than that of its current clinical application. This is a paradigm-setting concept that lays the foundation for the use of chemical genetics to enhance therapeutic outcomes in a myriad of fields.

Current Perspectives on Pathobiology of the Ductus Arteriosus

The ductus arteriosus (DA) shunts blood away from the lungs during fetal life, but at birth this shunt is no longer needed and the vessel rapidly constricts. Postnatal persistence of the DA, patent ductus arteriosus (PDA), is predominantly a detrimental condition for preterm infants but is simultaneously a condition required to maintain systemic blood flow for infants born with certain severe congenital heart defects. Although PDA in preterm infants is associated with significant morbidities, there is controversy regarding whether PDA is truly causative. Despite advances in our understanding of the pathobiology of PDA, the optimal treatment strategy for PDA in preterm infants is unclear. Here we review recent studies that have continued to elucidate the fundamental mechanisms of DA development and pathogenesis.

Basics and dynamics of neonatal and pediatric pharmacology

Understanding the role of ontogeny in the disposition and actions of medicines is the most fundamental prerequisite for safe and effective pharmacotherapeutics in the pediatric population. The maturational process represents a continuum of growth, differentiation, and development, which extends from the very small preterm newborn infant through childhood, adolescence, and to young adulthood. Developmental changes in physiology and, consequently, in pharmacology influence the efficacy, toxicity, and dosing regimen of medicines. Relevant periods of development are characterized by changes in body composition and proportion, developmental changes of physiology with pathophysiology, exposure to unique safety hazards, changes in drug disposition by major organs of metabolism and elimination, ontogeny of drug targets (e.g., enzymes, transporters, receptors, and channels), and environmental influences. These developmental components that result in critical windows of development of immature organ systems that may lead to permanent effects later in life interact in a complex, nonlinear fashion. The ontogeny of these physiologic processes provides the key to understanding the added dimension of development that defines the essential differences between children and adults. A basic understanding of the developmental dynamics in pediatric pharmacology is also essential to delineating the future directions and priority areas of pediatric drug research and development.

Patterns of gene expression in the ductus arteriosus are related to environmental and genetic risk factors for persistent ductus patency

Three independent risk factors (immature gestation, absence of antenatal glucocorticoid exposure, and presence of the rs2817399(A) allele of the gene TFAP2B) are associated with patent ductus arteriosus (PDAs) that fail to close during prostaglandin inhibition. We hypothesized that these three factors may affect a common set of genes that increase the risk of persistent PDA after birth. We studied baboon ductus from term, preterm, and glucocorticoid-treated preterm fetuses and found that both immature gestation and absence of antenatal glucocorticoid exposure decreased RNA expression of calcium- and potassium-channel genes involved in oxygen-induced constriction, and phosphodiesterase genes (that modulate cAMP/cGMP signaling). Ductus obtained from second trimester human pregnancies were genotyped for TFAP2B polymorphisms. When present, the rs2817399(A) allele also was associated with decreased expression of calcium- and potassium-channel genes. In contrast, alleles of two other TFAP2B polymorphisms, rs2817419(G) and rs2635727(T), which are not related to the incidence of PDA after birth, had no effect on RNA expression. In conclusion, three calcium- and potassium-channel genes (CACNA1G/ alpha1G, CACNB 2/CaL-beta2, and KCNA2/ Kv1.2) were similarly affected by each of the PDA risk factors. We speculate that these channels may play a significant role in closing the preterm ductus during prostaglandin inhibition and may be potential targets for future pharmacologic manipulations.

Inadvertent relaxation of the ductus arteriosus by pharmacologic agents that are commonly used in the neonatal period

Premature birth and disruption of the normal maturation process leave the immature ductus arteriosus unable to respond to postnatal cues for closure. Strategies that advocate conservative management of the patent ductus arteriosus (PDA) in premature infants are dependent on identification of the symptomatic PDA and understanding the risk factors that predispose to PDA. Exposure of premature infants to unintended vasodilatory stimuli may be one of the risk factors for PDA that is under recognized. In this article, we summarize the clinical factors that are associated with PDA and review commonly used neonatal drugs for their vasodilatory properties. Data demonstrating relaxation of the ductus arteriosus by gentamicin and other aminoglycoside antibiotics, by cimetidine and other H2 receptor antagonists, and by heparin are provided as examples of neonatal therapies that have unanticipated effects that may promote PDA.

Failure of postnatal ductus arteriosus closure in prostaglandin transporter-deficient mice

BACKGROUND

Prostaglandin E(2) (PGE(2)) plays a major role both in maintaining patency of the fetal ductus arteriosus and in closure of the ductus arteriosus after birth. The rate-limiting step in PGE(2) signal termination is PGE(2) uptake by the transporter PGT.

METHODS AND RESULTS

To determine the role of PGT in ductus arteriosus closure, we used a gene-targeting strategy to produce mice in which PGT exon 1 was flanked by loxP sites. Successful targeting was obtained because neither mice hypomorphic at the PGT allele (PGT Neo/Neo) nor global PGT knockout mice (PGT(-/-)) exhibited PGT protein expression; moreover, embryonic fibroblasts isolated from targeted mice failed to exhibit carrier-mediated PGE(2) uptake. Although born in a normal mendelian ratio, no PGT(-/-) mice survived past postnatal day 1, and no PGT Neo/Neo mice survived past postnatal day 2. Necropsy revealed patent ductus arteriosus with normal intimal thickening but dilated cardiac chambers. Both PGT Neo/Neo and PGT(-/-) mice could be rescued through the postnatal period by giving the mother indomethacin before birth. Rescued mice grew normally and had no abnormalities by gross and microscopic postmortem analyses. In accordance with the known role of PGT in metabolizing PGE(2), rescued adult PGT(-/-) mice had lower plasma PGE(2) metabolite levels and higher urinary PGE(2) excretion rates than wild-type mice.

CONCLUSIONS

PGT plays a critical role in closure of the ductus arteriosus after birth by ensuring a reduction in local and/or circulating PGE(2) concentrations.