Responses of the post-term arterial duct to oxygen, prostaglandin E2, and the nitric oxide donor, 3-morpholinosydnonimine, in lambs and their clinical implications

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.

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.

The dark side of ibuprofen in the treatment of patent ductus arteriosus: could paracetamol be the solution?

INTRODUCTION

Patent ductus arteriosus (PDA) persistence is associated, in prematures, to several complications. The optimal PDA management is still under debate, especially regarding the best therapeutic approach and the time to treat. The available drugs are not exempt from contraindications and side effects; ibuprofen itself, although representing the first-choice therapy, can show nephrotoxicity and other complications. Paracetamol seems a valid alternative to classic nonsteroidal anti-inflammatory Drugs, with a lower toxicity. Areas covered: Through an analysis of the published literature on ibuprofen and paracetamol effects in preterm neonates, this review compares the available treatments for PDA, analyzing the mechanisms underlining ibuprofen-associated nephrotoxicity and the eventual paracetamol-induced hepatic damage, also providing an update of what has been yet demonstrated and a clear description of the still open issues. Expert Opinion: Paracetamol is an acceptable alternative in case of contraindication to ibuprofen; its toxicity, in this setting, is very low. Lower doses may be effective, with even fewer risks. In the future, paracetamol could represent an efficacious first-line therapy, although its safety, optimal dosage, and global impact have to be fully clarified through long-term trials, also in the perspective of an individualized and person-based therapy taking into account the extraordinary individual variability.

Paracetamol in Patent Ductus Arteriosus Treatment: Efficacious and Safe?

In preterm infants, failure or delay in spontaneous closure of Ductus Arteriosus (DA), resulting in the condition of Patent Ductus Arteriosus (PDA), represents a significant issue. A prolonged situation of PDA can be associated with several short- and long-term complications. Despite years of researches and clinical experience on PDA management, unresolved questions about the treatment and heterogeneity of clinical practices in different centers still remain, in particular regarding timing and modality of intervention. Nowadays, the most reasonable strategy seems to be reserving the treatment only to hemodynamically significant PDA. The first-line therapy is medical, and ibuprofen, related to several side effects especially in terms of nephrotoxicity, is the drug of choice. Administration of oral or intravenous paracetamol (acetaminophen) recently gained attention, appearing effective as traditional nonsteroidal anti-inflammatory drugs (NSAIDs) in PDA closure, with lower toxicity. The results of the studies analyzed in this review mostly support paracetamol efficacy in ductal closure, with inconstant low and transient elevation of liver enzymes as reported side effect. However, more studies are needed to confirm if this therapy shows a real safety profile and to evaluate its long-term outcomes, before considering paracetamol as first-choice drug in PDA treatment.

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.

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.

Effect of aerosolized PGE(1) on the ductus arteriosus of neonatal swine

BACKGROUND

Inhaled PGE(1) (IPGE(1)) is a potential pulmonary vasodilator in neonatal respiratory failure. However, its effect on the patency of the ductus arteriosus (DA) has not been described.

OBJECTIVE

To investigate the effect of IPGE(1) on the DA in healthy piglets.

DESIGN/METHODS

IPGE(1) (1200ng/kg/min) [Study] or nebulized saline [Control] was administered using a jet nebulizer. Transthoracic echocardiography (TTE) was performed prior to (T0) and after 24h of aerosol therapy (T24). The DA was also evaluated histomorphologically at autopsy.

RESULTS

Fifteen piglets, 1-9 days old (study=9; control=6), were evaluated for DA patency. Study piglets received IPGE(1) for 12-24h. TTE was performed on 12 piglets at T0. Nine animals showed no ductal flow and 3 (1 study, 2 control) had a small DA. TTE at T24 in 5 animals showed no change in DA. At autopsy, the ductal diameter and histologic maturity stage were comparable in study and control animals.

CONCLUSIONS

High dose IPGE(1) given for 12-24h does not exert significant effect on the DA of healthy term piglets as evaluated by echocardiography and histomorphology. We conclude that ductal patency in neonates is influenced not only by prostaglandins but also by factors like hypoxemia, prematurity, and heart disease.

Urinary prostaglandin E2 in the newborn and infant

Prostaglandin E(2) (PGE(2)) belongs to a family of biologically active lipids derived from the 20-carbon essential fatty acids. Renal PGE(2) is involved in the development of the kidney; it also contributes to regulate renal perfusion and glomerular filtration rate, and controls water and electrolyte balance. Furthermore, this mediator protects the kidney against excessive functional changes during the transition from fetal to extrauterine life, when it counteracts the vasoconstrictive effects of high levels of angiotensin II and other mediators. There is evidence that PGE(2) plays an important pathophysiological role in neonatal conditions of renal stress, and in congenital or acquired nephropaties. Thus, measurement of urinary PGE(2) as an index of renal synthesis of this primary prostaglandin may represent a non-invasive and sensitive method of investigating the homeostatic function of the kidney in early life. The aim of this literature review is to examine urinary PGE(2) as a non-invasive marker of renal homeostasis in the newborn and infant under both physiological and pathological conditions, or during treatments with widely used, potentially toxic drugs.

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.

Prostanoid receptors: ontogeny and implications in vascular physiology

Prostanoids exert significant effects on circulatory beds. They play a role in the response of the vasculature to adjustments in perfusion pressure and oxygen and carbon dioxide tension, and they mediate the actions of numerous factors. The role of prostanoids in governing circulation of the perinate is suggested to surpass that in the adult. Prostanoids are abundantly generated in the perinate. They have been implicated in autoregulation of blood flow as studied in brain and eyes. Prostaglandins are also dominant regulators of ductus arteriosus tone. The effects of these autacoids are mediated through specific G protein-coupled receptors. In addition to the pharmacological characterization of the prostanoid receptors, important advances in understanding the biology of these receptors have been made in the last decade. Their cloning and the development of animals with disrupted genes of these receptors have been very informative. The involvement of prostanoid receptors in the developing subject, especially on brain and ocular vasculature and on ductus arteriosus, has also begun to be investigated; the expression of these receptors changes with development. Some but not all of the ontogenic changes in these receptors are attributed to homologous regulation. Interestingly, in the process of elucidating their effects, functional perinuclear prostaglandin E2 receptors have been uncovered. This article reviews prostanoid receptors and addresses implications on the developing subject with attention to vascular physiology.

Characterization of PGE2 receptors in fetal and newborn lamb ductus arteriosus

Although the role of PGE2 in maintaining ductus arteriosus (DA) patency is well established, the specific PGE2 receptor subtype(s) (EP) involved have not been clearly identified. We used late gestation fetal and neonatal lambs to study developmental regulation of EP receptors. In the fetal DA, radioligand binding and RT-PCR assays virtually failed to detect EP1 but detected EP2, EP3D, and EP4 receptors in equivalent proportions. In the newborn lamb, DA total density was one-third of that found in the fetus and only EP2 was detected. Stimulation of EP2 and EP4 increased cAMP formation and was associated with DA relaxation. Though stimulation of EP3 inhibited cAMP formation, it surprisingly relaxed the fetal DA both in vitro and in vivo. This EP3-induced relaxation was specifically diminished by the ATP-sensitive K(+) (K(ATP)) channel blocker glibenclamide. In conclusion, PGE2 dilates the late gestation fetal DA through pathways that involve either cAMP (EP2 and EP4) or K(ATP) channels (EP3). The loss of EP3 and EP4 receptors in the newborn DA is consistent with its decreased responsiveness to PGE2.

Characterization of PGE2 receptors in fetal and newborn ductus arteriosus in the pig

We compared the total density and the relative expression of EP receptor (EP) subtypes in ductus arteriosus (DA) of the newborn with that of the fetal piglet. Saturation binding experiments showed 3-fold less PGE2 receptors in the newborn than in the fetus because of loss of EP3 and EP4 receptors thus explaining, at least partly, the reduced responsiveness to PGE2 of the newborn DA. Displacement experiments showed that the relative proportions of EP2, EP3, and EP4 were similar in the fetal DA but only EP2 was detected in the DA of the newborn pig. Hence, PGE2 effects in the newborn DA seem to be exclusively mediated by EP2 receptors both in vitro and in vivo. These findings may help to propose more specific therapies for regulation of DA's tone in certain newborns for whom conventional therapy is contraindicated.

Developmental changes in prostaglandin E(2) receptor subtypes in porcine ductus arteriosus. Possible contribution in altered responsiveness to prostaglandin E(2)

BACKGROUND

Prostaglandin E(2) (PGE(2)) is important in ductus arteriosus (DA) patency, but the types of functional PGE(2) receptors (EP) in the developing DA are not known. We postulated that age-dependent alterations in EP and/or their subtypes may possibly contribute to the reduced responsiveness of the newborn DA to PGE(2).

METHODS AND RESULTS

We determined PGE(2) receptor subtypes by competition binding and immunoblot studies on the DA of fetal ( approximately 75% and 90% gestation) and newborn (<45 minutes old) pigs. We studied the effects of EP receptor stimulation on cAMP signaling in vitro and on term newborn (<3 hours old) DA patency in vivo. Fetal pig DA expressed EP(2), EP(3), and EP(4) receptors equivalently, but not EP(1). In neonatal DA, EP(1), EP(3), and EP(4) were undetectable, whereas EP(2) density was similar in fetus and newborn. Prostaglandin-induced changes in cAMP mirrored binding data. 16,16-Dimethyl PGE(2) and 11-deoxy PGE(1) (EP(2)/EP(3)/EP(4) agonist) produced more cAMP in fetus than newborn, but butaprost (selective EP(2) agonist) caused similar cAMP increases in both; EP(3) and EP(4) ligands (M&B28767 and AH23848B, respectively) affected cAMP production only in fetus. After birth, administration of butaprost alone was as effective as 11-deoxy PGE(1) and 16,16-dimethyl PGE(2) in dilating DA in vivo.

CONCLUSIONS

The data reveal fewer PGE(2) receptors in the DA of the newborn than in that of the fetus; this may contribute to the decreased responsiveness of the DA to PGE(2) in newborn. Because EP(2) receptors seem to mediate the effects of PGE(2) on the newborn DA, one may propose that a selective EP(2) agonist may be preferred as a pharmacological agent to maintain DA patency in infants with certain congenital heart diseases.