Calcium-dependent and calcium-sensitizing pathways in the mature and immature ductus arteriosus

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.

Reactive oxygen species as mediators of oxygen signaling during fetal-to-neonatal circulatory transition

Reactive oxygen species (ROS) are frequently seen as pathological agents of oxidative stress. However, ROS are not always deleterious and can also act as cell signaling molecules. Vascular oxygen sensing and signaling during fetal-to-neonatal circulatory transition is a remarkable example of the physiological regulatory actions of ROS. The fetal relative hypoxic environment induces hypoxic pulmonary vasoconstriction (HPV) and ductus arteriosus (DA) relaxation favoring the presence of high pulmonary vascular resistance and right-to-left ductal shunt. At birth, the increase in oxygen tension causes relaxation of pulmonary arteries (PAs) and normoxic DA vasoconstriction (NDAV), thus diverting blood flow to the lungs. Although the response to changes in oxygen tension is diametrically opposite, the mechanisms responsible for HPV and NDAV appear to be the result of a similar interaction between triggering and modulating factors that lead to an increase in cytosolic Ca²⁺ concentration and Ca²⁺ sensitization of the contractile apparatus. Growing evidence points to an increase in ROS (mitochondria- and/or NADPH-derived superoxide and/or H₂O₂), leading to inhibition of voltage-gated K⁺ channels, membrane depolarization, and activation of voltage-gated L-type Ca²⁺ channels as critical events in the signaling pathway of both HPV and NDAV. Several groups of investigators have completed this pathway adding other elements such as neutral sphingomyelinase-derived ceramide, the sarcoplasmic/endoplasmic reticulum (through ryanodine and inositol 1,4,5-trisphosphate receptors), Rho kinase-mediated Ca²⁺ sensitization, or transient receptor potential channels. The present review focus on the role of ROS as mediators of the homeostatic oxygen sensing system during fetal and neonatal life not only in the PAs and DA but also in systemic arteries.

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 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.

Activation of the EGFR/p38/JNK pathway by mitochondrial-derived hydrogen peroxide contributes to oxygen-induced contraction of ductus arteriosus

Oxygen-induced contraction of the ductus arteriosus (DA) involves a mitochondrial oxygen sensor, which signals pO2 in the DA smooth muscle cell (DASMC) by increasing production of diffusible hydrogen peroxide (H2O2). H2O2 stimulates vasoconstriction by regulating ion channels and Rho kinase, leading to calcium influx and calcium sensitization. Because epidermal growth factor receptor (EGFR) signaling is also redox regulated and participates in oxygen sensing and vasoconstriction in other systems, we explored the role of the EGFR and its signaling cascade (p38 and c-Jun N-amino-terminal kinase (JNK)) in DA contraction. Experiments were performed in DA rings isolated from full-term New Zealand white rabbits and human DASMC. In human DASMCs, increasing pO2 from hypoxia to normoxia (40 to 100 mmHg) significantly increased cytosolic calcium, p < 0.01. This normoxic rise in intracellular calcium was mimicked by EGF and inhibited by EGFR siRNA. In DA rings, EGF caused contraction while the specific EGFR inhibitor (AG1478) and the tyrosine kinase inhibitors (genistein or tyrphostin A23) selectively attenuated oxygen-induced contraction (p < 0.01). Conversely, orthovanadate, a tyrosine phosphatase inhibitor known to activate EGFR signaling, caused dose-dependent contraction of hypoxic DA and superimposed increases in oxygen caused minimal additional contraction. Anisomycin, an activator of EGFR's downstream kinases, p38 and JNK, caused DA contraction; conversely, oxygen-induced DA contraction was blocked by inhibitors of p38 mitogen-activated protein kinases (MAPK) (SB203580) or JNK (JNK inhibitor II). O2-induced phosphorylation of EGFR occurred within 5 min of increasing pO2 and was inhibited by mitochondrial-targeted overexpression of catalase. AG1478 prevented the oxygen-induced p38 and JNK phosphorylation. In conclusion, O2-induced EGFR transactivation initiates p38/JNK-mediated increases in cytosolic calcium and contributes to DA contraction. The EGFR/p38/JNK pathway is regulated by mitochondrial redox signaling and is a promising therapeutic target for modulation of the patent ductus arteriosus.

KEY MESSAGES

Oxygen activates epidermal growth factor receptor (EGFR) in ductus arteriosus (DA) smooth muscle cells. EGFR inhibition selectively attenuates O2-induced DA constriction. pO2-induced EGFR activation is mediated by mitochondrial-derived hydrogen peroxide. p38 MAPK and JNK mediated EGFR's effects on oxygen-induced DA contraction. Tyrosine kinases and phosphatases participate in oxygen sensing in the DA. The EGFR pathway offers new therapeutic targets to modulate patency of the ductus arteriosus.

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.

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.

Effects of sex and estrogen on chicken ductus arteriosus reactivity

Sex hormones have an important influence on cardiovascular physiology and pathophysiology and sex differences in vascular reactivity have been widely demonstrated. In the present study we hypothesized 1) the presence of sexual dimorphism in chicken ductus arteriosus (DA) responsiveness to contractile and relaxant stimuli and 2) that estrogens are vasoactive in the chicken DA. In vitro contractions (assessed with a wire myograph) induced by normoxia, KCl, 4-aminopyridine, norepinephrine, phenylephrine, U46619, or endothelin-1, as well as relaxations induced by ACh, sodium nitroprusside, BAY 41-2272, PGE(2), isoproterenol, forskolin,Y-27632, and hydroxyfasudil were not significantly different between males and females. The estrogen 17beta-estradiol elicited concentration-dependent relaxation of KCl-, phenylephrine-, and oxygen-induced active tone in male and female chicken DA. The stereoisomer 17alpha-estradiol showed lesser relaxant effects, and the selective estrogen receptor (ER) agonists 4,4',4''-(4-propyl-[(1)H]pyrazole-1,3,5-triyl)tris-phenol (ERalpha) and 2,3-bis(4-hydroxyphenyl)-propionitrile (ERbeta) did not show any effect. There were no sex differences in the responses to estrogen. Endothelium removal or the presence of the soluble guanylate cyclase inhibitor ODQ, the K(+) channel blockers tetraethylammonium, glibenclamide, and charybdotoxin, or the ER antagonist fulvestrant did not modify 17beta-estradiol-induced relaxation. CaCl(2) (30 muM-10 mM) induced concentration-dependent contraction in DA rings depolarized by 62.5 mM KCl or stimulated with 21% O(2) in Ca(2+)-free medium. Preincubation with 17beta-estradiol or the L-type Ca(2+) channel blocker nifedipine produced an inhibition of CaCl(2)-induced contractions. In conclusion, there are no sex-related differences in chicken DA reactivity. The estrogen 17beta-estradiol induces an endothelium-independent relaxation of chicken DA that is not mediated by ER activation. This relaxant effect is, at least partially, due to inhibition of Ca(2+) entry from extracellular space.

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

Although prostaglandin E2 (PGE2) vasodilates the ductus arteriosus, tocolysis with cyclooxygenase (COX) inhibitors delays postnatal ductus arteriosus closure. We used fetal mice and sheep to determine whether PGE2 has a role in the development of ductus contractility that is distinct from its function as a vasodilator. Prolonged exposure of fetal ductus to PGE2 in vitro increased the expression of CaL- and K+-channel genes (CaLalpha1c, CaLbeta2, Kir6.1, and Kv1.5, which regulate oxygen-induced constriction) without affecting the genes that regulate Rho-kinase-mediated calcium sensitization. Conversely, chronic exposure to COX inhibitors in utero decreased expression of CaL- and K+-channel genes, without affecting Rho-kinase-associated genes. Chronic COX inhibition in utero decreased the ductus' in vitro contractile response to stimuli that use CaL- and K+-channels (like O2 and K+), whereas the response to stimuli that act through Rho-kinase-mediated pathways (like U46619) was not significantly affected. Phosphodiesterase expression, which decreases the ductus' sensitivity to cAMP- or cGMP-dependent vasodilators, was increased by PGE2 exposure and decreased by COX inhibition, respectively. These studies identify potential downstream effectors of a PGE2-mediated, developmental program, regulating oxygen-induced ductus closure. Alterations in these effectors may explain the increased risk of patent ductus arteriosus (PDA) after in utero COX inhibition.

Maturation of O2 sensing and signaling in the chicken ductus arteriosus

The increase in O(2) tension after birth is a major factor stimulating ductus arteriosus (DA) constriction and closure. Here we studied the role of the mitochondrial electron transport chain (ETC) as sensor, H(2)O(2) as mediator, and voltage-gated potassium (K(V)) channels and Rho kinase as effectors of O(2)-induced contraction in the chicken DA during fetal development. Switching from 0% to 21% O(2) contracted the pulmonary side of the mature DA (mature pDA) but had no effect in immature pDA and relaxed the aortic side of the mature DA (mature aDA). This contraction of the pDA was attenuated by inhibitors of the mitochondrial ETC and by the H(2)O(2) scavenger polyethylene glycol (PEG)-catalase. Moreover, O(2) increased reactive oxygen species (ROS) production, measured with the fluorescent probes dihydroethidium and 2',7'-dichlorofluorescein, only in mature pDA. The H(2)O(2) analog t-butyl-hydroperoxide mimicked the responses to O(2) in the three vessels. In contrast to immature pDA cells, mature pDA cells exhibited high-amplitude O(2)-sensitive potassium currents. The K(V) channel blocker 4-aminopyridine prevented the current inhibition elicited by O(2). The L-type Ca(2+) (Ca(L)) channel blocker nifedipine and the Rho kinase inhibitors Y-27632 and hydroxyfasudil induced a similar relaxation when mature pDA were stimulated with O(2) or H(2)O(2). Moreover, the sensitivity to these drugs increased with maturation. Our results indicate the presence of a common mechanism for O(2) sensing/signaling in mammalian and nonmammalian DA and favor the idea that, rather than a single mechanism, a parallel maturation of the sensor and effectors is critical for O(2) sensitivity appearance during development.

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.

Oxygen-induced tension in the sheep ductus arteriosus: effects of gestation on potassium and calcium channel regulation

Compared with the full-term ductus arteriosus, the premature ductus is less likely to constrict when exposed to postnatal oxygen concentrations. We used isolated fetal sheep ductus arteriosus (pretreated with inhibitors of prostaglandin and nitric oxide production) to determine whether changes in K+ - and CaL-channel activity could account for the developmental differences in oxygen-induced tension. In the mature ductus, KV-channels appear to be the only K+-channels that oppose ductus tension. Oxygen concentrations between (2% and 15%) inhibit KV-channel activity, which increases the CaL-channel-mediated increase in tension. Low oxygen concentrations have a direct inhibitory effect on CaL-channel activity in the immature ductus; this is not the case in the mature ductus. In the immature ductus, three different K+-channel activities (KV, KCa, and KATP) oppose ductus tension and contribute to its decreased tone. Oxygen inhibits the activities of all three K+ -channels. The inhibitory effects of the three K+-channel activities decline with advancing gestation. The decline in K+ -channel activity is not due to decreased K+ -channel expression. Super-physiologic oxygen concentrations (>or=30% O2) constrict the ductus by using calcium-dependent pathways that are independent of K+- and CaL-channel activities. Super-physiologic oxygen concentrations eliminate the difference in tensions between the two age groups.

Mechanisms mediating the oxygen-induced vasoreactivity of the ductus arteriosus in the chicken embryo

The avian embryo provides a novel model for studying the ductus arteriosus (DA) during the transition from in ovo to ex ovo life. Here we examined the mechanisms regulating the vasoreactivity of the two morphologically distinct portions of the chicken DA (proximal and distal) in response to O(2). Oxygen-induced contraction is redox sensitive and reversed by the reducing agent dithiothreitol and the H(2)O(2) scavenger N-mercaptopropionylglycine. As in the mammalian DA, inhibiting mitochondrion-derived reactive oxygen species production with rotenone and antimycin A relaxed the O(2)-constricted DA. The contractile response to O(2) matures during hatching and is mimicked by the K(v) channel inhibitor 4-aminopyridine (4-AP) on day 19 and externally pipped (EP) embryos. Together, O(2) and 4-AP significantly increase DA tone above that observed with either alone. The O(2)-induced contraction is mediated by influx of extracellular Ca(2+) through l-type Ca(2+) and store-operated channels. Inositol 1,4,5-trisphosphate-sensitive Ca(2+) stores play a minor role in the O(2)-induced contraction. The O(2)-induced contraction is mediated by the Rho kinase pathway, as fasudil and Y-27632 significantly relax the O(2) contracted DA. Prostaglandins E(2), F(2alpha), and D(2) produce significant contraction of the proximal DA. The O(2)-induced relaxation of the distal portion of the DA is mediated by an endothelial-derived nitric oxide/cGMP pathway. Both 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one and endothelial cell removal inhibit O(2)-induced relaxation in the distal segment. Mechanisms regulating O(2)-induced contraction in chicken proximal DA are similar to those found in mammalian DA, making the chicken a useful model for studying development of this O(2)-sensitive vessel.

Increased indomethacin dosing for persistent patent ductus arteriosus in preterm infants: a multicenter, randomized, controlled trial

OBJECTIVE

We conducted a multicenter, randomized, controlled trial to determine whether higher doses of indomethacin would improve the rate of patent ductus arteriosus (PDA) closure.

STUDY DESIGN

Infants (<28 weeks gestation) who received a conventional, prophylactic 3-dose course of indomethacin were eligible if they had continued evidence of persistent ductus patency on an echocardiogram obtained before the third prophylactic indomethacin dose. Infants (n = 105) were randomized to receive an extended 3-day course of either low-dose (0.1 mg/kg/d) or higher-dose (0.2 or 0.5 mg/kg/d) indomethacin. An echocardiogram was obtained 24 hours after the last dose of study drug.

RESULTS

Despite increasing serum indomethacin concentrations by 2.9-fold in the higher-dose group, we failed to detect a significant decrease in the rate of persistent PDA (low = 52%; higher = 45%, P = .50). The higher-dose group had a significantly higher occurrence of serum creatinine >2 mg/100 mL (low = 6%, higher = 19%, P < .05) and moderate/severe retinopathy of prematurity (ROP) (low = 15%, higher = 36%, P < .025). The incidence of moderate/severe ROP was directly related to the poststudy indomethacin concentrations (odds ratio = 1.75, confidence interval: 1.15-2.68, P < .01).

CONCLUSION

Increasing indomethacin concentrations above the levels achieved with a conventional dosing regimen had little effect on the rate of PDA closure but was associated with higher rates of moderate/severe ROP and renal compromise.